Synthesis and hplc-ecd study of cytostatic condensed o,n-heterocycles obtained from 3-aminoflavanones

Article abstract of DOI:10.3390/biom10101462

Racemic chiral O,N-heterocycles containing 2-arylchroman or 2-aryl-2H-chromene subunit condensed with morpholine, thiazole, or pyrrole moieties at the C-3-C-4 bond were synthesized with various substitution patterns of the aryl group by the cyclization of cis- or trans-3- aminoflavanone analogues. The 3-aminoflavanone precursors were obtained in a Neber rearrangement of oxime tosylates of flavanones, which provided the trans diastereomer as the major product and enabled the isolation of both the cis- and trans-diastereomers. The cis- and transaminoflavanones were utilized to prepare three diastereomers of 5-aryl-chromeno[4,3- b][1,4]oxazines. Antiproliferative activity of the condensed heterocycles and precursors was evaluated against A2780 and WM35 cancer cell lines. For a 3-(N-chloroacetylamino)-flavan-4-ol derivative, showing structural analogy with acyclic acid ceramidase inhibitors, 0.15 μM, 3.50 μM, and 6.06 μM IC₅₀ values were measured against A2780, WM35, and HaCat cell lines, and apoptotic mechanism was confirmed. Low micromolar IC50 values down to 2.14 μM were identified for the thiazole- and pyrrole-condensed 2H-chromene derivatives. Enantiomers of the condensed heterocycles were separated by HPLC using chiral stationary phase, HPLC-ECD spectra were recorded and TDDFT-ECD calculations were performed to determine the absolute configuration and solution conformation. Characteristic ECD transitions of the separated enantiomers were correlated with the absolute configuration and effect of substitution pattern on the HPLC elution order was determined.

Full text of DOI:10.3390/biom10101462

biomolecules
Article
Synthesis and HPLC-ECD Study of Cytostatic
Condensed O,N-Heterocycles Obtained
from 3-Aminoflavanones
Ádám Szappanos 1,2 , Attila Mándi 1 , Katalin Gulácsi 1,†, Erika Lisztes 3
,
Balázs István Tóth 3 , Tamás Bíró 4, Anita Kónya-Ábrahám 1, Attila Kiss-Szikszai 1
,
Attila Bényei 5, Sándor Antus 1 and Tibor Kurtán 1,
*
1
Department of Organic Chemistry, University of Debrecen, P. O. Box 400, 4002 Debrecen, Hungary;
szappanos.adam@gmail.com (Á.S.); mandi.attila@science.unideb.hu (A.M.);
gulacsi.katalin@science.unideb.hu (K.G.); dulryc@unideb.hu (A.K.-Á.);
kiss.attila@science.unideb.hu (A.K.-S.); antus.sandor@science.unideb.hu (S.A.)
Doctoral School of Chemistry, University of Debrecen, Egyetem tér 1, 4032 Debrecen, Hungary
Department of Physiology, University of Debrecen, 4012 Debrecen, Hungary;
lisztes.erika@med.unideb.hu (E.L.); toth.istvan@med.unideb.hu (B.I.T.)
Department of Immunology, University of Debrecen, 4032 Debrecen, Hungary; biro.tamas@med.unideb.hu
Department of Physical Chemistry, University of Debrecen, 4032 Debrecen, Hungary;
benyei.attila@science.unideb.hu
2
3
4
5
*
†
Correspondence: kurtan.tibor@science.unideb.hu; Fax: +36-52-512-744
Deceased.
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀꢁꢂꢃꢄꢅꢆ
Received: 23 August 2020; Accepted: 15 October 2020; Published: 20 October 2020
Abstract: Racemic chiral O,N-heterocycles containing 2-arylchroman or 2-aryl-2H-chromene subunit
condensed with morpholine, thiazole, or pyrrole moieties at the C-3-C-4 bond were synthesized with
various substitution patterns of the aryl group by the cyclization of cis- or trans-3-aminoflavanone
analogues. The 3-aminoflavanone precursors were obtained in a Neber rearrangement of oxime
tosylates of flavanones, which provided the trans diastereomer as the major product and enabled the
isolation of both the cis- and trans-diastereomers. The cis- and trans-aminoflavanones were utilized to
prepare three diastereomers of 5-aryl-chromeno[4,3-b][1,4]oxazines. Antiproliferative activity of the
condensed heterocycles and precursors was evaluated against A2780 and WM35 cancer cell lines.
For a 3-(N-chloroacetylamino)-flavan-4-ol derivative, showing structural analogy with acyclic acid
ceramidase inhibitors, 0.15
WM35, and HaCat cell lines, and apoptotic mechanism was confirmed. Low micromolar IC50 values
down to 2.14 M were identified for the thiazole- and pyrrole-condensed 2H-chromene derivatives.
µM, 3.50 µM, and 6.06 µM IC50 values were measured against A2780,
µ
Enantiomers of the condensed heterocycles were separated by HPLC using chiral stationary phase,
HPLC-ECD spectra were recorded and TDDFT-ECD calculations were performed to determine the
absolute configuration and solution conformation. Characteristic ECD transitions of the separated
enantiomers were correlated with the absolute configuration and effect of substitution pattern on the
HPLC elution order was determined.
Keywords: neber rearrangement; 3-aminoflavanones; antiproliferative activity; TDDFT-ECD
calculations; HPLC-ECD; 3-(N-chloroacetylamino)-flavan-4-ol; thiazole-condensed 2H-chromene;
pyrrole-condensed 2H-chromene; lamellarin analogues
1. Introduction
The 3-aminoflavanone scaffold
1 is considered an efficient building block for the preparation
of condensed chiral O,N-heterocycles
2-
4
(Scheme 1), which contain a 2-arylchroman or
Biomolecules 2020, 10, 1462; doi:10.3390/biom10101462
www.mdpi.com/journal/biomolecules

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2-aryl-2H-chromene moiety fused at the C-3
−
C-4 bond with azine- or azole-type heterocycles.
The 3-aminoflavanone derivatives can be obtained by the Neber rearrangement [
derivative , readily available from flavanones in two steps. The Neber rearrangement involves the
conversion of the oxime tosylate of a ketone to a reactive 2H-azirine intermediate in the presence of an
alkoxide base, the ring-opening of which produces an -aminoketone [ ]. Although oxime tosylate of
flavanone rac- were converted to 3-aminoflavanone in a Neber reaction as early as 1959 [ ] and isolation
of trans-3-aminoflavanone rac- were reported [ ], the synthetic potential of 3-aminoflavanones
for the preparation of condensed O,N-heterocycles has been underutilized (Scheme 1). Only the
preparation of oxazoline- and imidazole-condensed derivatives rac- and rac- was reported with a
1] of the oxime tosylate
5
6
α
2,3
E
4
C
5,6
A
B
few examples. Moreover, in this work the diastereoselectivity and side-products of the Neber reaction
in the presence of an inherent C-2 chirality center of flavanones were studied further by modifying
the reaction conditions and isolation of the diastereomeric products. Asymmetric organocatalytic
Neber reactions of oxime tosylates producing optically active 2H-azirine derivatives have been recently
reported, in which the reaction conditions are adjusted to stop the transformation at the stage of the
2H-azirine intermediates [7–9].
Scheme 1. Retrosynthetic schemes for the reported and proposed preparation of the condensed
O,N-heterocycles rac-A,B and rac-2-4 from 3-aminoflavanone derivatives.
The condensed O,N-heterocyclic target molecules
thiazole, or pyrrole unit fused at the C-3 C-4 bond of the 2-arylchroman or 2H-chromene skeleton
and each of them are represented by 7 analogues differing in the C-2 aryl substituents. A literature
2-4 of the recent work contain a morpholine,
−

Biomolecules 2020, 10, 1462
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survey showed that analogous O,N-heterocycles with condensed morpholine, pyrrole, and thiazole
subunits received great attention because of their remarkable pharmacological activities such as tau
protein kinase 1 (TPK1) inhibitory activity of
channel modulatory activity of 12], interleukin-2 (IL-2) inhibitory activity of 10
inhibitory activity of 11 14], and antibacterial activity of 12 15] (Figure 1). The synthetic derivative
7
[10], dopamine D3 receptor agonist activity of
8 [11], ion
9
[
[13], topoisomerase I
[
[
11 is a simplified analogue of natural lemallarins, cytotoxic marine natural products with potent
topoisomerase I inhibitory activity isolated from molluscs, ascidians, and sponges [16,17].
Figure 1. Structures of bioactive chroman, 2H-chromene and coumarine derivatives condensed with
morpholine, thioazole, and pyrrole units at the C-3−C-4 bond.
In this work, the synthesis of the target heterocycles 2-4 is carried out through the 3-aminoflavanone
derivatives and their antiproliferative activity was tested on WM35 melanoma and A2780 ovarian
human cancer cell lines by MTT assay. Low micromolar IC50 values could be measured for several
chiral racemic O,N-heterocyclic derivatives, which prompted us to separate the enantiomers with
chiral HPLC, record the online HPLC-ECD spectra and determine the absolute configuration by
TDDFT-ECD calculations.
2. Materials and Methods
2.1. Chemicals
Melting points were determined on a Kofler hot-stage apparatus and are uncorrected. The NMR
spectra were recorded on Bruker Aspect 3000 (1H: 360 MHz, 13C: 90 MHz) and Bruker Avance II
400 (1H: 400 MHz; 13C: 100 MHz) spectrometers using TMS as internal standard. Chemical shifts
3
were reported as ppm and JH,H coupling constants in Hz. Chiral HPLC separation of rac-20a-g
,
rac-23a-g, rac-3a-g, and rac-4a-g were performed on a JASCO HPLC system with Chiralpak-IA column
(5
Chiralpak-IC column (5
flow rate) and HPLC-ECD spectra were recorded in stopped-flow mode on a JASCO J-810 electronic
circular dichroism spectropolarimeter equipped with a 10 mm HPLC flow cell. ECD ellipticity (
µm, 150
×
4.6 mm, hexane/2-propanol 80:20, 90:10 eluent, respectively, 1 mL min−1 flow rate) or
µm, 250
×
4.6 mm, hexane/2-propanol 70:30 eluent, respectively, 1 mL min−1
φ)
values were not corrected for concentration. For an HPLC-ECD spectrum, three consecutive scans were
recorded and averaged with 2 nm bandwidth, 1 s response, and standard sensitivity. The HPLC-ECD
spectrum of the eluent recorded in the same way was used as background. The concentration of the
injected sample was set so that the HT value did not exceed 500 V in the HT channel down to 230 nm.

Biomolecules 2020, 10, 1462
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IR spectra were recorded on a JASCO FT/IR-4100 spectrometer and absorption bands are presented as
wavenumber in cm−1. Electrospay quadrupole time-of-flight HRMS measurements were performed
with a MicroTOF-Q type QqTOF MS or maXis II UHR ESI- QTOF MS instrument equipped with an ESI
source from Bruker (Bruker Daltoniks, Bremen, Germany).
2.2. General Procedure for the Synthesis of Tosyl Oxime Analogues (5a-g)
Oxime derivative 16a-g (12.54 mmol) and Et3N (2.11 mL, 15.04 mmol) were dissolved in anhydrous
CH2Cl2 (50 mL) under inert atmosphere. At room temperature, p-toluenesulfonyl chloride (15.04 mmol)
was added to the solution. The mixture was refluxed for 3 h. Extraction with water, drying over
MgSO4 and concentration under reduced pressure afforded the crude product as orange oil. The oil
was triturated with cold hexane, which resulted in the pure product.
N-{[(4-methylphenyl)sulfonyl]oxy}-2-phenyl-2,3-dihydro-4H-chromen-4-imine (5a). White crystals, yield
87%, mp 142–143 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 2.43 (s, 3H, CH3), 2.75 (dd, J = 17.2, 12.4 Hz, 1H,
3-Ha), 3.44 (dd, J = 17.2, 2.8 Hz, 1H, 3-Hb), 5.01 (dd, J = 12.4, 2.8 Hz, 1H, 2-H), 6.94 (m, 2H, 6-H, 8-H),
7.34 (m, 8H, 7-H, 20-H, 30-H, 40-H, 50-H, 60-H, 3”-H, 5”-H) 7.81 (dd, J = 8.0, 1.6 Hz, 1H, 5-H), 7.92 (d, 2H,
2”-H, 6”-H); 13C-NMR (100 MHz, CDCl3):
δ: 21.8 (C-CH3), 31.9 (C-3), 76.8 (C-2), 115.6 (C-4a), 118.3
(C-8), 121.8 (C-6), 125.1 (C-5), 126.2 (C-20, C-60), 128.9 (C-30, C-40, C-50), 129.1 (C-3”, C-5”), 129.7 (C-2”,
C-6”), 132.6 (C-1”), 133.5 (C-7), 138.7 (C-10), 145.3 (C-4”), 157.2 (C-4), 157.9 (C-8a); HRMS (ESI) calcd.
for C22H19NaNO4S [M+Na]+ 416.093; found 416.093.
N-{[(4-methylphenyl)sulfonyl]oxy}-2-(4-methoxyphenyl)-2,3-dihydro-4H-chromen-4-imine (5b). Off-white
crystals, yield 93%, mp 165–167 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 2.44 (s, 3H, CH3), 2.78 (dd, J =
17.6, 12.8 Hz, 1H, 3-Ha), 3.42 (dd, J = 17.6, 2.8 Hz, 1H, 3-Hb), 3.81 (s, 3H, OCH3), 4.97 (dd, J = 12.8,
2.8 Hz, 1H, 2-H), 6.91 (m, 4 H, 6-H, 8-H, 30-H, 50-H), 7.32 (m, 5H, 7-H, 20-H, 60-H, 3”-H, 5”-H), 7.81
(dd, J = 8.0, 1.2 Hz, 1H, 5-H), 7.93 (d, 2H, 2”-H, 6”-H); 13C-NMR (100 MHz, CDCl3)
δ: 21.8 (C-CH3),
31.6 (C-3), 55.4 (C-OCH3), 76.5 (C-2), 114.2 (C-30, C-50) 115.5 (C-4a), 118.3 (C-8), 121.7 (C-6), 125.1 (C-5),
127.7 (C-20, C-60), 129.1 (C-3”, C-5”), 129.7 (C-2”, C-6”), 130.7 (C-10), 132.6 (C-1”), 133.5 (C-7), 145.3
(C-4”), 157.5 (C-4), 158.0 (C-8a), 160.0 (C-40); HRMS (ESI) calcd. for C23H21NaNO5S [M+Na]+ 446.104;
found 446.105.
N-{[(4-methylphenyl)sulfonyl]oxy}-2-(3,4-dimethoxyphenyl)-2,3-dihydro-4H-chromen-4-imine (5c). Off-white
crystals, yield 92%, mp 148–150 ◦C; 1H-NMR (400 MHz, CDCl3)
δ
: 2.44 (s, 3H, CH3), 2.82 (dd, J = 17.6,
OCH3), 4.99 (d, J = 12.4 Hz, 1H, 2-H),
6.87 (d, J = 7.6 Hz, 1H, 8-H), 6.94 (m, 4 H, 6-H, 20-H, 50-H, 60-H), 7.35 (m, 3H, 7-H, 3”-H, 5”-H), 7.80 (d,
J = 8.4 Hz, 1H, 5-H), 7.93 (d, 2H, 2”-H, 6”-H); 13C-NMR (100 MHz, CDCl3):
= 21.7 (C-CH3), 31.7
(C-3), 56.0 (2
C-OCH3), 76.7 (C-2), 109.4 (C-50), 111.2 (C-20), 115.5 (C-4a), 118.3 (C-8), 118.9 (C-60),
12.4 Hz, 1H, 3-Ha), 3.43 (d, J = 17.6 Hz, 1H, 3-Hb), 3.89 (d, 6H, 2
×
δ
×
121.8 (C-6), 125.0 (C-5), 129.0 (C-3”, C-5”), 129.7 (C-2”, C-6”), 131.1 (C-1”), 132.5 (C-10), 133.4 (C-7),
145.3 (C-4”), 149.3 (C-40), 149.5 (C-30), 157.3 (C-4), 157.8 (C-8a); HRMS (ESI) calcd. for C24H23NaNO6S
[M+Na]+ 476.114; found 476.113.
N-{[(4-methylphenyl)sulfonyl]oxy}-2-(3,5-dimethoxyphenyl)-2,3-dihydro-4H-chromen-4-imine (5d). Off-white
crystals, yield: 89%, mp 142–144 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 2.44 (s, 3H, CH3), 2.76 (d, J =
17.6, 12.8 Hz, 1H, 3-Ha), 3.44 (dd, J = 17.6, 3.2 Hz, 1H, 3-Hb), 3.8 (s, 6H, 2xOCH3), 4.96 (dd, J = 12.8,
3.2 Hz, 1H, 2-H), 6.44 (t, J = 2.4 Hz, 1H, 40-H), 6.55 (d, 2H, 20-H, 60-H), 6.94 (m, 2H, 6-H, 8-H), 7.32 (7-H,
3”-H, 5”-H), 7.80 (dd, J = 8.4, 1.6 Hz, 1H, 5-H), 7.92 (d, 2H, 2”-H, 6”-H); 13C-NMR (100 MHz, CDCl3)
δ
: 21.8 (C-CH3), 32.0 (C-3), 55.5 (2xC-OCH3), 76.8 (C-2), 100.6 (C-40), 104.2 (C-20, C-60), 115.6 (C-4a),
118.4 (C-8), 121.9 (C-6), 125.1 (C-5), 129.1 (C-3”, C-5”), 129.7 (C-2”, C-6”), 132.6 (C-1”), 133.5 (C-7), 141.1
(C-10), 145.3 (C-4”), 157.2 (C-4), 157.7 (C-8a), 161.2 (C-30, C-50); HRMS (ESI) calcd. for C24H23NO6S [M
+ H]+ 454.132; found 454.131.

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N-{[(4-methylphenyl)sulfonyl]oxy}-2-(3,4,5-trimethoxyphenyl)-2,3-dihydro-4H-chromen-4-imine
(5e).
Off-white crystals, yield: 84%, mp 157–159 ◦C; 1H-NMR (400 MHz, CDCl3)
δ
: 2.45 (s, 3H, CH3), 2.81
(dd, J = 17.6, 12.4 Hz, 1H, 3-Ha), 3.45 (dd, J = 17.6, 3.2 Hz, 1H, 3-Hb), 3.85 (m, 9H, 3 OCH3), 4.98
(dd, J = 12.8, 2.8 Hz, 1H, 2-H), 6.65 (s, 2H, 20-H, 60-H), 6.95 (m, 2H, 6-H, 8-H), 7.34 (m, 3H, 7-H, 3”-H,
5”-H), 7.81 (dd, J = 8.4, 1.6 Hz, 1H, 5-H), 7.92 (d, 2H, 2”-H, 6”-H); 13C-NMR (100 MHz, CDCl3)
: 21.8
×
δ
(C-CH3), 32.0 (C-3), 56.3 (2xC-OCH3), 60.9 (C-OCH3), 77.0 (C-2), 103.3 (C-20, C-60), 115.6 (C-4a), 118.3
(C-8), 121.9 (C-6), 125.1 (C-5), 129.1 (C-3”, C-5”), 129.7 (C-2”, C-6”), 132.5 (C-1”), 133.5 (C-7), 134.3
(C-10), 138.3 (C-40), 145.3 (C-4”), 153.6 (C-30, C-50), 157.1 (C-4), 157.7 (C-8a); HRMS (ESI) calcd. for
C25H25NO7S [M + H]+ 484.143; found 484.141.
N-{[(4-methylphenyl)sulfonyl]oxy}-2-(naphthalene-1-yl)-2,3-dihydro-4H-chromen-4-imine (5f). Off-white
crystals, yield 80%, mp 136–138 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 2.40 (s, 3H, CH3), 2.93 (dd, J = 17.6,
12.8 Hz, 1H, 3-Ha), 3.61 (dd, J = 17.6, 3.2 Hz, 1H, 3-Hb), 5.69 (dd, J = 12.8, 2.8 Hz, 1H, 2-H), 6.95 (m, 2H,
6-H, 8-H), 7.31 (m, 3H, 7-H, 3”-H, 5”-H), 7.44 (m, 3H, 20-H, 30-H, 70-H), 7.62 (d, J = 6.8 Hz, 1H, 60-H),
7.82 (m, 5H, 5-H, 40-H, 50-H, 80-H, 2”-H, 6”-H); 13C-NMR (100 MHz, CDCl3)
δ: 21.8 (C-CH3), 31.1 (C-3),
74.2 (C-2), 115.8 (C-4a), 118.4 (C-8), 122.0 (C-6), 122.9 (C-80), 124.0 (C-5), 125.2 (C-20), 125.4 (C-30), 126.0
(C-70), 126.8 (C-60), 129.0 (C-3”, C-5”), 129.2 (C-50), 129.5 (C-40), 129.7 (C-2”, C-6”), 130.3 (C-8a’), 132.5
(C-1”), 133.5 (C-7), 133.9 (C-4a’), 134.0 (C-20), 145.3 (C-4”), 157.5 (C-4), 158.1 (C-8a); HRMS (ESI) calcd.
for C26H21NaNO4S [M+Na]+ 466.109; found 466.108.
N-{[(4-methylphenyl)sulfonyl]oxy}-2-(naphthalene-2-yl)-2,3-dihydro-4H-chromen-4-imine (5g). Off-white
crystals, yield: 83%, mp 207–209 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 2.45 (s, 3H, CH3), 2.90 (dd, J = 17.6,
12.4 Hz, 1H, 3-Ha), 3.55 (dd, J = 17.6, 3.2 Hz, 1H, 3-Hb), 5.22 (dd, J = 12.4, 3.2 Hz, 1H, 2-H), 6.96 (m,
2H, 6-H, 8-H), 7.35 (m, 3H, 7-H, 3”-H, 5”-H), 7.50 (m, 3H, 30-H, 60-H, 70-H), 7.85 (m, 7H, 5-H, 10-H,
40-H, 50-H, 80-H, 2”-H, 6”-H); 13C-NMR (100 MHz, CDCl3)
δ: 21.9 (C-CH3), 31.8 (C-3), 76.9 (C-2), 115.7
(C-4a), 118.4 (C-8), 121.9 (C-6), 123.7 (C-5), 125.2 (C-10), 125.5 (C-80), 126.7 (C-30, C-70), 127.9 (C-60),
128.3 (C-50), 128.9 (C-40), 129.2 (C-3”, C-5”), 129.8 (C-2”, C-6”), 132.6 (C-8a’), 133.3 (C-1”), 133.5 (C-4a’),
133.6 (C-7), 136.1 (C-20), 145.4 (C-4”), 157.3 (C-4), 157.9 (C-8a); HRMS (ESI) calcd. for C26H21NaNO4S
[M+Na]+ 466.109; found 466.108.
2.3. General Procedure for Neber Rearrangement (rac-cis-1a-g, rac-trans-1a-g, 17a-g)
Tosyl oxime derivatives 5a-g (8.895 mmol) were dissolved in anhydrous toluene (50 mL) under
inert atmosphere and then 10.9 mL NaOEt (940 mg Na in 50 mL EtOH) was added dropwise to the
solution. Stirring for 1 day at room temperature afforded an orange suspension. The suspension was
filtered through cellite and washed with EtOH. Concentration of the filtrate under vacuum provided the
crude product as an orange oil. Then it was dissolved in CH2Cl2 and 3 N HCl solution (3 mL) was added
to it. After 2 h stirring at room temperature, an orange suspension was obtained. Filtration and washing
with acetone provided the cis product as white powder. Then the filtrate was thoroughly concentrated
under reduced pressure and trituration with acetone afforded the trans product as off-white powder.
The residue filtrate was purified after concentration by column chromatography using toluene/ethyl
acetate 4:1 as eluent. The benzoxazole derivates 17a-g were obtained by this procedure.
(
±
)-(2R*,3R*)-3-amino-2-phenyl-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-trans-1a) [
5
]: Off-white
solid, yield 30%, mp 197–199 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ: 5.01 (d, J = 12.4 Hz, 1H, 3-H), 5.77
(d, J = 12.4 Hz, 1H, 2-H), 7.13 (d, J = 8 Hz, 1H, 8-H), 7.20 (m, 1H, 6-H), 7.50 (m, 3H, 30-H, 40-H, 50-H),
7.68 (m, 3H, 7-H, 20-H, 60-H), 7.87 (dd, J = 8.0, 1.6 Hz, 1H, 5-H), 8.72 (bs, 3H, NH3); 13C-NMR (100 MHz,
DMSO-d6) δ
: 55.7 (C-3), 80.2 (C-2), 118.0 (C-8), 118.5 (C-4a), 122.5 (C-6), 126.9 (C-5), 128.6 (C-20, C-60),
128.8 (C-30, C-50), 129.9 (C-40), 134.3 (C-10), 137.6 (C-7), 160.8 (C-8a), 187.6 (C-4); HRMS (ESI) calcd. for
C15H13NO2 [M + H]+ 240.102; found 240.101.

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( )-(2R*,3R*)-3-amino-2-(4-methoxyphenyl)-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-trans-1b):
±
Off-white solid, yield 32%, mp 206–209 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ: 3.80 (s, 3H, OCH3), 5.03
(d, J = 12.4 Hz, 1H, 3-H), 5.83 (d, J = 12.4 Hz, 1H, 2-H), 7.03 (d, 2H, 30-H, 50-H), 7.10 (d, J = 8.0 Hz, 1H,
8-H), 7.18 (t, J = 7.6 Hz, 1H, 6-H), 7.64 (m, 3H, 7-H, 20-H, 60-H), 7.85 (d, J = 7.6 Hz, 1H, 5-H), 8.83 (s, 3H,
NH3); 13C-NMR (100 MHz, DMSO-d6) : 55.4 (C-OCH3), 55.9 (C-3), 80.0 (C-2), 114.2 (C-30, C-50), 118.0
δ
(C-8), 118.6 (C-4a), 122.4 (C-6), 126.5 (C-10), 126.9 (C-5), 130.2 (C-20, C-60), 137.5 (C-7), 160.4 (C-40), 160.9
(C-8a), 187.8 (C-4); HRMS (ESI) calcd. for C16H15NO3 [M + H]+ 270.113; found 270.111.
(
±
)-(2R*,3R*)-3-amino-2-(3,4-dimethoxyphenyl)-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-trans-1c):
Off-white solid, yield 39%, mp 187–189 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ
: 3.80 (s, 6H, 2 OCH3),
×
5.08 (d, J = 12.6 Hz, 1H, 3-H), 5.71 (d, J = 12.6 Hz, 1H, 2-H), 7.03 (d, J = 9.2 Hz, 1H, 8-H), 7.12 (m, 3H,
6-H, 50-H, 60-H), 7.38 (s, 1H, 20-H), 7.67 (t, J = 8.0 Hz, 1H, 7-H), 7.86 (d, J = 8.0 Hz, 1H, 5-H), 8.71 (bs,
3H, NH3); 13C-NMR (100 MHz, DMSO-d6)
δ: 55.6 (2
×
C-OCH3), 55.9 (C-3), 80.3 (C-2), 111.7 (C-20),
111.9 (C-50), 118.0 (C-8), 118.5 (C-4a), 121.6 (C-60), 122.3 (C-6), 126.5 (C-10), 126.8 (C-5), 137.4 (C-7), 148.9
(C-40), 150.0 (C-30), 160.8 (C-8a), 187.7 (C-4); HRMS (ESI) calcd. for C17H17NO4 [M + H]+ 300.123;
found 300.122.
( )-(2R*,3R*)-3-amino-2-(3,5-dimethoxyphenyl)-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-trans-1d):
±
Off-white solid, yield: 46%, mp 187–189 ◦C; 1H-NMR (360 MHz, DMSO-d6)
δ
: 3.79 (s, 6H, 2
×
OCH3),
5.04 (d, J = 12.6 Hz, 1H, 3-H), 5.68 (d, J = 12.6 Hz, 1H, 2-H), 6.60 (t, J = 1.8 Hz, 1H, 40-H), 6.88 (d, 2 H,
20-H, 60-H), 7.17 (d, J = 8.3 Hz, 1H, 8-H), 7.20 (t, J = 7.9 Hz, 1H, 6-H), 7.69 (m, 1H, 7-H), 7.87 (dd, J = 7.9,
1.4 Hz, 1H, 5-H), 8.69 (bs, 3H, NH3); 13C-NMR (90 MHz, DMSO-d6)
δ: 55.8 (2
×
C-OCH3), 56.2 (C-3),
80.7 (C-2), 102.0 (C-40), 107.0 (C-20, C-60), 118.5 (C-8), 118.9 (C-4a), 123.0 (C-6), 127.3 (C-5), 136.7 (C-10),
138.1 (C-7), 161.2 (C-8a, C-30, C-50), 188.1 (C-4); HRMS (ESI) calcd. for C17H17NO4 [M + H]+ 300.123;
found 300.124.
(
±
)-(2R*,3R*)-3-amino-2-(3,4,5-trimethoxyphenyl)-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-trans-1e):
Off-white solid, yield 48%, mp 188–190 ◦C; 1H-NMR (400 MHz, DMSO-d6)
: 3.71 (s, 3H, OCH3), 3.82
(s, 6H, 2
OCH3), 5.09 (d, J = 12.4 Hz, 1H, 3-H), 5.65 (d, J = 12.4 Hz, 1H, 2-H), 7.05 (s, 2H, 20-H, 60-H),
7.15 (d, J = 8.4 Hz, 1H, 8-H), 7.20 (m, 1H, 6-H), 7.69 (m, 1H, 7-H), 7.87 (d, J = 8.0, 1.6 Hz, 1H, 5-H), 8.63
δ
×
(bs, 3H, NH3); 13C-NMR (100 MHz, DMSO-d6)
δ
: 55.9 (C-3), 56.0 (2
×
C-OCH3), 60.0 (C-OCH3), 80.5
(C-2), 106.1 (C-20, C-60), 118.1 (C-8), 118.5 (C-4a), 122.5 (C-6), 126.9 (C-5), 129.6 (C-10), 137.6 (C-7), 138.5
(C-40), 153.1 (C-30, C-50), 160.8 (C-8a), 187.8 (C-4); HRMS (ESI) calcd. for C18H19NO5 [M + H]+ 330.134;
found 330.133.
(
±
)-(2R*,3R*)-3-amino-2-naphthalen-1-yl-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-trans-1f):
Off-white solid, yield 64%, mp 212–215 ◦C; 1H-NMR (360 MHz, DMSO-d6)
δ
: 5.40 (d, J = 12.6 Hz, 1H,
3-H), 6.53 (d, J = 12.6 Hz, 1H, 2-H), 7.11 (d, J = 8.3 Hz, 1H, 8-H), 7.23 (t, J = 7.9 Hz, 1H, 6-H), 7.56 (m,
3H, 20-H, 30-H, 70-H), 7.68 (t, J = 7.9 Hz, 1H, 7-H), 7.94 (m, 2H, 5-H, 60-H), 8.04 (m, 2H, 40-H, 50-H), 8.49
(d, J = 7.9 Hz, 1H, 80-H), 8.79 (bs, 3H, NH3); 13C-NMR (90 MHz, DMSO-d6)
δ: 55.2 (C-3), 78.8 (C-2),
118.5 (C-8), 119.3 (C-4a), 123.0 (C-6), 124.6 (C-80), 125.9 (C-20), 126.5 (C-30), 126.5 (C-5), 127.1 (C-70),
127.5 (C-60), 129.3 (C-50), 130.1 (C-8a’), 131.1 (C-40), 131.7 (C-10), 134.4 (C-4a’), 137.9 (C-7), 161.3 (C-8a),
188.2 (C-4); HRMS (ESI) calcd. for C19H15NO2 [M + H]+ 290.118; found 290.118.
(
±
)-(2R*,3R*)-3-amino-2-naphthalen-2-yl-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-trans-1g):
Off-white solid, yield 48%, mp 201–203 ◦C; 1H-NMR (360 MHz, DMSO-d6)
δ: 5.16 (d, J = 12.6 Hz,
1H, 3-H), 5.96 (d, J = 12.6 Hz, 1H, 2-H), 7.16 (d, J = 8.3 Hz, 1H, 8-H), 7.22 (m, 1H, 6-H), 7.60 (m, 2H,
30-H, 70-H), 7.70 (m, 1H, 7-H), 7.84 (d, J = 8.3 Hz, 1H, 5-H), 7.90 (d, J = 8.3 Hz, 1H, 60-H), 7.97 (m, 2H,
40-H, 50-H), 8.06 (d, J = 8.6 Hz, 1H, 80-H), 8.21 (s, 1H, 10-H), 8.74 (bs, 3H, NH3); 13C-NMR (90 MHz,
DMSO-d6) δ
: 55.8 (C-3), 80.4 (C-2), 118.0 (C-6), 118.6 (C-4a), 122.5 (C-8), 125.1 (C-5), 126.5 (C-10), 126.9
(C-80), 127.7 (C-60, C-70), 128.2 (C-30), 128.7 (C-50), 128.8 (C-40), 131.8 (C-20), 132.6 (C-8a’), 133.7 (C-4a’),
137.5 (C-7), 160.8 (C-8a), 187.4 (C-4).

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(
±
)-(2R*,3S*)-3-amino-2-phenyl-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-cis-1a): White solid, yield
30%, mp 202–204 ◦C; 1H-NMR (400 MHz, DMSO-d6)
: 5.09 (d, J = 5.6 Hz, 1H, 3-H), 6.23 (d, J = 5.6 Hz,
1H, 2-H), 7.15 (m, 2H, 6-H, 8-H), 7.38 (m, 5 H, 20-H, 30-H, 40-H, 50-H, 60-H), 7.68 (m, 1H, 7-H), 7.82
δ
(dd, J = 7.6, 1.6 Hz, 1H, 5-H), 9.09 (bs, 3H, NH3); 13C-NMR (100 MHz, DMSO-d6):
δ = 54.8 (C-3), 78.6
(C-2), 118.4 (C-8), 119.6 (C-4a), 122.4 (C-6), 126.7 (C-5), 127.7 (C-20, C-60), 129.2 (C-30, C-50), 129.6 (C-40),
133.7 (C-10), 138.0 (C-7), 160.2 (C-8a), 187.2 (C-4); HRMS (ESI) calcd. for C15H13NO2 [M + H]+ 240.102;
found 240.101.
( )-(2R*,3S*)-3-amino-2-(4-methoxyphenyl)-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-cis-1b): white
±
solid, yield 14%. mp 186–188 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ: 3.72 (s, 3H, OCH3), 5.11 (d, J =
6.0 Hz, 1H, 3-H), 6.18 (d, J = 6.0 Hz, 1H, 2-H), 6.90 (d, 2H, 30-H, 50-H), 7.11 (d, J = 8.4 Hz, 1H, 8-H), 7.14
(t, J = 7.6 Hz, 1H, 6-H), 7.28 (d, 2H, 20-H, 60-H), 7.65 (m, 1H, 7-H), 7.80 (d, J = 7.6 Hz, 1H, 5-H), 9.08 (bs,
3H, NH3); 13C-NMR (100 MHz, DMSO-d6) : 54.5 (C-3), 55.0 (C-OCH3), 78.0 (C-2), 114.1 (C-30, C-50),
δ
118.0 (C-8), 119.2 (C-4a), 121.8 (C-6), 125.1 (C-10), 126.1 (C-5), 128.9 (C-20, C-60), 137.5 (C-7), 159.6 (C-40),
159.8 (C-8a), 187.1 (C-4); HRMS (ESI) calcd. for C16H15NO3 [M + H]+ 270.113; found 270.111.
(
±
)-(2R*,3S*)-3-amino-2-(3,4-dimethoxyphenyl)-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-cis-1c):
White solid, yield 23%, mp 191–195◦C; 1H-NMR (400 MHz, DMSO-d6)
δ
: 3.70 (d, 6H, 2 OCH3), 5.09
×
(d, J = 5.6 Hz, 1H, 3-H), 6.16 (d, J = 5.6 Hz, 1H, 2-H), 6.76 (dd, J = 8.4, 2.0 Hz, 1H, 8-H), 6.89 (d, J =
8.4 Hz, 1H, 50-H), 7.14 (m, 3H, 6-H, 20-H, 60-H), 7.68 (m, 1H, 7-H), 7.80 (dd, J = 8.0, 1.6 Hz, 1H, 5-H),
9.07 (bs, 3H, NH3); 13C-NMR (100 MHz, DMSO-d6)
δ: 54.8 (C-3), 55.4 (C-OCH3), 55.5 (C-OCH3), 78.2
(C-2), 111.8 (C-20, C-50), 118.1 (C-8), 119.2 (C-60), 119.4 (C-4a), 122.1 (C-6), 125.5 (C-10), 126.3 (C-5), 137.7
(C-7), 148.6 (C-40), 149.4 (C-30), 160.1 (C-8a), 187.2 (C-4); HRMS (ESI) calcd. for C17H17NO4 [M + H]+
300.123; found 300.122.
( )-(2R*,3S*)-3-amino-2-(3,5-dimethoxyphenyl)-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-cis-1d):
±
White solid, yield 20%, mp 195–197 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ
: 3.68 (s, 6H, 2
×
OCH3), 5.05
(d, J = 5.6 Hz, 1H, 3-H), 6.15 (d, J = 5.6 Hz, 1H, 2-H), 6.49 (t, J = 2.4 Hz, 1H, 40-H), 6.56 (d, 2H, 20-H,
60-H), 7.16 (m, 2H, 6-H, 8-H), 7.68 (m, 1H, 7-H), 7.79 (dd, J = 8.0, 1.6 Hz, 1H, 5-H), 9.08 (bs, 3H, NH3);
13C-NMR (100 MHz, DMSO-d6)
δ: 54.6 (C-3), 55.3 (2
×
C-OCH3), 78.2 (C-2), 100.5 (C-40), 105.5 (C-20,
C-60), 118.1 (C-8), 119.4 (C-4a), 122.2 (C-6), 126.4 (C-5), 135.5 (C-10), 137.8 (C-7), 160.1 (C-8a), 160.6 (C-30,
C-50), 186.8 (C-4); HRMS (ESI) calcd. for C17H17NO4 [M + H]+ 300.123; found 300.124.
( )-(2R*,3S*)-3-amino-(3,4,5-trimethoxyphenyl)-2,3-dihydro-4H-chroman-4-one hydrochloride (rac-cis-1e):
±
Off-white solid, yield 17%, mp 194–196 ◦C; 1H-NMR (400 MHz, DMSO-d6) δ: 3.64 (d, 9H, 3 × OCH3),
5.01 (d, J = 5.2 Hz, 1H, 3-H), 6.14 (d, J = 5.2 Hz, 1H, 2-H), 6.75 (s, 2H, 20-H, 60-H), 7.17 (m, 2H, 6-H,
8-H), 7.70 (t, J = 7.6 Hz, 1H, 7-H), 7.82 (d, J = 8.0 Hz, 1H, 5-H), 9.08 (bs, 3H, NH3); 13C-NMR (100 MHz,
DMSO-d6)
δ
: 54.8 (C-3), 55.8 (2
×
C-OCH3), 59.9 (C-OCH3), 78.4 (C-2), 104.8 (C-20, C-60), 118.2 (C-8),
119.4 (C-4a), 122.3 (C-6), 126.4 (C-5), 128.8 (C-10), 137.8 (C-7), 137.9 (C-40), 153.0 (C-30, C-50), 160.2 (C-8a),
187.0 (C-4); HRMS (ESI) calcd. for C18H19NO5 [M + H]+ 330.134; found 330.133.
◦
2. -[(E)-2-phenylethenyl]-1,3-benzoxazole (17a) [18]: Pale yellow crystals, yield 15%, mp 62–64 C;
1H-NMR (400 MHz, CDCl3)
δ
: 7.05 (d, J = 16.4 Hz, 1H, 20-H), 7.30 (m, 2H, 4-H, 7-H), 7.36 (m, 3H, 50-H,
60-H, 70-H), 7.50 (m, 1H, 5-H), 7.57 (d, 2H, 40-H, 80-H), 7.69 (m, 1H, 6-H), 7.76 (d, J = 16.4 Hz, 1H, 10-H);
13C-NMR (100 MHz, CDCl3) : 110.4 (C-20), 114.0 (C-5), 119.9 (C-6), 124.6 (C-4), 125.3 (C-7), 127.6 (C-50,
δ
C-70), 129.0 (C-40, C-80), 129.9 (C-60), 135.2 (C-30), 139.6 (C-10), 142.2 (C-3a), 150.5 (C-7a), 162.9 (C-2);
HRMS (ESI) calcd. for C15H11NO [M + H]+ 222.092; found 222.089.
2. -[(E)-2-(4-methoxyphenyl)ethenyl]-1,3-benzoxazole (17b) [19]: White chrystals, yield 20%, mp 128–130 ◦C;
1H-NMR (400 MHz, CDCl3) : 3.79 (s, 3H, OCH3), 6.88 (m, 3H, 20-H, 50-H, 70-H), 7.27 (m, 2H, 4-H, 7-H),
δ
7.46 (m, 3H, 5-H, 40-H, 80-H), 7.67 (m, 2H, 1’-H, 6-H); 13C-NMR (100 MHz, CDCl3)
δ: 55.4 (C-OCH3),
110.2 (C-5), 111.5 (C-20), 114.4 (C-50, C-70), 119.7 (C-6), 124.4 (C-4), 124.9 (C-7), 127.9 (C-30), 129.1 (C-40,
C-80), 139.1 (C-10), 142.3 (C-3a), 150.4 (C-7a), 161.0 (C-60), 163.2 (C-2); HRMS (ESI) calcd. for C16H13NO2
[M + H]+ 252.102; found 252.103.

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2. -[(E)-2-(3,4-dimethoxyphenyl)ethenyl]-1,3-benzoxazole (17c): Pale yellow crystals, yield: 16%, mp
119–120 ◦C; 1H-NMR (400 MHz, CDCl3) OCH3), 6.86 (d, J = 8.0 Hz, 1H, 70-H), 6.91
: 3.90 (d, 6H, 2
(d, J = 16.4 Hz, 1H, 20-H), 7.11 (s, 1H, 40-H), 7.13 (d, J = 8.0 Hz, 1H, 80-H), 7.29 (m, 2H, 4-H, 7-H), 7.48
δ
×
(m, 1H, 5-H), 7.68 (m, 2H, 6-H, 10-H); 13C-NMR (100 MHz, CDCl3)
δ: 55.9 (C-OCH3), 56.0 (C-OCH3),
109.3 (C-40), 110.2 (C-5), 111.2 (C-70), 111.8 (C-20), 119.7 (C-6), 121.9 (C-80), 124.5 (C-4), 125.0 (C-7), 128.3
(C-30), 139.3 (C-10), 142.3 (C-3a), 149.4 (C-60), 150.4 (C-50), 150.8 (C-7a), 163.2 (C-2); HRMS (ESI) calcd.
for C17H15NO3 [M + H]+ 282.113; found 282.112.
2. -[(E)-2-(3,4,5-trimethoxyphenyl)ethenyl]-1,3-benzoxazole (17e): Pale yellow crystals, yield 14%, mp.
147–149 ◦C; 1H-NMR (400 MHz, CDCl3)
δ
: 3.91 (s, 9 H, 3
×
OCH3), 6.82 (s, 2H, 40-H, 80-H), 6.96 (d,
J = 16.0 Hz, 1H, 20-H), 7.33 (m, 2H, 4-H, 7-H), 7.50 (m, 1H, 5-H), 7.68 (m, 2H, 6-H, 10-H); 13C-NMR
(100 MHz, CDCl3)
δ
: 56.2 (2
×
C-OCH3), 61.1 (C-OCH3), 104.7 (C-40, C-80), 110.3 (C-5), 113.3 (C-20),
119.9 (C-6), 124.6 (C-4), 125.2 (C-7), 130.8 (C-30), 139.4 (C-10), 139.8 (C-60), 142.3 (C-3a), 150.5 (C-7a),
153.6 (C-50, C-70), 162.8 (C-2); HRMS (ESI) calcd. for C18H17NO4 [M + H]+ 312.123; found 312.125.
2. -[(E)-2-(naphthalen-1-yl)ethenyl]-1,3-benzoxazole (17f): Pale yellow crystals, yield: 10%, mp 124–126 ◦C;
1H-NMR (400 MHz, CDCl3) : 7.15 (d, J = 16.0 Hz, 1H, 20-H), 7.34 (m, 2H, 4-H, 7-H), 7.50 (m, 4 H,
δ
5-H, 40-H, 50-H, 90-H), 7.74 (m, 1H, 6-H), 7.84 (m, 3H, 60-H, 70-H, 80-H), 8.28 (d, J = 8.4 Hz, 1H, 100-H),
8.59 (d, J = 16.0 Hz, 1H, 10-H); 1H-NMR (400 MHz, CDCl3) : 110.5 (C-5), 116.5 (C-20), 120.1 (C-6),
δ
123.5 (C-100), 124.6 (C-4), 124.7 (C-40), 125.4 (C-7), 125.7 (C-50), 126.3 (C-90), 126.9 (C-80), 128.9 (C-70),
130.2 (C-60), 131.4 (C-6a’), 132.6 (C-10a’), 133.9 (C-30), 136.4 (C-10), 142.4 (C-3a), 150.6 (C-7a), 162.9 (C-2);
HRMS (ESI) calcd. for C19H13NO [M + H]+ 272.107; found 272.106.
2. -[(E)-2-(naphthlaen-2-yl)ethenyl]-1,3-benzoxazole (17g) [18]: White crystals, yield 11%, mp 129–131 ◦C;
1H-NMR (400 MHz, CDCl3) : 7.11 (d, J = 16.4 Hz, 1H, 20-H), 7.28 (m, 2H, 4-H, 7-H), 7.45 (m, 3H, 5-H,
δ
40-H, 80-H), 7.68 (m, 2H, 6-H, 70-H), 7.77 (m, 3H, 50-H, 60-H, 90-H), 7.90 (m, 2H, 100-H, 10-H); 1H-NMR
(400 MHz, CDCl3) δ
: 110.4 (C-5), 114.1 (C-20), 120.0 (C-6), 123.2 (C-100), 124.6 (C-4), 125.3 (C-7), 126.8
(C-90), 127.1 (C-40), 127.9 (C-80), 128.5 (C-70), 128.8 (C-60), 129.2 (C-50), 132.7 (C-5a’), 133.5 (C-9a’), 134.0
(C-30), 139.5 (C-10), 142.3 (C-3a), 150.5 (C-7a), 162.9 (C-2); HRMS (ESI) calcd. for C19H13NO [M + H]+
272.107; found 272.107.
2.4. General Procedure for the Synthesis of 2-Chloroacetamide Derivatives (rac-trans-18a-g)
The hydrochloride salt of 3-aminoflavanone derivatives rac-cis-1a-g or rac-trans-1a-g (1.452 mmol)
was suspended in anhydrous THF under inert atmosphere. After addition of Et3N (510 µL, 3.630 mmol),
the reaction was stirred for 5 min at room temperature or at 0 ◦C. Then chloroacetyl chloride (139 µL,
1.742 mmol) was added dropwise to the suspension and it was stirred further for 15 min. The reaction
was quenched with water and then it was extracted with CH2Cl2. The combined organic phases were
dried over MgSO4 and concentrated under reduced pressure. Trituration with cold Et2O afforded the
pure product.
(
±
)-2-chloro-N-[(2R*,3R*)-2-phenyl-4-oxochroman-3-yl]acetamide (rac-trans-18a): White crystals, yield 77%,
mp 214–216 ◦C; 1H-NMR (400 MHz, CDCl3)
δ
: 3.82 (d, J = 15.6 Hz, 1H, CH2-Ha), 3.95 (d, J = 15.6 Hz,
1H, CH2-Hb), 5.08 (dd, J = 12.0, 8.4 Hz, 1H, 3-H), 5.39 (d, J = 12.0 Hz, 1H, 2-H), 6.79 (d, J = 8.0 Hz, 1H,
NH), 7.06 (d, J = 8.4 Hz, 1H, 8-H), 7.09 (t, J = 7.6 Hz, 1H, 6-H), 7.41 (m, 3H, 30-H, 40-H, 50-H), 7.50 (m,
3H, 7-H, 20-H, 60-H), 7.93 (dd, J = 7.6, 1.2 Hz, 1H, 5-H); 13C-NMR (100 MHz, CDCl3)
δ: 42.4 (C-CH2),
58.4 (C-3), 83.2 (C-2), 118.2 (C-8), 120.0 (C-4a), 122.4 (C-6), 127.7 (C-20, C-60), 127.8 (C-5), 128.7 (C-30,
C-50), 129.6 (C-40), 135.7 (C-10), 136.9 (C-7), 161.4 (C-8a), 166.2 (amide carbonyl), 189.9 (C-4); HRMS
(ESI) calcd. for C17H14ClNaNO3 [M+Na]+ 338.056; found 338.056.
( )-2-chloro-N-[(2R*,3R*)-2-(4-methoxyphenyl)-4-oxochroman-3-yl]acetamide (rac-trans-18b): White crystals,
±
yield 71%, mp 179–180 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ: 3.77 (s, 3H, OCH3), 3.99 (m, 2H, CH2),
5.00 (dd, J = 12.4, 8.4 Hz, 1H, 3-H), 5.57 (d, J = 12.4 Hz, 1H, 2-H), 6.95 (d, 2H, 30-H, 50-H), 7.07 (d, J =
8.0 Hz, 1H, 8-H), 7.13 (m, 1H, 6-H), 7.42 (d, 2H, 20-H, 60-H), 7.61 (m, 1H, 7-H), 7.81 (dd, J = 7.6, 1.6 Hz,

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1H, 5-H), 8.51 (d, J = 8.4 Hz, 1H, NH); 13C-NMR (100 MHz, DMSO-d6)
δ
: 42.3 (C-CH2), 55.3 (C-OCH3),
57.8 (C-3), 81.2 (C-2), 113.8 (C-30, C-50), 118.2 (C-8), 120.1 (C-4a), 122.1 (C-6), 127.1 (C-5), 128.9 (C-10),
129.4 (C-20, C-60), 136.7 (C-7), 159.8 (C-40), 161.1 (C-8a), 166.2 (amide carbonyl), 190.0 (C-4); HRMS (ESI)
calcd. for C18H16ClNaNO4 [M+Na]+ 368.066; found 368.067.
(
±
)-2-chloro-N-[(2R*,3R*)-2-(3,4-dimethoxyphenyl)-4-oxochroman-3-yl]acetamide (rac-trans-18c): White
crystals, yield 80%, mp 183–185 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ: 3.77 (s, 6H, 2xOCH3), 3.96 (m,
2H, CH2), 5.03 (dd, J = 12.4, 8.4 Hz, 1H, 3-H), 5.56 (d, J = 12.4 Hz, 1H, 2-H), 6.95 (d, J = 8.4 Hz, 1H,
50-H), 7.00 (dd, J = 8.4, 1.6 Hz, 1H, 60-H), 7.08 (d, J = 8.0 Hz, 1H, 8-H), 7.12 (m, 2H, 6-H, 20-H), 7.60
(m, 1H, 7-H), 7.82 (dd, J = 7.6, 1.6 Hz, 1H, 5-H), 8.52 (d, J = 8.4 Hz, 1H, NH); 13C-NMR (100 MHz,
DMSO-d6) δ
: 42.2 (C-CH2), 55.5 (2xC-OCH3), 57.6 (C-3), 81.2 (C-2), 109.5 (C-20), 111.2 (C-50), 118.0 (C-8),
119.9 (C-4a), 120.7 (C-60), 121.9 (C-6), 126.9 (C-5), 129.0 (C-10), 136.4 (C-7), 148.4 (C-40), 149.2 (C-30),
160.8 (C-8a), 166.0 (amide carbonyl), 189.8 (C-4); HRMS (ESI) calcd. for C19H18ClNaNO5 [M+Na]+
398.077; found 398.078.
( )-2-chloro-N-[(2R*,3R*)-2-(3,5-dimethoxyphenyl)-4-oxochroman-3-yl]acetamide (rac-trans-18d): White
±
crystals, yield 80%, mp 206–208 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ: 3.74 (s, 6 H, 2
×
OCH3), 4.01 (s,
2H, CH2), 4.96 (dd, J = 12.0, 8.4 Hz, 1H, 3-H), 5.57 (d, J = 12.0 Hz, 1H, 2-H), 6.49 (t, J = 2.4 Hz, 1H, 40-H),
6.68 (d, 2H, 20-H, 60-H), 7.09 (d, J = 8.0 Hz, 1H, 8-H), 7.13 (t, J = 7.6 Hz, 1H, 6-H), 7.61 (m, 1H, 7-H), 7.80
(dd, J = 7.6, 1.6 Hz, 5-H), 8.67 (d, J = 8.4 Hz, 1H, NH); 13C-NMR (100 MHz, DMSO-d6)
δ: 42.1 (C-CH2),
55.3 (2
×
C-OCH3), 57.6 (C-3), 81.0 (C-2), 100.7 (C-40), 105.8 (C-20, C-60), 118.0 (C-8), 119.8 (C-4a), 122.0
(C-6), 126.9 (C-5), 136.5 (C-7), 138.8 (C-10), 160.2 (C-30, C-50), 160.7 (C-8a), 166.1 (amide carbonyl), 189.5
(C-4); HRMS (ESI) calcd. for C19H18ClNaNO5 [M+Na]+ 398.077; found 398.077.
( )-2-chloro-N-[(2R*,3R*)-2-(3,4,5-trimethoxyphenyl)-4-oxochroman-3-yl]acetamide (rac-trans-18e): White
±
crystals, yield 74%, mp 140–142 ◦C; 1H-NMR (400 MHz, CDCl3)
δ
: 3.83 (m, 9H, 3
×
OCH3), 3.84 (m, 2H,
CH2), 5.03 (dd, J = 12.4, 8.8 Hz, 1H, 3-H), 5.41 (d, J = 12.4 Hz, 1H, 2-H), 6.74 (s, 2H, 20-H, 60-H), 6.99 (m,
2H, 6-H, 8-H), 7.29 (d, J = 8.8 Hz, 1H, NH), 7.47 (m, 1H, 7-H), 7.80 (d, J = 7.6, 1.2 Hz, 1H, 5-H); 13C-NMR
(100 MHz, CDCl3)
δ
: 41.9 (C-CH2), 55.8 (2
×
C-OCH3), 57.8 (C-3), 60.4 (C-OCH3), 82.2 (C-2), 104.4
(C-20, C-60), 117.7 (C-8), 119.5 (C-4a), 121.8 (C-6), 127.1 (C-5), 131.0 (C-10), 136.2 (C-7), 138.1 (C-40), 152.8
(C-30, C-50), 160.7 (C-8a), 166.3 (amide carbonyl), 189.5 (C-4); HRMS (ESI) calcd. for C20H20ClNaNO6
[M+Na]+ 428.088; found 428.089.
(
±
)-2-chloro-N-[(2R*,3R*)-2-(naphthalen-1-yl)-4-oxochroman-3-yl]acetamide (rac-trans-18f): White crystals,
yield 79%, mp 252–254 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ
: 3.80 (q, 2H, CH2), 5.33 (t, J = 10.8 Hz, 1H,
3-H), 6.48 (d, J = 12.0 Hz, 1H, 2-H), 7.09 (d, J = 8.0 Hz, 1H, 8-H), 7.18 (t, J = 7.6 Hz, 1H, 6-H), 7.55 (m,
4 H, 7-H, 20-H, 30-H, 70-H), 7.82 (s, 1H, 60-H), 7.90 (d, J = 7.6 Hz, 1H, 5-H), 7.98 (m, 2H, 40-H, 50-H), 8.29
(s, 1H, 80-H), 8.57 (d, J = 8.0 Hz, 1H, NH); 13C-NMR (100 MHz, DMSO-d6)
δ: 42.0 (C-CH2), 57.3 (C-3),
78.1 (C-2), 118.0 (C-8), 120.1 (C-4a), 122.1 (C-6), 125.2 (C-5), 125.8 (C-20, C-30), 126.5 (C-70), 127.0 (C-60),
128.7 (C-40), 129.5 (C-50), 131.2 (C-4a’), 132.4 (C-8a’), 133.3 (C-10), 136.5 (C-7), 160.9 (C-8a), 166.1 (amide
carbonyl), 189.6 (C-4); HRMS (ESI) calcd. for C21H16ClNaNO3 [M+Na]+ 388.072; found 388.073.
( )-2-chloro-N-[(2R*,3R*)-2-(naphthalen-2-yl)-4-oxochroman-3-yl]acetamide (rac-trans-18g). White crystals,
±
yield, 82%, mp 226–228 ◦C; 1H-NMR (360 MHz, DMSO-d6)
δ: 3.91 (q, 2H, CH2), 5.11 (dd, J = 12.2,
8.3 Hz, 1H, 3-H), 5.82 (d, J = 12.2 Hz, 1H, 2-H), 7,12 (m, 2H, 6-H, 8-H), 7.54 (m, 2H, 30-H, 70-H), 7.62 (m,
1H, 7-H), 7.69 (dd, J = 8.6, 1.4 Hz, 1H, 5-H), 7.85 (dd, J = 7.6, 1.4 Hz, 1H, 60-H), 7.94 (m, 4 H, 10-H, 40-H,
50-H, 80-H), 8.59 (d, J = 8.3 Hz, 1H, NH); 13C-NMR (90 MHz, DMSO-d6)
δ: 42.0 (C-CH2), 57.7 (C-3),
81.3 (C-2), 118.0 (C-8), 120.0 (C-4a), 122.0 (C-6), 124.9 (C-5), 126.3 (C-10), 126.5 (C-80), 126.9 (C-30), 127.2
(C-70), 127.5 (C-60), 127.8 (C-50), 128.0 (C-40), 132.4 (C-8a’), 133.1 (C-4a’), 134.2 (C-20), 136.4 (C-7), 160.7
(C-8a), 166.0 (amide carbonyl), 189.4 (C-4); HRMS (ESI) calcd. for C21H16ClNaNO3 [M+Na]+ 388.072;
found 388.073.

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2.5. General Procedure for the Synthesis of Flavan-4-ol Derivatives rac-19a-g and rac-22a-g
To the solution of the chloroacetamide derivatives (0.958 mmol) in MeOH (10 mL), NaBH4
(1.150 mmol) was added and reaction mixture was stirred at room temperature. The reaction was
completed in 10 min. The pH was adjusted to about 5 with 10% HCl solution and the mixture was
concentrated and the residue was extracted with ethyl acetate and water. The combined organic phase
was dried over MgSO4 and the solvent was evaporated in vacuum. Column chromatography with
CHCl3 as eluent provided the pure product.
(±
)-2-chloro-N-[(2R*,3S*,4R*)-4-Hydroxy-2-phenyl-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-19a): White
crystals, yield 90%, mp 157–159 ◦C; 1H-NMR (400 MHz, acetone-d6)
δ: 3.76 (d, J = 14.0 Hz, 1H, CH2-Ha),
3.86 (d, J = 14.0 Hz, 1H, CH2-Hb), 4.31 (q, J = 9.2 Hz, 1H, 3-H), 4.87 (d, J = 6.4 Hz, 1H, OH), 5.11 (dd, J =
9.2, 6.4 Hz, 1H, 4-H), 5.22 (d, J = 10.4 Hz, 1H, 2-H), 6.80 (dd, J = 8.0, 0.8 Hz, 1H, 8-H), 6.96 (m, 1H, 6-H),
7.17 (m, 1H, 7-H), 7.32 (m, 3H, 30-H, 40-H, 50-H), 7.47 (m, 2H, 20-H, 60-H), 7.54 (d, J = 8.0 Hz, 1H, 5-H),
7.61 (d, J = 8.8 Hz, NH); 13C-NMR (100 MHz, acetone-d6)
δ: 43.2 (C-CH2), 56.6 (C-3), 69.6 (C-4), 80.5
(C-2), 116.7 (C-8), 121.7 (C-6), 126.6 (C-4a), 128.7 (C-20, C-60), 128.8 (C-30, C-50), 128.9 (C-40), 129.1 (C-5),
129.5 (C-7), 138.8 (C-10), 154.9 (C-8a), 166.6 (amide carbonyl); HRMS (ESI) calcd. for C17H16ClNaNO3
[M+Na]+ 340.071; found 340.073.
(±
)-2-chloro-N-[(2R*,3S*,4R*)-4-Hydroxy-2-(4-methoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide
(rac-19b): White crystals, yield 92%, mp 163–164 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ
: 3.74 (bs, 1H,
OH), 3.81 (m, 4 H, CH2-Ha, OCH3), 3.99 (d, J = 15.6 Hz, 1H, CH2-Hb), 4.27 (m, 1H, 3-H), 4.99 (d, 2H,
2-H, 4-H), 6.51 (d, J = 6.4 Hz, 1H, NH), 6.88 (d, J = 7.2 Hz, 1H, 8-H), 6.92 (d, 2H, 30-H, 50-H), 7.02 (m,
1H, 6-H), 7.21 (m, 1H, 7-H), 7.35 (d, 2H, 20-H, 60-H), 7.54 (d, J = 7.6 Hz, 1H, 5-H); 13C-NMR (100 MHz,
DMSO-d6) δ
: 42.9 (C-CH2), 55.8 (C-OCH3), 57.5 (C-3), 70.8 (C-4), 79.4 (C-2), 114.8 (C-30, C-50), 116.9
(C-8), 122.3 (C-6), 124.4 (C-4a), 128.6 (C-10), 128.7 (C-5), 129.3 (C-20, C-60), 129.9 (C-7), 154.0 (C-8a), 160.8
(C-40), 167.5 (amide carbonyl); HRMS (ESI) calcd. for C18H18NaNO4 [M+Na]+ 370.109; found 370.110.
(±
)-2-chloro-N-[(2R*,3S*,4R*)-4-Hydroxy-2-(3,4-dimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide
(rac-19c): White crystals, yield 98%, mp 156–158 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 3.78 (d, J = 15.2 Hz,
1H, CH2-Ha), 3.87 (d, 6H, 2
×
OCH3), 3.92 (m, 2H, CH2-Hb, OH), 4.26 (q, J = 9.2 Hz, 1H, 3-H), 4.96 (m,
2H, 2-H, 4-H), 6.56 (d, J = 6.8 Hz, 1H, NH), 6.85 (m, 2H, 20-H, 50-H), 6.95 (m, 3H, 8-H, 20-H, 60-H), 7.00
(t, J = 7.6 Hz, 1H, 6-H), 7.19 (t, J = 8.0 Hz, 1H, 7-H), 7.51 (d, J = 7.6 Hz, 1H, 5-H); 13C-NMR (100 MHz,
CDCl3) δ
: 42.6 (C-CH2), 56.0 (C-OCH3), 56.1 (C-OCH3), 56.9 (C-3), 70.3 (C-4), 79.3 (C-2), 110.1 (C-50),
111.1 (C-20), 116.6 (C-60), 120.5 (C-8), 121.9 (C-6), 124.2 (C-4a), 128.3 (C-5), 128.7 (C-10), 129.5 (C-7),
149.5 (C-40), 149.9 (C-30), 153.6 (C-8a), 167.2 (amide carbonyl); HRMS (ESI) calcd. for C19H20ClNaNO5
[M+Na]+ 400.092; found 400.094.
(±
)-2-chloro-N-[(2R*,3S*,4R*)-4-Hydroxy-2-(3,5-dimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide
(rac-19d). White crystals, yield 94%, mp 160–162 ◦C; 1H-NMR (400 MHz, acetone-d6)
δ: 3.78 (d, 6H,
2xOCH3), 3.83 (d, J = 14.0 Hz, 1H, CH2-Ha), 3.92 (d, J = 14.0 Hz, 1H, CH2-Hb), 4.31 (q, J = 9.2 Hz, 1H,
3-H), 4.90 (d, J = 6.0 Hz, 1H, OH), 5.11 (dd, J = 9.2, 6.0 Hz, 1H, 4-H), 5.17 (d, J = 10.4 Hz, 1H, 2-H), 6.44
(t, J = 2.4 Hz, 1H, 40-H), 6.69 (d, 2H, 20-H, 60-H), 6.81 (d, J = 8.4 Hz, 1H, 8-H), 6.96 (m, 1H, 6-H), 7.17 (m,
1H, 7-H), 7.54 (d, J = 7.6 Hz, 1H, 5-H), 7.64 (d, J = 9.2 Hz, 1H, NH); 13C-NMR (101 MHz, acetone-d6)
δ:
44.2 (C-CH2), 56.6 (2xC-OCH3), 57.4 (C-3), 70.6 (C-4), 81.4 (C-2), 102.2 (C-40), 107.5 (C-20, C-60), 117.7
(C-8), 122.7 (C-6), 127.5 (C-4a), 129.8 (C-5), 130.4 (C-7), 141.9 (C-10), 155.8 (C-8a), 162.4 (C-30, C-50), 167.7
(amide carbonyl); HRMS (ESI) calcd. for C19H19NaNO5 [M+Na]+ 364.116; found 364.118; HRMS (ESI)
calcd. for C19H20ClNaNO5 [M+Na]+ 400.092; found 400.094.
(±
)-2-chloro-N-[(2R*,3S*,4R*)-4-Hydroxy-2-(3,4,5-trimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide
(rac-19e): White crystals, yield 92%, mp 155–157 ◦C; 1H-NMR (400 MHz, CDCl3)
δ
: 3.79 (m, 10 H,
CH2-Ha, 3xOCH3), 3.92 (d, J = 15.2 Hz, 1H, CH2-Hb), 4.06 (bs, 1H, OH), 4.23 (q, J = 8.8 Hz, 1H, 3-H),
4.96 (m, 2H, 2-H, 4-H), 6.64 (m, 3H, NH, 20-H, 60-H), 6.88 (d, J = 8.4 Hz, 1H, 8-H), 7.00 (t, J = 7.6 Hz,
1H, 6-H), 7.20 (t, J = 7.2 Hz, 1H, 7-H), 7.50 (d, J = 7.6 Hz, 1H, 5-H); 13C-NMR (100 MHz, CDCl3)
δ:

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42.2 (C-CH2), 55.9 (2xC-OCH3), 56.6 (C-3), 60.5 (C-OCH3), 69.6 (C-4), 79.2 (C-2), 104.2 (C-20, C-60),
116.1 (C-8), 121.6 (C-6), 123.8 (C-4a), 127.8 (C-5), 129.1 (C-7), 131.5 (C-10), 138.2 (C-40), 153.1 (C-8a),
153.2 (C-30, C-50), 166.8 (amide carbonyl); HRMS (ESI) calcd. for C20H22ClNaNO6 [M+Na]+ 430.103;
found 430.104.
(
±
)-2-chloro-N-[(2R*,3S*,4R*)-4-Hydroxy-2-(naphthalen-1-yl)-3,4-dihydro-2H-chromen-3-yl]acetamide
(rac-19f): White crystals, yield 88%, mp 247–249 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ: 3.64 (m, 2H,
CH2), 4.49 (q, J = 9.6 Hz, 1H, 3-H), 5.00 (t, J = 8.0 Hz, 1H, 4-H), 5.77 (d, J = 6.8 Hz, 1H, OH), 5.89 (d, J =
10.4 Hz, 1H, 2-H), 6.80 (d, J = 8.0 Hz, 1H, 8-H), 7.00 (t, J = 7.6 Hz, 1H, 6-H), 7.18 (t, J = 7.2 Hz, 1H, 7-H),
7.48 (m, 4 H, 20-H, 30-H, 60-H, 70-H), 7.65 (d, J = 7.2 Hz, 1H, 5-H), 7.90 (m, 2H, 40-H, 50-H), 8.21 (d,
J = 9.2 Hz, 1H, NH), 8.28 (d, J = 9.2 Hz, 1H, 80-H); 13C-NMR (100 MHz, DMSO-d6)
δ: 42.4 (C-CH2),
53.8 (C-3), 67.9 (C-4), 76.2 (C-2), 115.7 (C-8), 120.9 (C-6), 124.0 (C-80), 125.1 (C-20, C-30), 125.5 (C-5),
126.0 (C-70), 126.2 (C-4a), 128.1 (C-60), 128.5 (C-7, C-50), 128.8 (C-40), 131.4 (C-10), 133.2 (C-4a’), 133.3
(C-8a’), 153.5 (C-8a), 165.3 (amide carbonyl); HRMS (ESI) calcd. for C21H18ClNaNO3 [M+Na]+ 390.087;
found 390.088.
(
±
)-2-chloro-N-[(2R*,3S*,4R*)-4-Hydroxy-2-(naphthalen-2-yl)-3,4-dihydro-2H-chromen-3-yl]acetamide
(rac-19g): White crystals, yield 89%, mp 210–212 ◦C; 1H-NMR (400 MHz, acetone-d6)
δ: 3.69 (d, J =
14.0 Hz, 1H, CH2-Ha), 3.83 (d, J = 14.0 Hz, 1H, CH2-Hb), 4.41 (q, J = 9.2 Hz, 1H, 3-H), 4.89 (d, J =
6.4 Hz, 1H, OH), 5.20 (dd, J = 9.2, 6.8 Hz, 1H, 4-H), 5.43 (d, J = 10.4 Hz, 1H, 2-H), 6.85 (d, J = 8.4 Hz, 1H,
8-H), 6.99 (m, 1H, 6-H), 7.20 (m, 1H, 7-H), 7.50 (m, 2H, 30-H, 70-H), 7.58 (d, J = 7.6 Hz, 1H, 5-H), 7.64 (m,
2H, 60-H, NH), 7.88 (m, 3H, 40-H, 50-H, 80-H), 7.98 (s, 1H, 10-H); 13C-NMR (100 MHz, acetone-d6)
δ:
43.2 (C-CH2), 56.7 (C-3), 69.6 (C-4), 80.6 (C-2), 116.8 (C-8), 121.8 (C-6), 126.1 (C-80), 126.7 (C-4a), 126.9
(C-10), 127.0 (C-30), 128.2 (C-5), 128.5 (C-70), 128.6 (C-60), 128.9 (C-40, C-50), 129.5 (C-7), 133.9 (C-4a’),
134.4 (C-8a’), 136.4 (C-20), 154.9 (C-8a), 166.6 (amide carbonyl); HRMS (ESI) calcd. for C21H18ClNaNO3
[M+Na]+ 390.087; found 390.087.
(
±
)-2-chloro-N-[(2R*,3R*,4R*)-4-Hydroxy-2-phenyl-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-22a): White
crystals, overall yield of acylation and reduction 62%, mp 142–144 ◦C; 1H-NMR (400 MHz, CDCl3)
δ:
3.70 (d, J = 15.2 Hz, 1H, CH2-Ha), 3.84 (d, J = 15.2 Hz, 1H, CH2-Hb), 3.90 (d, J = 5.2 Hz, 1H, OH), 4.72
(dd, J = 9.2, 5.2 Hz, 1H, 3-H), 5.27 (t, J = 5.2 Hz, 1H, 4-H), 5.34 (s, 1H, 2-H), 6.80 (d, J = 9.2 Hz, 1H, NH),
6.98 (d, J = 8.0 Hz, 1H, 8-H), 7.02 (t, J = 7.2 Hz, 1H, 6-H), 7.22 (t, J = 7.2 Hz, 1H, 7-H), 7.32 (m, 5H, 20-H,
30-H, 40-H, 50-H, 60-H), 7.54 (d, J = 8.0 Hz, 1H, 5-H); 13C-NMR (100 MHz, CDCl3)
δ: 42.6 (C-CH2), 51.8
(C-3), 67.4 (C-4), 77.3 (C-2), 116.6 (C-8), 122.4 (C-6), 122.9 (C-4a), 125.8 (C-20, C-60), 128.3 (C-5), 128.4
(C-40), 128.6 (C-30, C-50), 129.5 (C-7), 136.9 (C-10), 153.2 (C-8a), 168.1 (amide carbonyl); HRMS (ESI)
calcd. for C17H16ClNaNO3 [M+Na]+ 340.071; found 340.073.
( )-2-chloro-N-[(2R*,3R*,4R*)-4-Hydroxy-2-(4-methoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide
±
◦
1
(rac-22b): White crystals, overall yield of acylation and reduction 54%, mp 179–181 C; H-NMR
(400 MHz, CDCl3) : 3.18 (bs, 1H, OH), 3.82 (s, 3H, OCH3), 3.83 (d, J = 15.2 Hz, 1H, CH2-Ha), 3.95 (d,
δ
J = 15.2 Hz, 1H, CH2-Hb), 4.72 (m, 1H, 3-H), 5.31 (bs, 1H, 4-H), 5.34 (s, 1H, 2-H), 6.83 (d, J = 8.8 Hz, 1H,
NH), 6.91 (m, 2H, 30-H, 50-H), 6.98 (dd, J = 8.4, 1.2 Hz, 1H, 8-H), 7.05 (m, 1H, 6-H), 7.26 (m, 1H, 7-H),
7.36 (d, 2H, 20-H, 60-H), 7.56 (d, J = 7.6 Hz, 1H, 5-H); 13C-NMR (100 MHz, CDCl3)
δ: 42.6 (C-CH2), 52.1
(C-3), 55.4 (C-OCH3), 68.0 (C-4), 76.9 (C-2), 114.2 (C-30, C-50), 116.7 (C-8), 122.5 (C-6), 123.0 (C-4a), 127.1
(C-20, C-60), 128.4 (C-5), 128.8 (C-10), 129.6 (C-7), 153.3 (C-8a), 159.7 (C-40), 168.4 (amide carbonyl);
HRMS (ESI) calcd. for C18H18NaNO4 [M+Na]+ 370.109; found 370.110.
( )-2-chloro-N-[(2R*,3R*,4R*)-4-Hydroxy-2-(3,4-dimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide
±
◦
1
(rac-22c): White crystals, overall yield of acylation and reduction 70%, mp 124–126 C; H-NMR
(400 MHz, CDCl3) : 3.57 (d, J = 5.2 Hz, 1H, OH), 3.81 (d, J = 15.2 Hz, 1H, CH2-Ha), 3.88 (d, 6H,
δ
2xOCH3), 3.94 (d, J = 15.2 Hz, 1H, CH2-Hb), 4.71 (m, 1H, 3-H), 5.29 (m, 2H, 2-H, 4-H), 6.86 (m, 2H, NH,
50-H), 6.98 (m, 3H, 8-H, 20-H, 60-H), 7.05 (m, 1H, 6-H), 7.24 (m, 1H, 7-H), 7.55 (d, J = 7.6 Hz, 1H, 5-H);
13C-NMR (100 MHz, CDCl3)
δ: 42.7 (C-CH2), 52.0 (C-3), 56.0 (C-OCH3), 56.1 (C-OCH3), 67.7 (C-4), 77.0

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(C-2), 108.9 (C-50), 111.2 (C-20), 116.7 (C-60), 118.2 (C-8), 122.5 (C-6), 123.0 (C-4a), 128.3 (C-5), 129.3
(C-10), 129.5 (C-7), 149.0 (C-40), 149.1 (C-30), 153.2 (C-8a), 168.1 (amide carbonyl); HRMS (ESI) calcd. for
C19H20ClNaNO5 [M+Na]+ 400.092; found 400.094.
( )-2-chloro-N-[(2R*,3R*,4R*)-4-Hydroxy-2-(3,5-dimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide
±
◦
1
(rac-22d): White crystals, overall yield of acylation and reduction 59%, mp 156–158 C; H-NMR
(360 MHz, CDCl3) δ: 3.61 (d, J = 5.0 Hz, 1H, OH), 3.78 (m, 8 H, CH2, 2xOCH3), 4.72 (dd, J = 7.9, 5.0 Hz,
1H, 3-H), 5.30 (s, 2H, 2-H, 4-H), 6.42 (t, J = 2.4 Hz, 1H, 40-H), 6.60 (d, 2H, 20-H, 60-H), 6.87 (d, J = 9.0 Hz,
1H, NH), 6.99 (d, J = 7.9 Hz, 1H, 8-H), 7.04 (t, J = 7.6 Hz, 1H, 6-H), 7.24 (m, 1H, 7-H), 7.55 (d, J = 7.6 Hz,
1H, 5-H); 13C-NMR (90 MHz, CDCl3)
δ: 42.7 (C-CH2), 52.2 (C-3), 55.5 (2xC-OCH3), 67.9 (C-4), 77.1
(C-2), 100.4 (C-40), 103.9 (C-20, C-60), 116.6 (C-8), 122.5 (C-6), 123.1 (C-4a), 128.4 (C-5), 129.5 (C-7), 139.2
(C-10), 153.1 (C-8a), 161.2 (C-30, C-50), 168.3 (amide carbonyl); HRMS (ESI) calcd. for C19H20ClNaNO5
[M+Na]+ 400.092; found 400.094.
( )-2-chloro-N-[(2R*,3R*,4R*)-4-Hydroxy-2-(3,4,5-trimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide
±
◦
1
(rac-22e): White crystals, overall yield of acylation and reduction 66%, mp 76–78 C; H-NMR
(400 MHz, CDCl3)
δ
: 3.77 (m, 12H, CH2, OH, 3
×
OCH3), 4.70 (dd, J = 8.8, 4.8 Hz, 1H, 3-H), 5.27 (s, 2H,
2-H, 4-H), 6.66 (s, 2H, 20-H, 60-H), 6.84 (d, J = 9.2 Hz, 1H, NH), 6.98 (d, J = 8.4 Hz, 1H, 8-H), 7.02 (t, J =
7.6 Hz, 1H, 6-H), 7.22 (t, J = 7.6 Hz, 1H, 7-H), 7.52 (d, J = 7.6 Hz, 1H, 5-H); 13C-NMR (100 MHz, CDCl3)
δ
: 42.5 (C-CH2), 51.6 (C-3), 56.1 (2
×
C-OCH3), 60.7 (C-OCH3), 67.3 (C-4), 77.1 (C-2), 102.8 (C-20, C-60),
116.4 (C-8), 122.3 (C-6), 122.8 (C-4a), 128.1 (C-5), 129.3 (C-7), 132.2 (C-10), 137.7 (C-40), 152.9 (C-8a),
153.2 (C-30, C-50), 167.9 (amide carbonyl); HRMS (ESI) calcd. for C20H22ClNaNO6 [M+Na]+ 430.103;
found 430.104.
( )-2-chloro-N-[(2R*,3R*,4R*)-4-Hydroxy-2-(naphthalen-2-yl)-3,4-dihydro-2H-chromen-3-yl]acetamide
±
◦
1
(rac-22g): White crystals, overall yield of acylation and reduction 68%, mp 69–71 C; H-NMR
(360 MHz, acetone-d6) : 3.82 (q, 2H, CH2), 4.59 (d, J = 7.9 Hz, 1H, OH), 4.94 (m, 1H, 3-H), 5.40 (t, J =
δ
5.4 Hz, 1H, 4-H), 5.71 (s, 1H, 2-H), 6.95 (d, J = 8.3 Hz, 1H, 8-H), 7.01 (m, 1H, 6-H), 7.21 (m, 2H, 7-H,
NH), 7.48 (m, 2H, 60-H, 70-H), 7.58 (d, J = 7.6 Hz, 1H, 5-H), 7.69 (dd, J = 8.6, 1.4 Hz, 1H, 30-H), 7.9 (m,
3H, 40-H, 50-H, 80-H), 8.09 (s, 1H, 10-H); 13C-NMR (90 MHz, acetone-d6)
δ: 43.3 (C-CH2), 52.0 (C-3), 67.3
(C-4), 78.8 (C-2), 117.0 (C-8), 122.3 (C-6), 125.2 (C-80), 125.3 (C-4a), 126.0 (C-10), 126.8 (C-30), 126.9 (C-5),
128.5 (C-60, C-70), 128.9 (C-40), 129.1 (C-50), 129.6 (C-7), 134.0 (C-4a’, C-8a’), 136.6 (C-20), 154.6 (C-8a),
167.4 (amide carbonyl); HRMS (ESI) calcd. for C21H18ClNaNO3 [M+Na]+ 390.087; found 390.087.
2.6. General Procedure for the Synthesis of 1,4-oxazin-3-one Derivatives rac-20a-g and rac-23a-e, g
The flavan-4-ol derivative rac-19g or rac-22g (0.629 mmol) was dissolved in anhydrous THF
(10 mL) under inert atmosphere. To the stirred solution, 60% dispersion of NaH (0.755 mmol) was
added at room temperature. The reaction was quenched after 15 min with the addition of water.
The pH was adjusted to about 5 with 10% HCl solution and then the mixture was extracted with
CH2Cl2. The organic phases dried over MgSO4 and concentrated under reduced pressure. Column
chromatography using CHCl3 as eluent provided the pure product.
(±
)-(4aS*,5R*,10bR*)-5-phenyl-4,4a,5,10b-tetrahydrochromeno [4,3-b][1,4]oxazin-3(2H)-one (rac-20a): White
crystals, yield 88%, mp 255–257 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 3.84 (t, J = 10.0 Hz, 1H, 4a-H), 4.40
(q, 2H, 2-H), 4.83 (d, J = 9.2 Hz, 1H, 10b-H), 4.98 (d, J = 10.4 Hz, 1H, 5-H), 5.45 (bs, 1H, NH), 6.90 (d, J =
8.0 Hz, 1H, 7-H), 7.02 (t, J = 7.6 Hz, 1H, 9-H), 7.24 (t, J = 7.6 Hz, 1H, 8-H), 7.44 (m, 6 H, 10-H, 20-H,
30-H, 40-H, 50-H, 60-H); 13C-NMR (100 MHz, CDCl3)
δ: 55.6 (C-4a), 68.4 (C-2), 73.8 (C-10b), 79.4 (C-5),
116.5 (C-7), 120.1 (C-10a), 121.6 (C-9), 125.6 (C-10), 127.7 (C-20, C-60), 129.6 (C-30, C-50), 130.0 (C-8),
130.2 (C-40), 134.7 (C-10), 153.3 (C-6a), 168.9 (C-3); HRMS (ESI) calcd. for C17H15NO3 [M + H]+ 282.113;
found 282.115.
(4aS,5R,10bR)-20a: tR = 4.52 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}: 282sh (−3.79), 274 (−3.54), 228 (−11.27), 217 (4.28).

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(4aR,5S,10bS)-20a: tR = 5.30 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 282sh (4.70), 274 (5.26), 228 (14.69), 217 (−5.67).
λ
(
±
)-(4aS*,5SR*,10bR*)-5-(4-methoxyphenyl)-4,4a,5,10b-tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one
(rac-20b): White crystals, yield 89%, mp 224–226 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ: 3.79 (s, 3H,
OCH3), 3.90 (t, J = 10.0 Hz, 1H, 4-H), 4.33 (s, 2H, 2-H), 4.95 (d, J = 9.2 Hz, 1H, 10b-H), 5.11 (d, J =
10.0 Hz, 1H, 5-H), 6.80 (d, J = 8.0 Hz, 1H, 7-H), 6.98 (m, 4 H, 9-H, 30-H, 50-H, NH), 7.20 (t, J = 8.0 Hz,
1H, 8-H), 7.37 (d, J = 7.6 Hz, 1H, 10-H), 7.41 (d, 2H, 20-H, 60-H); 13C-NMR (100 MHz, DMSO-d6)
δ: 53.9
(C-OCH3), 55.2 (C-4a), 67.8 (C-2), 72.7 (C-10b), 78.6 (C-5), 114.2 (C-30, C-50), 115.7 (C-7), 120.7 (C-9),
120.9 (C-10a), 125.2 (C-10), 127.3 (C-10), 129.3 (C-8), 130.0 (C-20, C-60), 153.2 (C-6a), 160.1 (C-40), 168.3
(C-3); HRMS (ESI) calcd. for C18H17NO4 [M + H]+ 312.123; found 312.124.
(4aS,5R,10bR)-20b: tR = 5.82 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}: 273 (−3.94), 233 (7.54), 215 (−1.82).
(4aR,5S,10bS)-20b: tR = 6.85 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 273 (3.70), 233 (−9.20), 215 (2.98).
λ
(
±
)-(4aS*,5R*,10bR*)-5-(3,4-dimethoxyphenyl)-4,4a,5,10b-tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one
(rac-20c): White crystals, yield 90%, mp 255–257 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ
: 3.78 (d, 6H, 2
×
OCH3), 3.97 (t, J = 9.6 Hz, 1H, 4a-H), 4.33 (s, 2H, 2-Ha, 2-Hb), 4.95 (d, J = 9.2 Hz, 1H, 10b-H), 5.10 (d,
J = 10.4 Hz, 1H, 5-H), 6.81 (d, J = 8.0 Hz, 1H, 7-H), 6.97 (m, 4 H, 9-H, 20-H, 50-H, 60-H), 7.21 (t, J =
8.0 Hz, 1H, 8-H), 7.37 (d, J = 7.6 Hz, 1H, 10-H); 13C-NMR (100 MHz, DMSO-d6)
δ
: 53.8 (C-4a), 55.5 (2
×
C-OCH3), 67.7 (C-2), 72.6 (C-10b), 78.9 (C-5), 111.8 (C-50), 111.8 (C-20), 115.7 (C-60), 120.5 (C-7), 120.9
(C-10a), 121.3 (C-9), 125.1 (C-10), 127.4 (C-10), 129.2 (C-8), 149.1 (C-40), 150.2 (C-30), 153.2 (C-6a), 168.1
(C-3); HRMS (ESI) calcd. for C19H19NaNO5 [M+Na]+ 364.116; found 364.113.
(4aR,5S,10bS)-20c: tR = 7.86 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 287 (−0.89), 282sh (1.66), 274 (1.92), 235 (6.17), 224sh (4.71).
λ
(4aS,5R,10bR)-20c: tR = 9.50 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}:287 (0.35), 282sh (−1.61), 274 (−1.93), 235 (−6.62), 224sh (−5.44).
(
±
)-(4aS*,5R*,10bR*)-5-(3,5-dimethoxyphenyl)-4,4a,5,10b-tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one
(rac-20d): White crystals, yield 80%, mp 189–190 ◦C; 1H-NMR (400 MHz, CDCl3)
δ
: 3.77 (m, 7H, 4a-H,
2
×
OCH3), 4.38 (d, J = 17.2 Hz, 1H, 2-Ha), 4.45 (d, J = 17.2 Hz, 1H, 2-Hb), 4.78 (d, J = 9.2 Hz, 1H,
10b-H), 4.88 (d, J = 10.4 Hz, 1H, 5-H), 5.59 (s, 1H, NH), 6.50 (t, J = 2.4 Hz, 1H, 40-H), 6.56 (d, 2H, 20-H,
60-H), 6.91 (d, J = 8.0 Hz, 1H, 7-H), 7.01 (t, J = 7.6 Hz, 1H, 9-H), 7.23 (m, 1H, 8-H), 7.44 (d, J = 7.6 Hz,
1H, 10-H); 13C-NMR (100 MHz, CDCl3)
δ: 55.1 (C-4a), 55.2 (2
×
C-OCH3), 67.9 (C-2), 73.3 (C-10b), 79.0
(C-5), 101.2 (C-40), 105.1 (C-20, C-60), 116.1 (C-7), 119.8 (C-10a), 121.2 (C-9), 125.3 (C-10), 129.6 (C-8),
136.5 (C-10), 152.9 (C-6a), 161.3 (C-30, C-50), 168.5 (C-3); HRMS (ESI) calcd. for C19H19NaNO5 [M+Na]+
364.116; found 364.113.
(4aR,5S,10bS)-20d: tR = 6.72 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 283 (4.08), 240sh (−1.16), 233 (−3.03), 222 (1.82), 213 (−10.39).
λ
(4aS,5R,10bR)-20d: tR = 7.07 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}:283 (−4.52), 240sh (1.28), 233 (2.95), 222 (−3.55), 213 (6.44).
(±
)-(4aS*,5R*,10bR*)-5-(3,4,5-trimethoxyphenyl)-4,4a,5,10b-tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one
(rac-20e): White crystals, yield 83%, mp 146–148 ◦C; 1H-NMR (400 MHz, CDCl3)
δ
: 3.84 (m, 10 H,
4a-H, 3
×
OCH3), 4.41 (d, J = 16.8 Hz, 1H, 2-Ha), 4.48 (d, J = 16.8 Hz, 1H, 2-Hb), 4.82 (d, J = 9.2 Hz, 1H,
10b-H), 4.91 (d, J = 10.4 Hz, 1H, 5-H), 5.63 (s, 1H, NH), 6.65 (s, 2H, 20-H, 60-H), 6.92 (d, J = 8.4 Hz, 1H,
7-H), 7.03 (t, J = 7.2 Hz, 1H, 9-H), 7.26 (t, J = 7.2 Hz, 1H, 8-H), 7.46 (d, J = 7.6 Hz, 1H, 10-H); 13C-NMR
(101 MHz, CDCl3)
δ
: 55.2 (C-4a), 56.0 (2
×
C-OCH3), 60.6 (C-OCH3), 68.0 (C-2), 73.4 (C-10b), 79.3 (C-5),
104.2 (C-20, C-60), 116.2 (C-7), 119.8 (C-10a), 121.3 (C-9), 125.3 (C-10), 129.6 (C-10), 129.6 (C-8), 138.9

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(C-40), 152.9 (C-6a), 153.8 (C-30, C-50), 168.7 (C-3); HRMS (ESI) calcd. for C20H21NaNO6 [M+Na]+
394.126; found 394.124.
(4aR,5S,10bS)-20e: tR = 10.18 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 282 (1.51), 275sh (1.37), 245 (−1.52), 233sh (1.49), 225 (2.54), 216 (−0.36).
λ
λ
(4aS,5R,10bR)-20e: tR = 15.71 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}:282 (−1.44), 275sh (−1.31), 245 (0.65), 233sh (−1.82), 225 (−2.09), 216 (0.52).
(
±
)-(4aS*,5R*,10bR*)-5-(naphthalen-1-yl)-4,4a,5,10b-◦tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one
1
(rac-20f): White crystals, yield 83%, mp 254–255 C; H-NMR (360 MHz, DMSO-d6)
δ: 4.20 (t, J =
9.0 Hz, 1H, 4a-H), 4.37 (s, 2H, 2-H), 5.19 (d, J = 8.3 Hz, 1H, 10b-H), 6.12 (bs, 1H, 5-H), 6.83 (d, J = 7.9 Hz,
1H, 7-H), 7.01 (t, J = 7.2 Hz, 1H, 9-H), 7.24 (m, 2H, 8-H, NH), 7.44 (d, J = 7.2 Hz, 1H, 10-H), 7.59 (m, 3H,
20-H, 30-H, 70-H), 7.77 (m, 1H, 60-H), 8.01 (m, 2H, 40-H, 50-H), 8.28 (m, 1H, 80-H); 13C-NMR (91 MHz,
DMSO-d6) δ: 53.8 (C-4a), 67.8 (C-2), 72.7 (C-10b), 82.4 (C-5), 115.7 (C-7), 120.7 (C-9), 121.2 (C-10a),
123.3 (C-80), 125.2 (C-10), 125.7 (C-20, C-30), 126.3 (C-60, C-70), 128.8 (C-50), 129.3 (C-40), 129.6 (C-8),
131.0 (C-4a’), 131.9 (C-8a’), 133.7 (C-10), 153.2 (C-6a), 168.3 (C-3); HRMS (ESI) calcd. for C21H17NaNO3
[M+Na]+ 354.110; found 354.112.
(4aS,5R,10bR)-20f: tR = 5.71 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}: 293 (−1.64), 280 (−1.36), 270 (−1.79), 225 (34.72), 211 (−8.76).
(4aR,5S,10bS)-20f: tR = 7.06 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 293 (1.13), 280 (1.01), 270 (0.98), 225 (−34.55), 211 (13.28).
λ
(
±
)-(4aS*,5R*,10bR*)-5-(naphthalen-2-yl)-4,4a,5,10b-tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one
(rac-20g): White crystals, yield 91%, mp 273–275 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ: 4.04 (t, J =
10.0 Hz, 1H, 4a-H), 4.31 (m, 2H, 2-H), 5.03 (d, J = 9.6 Hz, 1H, 10b-H), 5.35 (d, J = 10.4 Hz, 1H, 5-H), 6.85
(d, J = 8.0 Hz, 1H, 7-H), 6.99 (m, 1H, 9-H), 7.23 (m, 1H, 8-H), 7.37 (s, 1H, NH), 7.41 (d, J = 7.6 Hz, 1H,
10-H), 7.56 (m, 2H, 60-H, 70-H), 7.62 (dd, J = 8.4, 1.2 Hz, 1H, 30-H), 7.96 (m, 3H, 40-H, 50-H, 80-H), 8.04 (s,
1H, 10-H); 13C-NMR (100 MHz, DMSO-d6)
δ: 54.0 (C-4a), 67.8 (C-2), 72.6 (C-10b), 79.3 (C-5), 115.7 (C-7),
120.8 (C-8), 121.0 (C-10a), 125.2 (C-10, C-80), 126.2 (C-30), 126.5 (C-70), 127.6 (C-9), 128.2 (C-60), 128.6
(C-50), 128.8 (C-40), 129.3 (C-10), 132.9 (C-4a’, C-8a’), 133.5 (C-20), 153.2 (C-6a), 168.3 (C-3); HRMS (ESI)
calcd. for C21H17NaNO3 [M+Na]+ 354.110; found 354.111.
(4aS,5R,10bR)-20g: tR = 21.46 min on Chiralpak IA column (hexane/2-propanol 90:10), HPLC-ECD {
[nm] (φ)}: 283 (−1.06), 240sh (1.27), 228 (9.56), 216 (−3.76).
λ
(4aR,5S,10bS)-20g: tR = 22.63 min on Chiralpak IA column (hexane/2-propanol 90:10), HPLC-ECD {
λ
[nm] (φ)}: 283 (1.35), 240sh (−0.81), 228 (−10.02), 216 (3.61).
(±
)-(4aR*,5R*,10bR*)-5-phenyl-4,4a,5,10b-tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one (rac-23a): White
crystals, yield 93%, mp 151–153 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 3.83 (d, J = 16.8 Hz, 1H, 2-Ha), 4.02
(d, J = 16.8 Hz, 1H, 2-Hb) 4.20 (d, J = 5.6 Hz, 1H, 4a-H), 5.29 (s, 1H, 5-H), 5.46 (d, J = 5.6 Hz, 1H, 10b-H),
5.70 (bs, 1H, NH), 6.98 (d, J = 8.0 Hz, 1H, 7-H), 7.06 (m, 1H, 9-H), 7.28 (m, 1H, 8-H), 7.40 (m, 1H, 40-H),
7.45 (m, 5H, 5-H, 20-H, 30-H, 50-H, 60-H); 13C-NMR (100 MHz, CDCl3)
δ: 52.4 (C-4a), 61.9 (C-2), 67.7
(C-10b), 76.4 (C-5), 117.5 (C-10a), 117.8 (C-7), 122.8 (C-9), 126.0 (C-20, C-60), 128.2 (C-5), 129.3 (C-40),
129.7 (C-30, C-50), 130.5 (C-8), 135.8 (C-10), 155.4 (C-6a), 169.1 (C-3); HRMS (ESI) calcd. for C17H15NO3
[M + H]+ 282.113; found 282.115.
(4aS,5S,10bS)-23a: tR = 6.38 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 283sh (10.79), 276 (11.06), 237 (3.05), 229 (−13.14), 214 (32.68).
λ
(4aR,5R,10bR)-23a: tR = 7.92 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}: 283sh (−7.27), 276 (−7.62), 237 (−1.40), 229 (11.40), 214 (−25.80).

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( )-(4aR*,5R*,10bR*)-5-(4-methoxyphenyl)-4,4a,5,10b-tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one
±
◦
1
(rac-23b): White crystals, yield 74%, mp 167–169 C; H-NMR (400 MHz, CDCl3)
δ: 3.79 (m, 4 H,
OCH3, 2-Ha), 3.98 (d, J = 16.8 Hz, 1H, 2-Hb), 4.12 (d, J = 5.6 Hz, 1H, 4a-H), 5.20 (s, 1H, 10b-H), 5.40
(d, J = 5.6 Hz, 1H, 5-H), 5.81 (s, 1H, NH), 6.92 (d, 2H, 30-H, 50-H), 6.96 (d, J = 8.4 Hz, 1H, 7-H), 7.04
(t, J = 7.6 Hz, 1H, 9-H), 7.24 (t, J = 7.2 Hz, 1H, 8-H), 7.38 (d, 2H, 20-H, 60-H), 7.43 (d, J = 7.6 Hz, 1H,
10-H); 13C-NMR (100 MHz, CDCl3)
δ: 51.9 (C-4a), 55.4 (C-OCH3), 61.5 (C-2), 67.2 (C-10b), 75.7 (C-5),
114.6 (C-30, C-50), 117.1 (C-10a), 117.3 (C-7), 122.3 (C-9), 126.8 (C-20, C-60), 127.2 (C-10), 127.9 (C-10),
130.0 (C-8), 155.1 (C-6a), 159.8 (C-40), 168.6 (C-3); HRMS (ESI) calcd. for C18H17NO4 [M + H]+ 312.123;
found 312.124.
(4aR,5R,10bR)-23b: tR = 8.78 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}: 283 (−7.85), 275 (−7.80), 231sh (−18.86), 225 (−19.61).
(4aS,5S,10bS)-23b: tR = 9.75 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 283 (8.34), 275 (7.98), 231sh (18.54), 225 (19.96).
λ
(
±
)-(4aR*,5R*,10bR*)-5-(3,4-dimethoxyphenyl)-4,4a,5,10b-tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one
(rac-23c): White crystals, yield 69%, mp 139–140 ◦C; 1H-NMR (400 MHz, CDCl3)
: 3.83 (d, J = 17.2 Hz,
1H, 2-Ha), 3.92 (d, 6H, 2 OCH3), 4.04 (d, J = 17.2 Hz, 1H, 2-Hb), 4.18 (d, J = 5.2 Hz, 1H, 4a-H), 5.24 (s,
1H, 10b-H), 5.45 (d, J = 5.2 Hz, 1H, 5-H), 5.73 (s, 1H, NH), 6.94 (m, 3H, 7-H, 20-H, 50-H), 7.05 (m, 2H,
9-H, 60-H), 7.27 (m, 1H, 8-H), 7.46 (d, J = 7.2 Hz, 1H, 10-H); 13C-NMR (100 MHz, CDCl3)
: 52.2 (C-4a),
δ
×
δ
56.2 (2
×
C-OCH3), 61.6 (C-2), 67.3 (C-10b), 75.9 (C-5), 108.6 (C-50), 111.8 (C-20), 117.2 (C-10a), 117.5
(C-60), 117.9 (C-7), 122.5 (C-9), 127.8 (C-10), 127.9 (C-10), 130.2 (C-8), 149.4 (C-40), 149.8 (C-30), 155.1
(C-6a), 168.7 (C-3); HRMS (ESI) calcd. for C19H19NaNO5 [M+Na]+ 364.116; found 364.113.
(4aR,5R,10bR)-23c: tR = 12.43 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 283 (−10.06), 276sh (−9.22), 235 (−10.58), 224sh (−2.55), 211 (−18.11).
λ
λ
(4aS,5S,10bS)-23c: tR = 15.97 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 283 (10.17), 276sh (9.61), 235 (11.92), 224sh (4.81), 211 (11.93).
(±
)-(4aR*,5R*,10bR*)-5-(3,5-dimethoxyphenyl)-4,4a,5,10b-tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one
(rac-23d): White crystals, yield 96%, mp 136–138 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 3.83 (m, 7H, 2-Ha,
2
×
OCH3), 4.02 (d, J = 16.8 Hz, 1H, 2-Hb), 4.18 (d, J = 5.6 Hz, 1H, 4a-H), 5.20 (s, 1H, 10b-H), 5.44 (d, J
= 5.6 Hz, 1H, 5-H), 5.73 (s, 1H, NH), 6.47 (s, 1H, 40-H), 6.64 (s, 2H, 20-H, 60-H), 6.98 (d, J = 8.0 Hz,
1H, 7-H), 7.05 (t, J = 7.6 Hz, 1H, 9-H), 7.26 (t, J = 8.0 Hz, 1H, 8-H), 7.44 (d, J = 7.6 Hz, 1H, 10-H);
13C-NMR (100 MHz, CDCl3)
δ: 52.2 (C-4a), 55.6 (2
×
C-OCH3), 61.6 (C-2), 67.3 (C-10b), 76.0 (C-5), 100.4
(C-40), 103.7 (C-20, C-60), 117.2 (C-10a), 117.5 (C-7), 122.5 (C-8), 127.9 (C-9), 130.2 (C-10), 137.8 (C-10),
154.9 (C-6a), 161.7 (C-30, C-50), 168.6 (C-3); HRMS (ESI) calcd. for C19H19NaNO5 [M+Na]+ 364.116;
found 364.113.
(4aS,5S,10bS)-23d: tR = 10.35 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 283 (2.62), 276sh (2.71), 241 (0.83), 231 (−3.03), 222sh (4.32), 210 (15.46).
λ
(4aR,5R,10bR)-23d: tR = 11.98 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}: 283 (−3.52), 276sh (−3.47), 241 (−1.00), 231 (2.81), 222sh (−7.12), 210 (−27.95).
(±
)-(4aR*,5R*,10bR*)-5-(3,4,5-trimethoxyphenyl)-4,4a,5,10b-tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one
(rac-23e): White crystals, yield 89%, mp 148–150 ◦C; 1H-NMR (400 MHz, CDCl3)
δ
: 3.83 (m, 10 H, 2-Ha,
3
×
OCH3), 4.04 (d, J = 16.8 Hz, 1H, 2-Hb), 4.19 (d, J = 5.6 Hz, 1H, 4a-H), 5.22 (s, 1H, 10b-H), 5.45 (d, J =
5.6 Hz, 1H, 5-H), 5.73 (s, 1H, NH), 6.71 (s, 2H, 20-H, 60-H), 7.00 (d, J = 8.0 Hz, 1H, 7-H), 7.07 (t, J =
7.6 Hz, 1H, 9-H), 7.27 (t, J = 8.0 Hz, 1H, 8-H), 7.45 (d, J = 7.6 Hz, 1H, 10-H); 13C-NMR (100 MHz, CDCl3)
δ
117.0 (C-10a), 117.3 (C-7), 122.4 (C-9), 127.7 (C-10), 130.0 (C-8), 130.8 (C-10), 138.0 (C-40), 153.8 (C-30,
C50), 154.7 (C-6a), 168.5 (C-3); HRMS (ESI) calcd. for C20H21NaNO6 [M+Na]+ 394.126; found 394.124.
: 52.1 (C-4a), 56.2 (2
×
C-OCH3), 60.8 (C-OCH3), 61.4 (C-2), 67.1 (C-10b), 75.8 (C-5), 102.3 (C-20, C-60),

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(4aR,5R,10bR)-23e: tR = 12.23 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 283 (−4.07), 276sh (−4.33), 240 (−6.43), 228 (1.76), 212 (−21.15).
(4aS,5S,10bS)-23e: tR = 16.85 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 283 (3.63), 276sh (3.23), 240 (5.25), 228 (−0.84), 212 (11.85).
λ
λ
(±
)-(4aR*,5R*,10bR*)-5-naphthalen-2-yl-4,4a,5,10b-tetrahydrochromeno[4,3-b][1,4]oxazin-3(2H)-one (rac-23g):
White crystals, yield 79%, mp 193–195 ◦C; 1H-NMR (360 MHz, CDCl3)
δ: 3.83 (d, J = 16.9 Hz, 1H,
2-Ha), 4.01 (d, J = 16.9 Hz, 1H, 2-Hb), 4.27 (d, J = 5.4 Hz, 1H, 4a-H), 5.41 (s, 1H, 5-H), 5.49 (d, J = 5.4 Hz,
1H, 10b-H), 5.69 (s, 1H, NH), 7.05 (m, 2H, 7-H, 9-H), 7.28 (t, J = 7.2 Hz,1H, 8-H), 7.44 (m, 4 H, 30-H, 60-H,
70-H, 10-H), 7.86 (m, 3H, 40-H, 50-H, 80-H), 8.08 (s, 1H, 10-H); 13C-NMR (90 MHz, CDCl3)
δ: 51.8 (C-4a),
61.6 (C-2), 67.4 (C-10b), 76.2 (C-5), 117.2 (C-10a), 117.5 (C-7), 122.5 (C-8), 122.8 (C-10), 125.2 (C-80), 126.9
(C-30), 127.0 (C-70), 127.9 (C-9), 128.0 (C-60), 128.3 (C-50), 129.3 (C-40), 130.2 (C-10), 132.6 (C-4a’), 133.2
(C-8a’), 133.3 (C-20), 155.1 (C-6a), 168.6 (C-3); HRMS (ESI) calcd. for C21H17NaNO3 [M+Na]+ 354.110;
found 354.111.
(4aR,5R,10bR)-23g: tR = 18.43 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}: 283 (−4.33), 234sh (−2.97), 219 (−30.92), 203 (21.46).
(4aS,5S,10bS)-23e: tR = 19.30 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
[nm] (φ)}: 283 (3.93), 234sh (2.35), 219 (28.64), 203 (−21.27).
λ
2.7. General Procedure for the Synthesis of Condensed Morpholinee Derivatives [rac-(4aR*,5S*,10aS*)-2a-g,
rac-(4aR*,5S*,10aR*)-2a-e, g, rac-(4aR*,5R*,10aR*)-2a-e, g]
Under inert atmosphere, the condensed 1,4-oxazinone derivatives rac-20a-g or rac-23a-e
,
g
(0.359 mmol) were dissolved in anhydrous dioxane (5 mL) and after heating the reaction mixture to
◦
90 C, 2 M LiAlH4 solution in THF (216
µL) was added. The reaction was quenched after 15 min
with the addition of ethyl acetate and water. The organic phase was collected and dried over MgSO4,
then it was concentrated under reduced pressure. Procedure A: The product was obtained as the
hydrochloride salt after stirring for 2 h at room temperature in a mixture of ethyl acetate (5 mL) and
3 N HCl solution (124
µL). Procedure B: The product was isolated as the amine base after column
chromatography using CHCl3 as eluent.
(
±
)-(4aR*,5S*,10bS*)-5-phenyl-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
hydrochloride
: 3.15
[rac-(4aR*,5S*,10aS*)-2a]: White solid, yield 72%, mp > 300 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ
(bs, 1H, 3-Ha), 3.23 (d, J = 12.4 Hz, 1H, 3-Hb), 3.84 (m, 1H, 4a-H), 4.17 (d, 2H, 2-Ha, 2-Hb), 5.30 (d, J =
9.6 Hz, 1H, 10b-H), 5.51 (d, J = 10.0 Hz, 1H, 5-H), 6.87 (d, J = 8.4 Hz, 1H, 7-H), 7.02 (t, J = 7.2 Hz, 1H,
9-H), 7.26 (t, J = 7.2 Hz, 1H, 8-H), 7.39 (d, J = 7.6 Hz, 1H, 10-H), 7.49 (m, 3H, 30-H, 40-H, 50-H), 7.63 (m,
2H, 20-H, 60-H), 8.38 (bs, 1H, NH2-Ha), 11.29 (bs, 1H, NH2-Hb); 13C-NMR (100 MHz, DMSO-d6)
δ:
43.9 (C-3), 55.5 (C-4a), 63.4 (C-2), 71.9 (C-10b), 76.4 (C-5), 116.0 (C-7), 120.4 (C-10a), 121.2 (C-9), 125.6
(C-10), 128.5 (C-20, C-60), 128.9 (C-30, C-50), 129.6 (C-8), 129.7 (C-40), 134.2 (C-10), 152.7 (C-6a); HRMS
(ESI) calcd. for C17H17NO2 [M + H]+ 268.1332; found 268.1137.
(
±
)-(4aR*,5S*,10bR*)-5-phenyl-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5S*,10aR*)-2a]. Colorless oil, yield 60%, 1H-NMR (400 MHz, CDCl3)
δ: 2.26 (s, 1H,
NH), 2.90 (m, 3H, 2-Ha, 3-Ha, 3-Hb), 3.56 (d, J = 11.6 Hz, 1H, 2-Hb), 4.36 (s, 1H, 5-H), 4.89 (d, J =
7.6 Hz, 1H, 4a-H), 5.41 (d, J = 7.6 Hz, 1H, 10b-H), 6.92 (m, 2H, 7-H, 9-H), 7.26 (m, 5H, 30-H, 40-H, 50-H,
8-H, 10-H), 7.48 (d, 20-H, 60-H); 13C-NMR (100 MHz, CDCl3)
δ: 50.5 (C-3), 61.2 (C-5), 68.3 (C-2), 78.9
(C-10b), 90.1 (C-4a), 110.4 (C-7), 121.4 (C-9), 124.8 (C-10a), 126.4 (C-40), 126.9 (C-20, C-60), 127.1 (C-10),
128.5 (C-30, C-50), 130.9 (C-8), 143.4 (C-10), 160.1 (C-10a); HRMS (ESI) calcd. for C17H17NO2 [M + H]+
268.1332; found 268.1132.

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(
-
±
)-(4aR*,5R*,10bR*)-5-phenyl-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine [rac-(4aR*,5R*,10aR*)
2a]: White crystals, yield 20%, mp 134–136 ◦C; 1H-NMR (400 MHz, acetone-d6)
δ: 2.64 (d, J = 12.0 Hz,
1H, 3-Ha), 2.75 (m, 1H, 3-Hb), 3.36 (4 H, 2-Ha, 2-Hb, 4a-H, NH), 5.13 (d, J = 4.0 Hz, 1H, 10b-H), 5.29 (s,
1H, 5-H), 6.89 (dd, J = 8.4, 1.2 Hz, 1H, 7-H), 6.97 (m, 1H, 9-H), 7.19 (m, 1H, 8-H), 7.23 (m, 1H, 40-H),
7.39 (m, 3H, 30-H, 50-H, 10-H), 7.55 (d, 2H, 20-H, 60-H); 13C-NMR (100 MHz, acetone-d6)
δ: 46.3 (C-3),
54.7 (C-4a), 61.2 (C-2), 70.5 (C-10b), 79.2 (C-5), 117.0 (C-7), 121.8 (C-9), 122.4 (C-10a), 127.1 (C-20, C-60),
128.3 (C-10), 128.5 (C-40), 129.0 (C-30, C-50), 129.2 (C-8), 139.4 (C-10), 156.2 (C-6a); HRMS (ESI) calcd. for
C17H17NO2 [M + H]+ 268.1332; found 268.1137.
(
±
)-(4aR*,5S*,10bS*)-5-(4-methoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
hydrochloride [rac-(4aR*,5S*,10aS*)-2b]: White crystals, yield 70%, mp 245–247 ◦C; 1H-NMR (400 MHz,
DMSO-d6) : 3.15 (bs, 1H, 3-Ha), 3.22 (d, J = 12.8 Hz, 1H, 3-Hb), 3.81 (m, 4 H, 4a-H, OCH3), 4.16 (d, 2H),
δ
5.28 (d, J = 10.0 Hz, 1H, 10b-H), 5.45 (d, J = 10.4 Hz, 1H, 5-H), 6.85 (d, J = 8.4 Hz, 1H, 7-H), 7.00 (m, 3H,
30-H, 50-H, 9-H), 7.24 (m, 1H, 8-H), 7.38 (d, J = 7.6 Hz, 1H, 10-H), 7.54 (d, 2H, 20-H, 60-H), 8.33 (bs,
1H, NH2-Ha), 11.25 (d, J = 5.6 Hz, 1H, NH2-Hb); 13C-NMR (100 MHz, DMSO-d6)
δ: 43.9 (C-3), 55.3
(C-OCH3), 55.6 (C-4a), 63.4 (C-2), 72.0 (C-10b), 76.0 (C-5), 114.3 (C-30, C-50), 116.0 (C-7), 120.4 (C-10a),
121.1 (C-9), 125.6 (C-10), 126.1 (C-10), 129.5 (C-8), 130.0 (C-20, C-60), 152.8 (C-6a), 160.3 (C-40); HRMS
(ESI) calcd. for C18H19NO3 [M + H]+ 298.1438; found 298.1439.
(
±
)-(4aR*,5S*,10bR*)-5-(4-methoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5S*,10aR*)-2b]: Colorless oil, yield: 41%, 1H-NMR (400 MHz, CDCl3)
δ
: 2.90 (m,
4 H, 2-Ha, 3-Ha, 3-Hb, NH), 3.56 (d, J = 11.6 Hz, 1H, 2-Hb), 3.80 (s, 3H, OCH3), 4.34 (s, 1H, 5-H), 4.88
(d, J = 7.6 Hz, 1H, 4a-H), 5.41 (d, J = 7.6 Hz, 1H, 10b-H), 6.90 (d, 2H, 30-H, 50-H), 6.94 (d, J = 8.4 Hz,
1H, 7-H), 6.97 (m, 1H, 9-H), 7.28 (m, 1H, 8-H), 7.39 (d, J = 7.2 Hz, 1H, 10-H), 7.43 (d, 2H, 20-H, 60-H);
13C-NMR (100 MHz, CDCl3)
δ: 50.6 (C-3), 55.4 (C-OCH3), 60.9 (C-5), 68.1 (C-2), 79.0 (C-10b), 90.2
(C-4a), 110.6 (C-7), 114.1 (C-30, C-50), 121.5 (C-9), 124.9 (C-10a), 126.5 (C-10), 128.2 (C-20, C-60), 131.1
(C-8), 135.5 (C-10), 158.8 (C-40), 160.3 (C-6a); HRMS (ESI) calcd. for C18H19NO3 [M + H]+ 298.1438;
found 298.1440.
(
±
)-(4aR*,5R*,10bR*)-5-(4-methoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5R*,10aR*)-2b]: White crystals, yield 13%, mp 153–155 ◦C; 1H-NMR (400 MHz,
aceton-d6) : 2.66 (d, J = 12.0 Hz, 1H, 3-Ha), 2.76 (m, 1H, 3-Hb), 3.33 (m, 4 H, 2-Ha, 2-Hb, 4a-H, NH),
δ
3.81 (s, 3H, OCH3), 5.10 (d, J = 4.8 Hz, 1H, 10b-H), 5.23 (s, 1H, 5-H), 6.86 (dd, J = 8.4, 1.2 Hz, 1H, 7-H),
6.96 (m, 3H, 30-H, 50-H, 9-H), 7.18 (m, 1H, 8-H), 7.42 (d, J = 7.6 Hz, 1H, 10-H), 7.46 (d, 2H, 20-H, 60-H);
13C-NMR (100 MHz, acetone-d6)
δ: 46.3 (C-3), 54.8 (C-4a), 55.5 (C-OCH3), 61.2 (C-2), 70.5 (C-10b), 78.9
(C-5), 114.4 (C-30, C-50), 116.9 (C-7), 121.6 (C-9), 122.4 (C-10a), 128.3 (C-20, C-60), 129.2 (C-8), 131.3 (C-10),
156.4 (C-6a), 160.2 (C-40); HRMS (ESI) calcd. for C18H19NO3 [M + H]+ 298.1438; found 298.1439.
(
±
)-(4aR*,5S*,10bS*)-5-(3,4-dimethoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5S*,10aS*)-2c]: White crystals, yield 55%, mp 178–180 ◦C; 1H-NMR (360 MHz, CDCl3)
δ
: 1.71
(bs, 1H, NH), 2.89 (m, 2H, 3-Ha, 3-Hb, 4a-H), 3.86 (m, 7H, 2-Ha, 2xOCH3), 4.04 (dd, J = 11.2, 2.2 Hz, 1H,
2-Hb), 4.56 (d, J = 9.0 Hz, 1H, 10b-H), 4.90 (d, J = 9.7 Hz, 1H, 5-H), 6.87 (m, 2H, 20-H, 50-H), 6.97 (m, 3H,
60-H, 7-H, 9-H), 7.21 (m, 1H, 8-H), 7.43 (d, J = 7.9 Hz, 1H, 10-H); 13C-NMR (90 MHz, CDCl3)
δ: 46.4
(C-3), 56.1 (2xC-OCH3), 59.1 (C-4a), 67.5 (C-2), 76.1 (C-10b), 80.3 (C-5), 110.0 (C-50), 111.3 (C-20), 116.2
(C-60), 120.2 (C-7), 121.0 (C-9), 122.3 (C-10a), 125.5 (C-10), 129.0 (C-8), 129.2 (C-10), 149.5 (C-30), 149.7
(C-40), 153.6 (C-6a); HRMS (ESI) calcd. for C19H21NO4 [M + H]+ 328.1543; found 328.1543.
(
±
)-(4aR*,5S*,10bR*)-5-(3,4-dimethoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5S*,10aR*)-2c]): White crystals, yield 34%, mp 124–126 ◦C; 1H-NMR (400 MHz, CDCl3)
δ:
2.31 (bs, 1H, NH), 2.90 (m, 3H, 2-Ha, 3-Ha, 3-Hb), 3.57 (d, J = 12.4 Hz, 1H, 2-Hb), 3.87 (s, 3H, OCH3),
3.93 (s, 3H, OCH3), 4.32 (s, 1H, 5-H), 4.89 (d, J = 7.6 Hz, 1H, 4a-H), 5.42 (d, J = 7.6 Hz, 1H, 10b-H),
6.85 (d, J = 8.4 Hz, 1H, 50-H), 6.94 (d, J = 8.0 Hz, 1H, 7-H), 6.98 (m, 1H, 9-H), 7.03 (dd, J = 8.0, 2.0 Hz,
1H, 60-H), 7.09 (d, J = 1.6 Hz, 1H, 20-H), 7.28 (m, 1H, 8-H), 7.40 (d, J = 7.6 Hz, 1H, 10-H); 13C-NMR

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(100 MHz, CDCl3)
δ
: 50.6 (C-3), 56.0 (2xC-OCH3), 61.2 (C-5), 68.1 (C-2), 79.0 (C-10b), 90.3 (C-4a), 110.5
(C-7), 110.6 (C-50), 111.3 (C-20), 119.1 (C-60), 121.5 (C-9), 124.9 (C-10a), 126.5 (C-10), 131.0 (C-8), 136.2
(C-10), 148.2 (C-40), 149.1 (C-30), 160.2 (C-6a); HRMS (ESI) calcd. for C19H21NO4 [M + H]+ 328.1543;
found 328.1544.
( )-(4aR*,5R*,10bR*)-5-(3,4-dimethoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
±
[rac-(4aR*,5R*,10aR*)-2c]: White crystals, yield 16%, mp 139–140 ◦C; 1H-NMR (400 MHz, acetone-d6)
2.66 (d, J = 12.0 Hz, 1H, 3-Ha), 2.77 (m, 1H, 3-Hb), 3.35 (m, 4 H, 2-Ha, 2-Hb, 4a-H, NH), 3.82 (d, 6H, 2
δ:
×
OCH3), 5.10 (d, J = 4.0 Hz, 1H, 10b-H), 5.23 (s, 1H, 5-H), 6.86 (dd, J = 8.4, 1.2 Hz, 1H, 7-H), 6.96 (m,
2H, 60-H, 9-H), 7.06 (m, 1H, 50-H), 7.16 (d, J = 2.0 Hz, 1H, 20-H), 7.18 (m, 1H, 8-H), 7.42 (d, J = 7.6 Hz,
1H, 10-H); 13C-NMR (100 MHz, acetone-d6)
δ: 45.5 (C-3), 54.1 (C-OCH3), 55.2 (C-4a), 55.3 (C-OCH3),
60.3 (C-2), 69.7 (C-10b), 78.1 (C-5), 110.3 (C-50), 111.7 (C-20), 116.1 (C-60), 118.4 (C-7), 120.7 (C-9), 121.5
(C-10a), 127.3 (C-10), 128.3 (C-8), 130.9 (C-10), 149.0 (C-40), 149.3 (C-30) 155.4 (C-6a); HRMS (ESI) calcd.
for C19H21NO4 [M + H]+ 328.1543; found 328.1543.
( )-(4aR*,5S*,10bS*)-5-(3,5-dimethoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
±
hydrochloride [rac-(4aR*,5S*,10aS*)-2d]: White crystals, yield 84%, mp 238–241 ◦C; 1H-NMR (400 MHz,
DMSO-d6) δ: 3.12 (m, 1H, 3-Ha), 3.24 (d, J = 12.8 Hz, 1H, 3-Hb), 3.75 (m, 7H, 4a-H, 2xOCH3), 4.08 (m,
1H, 2-Ha), 4.17 (dd, J = 12.4, 4.0 Hz, 1H, 2-Hb), 5.20 (d, J = 9.6 Hz, 1H, 10b-H), 5.38 (d, J = 10.4 Hz, 1H,
5-H), 6.58 (t, J = 2.0 Hz, 1H, 40-H), 6.60 (d, 2H, 20-H, 60-H), 6.89 (d, J = 8.4 Hz, 1H, 7-H), 7.01 (m, 1H,
9-H), 7.26 (m, 1H, 8-H), 7.38 (d, J = 7.6 Hz, 1H, 10-H), 8.33 (bs, 1H, NH2-Ha), 10.93 (bs, 1H, NH2-Hb);
13C-NMR (100 MHz, DMSO-d6)
δ
: 43.9 (C-3), 55.3 (2
×
C-OCH3), 55.6 (C-4a), 63.4 (C-2), 71.9 (C-10b),
76.2 (C-5), 101.3 (C-40), 106.2 (C-20, C-60), 116.1 (C-7), 120.5 (C-10a), 121.3 (C-9), 125.6 (C-10), 129.6 (C-8),
136.3 (C-10), 152.6 (C-6a), 160.7 (C-30, C-50); HRMS (ESI) calcd. for C19H21NO4 [M + H]+ 328.1543;
found 328.1544.
(
±
)-(4aR*,5S*,10bR*)-5-(3,5-dimethoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5S*,10aR*)-2d]. Colorless oil, yield 48%, 1H-NMR (400 MHz, CDCl3)
: 2.80 (m, 4 H, 2-Ha,
OCH3), 4.19 (s, 1H, 5-H), 4.78 (d, J =
δ
3-Ha, 3-Hb, NH), 3.46 (d, J = 12.0 Hz, 1H, 2-Hb), 3.71 (s, 6H, 2
×
7.6 Hz, 1H, 4a-H), 5.31 (d, J = 7.6 Hz, 1H, 10b-H), 6.27 (t, J = 2.0 Hz, 1H, 40-H), 6.57 (d, 2H, 20-H, 60-H),
6.82 (d, J = 8.4 Hz, 1H, 7-H), 6.87 (t, J = 7.2 Hz, 1H, 9-H), 7.18 (m, 1H, 8-H), 7.29 (d, J = 7.2 Hz, 1H,
10-H); 13C-NMR (100 MHz, CDCl3)
δ: 50.5 (C-3), 55.5 (2
×
C-OCH3), 61.5 (C-5), 68.2 (C-2), 79.0 (C-10b),
90.2 (C-4a), 99.2 (C-40), 105.2 (C-20, C-60), 110.6 (C-7), 121.5 (C-9), 124.8 (C-10a), 126.5 (C-10), 131.1 (C-8),
145.7 (C-10), 160.2 (C-6a), 161.0 (C-30, C-50); HRMS (ESI) calcd. for C19H21NO4 [M + H]+ 328.1543;
found 328.1543.
(
±
)-(4aR*,5R*,10bR*)-5-(3,5-dimethoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5R*,10aR*)-2d]: White crystals, yield 5%, mp 145–147 ◦C; 1H-NMR (400 MHz, acetone-d6)
δ:
2.68 (d, J = 12.0 Hz, 1H, 3-Ha), 2.79 (m, 2H, 3-Hb, NH), 3.38 (m, 3H, 2-Ha, 2-Hb, 4a-H), 3.81 (s, 6H,
2OCH3), 5.13 (d, J = 4.0 Hz, 1H, 10b-H), 5.25 (s, 1H, 5-H), 6.45 (t, J = 2.4 Hz, 1H, 40-H), 6.74 (d, 2H, 20-H,
60-H), 6.88 (d, J = 8.4 Hz, 1H, 7-H), 6.97 (t, J = 7.6 Hz, 1H, 9-H), 7.19 (m, 1H, 8-H), 7.42 (d, J = 7.6 Hz,
1H, 10-H); 13C-NMR (100 MHz, acetone-d6)
δ
: 46.3 (C-3), 54.9 (C-4a), 55.6 (2
×
C-OCH3), 61.1 (C-2),
70.4 (C-10b), 79.0 (C-5), 100.2 (C-40), 105.0 (C-20, C-60), 117.0 (C-7), 121.7 (C-9), 122.3 (C-10a), 128.2
(C-10), 129.3 (C-8), 141.7 (C-10), 156.1 (C-60), 161.9 (C-30, C-50); HRMS (ESI) calcd. for C19H21NO4 [M +
H]+ 328.1543; found 328.1543.
(
±
)-(4aR*,5S*,10bS*)-5-(3,4,5-trimethoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5S*,10aS*)-2e]: Colorless oil, yield 46%, 1H-NMR (360 MHz, CDCl3)
: 1.72 (bs, 1H, NH), 2.91
(m, 3H, 3-Ha, 3-Hb, 4a-H), 3.87 (m, 10 H, 2-Ha, 3 OCH3), 4.06 (dd, J = 11.2, 1.8 Hz, 1H, 2-Hb), 4.56 (d,
J = 9.4 Hz, 1H, 10b-H), 4.88 (d, J = 10.1Hz, 1H, 5-H), 6.70 (s, 2H, 20-H, 60-H), 6.89 (dd, J = 8.3, 1.1Hz, 1H,
7-H), 6.98 (m, 1H, 9-H), 7.20 (m, 1H, 8-H), 7.44 (d, J = 7.6 Hz, 1H, 10-H); 13C-NMR (90 MHz, CDCl3)
46.4 (C-3), 56.3 (2 C-OCH3), 59.2 (C-4a), 60.9 (C-OCH3), 67.5 (C-2), 76.1 (C-10b), 80.6 (C-5), 104.2
δ
×
δ:
×

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(C-20, C-60), 116.2 (C-7), 121.1 (C-9), 122.2 (C-10a), 125.5 (C-10), 129.1 (C-8), 132.5 (C-10), 138.4 (C-40),
153.5 (C-6a), 153.7 (C-30, C-50); HRMS (ESI) calcd. for C20H23NO5 [M + H]+ 358.1649; found 358.1648.
(
±
)-(4aR*,5S*,10bR*)-5-(3,4,5-trimethoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5S*,10aR*)-2e]: Colorless oil, yield 33%, 1H-NMR (400 MHz, CDCl3)
δ: 2.13 (bs, 1H, NH),
2.91 (m, 3H, 2-Ha, 3-Ha, 3-Hb), 3.58 (d, J = 12.0 Hz, 1H, 2-Hb), 3.83 (s, 3H, OCH3), 3.91 (s, 6 H, 2
×
OCH3), 4.30 (s, 1H, 5-H), 4.90 (d, J = 7.6 Hz, 1H, 4a-H), 5.43 (d, J = 7.6 Hz, 1H, 10b-H), 6.75 (s, 2H, 20-H,
60-H), 6.95 (d, J = 8.0 Hz, 1H, 7-H), 6.99 (t, J = 7.6, 7.2 Hz, 1H, 9-H), 7.23 (t, J = 8.0, 7.2 Hz, 1H, 8-H), 7.40
(d, J = 7.6 Hz, 1H, 10-H); 13C-NMR (100 MHz, CDCl3)
δ
: 50.5 (C-3), 56.3 (2
×
C-OCH3), 60.9 (C-OCH3),
61.7 (C-5), 68.2 (C-2), 79.0 (C-10b), 90.2 (C-4a), 104.2 (C-20, C-60), 110.6 (C-7), 121.6 (C-9), 124.8 (C-10a),
126.5 (C-10), 131.1 (C-8), 137.2 (C-40), 139.3 (C-10), 153.4 (C-30, C-50), 160.2 (C-6a); HRMS (ESI) calcd.
for C20H23NO5 [M + H]+ 358.1649; found 358.1649
(
±
)-(4aR*,5R*,10bR*)-5-(3,4,5-trimethoxyphenyl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5R*,10aR*)-2e]: White crystals, yield 7%, mp 164–166 ◦C; 1H-NMR (400 MHz, acetone-d6)
2.66 (d, J = 12.0 Hz, 1H, 3-Ha), 2.77 (m, 1H, 3-Hb), 3.37 (m, 4 H, 2-Ha, 2-Hb, 4a-H, NH), 3.74 (s, 3H,
OCH3), 3.85 (s, 6H, 2
OCH3), 5.10 (d, J = 4.0 Hz, 1H, 10b-H), 5.22 (s, 1H, 5-H), 6.87 (s, 3H, 20-H,
60-H, 7-H), 6.96 (m, 1H, 9-H), 7.18 (m, 1H, 8-H), 7.42 (d, J = 7.6 Hz, 1H, 10-H); 13C-NMR (100 MHz,
δ:
×
acetone-d6)
δ
: 46.4 (C-3), 55.0 (C-4a), 56.4 (2
×
C-OCH3), 60.5 (C-OCH3), 61.2 (C-2), 70.6 (C-10b), 79.2
(C-5), 104.5 (C-20, C-60), 117.0 (C-7), 121.7 (C-9), 122.5 (C-10a), 128.2 (C-10), 129.2 (C-8), 134.9 (C-10),
154.3 (C-30, C-50), 156.2 (C-6a); HRMS (ESI) calcd. for C20H23NO5 [M + H]+ 358.1649; found 358.1648.
(
±
)-(4aR*,5S*,10bS*)-5-(naphthalen-1-yl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
hydrochloride [rac-(4aR*,5S*,10aS*)-2f]: White crystals, yield 53%, mp 241–244 ◦C; 1H-NMR (400 MHz,
DMSO-d6) : 3.22 (s, 2H, 3-Ha, 3-Hb), 4.19 (m, 3H, 2-Ha, 2-Hb, 4a-H), 5.52 (s, 1H, 10b-H), 6.43 (bs, 1H,
δ
5-H), 6.87 (s, 1H, 7-H), 7.05 (t, J =7.6 Hz, 1H, 9-H), 7.27 (s, 1H, 8-H), 7.45 (d, J = 7.6 Hz, 1H, 10-H), 7.60
(s, 3H, 20-H, 30-H, 70-H), 7.94 (s, 1H, 60-H), 8.04 (m, 2H, 40-H, 50-H), 8.53 (s, 2H, 80-H, NH2-Ha), 11.06
(bs, 1H, NH2-Hb); 13C-NMR (100 MHz, DMSO-d6)
δ: 44.0 (C-3), 55.6 (C-4a), 63.4 (C-2), 70.8 (C-5), 71.9
(C-10b), 116.0 (C-7), 120.6 (C-10a), 121.3 (C-9), 124.2 (C-80), 125.5 (C-10), 126.0 (C-20, C-30, C-70), 126.7
(C-60), 128.8 (C-50), 129.6 (C-8), 130.7 (C-40); HRMS (ESI) calcd. for C21H19NO2 [M + H]+ 318.1489;
found 318.1486.
(
±
)-(4aR*,5S*,10bS*)-5-naphthalen-2-yl-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5S*,10aS*)-2g]: White crystals, yield 51%, mp 102–104 ◦C; 1H-NMR (360 MHz,
CDCl3) : 1.55 (bs, 1H, NH), 2.82 (m, 2H, 3-Ha, 3-Hb), 3.02 (t, J = 9.7, 9.4 Hz,1H, 4a-H), 3.86 (m, 1H,
δ
2-Ha), 4.03 (dd, J = 11.5, 2.2 Hz, 1H, 2-Hb), 4.62 (d, J = 9.4 Hz, 1H, 10b-H), 5.11 (d, J = 9.7 Hz, 1H, 5-H),
6.90 (d, J = 8.3 Hz, 1H, 7-H), 6.98 (m, 1H, 9-H), 7.15 (m, 1H, 8-H), 7.46 (m, 3H, 10-H, 60-H, 70-H), 7.59
(dd, J = 8.3, 1.4 Hz, 1H, 30-H), 7.85 (m, 4 H, 10-H, 40-H, 50-H, 80-H); 13C-NMR (90 MHz, CDCl3)
δ: 46.3
(C-3), 59.0 (C-4a), 67.5 (C-2), 76.1 (C-10b), 80.6 (C-5), 116.2 (C-7), 121.1 (C-8), 122.3 (C-10a), 124.3 (C-10),
125.5 (C-80), 126.6 (C-30), 126.7 (C-70), 127.4 (C-9), 127.9 (C-60), 128.2 (C-50), 129.1 (C-10, C-40), 133.2
(C-4a’), 133.8 (C-8a’), 134.3 (C-20), 153.6 (C-6a); HRMS (ESI) calcd. for C21H19NO2 [M + H]+ 318.1489;
found 318.1486.
(
±
)-(4aR,5S,10bR)-5-(naphthalen-2-yl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5S*,10aR*)-2g]: White crystals, yield 44%, mp 154–156 ◦C; 1H-NMR (360 MHz,
CDCl3) : 2.26 (bs, 1H, NH), 3.05 (m, 3H, 2-Ha, 3-Ha, 3-Hb), 3.70 (m, 1H, 2-Hb), 4.64 (s, 1H, 5-H), 5.11
δ
(d, J = 7.9 Hz, 1H, 4a-H), 5.56 (d, J = 7.6 Hz, 1H, 10b-H), 7.04 (m, 2H, 7-H, 9-H), 7.39 (m, 1H, 8-H), 7.51
(m, 3H, 60-H, 70-H, 10-H), 7.70 (dd, J = 8.6, 1.8 Hz, 1H, 30-H), 7.90 (m, 3H, 40-H, 50-H, 80-H), 8.06 (s, 1H,
10-H); 13C-NMR (90 MHz, CDCl3)
δ: 50.7 (C-3), 61.4 (C-5), 68.5 (C-2), 79.1 (C-10b), 90.2 (C-4a), 110.6
(C-7), 121.5 (C-8), 124.9 (C-10a), 125.5 (C-10), 125.6 (C-80), 125.8 (C-30), 126.2 (C-70), 126.6 (C-9), 127.7
(C-60), 128.2 (C-50), 128.4 (C-40), 131.1 (C-10), 132.7 (C-4a’), 133.5 (C-8a’), 140.8 (C-20), 160.3 (C-6a);
HRMS (ESI) calcd. for C21H19NO2 [M + H]+ 318.1489; found 318.1488.

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(
±
)-(4aR*,5R*,10bR*)-5-(naphthalen-2-yl)-2,3,4,4a,5,10b-hexahydrochromeno[4,3-b][1,4]oxazine
[rac-(4aR*,5R*,10aR*)-2g]: White crystals, yield 11%, mp 117–119 ◦C; 1H-NMR (360 MHz,
acetone-d6) : 2.63 (d, J = 11.9 Hz, 1H, 3-Ha), 2.75 (m, 2H, 3-Hb, NH), 3.38 (m, 2H, 2-Ha, 2-Hb), 3.52 (d,
δ
J = 4.7 Hz, 1H, 4a-H), 5.19 (d, J = 4.0 Hz, 1H, 10b-H), 5.48 (s, 1H, 5-H), 6.95 (d, J = 8.3 Hz, 1H, 7-H),
7.00 (t, J = 7.6 Hz, 1H, 9-H), 7.22 (t, J = 7.2 Hz, 1H, 8-H), 7.46 (d, J = 7.6 Hz, 1H, 10-H), 7.52 (m, 2H,
60-H, 70-H), 7.66 (d, J = 8.6 Hz, 1H, 30-H), 7.94 (m, 3H, 40-H, 50-H, 80-H), 8.09 (s, 1H, 10-H); 13C-NMR
(90 MHz, acetone-d6) δ: 45.4 (C-3), 53.9 (C-4a), 60.3 (C-2), 69.6 (C-10b), 78.3 (C-5), 116.1 (C-7), 120.9
(C-8), 121.6 (C-10a), 124.2 (C-10), 125.0 (C-80), 125.9 (C-30), 126.1 (C-70), 127.4 (C-9), 127.6 (C-60), 127.8
(C-50), 128.0 (C-40), 128.4 (C-10), 133.1 (C-4a’), 133.2 (C-8a’), 136.1 (C-20), 155.3 (C-6a); HRMS (ESI)
calcd. for C21H19NO2 [M + H]+ 318.1489; found 318.1488.
2.8. General Procedure for the Synthesis of Acetamide Derivatives rac-cis-24a-e,g and rac-trans-24a-g
3-Aminoflavanone hydrochloride salts rac-cis-1a-e
suspended in anhydrous THF (5 mL) under inert atmosphere. Under stirring, Et3N (230
was added to the suspension at room temperature or at 0 ◦C. After 10 min, acetyl chloride (56
,
g
or rac-trans-1a-g (0.655 mmol) were
L, 1.64 mmol)
L,
µ
µ
0.786 mmol) was added dropwise to the reaction mixture and stirred for additional 10 min. Extraction
with ethyl acetate and water, drying over MgSO4, and concentration under reduced pressure provided
the crude product, which was purified by column chromatography using hexane/ethyl acetate 1:1
as eluent.
( )-N-[(2S*,3R*)-4-oxo-2-phenyl-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-cis-24a): White crystals, yield
±
69%, mp 169–171 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 2.02 (s, 3H, CH3), 5.42 (t, J = 6.0 Hz, 1H, 3-H), 6.10
(d, J = 6.8 Hz, 1H, 2-H), 6.30 (d, J = 5.2 Hz, 1H, NH), 7.03 (m, 2H, 30-H, 50-H), 7.13 (m, 2H, 6-H, 8-H),
7.25 (m, 3H, 20-H, 40-H, 60-H), 7.54 (m, 1H, 7-H), 7.82 (dd, J = 8.0, 1.6 Hz, 1H, 5-H); 13C-NMR (100 MHz,
CDCl3) δ
: 23.2 (CH3), 56.5 (C-3), 79.7 (C-2), 118.1 (C-8), 120.1 (C-4a), 121.6 (C-6), 126.9 (C-5), 127.2 (C-20,
C-60), 128.7 (C-30, C-50), 128.9 (C-40), 135.1 (C-10), 137.2 (C-7), 160.5 (C-8a), 170.5 (amide carbonyl), 189.4
(C-4); HRMS (ESI) calcd. for C17H15NaNO3 [M+Na]+ 304.095; found 304.096.
( )-N-[(2S*,3R*)-4-oxo-2-(4-methoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-cis-24b): White
±
◦
1
crystals, yield 72%, mp 147–149 C; H-NMR (400 MHz, CDCl3) δ: 2.02 (s, 3H, CH3), 3.74 (s, 3H,
OCH3), 5.40 (t, J = 6.4 Hz, 1H, 3-H), 6.06 (d, J = 6.4 Hz, 1H, 2-H), 6.28 (d, J = 5.2 Hz, 1H, NH), 6.75
(d, 2H, 30-H, 50-H), 6.99 (m, 4 H, 6-H, 8-H, 20-H, 60-H), 7.50 (m, 1H, 7-H), 7.82 (dd, J = 7.6, 1.6 Hz, 1H,
5-H); 13C-NMR (100 MHz, CDCl3) : 23.5 (C-CH3), 55.6 (C-OCH3), 56.9 (C-3), 79.9 (C-2), 114.4 (C-30,
δ
C-50), 118.5 (C-8), 120.4 (C-4a), 121.8 (C-6), 127.2 (C-5), 127.4 (C-10), 129.0 (C-20, C-60), 137.4 (C-4), 160.3
(C-40), 160.7 (C-8a), 170.7 (amide carbonyl), 190.0 (C-4); HRMS (ESI) calcd. for C18H17NaNO4 [M+Na]+
334.105; found 334.107.
(±
)-N-[(2S*,3R*)-4-oxo-2-(3,4-dimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-cis-24c): White
crystals, yield 75%, mp 183–185 ◦C; 1H-NMR (400 MHz, CDCl3)
δ
: 2.03 (s, 3H, CH3), 3.72 (s, 3H, OCH3),
3.81 (s, 3H, OCH3), 5.41 (t, J = 6.4 Hz, 1H, 3-H), 6.06 (d, J = 6.4 Hz, 1H, 2-H), 6.30 (bs, 1H, NH), 6.68
(m, 3H, 20-H, 50-H, 60-H), 7.01 (m, 2H, 6-H, 8-H), 7.51 (m, 1H, 7-H), 7.83 (dd, J = 7.6, 1.6 Hz, 1H, 5-H);
13C-NMR (100 MHz, CDCl3)
δ: 23.1 (C-CH3), 55.7 (C-OCH3), 55.8 (C-OCH3), 56.5 (C-3), 79.7 (C-2),
110.8 (C-50), 111.0 (C-20), 118.1 (C-8), 119,4 (C-60), 120.0 (C-4a), 121.5 (C-6), 126.7 (C-5), 127.3 (C-10),
137.1 (C-7), 148.9 (C-40), 149.4 (C-30), 160.2 (C-8a), 170.4 (amide carbonyl), 189.5 (C-4); HRMS (ESI)
calcd. for C19H19NaNO5 [M+Na]+ 364.116; found 364.118.
(
±
)-N-[(2S*,3R*)-4-oxo-2-(3,5-dimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide
(rac-cis-24d):
White crystals, yield 67%, mp 144–147 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 2.03 (s, 3H, CH3), 3.65 (s, 6H,
2
×
OCH3), 5.39 (t, J = 6.4 Hz, 1H, 3-H), 6.00 (d, J = 6.4 Hz, 1H, 2-H), 6.30 (d, 2H, 20-H, 60-H), 6.34
(d, J = 2.0 Hz, 1H, 40-H), 6.43 (d, J = 5.6 Hz, 1H, NH), 7.01 (m, 2H, 6-H, 8-H), 7.50 (m, 1H, 7-H), 7.80
(dd, J = 8.0, 1.6 Hz, 1H, 5-H); 13C-NMR (100 MHz, CDCl3)
: 23.1 (C-CH3), 55.3 (2 C-OCH3), 56.3
(C-3), 79.6 (C-2), 100.4 (C-40), 105.4 (C-20, C-60), 118.0 (C-8), 120.1 (C-4a), 121.6 (C-6), 126.8 (C-5), 137.0
δ
×

Biomolecules 2020, 10, 1462
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(C-10), 137.2 (C-7), 160.3 (C-8a), 160.8 (C-30, C-50), 170.4 (amide carbonyl), 189.2 (C-4); HRMS (ESI)
calcd. for C19H19NO5 [M + H]+ 342.134; found 342.134.
(
±
)-N-[(2S*,3R*)-4-oxo-(3,4,5-trimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide
(rac-cis-24e):
White crystals, yield 64%, mp 170–172 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 2.04 (s, 3H, CH3), 3.67 (s, 6H,
2
×
OCH3), 3.79 (s, 3H, OCH3), 5.41 (t, J = 6.0 Hz, 1H, 3-H), 6.03 (d, J = 6.4 Hz, 1H, 2-H), 6.38 (s, 2H,
20-H, 60-H), 6.42 (d, J = 5.6 Hz, 1H, NH), 7.04 (m, 2H, 6-H, 8-H), 7.53 (m, 1H, 7-H), 7.83 (dd, J = 8.0,
1.2 Hz, 1H, 5-H); 13C-NMR (100 MHz, CDCl3)
δ: 23.1 (C-CH3), 56.0 (2
×
C-OCH3), 56.4 (C-3), 60.8
(C-OCH3), 79.9 (C-2), 104.4 (C-20, C-60), 118.0 (C-8), 120.0 (C-4a), 121.6 (C-6), 126.7 (C-5), 130.4 (C-10,
C-40), 137.1 (C-7), 153.2 (C-30, C-50), 160.3 (C-8a), 170.4 (amide carbonyl), 189.3 (C-4); HRMS (ESI) calcd.
for C20H21NaNO6 [M+Na]+ 394.126; found 394.128.
(±
)-N-[(2S*,3S*)-4-oxo-2-phenyl-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-trans-24a): White crystals,
yield 75%, mp 192–194 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 1.86 (s, 3H, CH3), 5.02 (dd, J = 12.0, 8.4 Hz,
1H, 3-H), 5.38 (d, J = 12.4 Hz, 1H, 2-H), 6.03 (d, J = 8.4 Hz, 1H, NH), 7.02 (m, 2H, 6-H, 8-H), 7.39 (m, 3H,
30-H, 50-H, 7-H), 7.49 (m, 3H, 20-H, 40-H, 60-H), 7.88 (dd, J = 7.6, 0.8 Hz, 1H, 5-H); 13C-NMR (100 MHz,
CDCl3) δ: 22.9 (C-CH3), 58.3 (C-3), 83.2 (C-2), 118.1 (C-8), 120.2 (C-4a), 122.1 (C-6), 127.7 (C-5), 127.8
(C-20, C-60), 128.6 (C-30, C-50), 129.4 (C-40), 136.2 (C-10), 136.6 (C-7), 161.4 (C-8a), 170.3 (amide carbonyl),
191.0 (C-4); HRMS (ESI) calcd. for C17H15NaNO3 [M+Na]+ 304.095; found 304.096.
(±
)-N-[(2S*,3S*)-4-oxo-2-(4-methoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-trans-24b): White
crystals, yield 71%, mp 189–191 ◦C; 1H-NMR (400 MHz, CDCl3)
δ
: 1.88 (s, 3H, CH3), 3.82 (s, 3H, OCH3),
5.08 (dd, J = 12.4, 8.4 Hz, 1H, 3-H), 5.31 (d, J = 12.4 Hz, 1H, 2-H), 5.90 (d, J = 8.4 Hz, 1H, NH), 6.92 (d,
2H, 30-H, 50-H), 7.00 (d, J = 8.4 Hz, 1H, 8-H), 7.05 (t, J = 7.2 Hz, 1H, 6-H), 7.42 (d, 2H, 20-H, 60-H), 7.49
(m, 1H, 7-H), 7.88 (dd, J = 7.2, 1.2 Hz, 1H, 5-H); 13C-NMR (100 MHz, CDCl3)
δ: 23.0 (C-CH3), 55.4
(C-OCH3), 58.0 (C-3), 83.1 (C-2), 114.0 (C-30, C-50), 118.1 (C-8), 120.2 (C-4a), 122.0 (C-6), 127.6 (C-5),
128.2 (C-10), 129.3 (C-20, C-60), 136.6 (C-7), 160.4 (C-40), 161.4 (C-8a), 170.2 (amide carbonyl), 191.3 (C-4);
HRMS (ESI) calcd. for C18H17NaNO4 [M+Na]+ 334.105; found 334.107.
( )-N-[(2S*,3S*)-4-oxo-2-(3,4-dimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-trans-24c):
±
◦
1
White crystals, yield 82%, mp 180–181 C; H-NMR (400 MHz, DMSO-d6)
3.76 (d, 6 H, 2 OCH3), 4.92 (dd, J = 12.4, 8.4 Hz, 1H, 3-H), 5.49 (d, J = 12.4 Hz, 1H, 2-H), 6.94 (m, 2H,
20-H, 50-H), 7.06 (d, J = 8.4 Hz, 1H, 8-H), 7.11 (m, 2H, 6-H, 60-H), 7.58 (m, 1H, 7-H), 7.79 (dd, J = 7.6,
δ: 1.72 (s, 3H, CH3),
×
1.2 Hz, 1H, 5-H), 8.14 (d, J = 8.4 Hz, 1H, NH); 13C-NMR (100 MHz, DMSO-d6)
δ: 22.3 (C-CH3), 55.4
(C-OCH3), 55.5 (C-OCH3), 57.4 (C-3), 81.5 (C-2), 111.1 (C-50), 111.2 (C-20), 118.0 (C-8), 120.0 (C-4a), 120.7
(C-60), 121.8 (C-6), 126.9 (C-5), 129.3 (C-10), 136.3 (C-7), 148.4 (C-40), 149.2 (C-30), 160.8 (C-8a), 169.1
(amide carbonyl), 190.5 (C-4); HRMS (ESI) calcd. for C19H19NaNO5 [M+Na]+ 364.116; found 364.118.
( )-N-[(2S*,3S*)-4-oxo-2-(3,5-dimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-trans-24d):
±
◦
1
White crystals, yield 72%, mp 192–193 C; H-NMR (400 MHz, DMSO-d6) δ: 1.74 (s, 3H, CH3),
3.75 (s, 6H, 2
×
OCH3), 4.85 (dd, J = 12.0, 8.4 Hz, 1H, 3-H), 5.51 (d, J = 12.0 Hz, 1H, 2-H), 6.51 (t, J =
2.0 Hz, 1H, 40-H), 6.66 (d, 2H, 20-H, 60-H), 7.07 (d, J = 8.4 Hz, 1H, 8-H), 7.12 (t, J = 7.6 Hz, 1H, 6-H),
7.59 (m, 1H, 7-H), 7.79 (dd, J = 8.0, 1.6 Hz, 1H, 5-H), 8.18 (d, J = 8.4 Hz, 1H, NH); 13C-NMR (100 MHz,
DMSO-d6)
δ
: 22.3 (C-CH3), 55.3 (2
×
C-OCH3), 57.5 (C-3), 81.3 (C-2), 100.4 (C-40), 105.8 (C-20, C-60),
118.0 (C-8), 120.0 (C-4a), 121.9 (C-6), 126.9 (C-5), 136.3 (C-7), 139.2 (C-10), 160.2 (C-30, C-50), 160.7 (C-8a),
169.2 (amide carbonyl), 190.2 (C-4); HRMS (ESI) calcd. for C19H19NO5 [M + H]+ 342.134; found 342.134.
(
±
)-N-[(2S*,3S*)-4-oxo-2-(3,4,5-trimethoxyphenyl)-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-trans-24e):
White crystals, yield 74%, mp 147–149 ◦C; 1H-NMR (400 MHz, CD3OD)
: 1.89 (s, 3H, CH3), 3.80 (s,
3H, OCH3), 3.87 (s, 6H, 2 OCH3), 5.04 (d, J = 12.4 Hz, 1H, 3-H), 5.42 (d, J = 12.4 Hz, 1H, 2-H), 6.84 (s,
2H, 20-H, 60-H), 7.07 (d, J = 8.4 Hz, 1H, 8-H), 7.13 (m, 1H, 6-H), 7.58 (m, 1H, 7-H), 7.89 (dd, J = 8.0,
1.6 Hz, 1H, 5-H); 13C-NMR (100 MHz, CD3OD)
: 22.3 (C-CH3), 56.7 (2 C-OCH3), 59.3 (C-3), 61.1
(C-OCH3), 83.9 (C-2), 106.3 (C-20, C-60), 119.1 (C-8), 121.3 (C-4a), 123.1 (C-6), 128.3 (C-5), 133.8 (C-10),
δ
×
δ
×

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137.7 (C-7), 139.6 (C-40) 154.4 (C-30, C-50), 162.7 (C-8a), 173.2 (amide carbonyl), 192.1 (C-4); HRMS (ESI)
calcd. for C20H21NaNO6 [M+Na]+ 394.126; found 394.128.
(
±
)-N-[(2S*,3S*)-4-oxo-2-(naphthalen-1-yl)-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-trans-24f): White
crystals, yield 81%, mp 248–250 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ
: 1.58 (s, 3H, CH3), 5.12 (t, J =
11.6 Hz, 1H, 3-H), 6.42 (d, J = 12.0 Hz, 1H, 2-H), 7.07 (d, J = 8.0 Hz, 1H, 8-H), 7.17 (t, J = 8.0 Hz, 1H, 6-H),
7.21 (m, 4 H, 7-H, 20-H, 30-H, 70-H), 7.81 (d, J = 5.6 Hz, 1H, 60-H), 7.87 (dd, J = 8.0, 1.6 Hz, 1H, 5-H),
7.98 (m, 2H, 40-H, 50-H), 8.20 (m, 2H, 80-H, NH); 13C-NMR (100 MHz, DMSO-d6)
δ: 22.1 (C-CH3), 57.5
(C-3), 78.3 (C-2), 118.0 (C-6), 120.3 (C-4a), 122.1 (C-8), 123.5 (C-80), 125.2 (C-5), 125.8 (C-20, C-30), 126.4
(C-70), 127.0 (C-60), 128.7 (C-50), 129.4 (C-40), 131.3 (C-10), 132.8 (C-4a’), 133.3 (C-8a’), 136.4 (C-7), 160.9
(C-8a), 169.4 (amide carbonyl), 190.2 (C-4); HRMS (ESI) calcd. for C21H17NaNO3 [M+Na]+ 354.110;
found 354.113.
(
±
)-N-[(2S*,3S*)-4-oxo-2-(naphthalen-2-yl)-3,4-dihydro-2H-chromen-3-yl]acetamide (rac-trans-24g): White
crystals, yield 73%, mp 200–202 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ: 1.68 (s, 3H, CH3), 5.00 (dd, J =
12.4, 8.4 Hz, 1H, 3-H), 5.76 (d, J = 12.4 Hz, 1H, 2-H), 7.11 (d, J = 8.4 Hz, 1H, 8-H), 7.15 (m, 1H, 6-H), 7.55
(m, 2H, 30-H, 70-H), 7.61 (m, 1H, 7-H), 7.68 (dd, J = 8.4, 1.6 Hz, 1H, 5-H), 7.84 (dd, J = 8.0, 1.6 Hz, 1H,
60-H), 7.95 (m, 3H, 40-H, 50-H, 80), 8.02 (s, 1H, 10-H), 8.21 (d, J = 8.4 Hz, 1H, NH); 13C-NMR (100 MHz,
DMSO-d6) δ: 22.2 (C-CH3), 57.7 (C-3), 81.7 (C-2), 118.0 (C-8), 120.1 (C-4a), 122.0 (C-6), 125.1 (C-5), 126.4
(C-10), 126.5 (C-80), 126.9 (C-30), 127.2 (C-70), 127.6 (C-60), 127.8 (C-50), 128.0 (C-40), 132.4 (C-10), 133.1
(C-4a’), 134.5 (C-8a’), 136.4 (C-7), 160.8 (C-8a), 169.2 (amide carbonyl), 190.2 (C-4); HRMS (ESI) calcd.
for C21H17NO3 [M + H]+ 332.128; found 332.128.
2.9. General Procedure for the Synthesis of Condensed Thiazole Derivatives 3a-g
Under inert atmosphere, acetamide derivatives rac-cis-24a-e, g or rac-trans-24a-g (0.355 mmol) and
Lawesson’s reagent (0.355 mmol) were dissolved in anhydrous toluene (5 mL). The mixture was stirred
for 4 h at 70 ◦C. After cooling, toluene was evaporated and the crude product was purified by column
chromatography using hexane/ethyl acetate 8:1 or toluene/ethyl acetate 8:1 as eluent, which provided
the pure product.
(
±
)-2-methyl-4-phenyl-4H-chromeno[3,4-d][1,3]thiazole (3a): White crystals, yield 82%, mp 101–103 ◦C;
1H-NMR (400 MHz, CDCl3)
: 2.67 (s, 3H, CH3), 6.54 (s, 1H, 4-H), 6.89 (m, 2H, 6-H, 8-H), 7.12 (m, 2H,
: 19.6
δ
7-H, 9-H), 7.28 (m, 3H, 20-H, 40-H, 60-H), 7.37 (m, 2H, 30-H, 50-H); 13C-NMR (100 MHz, CDCl3)
δ
(CH3), 78.7 (C-4), 117.0 (C-6), 118.2 (C-5a), 121.9 (C-8), 124.3 (C-9), 126.2 (C-9b), 127.3 (C-30, C-50), 128.6
(C-40), 128.7 (C-20, C-60), 129.3 (C-7), 139.8 (C-10), 147.4 (C-3a), 151.2 (C-9a), 165.2 (C-2); HRMS (ESI)
calcd. for C17H13NaNOS [M+Na]+ 362.061; found 362.067.
(4R)-3a: tR = 3.20 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (
φ)}:
326sh (−3.68), 293 (−9.35), 280sh (−8.29), 243 (40.45), 218 (−169.42).
(4S)-3a: tR = 3.78 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
326sh (4.65), 293 (10.30), 280 (9.23), 243 (−43.81), 218 (173.68).
λ
[nm] (φ)}:
(
±
)-2-methyl-4-(4-methoxyphenyl)-4H-chromeno[3,4-d][1,3]thiazole (3b): White crystals, yield 52%. mp
108–109 ◦C; 1H-NMR (400 MHz, CDCl3)
: 2.69 (s, 3H, CH3), 3.74 (s, 3H, OCH3), 6.49 (s, 1H, 4-H), 6.82
(d, 2H, 30-H, 50-H), 6.89 (m, 2H, 6-H, 8-H), 7.09 (m, 2H, 7-H, 9-H), 7.26 (d, 2H, 20-H, 60-H); 13C-NMR
δ
(100 MHz, CDCl3) δ
: 19.6 (C-CH3), 55.3 (C-OCH3), 78.5 (C-4), 114.1 (C-30, C-50), 117.1 (C-6), 118.3 (C-5a),
121.8 (C-8), 124.3 (C-9), 126.3 (C-9b), 128.9 (C-20, C-60), 129.2 (C-7), 131.9 (C-10), 147.7 (C-40), 151.2 (C-3a),
159.9 (C-9a), 165.2 (C-2); HRMS (ESI) calcd. for C18H15NaNO2S [M+Na]+ 332.072; found 332.070.
(4R)-3b: tR = 4.36 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
326sh (−1.96), 292 (−11.31), 280sh (−9.34), 257 (32.56), 223 (−86.35).
λ
[nm] (
φ
)}:
)}:
(4S)-3b: tR = 5.02 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
326sh (1.87), 292 (7.45), 280sh (5.86), 257 (−17.30), 223 (50.79).
λ
[nm] (
φ

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(
±
)-2-met◦hyl-4-(3,4-dimethoxyphenyl)-4H-chromeno[3,4-d][1,3]thiazole (3c): White crystals, yield 66%, mp
1
119–121 C; H-NMR (400 MHz, CDCl3) δ: 2.71 (s, 3H, CH3), 3.81 (d, 6H, 2xOCH3), 6.48 (s, 1H,
4-H), 6.77 (d, J = 8.0 Hz, 1H, 6-H), 6.84 (d, J = 8.4 Hz, 1H, 8-H), 6.92 (m, 3H, 20-H, 50-H, 60-H), 7.11
(m, 2H, 7-H, 9-H); 13C-NMR (100 MHz, CDCl3)
δ: 19.6 (C-CH3), 55.9 (2xC-OCH3), 78.8 (C-4), 110.7
(C-50), 111.1 (C-20), 117.1 (C-6), 118.3 (C-5a), 120.0 (C-60), 121.9 (C-8), 124.3 (C-9), 126.3 (C-9b), 129.3
(C-7), 132.2 (C-10), 147.7 (C-3a), 149.1 (C-40), 149.4 (C-30), 151.2 (C-9a), 165.2 (C-2); HRMS (ESI) calcd.
for C19H17NaNO3S [M+Na]+ 362.082; found 362.080.
(4S)-3c: tR = 7.25 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (
φ)}:
326sh (5.55), 294 (15.61), 263sh (−8.66), 241 (−22.57), 217 (103.93).
(4R)-3c: tR = 7.58 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
326sh (−4.29), 294 (−14.08), 263sh (10.85), 241 (25.19), 217 (−98.22).
λ
[nm] (
φ)}:
(
±
)-2-methyl-4-(3,5-dimethoxyphenyl)-4H-chromeno[3,4-d][1,3]thiazole (3d): White crystals, yield 70%, mp
75–76 ◦C; 1H-NMR (360 MHz, CDCl3) : 2.67 (s, 3H, CH3), 3.69 (s, 6H, 2xOCH3), 6.36 (s, 1H, 40-H), 6.47
(s, 1H, 4-H), 6.54 (d, 2H, 20-H, 60-H), 6.87 (m, 2H, 6-H, 8-H), 7.09 (m, 2H, 7-H, 9-H); 13C-NMR (90 MHz,
δ
CDCl3)
δ: 19.5 (C-CH3), 55.3 (2
×
C-OCH3), 78.4 (C-4), 100.2 (C-40), 105.3 (C-20, C-60), 116.9 (C-6), 118.1
(C-5a), 121.9 (C-8), 124.3 (C-9), 126.2 (C-9b), 129.2 (C-7), 141.9 (C-10), 147.1 (C-3a), 151.1 (C-9a), 160.8
(C-30, C-50), 165.2 (C-2); HRMS (ESI) calcd. for C19H17NaNO3S [M+Na]+ 362.082; found 362.081.
(4R)-3d: tR = 4.80 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
326sh (−6.17), 294 (−10.80), 283sh (−3.78), 244 (29.05), 218 (−143.69).
λ
[nm] (
φ
)}:
)}:
(4S)-3d: tR = 5.78 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
326sh (5.29), 294 (8.26), 283sh (2.36), 244 (−24.94), 218 (114.38).
λ
[nm] (
φ
(
±
)-2-methyl-4-(3,4,5-trimethoxyphenyl)-4H-chromeno[3,4-d][1,3]thiazole (3e): White crystals, yield 84%,
mp 113–115 ◦C; 1H-NMR (400 MHz, CDCl3)
: 2.72 (s, 3H, CH3), 3.77 (m, 9H, 3 OCH3), 6.46 (s, 1H,
4-H), 6.62 (s, 2H, 20-H, 60-H), 6.93 (m, 2H, 6-H, 8-H), 7.16 (m, 2H, 7-H, 9-H); 13C-NMR (101 MHz, CDCl3)
δ
×
δ
: 20.0 (C-CH3), 56.5 (2
×
C-OCH3), 61.2 (C-OCH3), 79.4 (C-4), 104.9 (C-20, C-60), 117.3 (C-6), 118.5
(C-5a), 122.4 (C-8), 124.7 (C-9), 126.7 (C-9b), 129.7 (C-7), 135.5 (C-10, C-40), 147.8 (C-3a), 151.6 (C-9a),
153.7 (C-30, C-50), 165.6 (C-2); HRMS (ESI) calcd. for C20H19NaNO4S [M+Na]+ 392.093; found 392.095.
(4R)-3e: tR = 6.51 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
326sh (−4.54), 293 (−9.61), 285sh (−4.80), 263sh (7.01), 240 (13.85), 218 (−75.26).
(4S)-3e: tR = 6.67 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
326sh (4.66), 293 (8.98), 285sh (4.36), 263sh (−6.88), 240 (−14.89), 218 (67.60).
λ
λ
[nm] (
φ
)}:
[nm] (
φ)}:
( )-2-methyl-4-(naphthalen-1-yl)-4H-chromeno[3,4-d][1,3]thiazole (3f): White crystals, yield 60%, mp
±
173–175 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 2.69 (s, 3H, CH3), 6.77 (d, J = 8.0 Hz, 1H, 6-H), 6.90 (t, J =
7.2 Hz, 1H, 8-H), 7.04 (s, 2H, 4-H, 7-H), 7.20 (m, 3H, 9-H, 20-H, 30-H), 7.50 (t, J = 7.6 Hz, 1H, 60-H), 7.55
(t, J = 7.6 Hz, 1H, 70-H), 7.77 (d, J = 8.0 Hz, 1H, 40-H), 7.84 (d, J = 7.6 Hz, 1H, 50-H), 8.45 (d, J = 8.4 Hz,
1H, 80-H); 13C-NMR (100 MHz, CDCl3)
δ: 19.7 (C-CH3), 76.2 (C-4), 117.3 (C-6), 118.5 (C-5a), 122.0 (C-8),
124.4 (C-9), 124.5 (C-80), 125.1 (C-30), 125.9 (C-60), 126.6 (C-20), 126.8 (C-70), 127.4 (C-9b), 128.7 (C-50),
129.2 (C-40), 129.8 (C-7), 131.7 (C-8a’), 134.1 (C-10), 134.3 (C-4a’), 147.1 (C-3a), 151.1 (C-9a), 165.2 (C-2);
HRMS (ESI) calcd. for C21H15NaNOS [M+Na]+ 352.077; found 352.076.
(4R)-3f: tR = 4.10 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ [nm] (φ)}:
316 (−1.29), 274sh (−5.17), 239sh (−6.11), 223 (−8.99), 216 (9.89).
(4S)-3f: tR = 5.62 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ [nm] (φ)}: 316
(0.40), 274sh (3.19), 239sh (2.89), 223 (4.81), 216 (−6.90).
(
±
)-2-methyl-4-(naphthalen-2-yl)-4H-chromeno[3,4-d][1,3]thiazole (3g): White crystals, yield 55%, mp
129–130 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 2.67 (s, 3H, CH3), 6.70 (s, 1H, 4-H), 6.89 (m, 2H, 7-H, 9-H),

Biomolecules 2020, 10, 1462
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7.10 (m, 2H, 6-H, 8-H), 7.40 (m, 2H, 60-H, 70-H), 7.52 (d, J = 8.8 Hz, 1H, 30-H), 7.74 (m, 4 H, 10-H, 40-H,
50-H, 80-H); 13C-NMR (100 MHz, CDCl3)
δ: 19.6 (C-CH3), 79.0 (C-4), 117.0 (C-6), 118.2 (C-5a), 122.0
(C-8), 124.4 (C-9), 125.0 (C-80), 126.2 (C-30), 126.4 (C-60), 126.4 (C-9b), 126.5 (C-10), 127.7 (C-70), 128.4
(C-50), 128.6 (C-40), 129.3 (C-7), 133.2 (C-4a’), 133.5 (C-8a’), 137.1 (C-20), 147.4 (C-3a), 151.3 (C-9a), 165.3
(C-2); HRMS (ESI) calcd. for C21H15NaNOS [M+Na]+ 352.077; found 352.077.
(4R)-3g: tR = 3.79 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ [nm] (φ)}:
239 (6.99), 225 (−28.42), 214 (7.25).
(4S)-3g: tR = 4.52 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
(−5.03), 225 (12.80), 214 (−1.62).
λ [nm] (φφ)}:239
2.10. General Procedure for the Knorr Reaction Affording the Pyrrole-Condensed Derivatives 4a-g
3-Aminoflavanone derivatives rac-cis-1a-e or rac-trans-1a-g (0.363 mmol) were dissolved in a
mixture of 96% ethanol (4 mL) and water (2 mL). Under stirring, ethyl acetoacetate (55 L, 0.436 mmol)
,
g
µ
and NaOAc x 3 H2O (300 mg, 2.178 mmol) were added to the reaction. The mixture was refluxed for
3 h and then water was added. Extraction with CH2Cl2, drying of the combined organic phases over
MgSO4, and concentration under reduced pressure provided the crude product as orange oil. Column
chromatography using toluene/ethyl acetate 4:1 with 0.1% Et3N as eluent and subsequent trituration in
cold Et2O afforded the pure product.
(±
)-ethyl 2-methyl-4-phenyl-3,4-dihydrochromeno[3,4-b]pyrrole-1-carboxylate (4a): Off-white crystals, yield
53%, mp 133–136 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 1.37 (t, 3H, CH3), 2.42 (s, 3H, 2-CH3), 4.31 (m, 2H,
CH2), 6.10 (s, 1H, 4-H), 6.91 (dd, J = 8.0, 1.6 Hz, 1H, 6-H), 6.97 (m, 1H, 8-H), 7.04 (m, 1H, 7-H), 7.40
(m, 5H, 20-H, 30-H, 40-H, 50-H, 60-H), 7.73 (bs, 1H, NH), 8.27 (dd, J = 8.0, 2.0 Hz, 1H, 9-H); 13C-NMR
(100 MHz, CDCl3) δ: 14.5 (2xCH3), 60.0 (C-CH2), 75.8 (C-4), 109.0 (C-5), 114.9 (C-9b), 116.8 (C-6), 121.6
(C-9a), 122.0 (C-8), 125.7 (C-3a), 126.1 (C-9), 126.9 (C-4), 128.0 (C-20, C-60), 129.1 (C-30, C-50), 129.4 (C-7),
136.7 (C-2), 138.2 (C-10), 152.0 (C-5a), 165.9 (ester carbonyl); HRMS (ESI) calcd. for C21H19NO3 [M +
H]+ 334.1438; found 334.1438.
(4R)-4a: tR = 3.20 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
300 (−3.47), 250 (−1.88), 235 (8.76), 214 (−28.73).
λ [nm] (φ)}:
(4S)-4a: tR = 3.43 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ [nm] (φφ)}:
300 (3.06), 250 (2.22), 235 (−10.08), 214 (30.02).
( )-ethyl 2-methyl-4-(4-methoxyphenyl)-3,4-dihydrochromeno[3,4-b]pyrrole-1-carboxylate (4b): White crystals,
±
yield 32%, mp 169–171 ◦C; 1H-NMR (400 MHz, CDCl3)
δ: 1.36 (t, 3H, CH3), 2.40 (s, 3H, 4-CH3), 3.76
(s, 3H, OCH3), 4.26 (m, 2H, CH2), 6.01 (s, 1H, 4-H), 6.86 (m, 3H, 6-H, 30-H, 50-H), 6.94 (t, J = 7.2 Hz,
1H, 7-H), 7.01 (t, J = 6.8 Hz, 1H, 8-H), 7.30 (d, 2H, 20-H, 60-H), 7.86 (bs 1H, NH), 8.25 (d, J = 6.8 Hz,
1H, 9-H); 13C-NMR (100 MHz, CDCl3)
δ: 14.4 (C-CH3), 14.5 (C-CH3), 55.4 (C-OCH3), 60.0 (C-CH2),
75.4 (C-4), 108.9 (C-1), 114.4 (C-30, C-50), 114.9 (C-9b), 116.8 (C-6), 121.6 (C-9a), 121.9 (C-8), 125.9 (C-3a),
126.0 (C-9), 126.8 (C-7), 129.5 (C-20, C-60), 130.2 (C-10), 136.7 (C-2), 152.0 (C-5a), 160.4 (C-40), 165.9 (ester
carbonyl); HRMS (ESI) calcd. for C22H21NaNO4 [M+Na]+ 364.1543; found 364.1546.
(4R)-4b: tR = 7.13 min on Chiralpak IA column (hexane/2-propanol 90:10), HPLC-ECD {
λ
[nm] (φ)}:
310sh (−4.28), 277 (−5.65), 237 (33.61), 219 (−31.69), 203 (25.66).
(4S)-4b: tR = 7.68 min on Chiralpak IA column (hexane/2-propanol 90:10), HPLC-ECD {
310 (3.55), 277 (4.50), 237 (−27.21), 219 (23.67), 203 (−26.07).
λ
[nm] (
φ)}:
(
±
)-ethyl 2-methyl-4-(3,4-dimethoxyphenyl)-3,4-dihydrochromeno[3,4-b]pyrrole-1-carboxylate (4c): White
crystals, yield 48%, mp 214–216 ◦C; 1H-NMR (400 MHz, CDCl3)
: 1.40 (t, 3H, CH3), 2.45 (s, 3H, 4-CH3),
3.78 (m, 6H, 2
OCH3), 4.35 (m, 2H, CH2), 6.02 (s, 1H, 4-H), 6.80 (d, J = 6.8 Hz, 1H, 50-H), 6.93 (m,
5H, 6-H, 7-H, 8-H 20-H, 60-H), 8.04 (bs, 1H, NH), 8.28 (d, J = 5.6 Hz, 1H, 9-H); 13C-NMR (100 MHz,
δ
×

Biomolecules 2020, 10, 1462
25 of 43
CDCl3)
δ
: 14.4 (C-CH3), 14.5 (C-CH3), 55.9 (2
×
C-OCH3), 60.2 (C-CH2), 75.9 (C-4), 109.0 (C-1), 110.8
(C-20), 111.0 (C-50), 115.0 (C-9b), 116.8 (C-60), 120.8 (C-6), 121.7 (C-9a), 122.0 (C-8), 126.0 (C-3a), 126.1
(C-9), 126.8 (C-7), 130.5 (C-10), 136.8 (C-2), 149.4 (C-40,), 149.8 (C-30), 152.2 (C-5a), 165.9 (ester carbonyl);
HRMS (ESI) calcd. for C23H23NaNO5 [M+Na]+ 416.1468; found 416.1466.
(4R)-4c: tR = 9.60 min on Chiralpak IA column (hexane/2-propanol 90:10), HPLC-ECD {
308 (−2.89), 238 (10.00), 215 (−15.99), 206 (−9.40).
λ [nm] (φ)}:
(4S)-4c: tR = 9.96 min on Chiralpak IA column (hexane/2-propanol 90:10), HPLC-ECD {
λ [nm] (φ)}: 308
(2.20), 238 (−8.41), 215 (10.48), 206 (−12.66).
( )-ethyl 2-methyl-4-(3,5-dimethoxyphenyl)-3,4-dihydrochromeno[3,4-b]pyrrole-1-carboxylate (4d): White
±
◦
1
crystals, yield 35%, mp 156–158 C; H-NMR (400 MHz, CDCl3)
4-CH3), 3.79 (s, 6H, 2
OCH3), 4.30 (m, 2H, CH2), 6.04 (s, 1H, 4-H), 6.49 (s, 1H, 40-H), 6.63 (d, 2H, 20-H,
60-H), 6.96 (m, 3H, 6-H, 7-H, 8-H), 7.60 (bs, 1H, NH), 8.27 (dd, J = 7.6, 1.2 Hz, 1H, 9-H); 13C-NMR
δ: 1.38 (t, 3H, CH3), 2.45 (s, 3H,
×
(100 MHz, CDCl3):
δ
: 14.6 (C-CH3), 55.6 (2
×
C-OCH3), 60.1 (C-CH2), 75.8 (C-4), 101.3 (C-40), 105.6
(C-20, C-60), 109.2 (C-1), 114.9 (C-9a), 116.9 (C-6), 121.6 (C-9a), 122.2 (C-8), 125.6 (C-3a), 126.2 (C-9),
126.9 (C-7), 136.6 (C-2), 140.4 (C-10), 152.2 (C-5a), 161.5 (C-30, C-50), 165.8 (ester carbonyl); HRMS (ESI)
calcd. for C23H23NaNO5 [M+Na]+ 416.1468; found 416.1464.
(4R)-4d: tR = 4.53 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}:
310 (−4.70), 254 (−2.22), 237 (10.34), 216 (−20.58), 205 (27.90).
(4S)-4d: tR = 4.80 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
310 (4.06), 254 (2.07), 237 (−9.85), 216 (19.44), 20 5(−21.99).
λ
[nm] (
φ)}:
(
±
)-ethyl 2-methyl-4-(3,4,5-trimethoxyphenyl)-3,4-dihydrochromeno[3,4-b]pyrrole-1-carboxylate
Pale yellow crystals, yield 55%, mp 199–201 ◦C; 1H-NMR (400 MHz, CDCl3):
: 1.40 (t, 3H, CH3), 2.51
(s, 3H, 4-CH3), 3.77 (m, 9H, 3
OCH3), 4.31 (m, 2H, CH2), 6.02 (s, 1H, 4-H), 6.66 (s, 2H, 20-H, 60-H),
6.93 (d, J = 7.6 Hz, 1H, 6-H), 6.99 (t, J = 7.6 Hz, 1H, 7-H), 7.05 (t, J = 7.2 Hz, 1H, 8-H), 8.28 (d, J = 7.2 Hz,
1H, 9-H), 8.44 (bs, 1H, NH); 13C-NMR (100 MHz, CDCl3)
: 14.4 (C-CH3), 14.6 (C-CH3), 56.1 (2
(4e):
δ
×
δ
×
C-OCH3), 60.0 (C-CH2), 60.7 (C-OCH3), 76.6 (C-4), 105.1 (C-20, C-60), 108.9 (C-1), 115.0 (C-9b), 116.7
(C-6), 121.7 (C-9a), 122.1 (C-8), 125.8 (C-3a), 126.1 (C-9), 126.8 (C-7), 134.0 (C-10), 136.8 (C-2), 138.1
(C-40),152.2 (C-5a), 153.4 (C-30, C-50), 166.0 (ester carbonyl); HRMS (ESI) calcd. for C24H25NaNO6
[M+Na]+ 446.1574; found 446.1571.
(4R)-4e: tR = 11.57 min on Chiralpak IC column (hexane/2-propanol 70:30), HPLC-ECD {
λ
[nm] (φ)}:
311 (−6.94), 291sh (−6.42), 240 (21.81), 217 (−36.71).
(4S)-4e: tR = 16.28 min on Chiralpak IC column (hexane/2-propanol 70:30), HPLC-ECD {
311 (9.81), 291sh (9.30), 240 (−30.91), 217 (51.74).
λ
[nm] (φ)}:
( )-ethyl 2-methyl-4-(naphthalen-1-yl)-3,4-dihydrochromeno[3,4-b]pyrrole-1-carboxylate (4f): White crystals,
±
yield 51%, mp 204–207 ◦C; 1H-NMR (400 MHz, DMSO-d6)
δ: 1.37 (t, 3H, CH3), 2.50 (s, 3H, 4-CH3),
4.32 (q, 2H, CH2), 6.68 (m, 1H, 6-H), 6.94 (m, 2H, 7-H, 8-H), 7.07 (d, J = 6.8 Hz, 1H, 20-H), 7.15 (s, 1H,
4-H), 7.41 (t, J = 7.6 Hz, 1H, 30-H), 7.59 (t, J = 7.2 Hz, 1H, 60-H), 7.66 (t, J = 7.2 Hz, 1H, 70-H), 7.95 (d,
J = 8.0 Hz, 1H, 40-H), 8.01 (d, J = 8.0 Hz, 1H, 50-H), 8.38 (m, 1H, 9-H), 8.55 (d, J = 8.0 Hz, 1H, 80-H),
11.50 (bs, 1H, NH); 13C-NMR (100 MHz, DMSO-d6)
δ: 14.07 (C-CH3), 14.4 (C-CH3), 59.3 (C-CH2), 72.0
(C-4), 107.5 (C-1), 114.0 (C-9b), 116.6 (C-6), 121.4 (C-8), 121.7 (C-9a), 124.4 (C-80), 125.2 (C-30), 125.2
(C-3a), 125.6 (C-9), 126.0 (C-60), 126.2 (C-7), 126.6 (C-20), 126.8 (C-70), 128.6 (C-50), 129.6 (C-2), 131.2
(C-4a’), 133.7 (C-8a’), 133.8 (C-10), 137.2 (C-4), 150.6 (C-5a), 165.2 (ester carbonyl); HRMS (ESI) calcd.
for C25H21NaNO3 [M+Na]+ 406.1414; found 406.1411.
(4R)-4f: tR = 3.66 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ [nm] (φ)}:
323 (0.91), 271 (−6.26), 238sh (−10.92), 225 (−73.35), 212 (47.44).

Biomolecules 2020, 10, 1462
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(4S)-4f: tR = 4.38 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}: 323
(−1.22), 271 (7.61), 238sh (12.80), 225 (78.13), 212 (−57.70).
(
±
)-ethyl 2-methyl-4-(naphthalen-2-yl)-3,4-dihydrochromeno[3,4-b]pyrrole-1-carboxylate (4g): White crystals,
yield 60%, mp 149–151 ◦C; 1H-NMR (400 MHz, CDCl3)
: 1.35 (s, 3H, CH3), 2.34 (s, 3H, 4-CH3), 4.29 (s,
2H, CH2), 6.21 (s, 1H, 4-H), 6.93 (m, 3H, 6-H, 8-H, 30-H), 7.48 (m, 3H, 7-H, 60-H, 70-H), 7.80 (m, 5H,
9-H, 40-H, 50-H, 80-H, NH), 8.28 (d, J = 6.0 Hz, 1H, 10-H); 13C-NMR (100 MHz, CDCl3)
: 14.4 (C-CH3),
δ
δ
14.5 (C-CH3), 60.0 (C-CH2), 75.9 (C-4), 109.0 (C-1), 114.9 (C-9b), 116.8 (C-6), 121.6 (C-9a), 122.2 (C-8),
125.2 (C-80), 125.6 (C-3a), 126.1 (C-30), 126.6 (C-9), 126.8 (C-60), 126.9 (C-7), 127.4 (C-10), 127.9 (C-70),
128.3 (C-50), 129.2 (C-40), 133.2 (C-4a’), 133.8 (C-8a’), 135.5 (C-20), 136.9 (C-2), 152.0 (C-5a), 165.9 (ester
carbonyl); HRMS (ESI) calcd. for C25H21NaNO3 [M+Na]+ 406.1414; found 406.1414.
(4R)-4g: tR = 3.86 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
λ
[nm] (φ)}:
317 (−6.27), 273 (−6.98), 236 (17.06), 222 (−37.60), 207 (55.29).
(4S)-4g: tR = 4.20 min on Chiralpak IA column (hexane/2-propanol 80:20), HPLC-ECD {
317 (5.90), 273 (6.95), 236 (−18.81), 222 (35.02), 207 (−37.51).
λ
[nm] (
φ)}:
2.11. X-Ray Diffraction Analysis
Single crystals of 17e have been obtained with the slow evaporation of its solution in chloroform.
Data collection was carried out at 298 K using Mo-K radiation ( = 0.71073 Å) with a Burker-Nonius
α
λ
MACH3 diffractometer equipped with point detector. The structure could be solved by SIR-92
program [20] and refined by full-matrix least-squares method on F2 using the SHELX program [21].
Non-hydrogen atoms were refined anisotropically, hydrogen atoms were placed into geometric positions
and methyl protons were fixed using the riding model. Publication material was prepared with the
WINGX-suite [22] and publCIF software [23]. ORTEP view of the structure with selected geometric
parameters are shown in Figure S342, other data are in the expected range. Further crystallographic
information is compiled in Table S2. The structure is deposited in the Cambridge Crystallographic
Data Centre under CCDC 2016874.
2.12. MTT Assay
The number of viable cells was indirectly determined by measuring the conversion of the
tetrazolium salt MTT (3-{4,5-dimethilthiasol-2-il}-2,5-diphenyltetrasolium bromide, Sigma-Aldrich) to
formazan by mitochondrial dehydrogenases. Cells were plated in 96-well multi-titer plates (10,000 cells
per well density) in quadruplicates and were cultured for 3 days and treated by the compounds daily.
Negative control group was treated with equal amount of vehicle solvent (DMSO) and positive control
group was treated with 1 µg/mL doxorubicin. Cells were then incubated with 5 mg/mL MTT for 3 h,
precipitated formazan crystals were dissolved in acidic isopropanol (10% 1 M HCl in isopropanol
supplemented with 10% Triton X 100), and concentration of formazan was assessed colorimetrical way
measuring absorbance at 565 nm.
Determination of IC50
Logistic dose-response curves were fitted using the equation y = A2 + (A1-A2)/(1 + (x/x0)ˆp)
where the parameters are: A1: initial value (ymin), A2: final value (ymax), x0: center (EC/IC50),
and p is the calculated power. Fittings were carried out and parameters were calculated using Origin
8.6 (OriginLab Corporation, Northampton, MA, USA).
2.13. MitoProbeTM DilC1(5) Assay and SYTOX Green Labeling
Decrease in mitochondrial membrane potential is an early hallmark of apoptosis and the disruption
of the plasma membrane integrity is characteristic for cellular necrosis. These events were investigated
simultaneously using MitoProbeTM DilC1(5) assay kit and SYTOX green (both from Molecular

Biomolecules 2020, 10, 1462
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Probes/ThermoiFisher) staining, respectively. DilC1(5) (1,10,3,3,30,30-hexamethylindodicarbo - cyanine
iodide) is a fluorescent cyanine dye which penetrates cytoplasm with intact membrane and accumulates
primarily in mitochondria depending on the mitochondrial membrane potential. Since decrease in
mitochondrial membrane potential is an early marker of apoptosis, the DilC1(5) staining intensity is
typically decreased in apoptotic cells. SYTOX Green is a nucleic acid stain impermeant to live cells
with intact plasma membrane, but it penetrates the compromised membrane of necrotic, dead cells
resulting in a bright green fluorescent nuclear staining.
Cells were plated in 96-well multi-titer plates (10,000 cells per well density) in quadruplicates and
were incubated for 24 h with various concentrations of rac-19g. Negative control group was treated
with equal amount of vehicle solvent (DMSO) and positive control groups were shortly treated with
50 µM carbonyl cyanide 3- chlorophenylhydrazone (CCCP) or lysis buffer (20 mM Tris HCl, 5 mM
EDTA in H2O) to disrupt mitochondrial membrane potential or to lyse cells and disrupt membrane
integrity, respectively. Then supernatant were removed and cells were incubated with DilC1(5) and
SYTOX Green following the manufacturer’s protocol. Finally, the excess of the dyes was removed,
cells were gently washed in PBS, and fluorescence of DilC1(5) and SYTOX Green was measured
at 630/680 nm and 490/520 nm (excitation/emission), respectively, using a FlexStation 3 (Molecular
Devices) multimodal microplate reader.
2.14. CyQUANT® Cell Proliferation Assay
CyQUANT assay assesses the cellular proliferation indirectly by directly determining the DNA
content in a cell population using CyQUANT fluorescent dye. The dye exhibits strong fluorescence
enhancement when bound to cellular DNA and the fluorescent intensity is proportional to the amount
of bound DNA in a high dynamic range. Therefore, it is suitable to asses DNA synthesis associated
with cellular proliferation. Cells were plated in 96-well multi-titer plates (10,000 cells per well density)
in quadruplicates and were incubated for 24 h with various concentrations of rac-19g, then assayed
for cellular proliferation following the manufacturer’s protocol. Briefly, supernatants were gently
◦
removed and the plate was snap frozen and stored at
−
70 C. Then plate was thawed, cells were
lysed and incubated with CyQUANT dye. The excess of the dye was removed and fluorescence was
measured at 490/520 nm (excitation/emission) using a FlexStation 3 (Molecular Devices) multimodal
microplate reader.
2.15. Computational Methods
Mixed torsional/low-frequency mode conformational searches were carried out by means of
the Macromodel 10.8.011 software using the Merck Molecular Force Field (MMFF) with an implicit
solvent model for CHCl3 [24]. Geometry reoptimizations were carried out at the B3LYP/6-31+G(d,p)
level in vacuo, the CAM-B3LYP/TZVP [25] and the
ωB97X/TZVP [26] levels with the PCM solvent
model for CHCl3. TDDFT ECD calculations were run with various functionals (B3LYP, BH&HLYP,
CAM-B3LYP, PBE0) and the TZVP basis set as implemented in the Gaussian 09 package with the same
or no solvent model as in the preceding DFT optimization step [27]. ECD spectra were generated
as sums of Gaussians with 1500–3000 cm−1 widths at half-height, using dipole-velocity-computed
rotational strength values [28]. Ball-and-stick representations of the conformers were generated by
using the Molekel software [29].
3. Results and Discussion
3.1. Synthesis
The tosyl oxime derivatives 5a
of 3-aminoflavanones 1a-g
-
g
, starting materials of the Neber rearrangement for the synthesis
(Scheme 1), were prepared from 20-hydroxyacetophenone (13) in four steps
(Scheme 2).

Biomolecules 2020, 10, 1462
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Scheme 2. Synthesis of tosyl oxime derivatives; i: NaOH, EtOH, rt, 1 d (65–98%). ii: NaOAc, EtOH,
reflux, 3 h (54–75%). iii: NH2OH
reflux, 3 h (80–93%).
·HCl, NaOH, EtOH, reflux, 6 h (81–98%). iv: TsCl, dry CH2Cl2, Et3N,
20-Hydroxyacetophenone (13) was reacted with seven different arenecarbaldehydes in a
Claisen-Schmidt condensation reaction to produce the corresponding chalcones 15a , which were
transformed to racemic flavanone analogues 6a in a biomimetic intramolecular oxa-Michael
cyclization. The flavanones 6a were converted to the oximes 16a with NH2OH HCl, which were
tosylated to afford the oxime tosylates 5a-g.
-g
-
g
-g
-g
·
The oxime tosylates of cyclic ketones are common starting materials of the Neber rearrangement
reaction, in which NaOEt or KOEt is generally used as a base in dry EtOH or benzene, followed by acidic
hydrolysis to produce the hydrochloric salt of the
Neber rearrangements, in which the isolation of the optically active 2H-azirine derivative is needed,
reactive oxime tosylates were reacted with thiourea [ ] or cinchona organocatalysts [30] in the
presence of an inorganic base and there was no subsequent acidic hydrolysis. In our experiments,
we treated the oxime tosylates 5a with NaOEt base in dry toluene for one day at room temperature
and performed the acidic hydrolysis with 3N HCl solution for two hours on the CH2Cl2 solution of
the concentrated filtrate. This condition resulted in the formation of both the cis- (rac-cis-1a-e ) and
α-aminoketone [2]. In enantioselective organocatalytic
7,9
-
g
,
g
trans-3-aminoflavanone (rac-trans-1a-g) derivatives, which could be readily separated and isolated in
the work-up procedure (Table 1).
After the acidic hydrolysis, the crude product was dissolved in CH2Cl2 and 3 N HCl solution
(3 mL) was added to it and the resultant orange suspension was filtered and the solid was washed with
acetone that afforded the hydrochloride salt of the pure rac-cis-1a-e, g as white powder. The filtrate
was concentrated and triturated with acetone to produce the hydrochloride salt of rac-trans-1a-g as
off-white powder. The values of the 3J2-H,3-H coupling constants were found in the range of 5.2–5.6 Hz
for rac-cis-1a-e
purification by column chromatography provided the 2-styrylbenzoxazole side-products 17a
10–20% yield, which were obtained by ring-opening of the -pyrone ring and intramolecular cyclization
,
g, while in the range of 12.4–12.6 Hz for trans-1a-g. The residue was concentrated and
-
g
with
γ
of the phenolic hydroxyl group on the intermediate of the Beckmann rearrangement. The planar
structure of 17e was also confirmed by single crystal X-ray diffraction analysis (see Figure S332
and Table S2 for details). The formation of similar 2-styrylbenzoxazoles was also reported in the
Beckmann reaction of flavanones through the trans-chalcone oximes [31]. The cis- (rac-cis-1a-e
and trans-3-aminoflavanones (rac-trans-1a-g) were isolated in 1:1 ratio with a C-2 phenyl substituent
1a) and with an approximate two-fold excess of the trans isomer with other C-2 aryl groups except
for 1f, where only the rac-trans-1f was obtained (Table 1). In the reported Neber rearrangements of
, g)
(

Biomolecules 2020, 10, 1462
29 of 43
flavanones, the acidic hydrolysis step was performed for a longer period of time and surprisingly
the trans isomer of 2-aminoflavanone could be isolated as the single product [ ]. The formation
5,6
of both cis- and trans-3-amino-2-methylchroman-4-one was described in the Neber reaction of the
O-(p-tolylsulfonyl)oxime of 2-methylchroman-4-one [32], and cis diastereoselectivity was reported
in the Neber reaction of a 2-aryl-4-piperidone derivative [33]. Our finding suggested that the
cis-3-aminoflavanone derivatives rac-cis-1a-e
F → cis-G → cis- ) either diastereoselectively or together with the trans isomer (F → trans-G →
trans- ) and then the acidic hydrolysis promoted the conversion of the cis isomer to the trans one by
enolization-induced epimerization of the α-aminoketones 1a-g (Scheme 3).
, g formed initially through the corresponding 2H-azirine
(
H
H
Table 1. Yields of the products obtained in the Neber reaction of 5a-g. i: (1) NaOEt, dry toluene, rt, 1 d.
(2) CH2Cl2, 3N HCl, rt, 2 h.
Yield of 17 b (%)
Entry Substrate
R1
R2
R3
Sum Yield of 1 a (%)
dr c
1
2
3
4
5
6
7
5a
5b
5c
5d
5e
5f
H
H
OMe
OMe
OMe
H
OMe
OMe
H
H
H
H
OMe
OMe
cis-1a+trans-1a (60)
cis-1b+trans-1b (46)
cis-1c+trans-1c (62)
cis-1d+trans-1d (66)
cis-1e+trans-1e (65)
trans-1f (64)
17a (15)
17b (20)
17c (16)
17d (n.d) d
17e (14)
17f (10)
1:1
1:2.3
1:1.7
1:2.2
1:2.8
0:1
OMe
C-2 aryl: 1-naphthyl
C-2 aryl: 2-naphthyl
5g
cis-1g+trans-1g (69)
17g (11)
1:2.2 e
a
c
sum isolated yield of diastereomers cis- and trans-1a- , isolated yield of the benzoxazole side-products 17a-g,
g b
ratio of diastereomers cis- and trans-1
as determined from the isolated yields, d not determined, since it could not
be isolated as a single component by column chromatography, e determined by NMR.
If the acidic treatment was maintained for a long time, all the cis-3-aminoflavanones were
transformed to the lower energy trans isomer by enolization at C-2 as reported in literature examples [5,6].
With bulky C-2 aryl group such as the 1-naphthyl one in 1f, only the trans product was isolated even
with our procedure (Table 1).
O
EtO
N
N
Cl
NH2
Ar
N
N
ii
TsO
O
O
Ar
Ar
O
cis-
EtO
Ar
Ar
N
O
1a g
rac-cis-
iii
-
G
cis-
H
i
5a-g
O
NH2 Cl
ii
Ar
F
O
trans-
O
O
Ar
1a g
G
H
trans-
rac-trans-
-
Scheme 3. Formation and interconversion of the cis- and trans-3-aminoflavanone derivatives rac-cis-1a-g
and rac-trans-1a-g. i: NaOEt, dry toluene, rt, 1 d. ii: CH2Cl2, 3N HCl, rt, 2 h. iii: acid-catalyzed
epimerization via the enol form.
Since the diastereomeric 2-aminoflavanone derivatives rac-cis-1a-g and rac-trans-1a-g could be
obtained in pure form by simple filtration and trituration, we could use this asset to synthesize different
stereoisomers of morpholine-condensed target molecules 1a-g in a four-step sequence. In the first step,

Biomolecules 2020, 10, 1462
30 of 43
rac-trans-1a-g were acylated with chloroacetyl chloride, which was followed by the diastereoselective
reduction of the carbonyl group with NaBH4 affording the sec-alcohols rac-19a-g with the all-trans
relative configuration (Scheme 4).
Scheme 4.
rac-(4aS*,5R*,10aR*)-2a-g
Transformation of rac-trans-1a-g to the morpholine-condensed derivatives
i: ClCH2COCl, Et3N, dry CH2Cl2, rt, 15 min (71–82%). ii: NaBH4,
.
MeOH, rt, 15 min (88–98%). iii: NaH, dry THF, rt (80–91%). iv: (1) LiAlH4, dry dioxane,
(2) 3N HCl, rt, 1H (46–84%).
∆, 10 min
The all trans relative configuration of rac-19a-g was confirmed by the 3J2-H,3-H and 3J3-H,4-H coupling
constants, the values of which were found in the range of 9.2–10.4 Hz indicating the trans-diaxial
relationship of 2-H/3-H and 3-H/4-H. The cyclization was carried out with NaH (rac-19a-g → rac-20a-g
and the resultant lactams were reduced with LiAlH4 to the target molecules rac-(4aS*,5R*,10bR*)-2a
by preserving the all-trans relative configuration. Most of the all-trans-rac-(4aS*,5R*,10bR*)-2a were
)
-
g
-g
isolated as the hydrochloride salt except for the rac-(4aS*,5R*,10bR*)-2c and -2d, since they had good
solubility in the organic solvent.
The same synthetic scheme was also utilized for the preparation of stereoisomeric rac-2a-e
molecules starting from the rac-cis-1a-e . When the acylation reaction rac-cis-1a-e
g → rac-cis-21a-e
was performed at room temperature (Scheme 5), partial epimerization occurred at C-3 and the
, g target
,
g
,
,
g
thermodynamically more stable rac-trans-18a-e
rac-cis-21a-e, g.
, g formed as the main product instead of the expected
During the separation of the diastereomers by column chromatography, we observed that the
whole amount of the cis isomer was converted to the trans one under the slightly acidic condition of
the silica gel. In order to avoid the epimerization at C-3, the acylation was carried out at 0 ◦C and
the crude product of rac-cis-21a-e
) without purification on column chromatography. The reduction of the ketone carbonyl group
occurred diastereoselectively (dr 95:5) and it provided the all-cis stereoisomer of the alcohols
rac-22a-e . The cis orientation of 2-H, 3-H, and 4-H was determined by the NOE correlations 2-H/3-H,
,
g
was reduced directly with NaBH4 (rac-cis-21a-e
,
g → rac-22a-e
,
g
≥
,
g
3
3
2-H/4-H, and 3-H/4-H as well as by the small values of J2-H,3-H and J3-H,4-H coupling constants.
The 3J3-H,4-H coupling constant was measured 5.2 Hz for rac-22a, while the 3J2-H,3-H was so small that
it could not be resolved, since the 2-H had a sharp singlet in the 1H NMR spectrum. Cyclization of
rac-22a-e
in refluxing dioxane to produce surprisingly the rac-(4aR*,5S*,10bR*)-2a-e
(33–60%) and rac-(4aR*,5R*,10bR*)-2a-e (5–20%) as the minor one (Scheme 5). In the major products
rac-(4aR*,5S*,10aR*)-2a-e , the C-5 chirality center was inverted to decrease the steric crowding of the
,
g
with NaH afforded the lactam derivatives rac-23a-e
,
g, which were reduced with LiAlH4
,
g
as the major product
,
g
,
g