Diastereoselective Synthesis of Rauhut-Currier-Type Adducts via an Unexpected α-Addition of α,β-Unsaturated γ-Butyrolactams to Coumarin Derivatives

Article abstract of DOI:10.1021/acs.joc.6b02526

A novel, base-catalyzed and highly diastereoselective direct Michael addition-isomerization sequence is presented for the efficient synthesis of Rauhut-Currier-type adducts. An unexpected α-addition of γ-butyrolactam onto the 3-acyl coumarin derivatives was observed rather than the γ-addition, which is more common. The adducts could further undergo hydrolysis/decarboxylation to generate the products which are equivalent to those obtained by α-addition of γ-butyrolactam onto the corresponding chalcones.

Full text of DOI:10.1021/acs.joc.6b02526

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Note
Diastereoselective Synthesis of Rauhut-Currier-
Type Adducts via An Unexpected #-Addition of #,#-
Unsaturated #-Butyrolactams to Coumarin Derivatives
Shu-Mei Yang, Ganapuram Madhusudhan Reddy, Meng-
Hsien Liu, Tzu-Ping Wang, Jhen-Kuei Yu, and Wenwei Lin
J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 01 Dec 2016
Downloaded from http://pubs.acs.org on December 1, 2016
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Diastereoselective Synthesis of Rauhut-Currier-Type Adducts via
An Unexpected α-Addition of α,β-Unsaturated γ-Butyrolactams to
Coumarin Derivatives
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Shu-Mei Yang,† Ganapuram Madhusudhan Reddy,† Meng-Hsien Liu, Tzu-Ping Wang, Jhen-
Kuei Yu, and Wenwei Lin*
Department of Chemistry, National Taiwan Normal University, 88, Sec. 4, Tingchow Road, Taipei 11677, Taiwan,
R.O.C.
*Tel.: +886-2-77346131. E-mail: wenweilin@ntnu.edu.tw
ABSTRACT: A novel, base-catalyzed and highly diastereoselective direct Michael addition-
isomerization sequence is presented for the efficient synthesis of Rauhut-Currier-type adducts.
An unexpected α-addition of γ-butyrolactam onto the 3-acyl coumarin derivatives was observed
rather than the γ-addition, which is more common. The adducts could further undergo
hydrolysis/decarboxylation to generate the products which are equivalent to those obtained by α-
addition of γ-butyrolactam onto the corresponding chalcones.
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A wide range of biologically active natural products are found to bear the nitrogen heterocycles
in their core structures.1 Among such heterocycles, the pyrrolidin-2-one ring systems are found
to be the common entities.2 For the synthesis of these ring systems, α,β-unsaturated γ-
butyrolactams have served as common precursors in recent times. Although there are many
reports on the γ-functionalization of α,β-unsaturated γ-butyrolactams with various electrophiles,3
there are relatively few instances where the α-4 or β-position5 of these substrates is exploited for
chemical transformations.
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In 1994, Royer et. al. first reported the mono- and bis- α-alkylation of α,β-unsaturated γ-
butyrolactams in presence of LDA.4a Later in 2013, Wang et. al. synthesized the Morita-Baylis-
Hillman (MBH)-type adducts by a direct asymmetric aldol addition-isomerization reaction of
α,β-unsaturated γ-butyrolactams with aryl α-ketoesters using a chiral thiourea catalyst (Scheme
1a).4b Following that, two groups have independantly reported the synthesis of MBH-type
adducts from α,β-unsaturated γ-butyrolactams and isatins (Scheme 1c).4c,4d Very recently,
Shibasaki et. al. reported the direct asymmetric Mannich-type reaction of α,β-unsaturated γ-
butyrolactams with ketimines resulting in aza-MBH-type products.4f However, till date, there
have been no reports on the 1,4-addition of α,β-unsaturated γ-butyrolactams on to the Michael
acceptors resulting in Rauhut-Currier-type (RC) adducts. An attempt towards such
transformation by Wang et. al. resulted in γ-addition leading to the vinylogous Michael addition
products (Scheme 1b).4b
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Scheme 1. α-functionalization of α,β-unsaturated γ-butyrolactams.
On the other hand, 3,4-dihydrocoumarin ring systems are the common motifs that are found in
natural products and biologically active compounds.6 But the coumarin derivatives have been
infrequently used as Michael acceptors for the synthesis of such systems due to their reluctance
in losing aromatic-like nature, hence requiring harsh reaction conditions.7 Herein, we report an
unprecedented α-addition of α,β-unsaturated γ-butyrolactams onto the 3-acyl coumarins for the
generation of RC-type adducts (Scheme 1d). Further, these adducts could be subjected to
hydrolysis/decarboxylation resulting in the products which are equivalent to those obtained by
the α-addition of α,β-unsaturated γ-butyrolactams onto the chalcones, whose synthesis using
alternative approaches appeared to be a challenging task.
We began our study towards the synthesis of RC adducts 3 by treating α,β-unsaturated γ-
butyrolactam (1) with 3-acyl coumarin (2aa) in presence of triphenylphosphine, an ideal
nucleophile for RC reaction (Table 1, entry 1). Unfortunately, the reaction did not proceed and
the starting materials could be recovered after 95 h. So we tried a stronger nucleophile, PBu3
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which resulted in trace amounts of the expected product (entry 2). We then switched on to other
nucleophilic bases and found that the results were optimistic with moderate yield of expected
product as a single diastereomer (entries 3-7), with DABCO giving the best results (entry 7). It
was observed that product 3 was susceptible towards hydrolysis and subsequent decarboxylation,
which is a common phenomenon observed with β-keto acids. The structures of 3 and 4 were also
confirmed by X-ray crystallographic analysis.8
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A quick solvent screening revealed THF as ideal solvent to carry out the reaction (entry 9). In
order to prevent the hydrolysis of product 3, we then carried out the reaction in anhydrous
solvents which increased the yield of the product 3 to a great extent (entries 10-12). Re-checking
the efficiency of previously tested nucleophilic bases under anhydrous conditions confirmed that
DABCO was still the best option (entry 12). Performing the reaction in presence of molecular
sieves was not favorable (entry 15). Hence the optimal conditions for carrying out α-
functionalization of 1 onto 2 were as established in entry 12, using 20 mol % of DABCO in
anhydrous THF.
Table 1. Optimization of reaction conditions.a
entry
1
cat.
solvent
DCM
DCM
DCM
DCM
DCM
DCM
DCM
Et2O
time (h)
3/4, yield (%)b
NRc
PPh3
95
3
2
3
PBu3
10/0
DBU
57
6
48/0
4
Et3N
64/9
5
DMAP
DPGN
DABCO
DABCO
DABCO
DABCO
10
12
10
8
67/13
55/16
64/21
72/2
6
7
8
9
THF
DCMd
8
74/11
73/12
76/3
10
11
12
3
DABCO Toluened
DABCO
THFd
4
5
99/0
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DMAP
Et3N
THFd
THFd
THF
THFd
THFf
12
5
79/11
62/0
67/0
10/0
60/0
DABCO
K2CO3
K2CO3
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a Unless otherwise specified, all the reactions were carried out
using 1 (0.12 mmol), 2aa (0.1 mmol), and catalyst (20 mol %)
9
1
in the indicated solvent (0.2 mL) at 30 °C. bDetermined by H
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NMR analysis of the crude reaction mixture using Ph3CH as an
internal standard. cNo reaction. dAnhydrous solvent was used. e4
Å molecular sieves were used. 0.1 mL H2O was added to the
f
reaction mixture. DPGN = N,N-Diphenylguanidinium nitrate.
Under the optimized conditions, the scope of this reaction was studied by varying the
substituents on coumarin ring as well as the acyl moiety and the results are presented in table 2.
The reaction was highly diastereoselective and formation of a single diastereomer could be
observed in all cases. Both the electron-withdrawing and electron-donating R1 substituents on
coumarin ring performed well resulting in the products in good to excellent yields (entries 1-4).
However, varying the R2 substitution of acyl moiety had an impact on the solubility of substrates
and the reaction had to be carried out in increased dilutions or mixed solvents in some cases,
which resulted in slightly varying results. Surprisingly, a 2-bromo substitution on the acyl group
inhibited the reaction and could not furnish the product (entry 14). In contrast, a 2-naphthyl
substitution or the heteroaromatic thienyl substitution could be tolerated well resulting in the
products in good yields (entries 15 and 16). Even the presence of aliphatic cyclohexyl group
resulted in the expected product albeit in the enolic form in slightly lower yield (entry 17).
Table 2. Substrate scope for the α-functionalization of 1 with 2.a
entry
R1
R2
Ph
Ph
time (h)b
3, yield (%)c
3aa, 99
1
2
6-Br
6-Cl
5
4
3ba, 82
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6,8-Cl
6-OMe
H
Ph
Ph
4
3
3ca, 91
3da, 98
3ea, 89
3eb, 74
3ec, 83
3db, 96
3dc, 73
3ab, 80
3ac, 66
3ad, 73
3ae, 80
3af, trace
3ag, 85
3ah, 85
3ai, 59
5
Ph
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H
4-OMePh
4-NO2Ph
4-OMePh
4-NO2Ph
4-OMePh
4-NO2Ph
4-BrPh
3-BrPh
2-BrPh
2-naphthyl
2-thienyl
Cy
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7
8d
H
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6-OMe
6-OMe
6-Br
6-Br
6-Br
6-Br
6-Br
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6-Br
6-Br
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H
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OEt
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3aj, 70
3dj, 91
3ea’, 94
OEt
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Ph
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a Unless otherwise specified, all the reactions were carried out
using 1 (0.12 mmol), 2 (0.1 mmol), and DABCO (20 mol %) in
anhydrous THF (0.2 mL) at 30 °C. bIndicates the time after
which no further increase in the yield of 3 was observed.
cIsolated yields. d0.6 mL of THF was used. eMixed solvent
f
(DCM:THF = 1:1) was used (0.6 mL). Reaction with 2’ (X=S)
instead of 2.
The reaction proceeded well even when the acyl functionality was replaced with an ester group
(Table 2, entries 18 and 19). Interestingly, even the sulfur analog of 2 could participate in the
reaction well resulting in the corresponding product in excellent yield (entry 20).
Scheme 2. Reaction with other EWGs on coumarin.
However, when the EWG was replaced by either a nitro, aldehyde or cyano group, corresponding
products decomposed and could not be isolated (Scheme 2, eq a). On the other hand, the reaction
did not work in the absence of an EWG indicating the importance of acyl or ester functionality
for the activation of coumarin towards a nucleophilic attack (Scheme 2, eq b).
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We were then interested in exploring the decarboxylated adduct 4 as there were no previous
methods reported for their synthesis. Also, an attempt to synthesize these adducts by a
straightforward Michael addition of 1 on to the chalcone 7 was not successful (Scheme 3),
thereby enhancing the significance of the present protocol for their synthesis. This also highlights
the importance of coumarin ring structure of the Michael acceptor, which could act as an
additional EWG to activate the β-position towards a nucleophilic attack.
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Scheme 3. Attempt towards a straightforward synthesis of hydrolysis/decarboxylation product 4 from 1 and 7.
Hence, we carried out the reaction in presence of water to accelerate the
hydrolysis/decarboxylation sequence under slightly modified reaction conditions.8 Under the
newly optimized conditions, substrate scope of this one-pot Michael addition/
Isomerization/Hydrolysis/Decarboxylation cascade was studied and the results are presented in
table 3. In all the cases, this one-pot strategy furnished the decarboxylated products 4 in good
yields.
Table 3. One-pot synthesis of the decarboxylated adduct 4.a
entry
R1
H
R2
Ph
time (h)b
32
4, yield (%)c
4ea, 86
1
2
3
4
5
6
7
6-Br
6-Cl
6,8-Cl
H
Ph
10
4aa, 82
4ba, 94
4ca, 98
Ph
10
Ph
14
4-OMePh
4-OMePh
2-naphthyl
37
4eb, 74
4ab, 80
4ag, 80
6-Br
6-Br
13
12
a Unless otherwise specified, all the reactions were carried out using 1
(0.12 mmol), 2 (0.1 mmol.), H2O (0.4 mmol) and DABCO (40 mol %)
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b
in EtOAc (0.2 mL) at 30 °C. Indicates the time after which no further
4
5
increase in the yield of 4 was observed. cIsolated yields.
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8
9
The scope of the reaction was further extended towards α-angelica lactone (8) which was never
been used as a nucleophile for its direct α-functionalization.9 Under similar reaction conditions
as in Table 2, α-angelica lactone (8) was treated with coumarin-derived Michael acceptor 2aa
which resulted in excellent yield of α-addition product 9aa (Scheme 4). However, because of the
generation of an additional methyl stereocenter which is away from the reactive site, the product
was obtained with poor diastereoinduction.
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Scheme 4. Extension of the reaction towards α-angelica lactone.
Mechanistically, α-functionalization of 1 could be facilitated by either of the two pathways, a RC
pathway or a Michael addition/isomerization sequence. However, the reaction could not be
assisted by a phosphine but proceeded well with an inorganic base or a non-nucleophilic tertiary
amine such as Et3N (Table 1, entries 4, 16 and 17), although resulting in the product in lower
yields. Moreover, the reaction was successful even with α-angelica lactone, which cannot act as
an activated alkene for RC reaction. Hence it could be ascertained that the reaction followed the
Michael addition/isomerization pathway furnishing the α-addition product (Scheme 5). The
organic base enables deprotonation of 1, resulting in the formation of a dienolate. This dienolate
then adds on to Michael acceptor 2, providing the intermediate which is susceptible towards
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isomerization, resulting in the formal RC adduct 3. This could undergo further hydrolysis and
decarboxylation to afford the adduct 4.
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In conclusion, we have successfully demonstrated the synthesis of RC-type α–functionalization
adducts of α,β-unsaturated γ-butyrolactam via a Michael addition-Isomerization sequence with 3-
substituted coumarins. The present report happens to be the first one that involves the use of a
Michael acceptor for the generation of RC-type α–functionalization adducts of α,β-unsaturated γ-
butyrolactams via a 1,4-addition. The transformation was further applied for the analogous α-
angelica lactone as well. More importantly, the decarboxylated products of the Michael addition-
Isomerization cascade could also be furnished in good yields via a one-pot operation.
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Scheme 5. Proposed mechanism for the Michael addition/Isomerization/Hydrolysis/Decarboxylation sequence.
EXPERIMENTAL SECTION:
General experimental methods:
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All solvents and reagents were used as purchased from commercial suppliers without further
purification. Analytical thin layer chromatography (TLC) was performed on precoated alumina-
backed silica gel plates (0.2 mm thickness) which were developed using UV florescence and
iodine. Flash-chromatography was performed on silica gel (230-400 mesh). Melting points were
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1
measured on a standard melting point apparatus and are uncorrected. H NMR spectra were
recorded on a 400 MHz spectrometer, while 13C NMR spectra were recorded on a 100 MHz
instrument. Chemical shifts are reported in δ ppm referenced to an internal TMS standard for 1H
NMR and chloroform-d (δ = 77.0 ppm) for 13C NMR. HRMS spectra were recorded using FAB
(TOF analyzer) or ESI (TOF analyzer). The X-ray diffraction measurements were carried out at
298 K on a CCD area detector system equipped with a graphite monochromator and a Mo-Kα
fine-focus sealed tube (k = 0.71073 Å ).
Characterization data for new compounds.
The coumarin substrates 2aa, 2ba, 2ca, 2ea, 2ab, 2ac, 2aj and 2ea’ were synthesized following
the procedure reported in the literature.7c Likewise, the substrates 2da, 2eb and 2db were
prepared according to the method reported by Vina et. al.10 The new coumarin substrates 2ec,
2dc, 2ad-2ai and 2dj were synthesized following a similar procedure which is mentioned below.
General procedure A for the synthesis of new coumarin substrates 2:
Piperidine (5 mol %) was added to a stirred solution of substituted salicylaldehyde (10 mmol)
and corresponding ethyl benzoylacetate (1.25 equiv) or ethyl acetoacetate (1.25 equiv.) in
CH3CN (10 mL) at room temperature. After stirring for 5 min, the contents were heated to 80°C
for 8h. After the reaction was completed, the reaction mixture was allowed to cool to room
temperature, solvent was removed in vacuo and the crude product was purified by column
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chromatography over silica gel using hexane/EtOAc as eluent to get the pure 3-acylcoumarin 2ec,
2dc, 2ad-2ai or 2dj.
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3-(4-Nitrobenzoyl)-2H-chromen-2-one (2ec): Following the general procedure A, 2ec was
obtained after flash chromatography (EtOAc/Hex = 1/3) as a pale yellow solid (99% yield, 2.923
g). Rf 0.47 (EtOAc/Hex = 1/3); m.p.: 266.1-267.3 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 8.47-
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8.16 (m, 3H), 8.11-7.86 (m, 2H), 7.85-7.57 (m, 2H), 7.53-7.34 (m, 2H); C NMR (400 MHz,
CDCl3) δ/ppm: 190.5, 150.4, 147.7, 144.5, 141.5, 134.6, 130.1, 129.7, 125.6, 125.3, 123.7, 118.1,
117.1; IR (KBr) ṽ (cm−1): 2067, 1638, 1520, 1351, 1234, 700; HRMS (ESI) calcd for
C16H10NO5, [M+H]+ 296.0559, found: 296.0557.
6-Methoxy-3-(4-Nitrobenzoyl)-2H-chromen-2-one (2dc): Following the general procedure A,
2dc was obtained after flash chromatography (EtOAc/Hex = 1/3) as a yellow solid (98% yield,
3.187 g). Rf 0.43 (EtOAc/Hex = 1/3); m.p.: 256.8-257.8 °C; 1H NMR (400 MHz, CDCl3) δ/ppm:
8.33 (d, J = 8.8 Hz, 2H), 8.25 (s, 1H), 7.99 (d, J = 8.9 Hz, 2H), 7.37 (d, J = 9.1 Hz, 1H), 7.28 (d,
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J = 9.1 Hz, 1H), 7.06 (d, J = 3.1 Hz, 1H), 3.89 (s, 3H); C NMR (400 MHz, CDCl3) δ/ppm:
190.6, 158.6, 156.6, 150.4, 149.8, 147.4, 141.5, 130.1, 125.8, 123.7, 122.8, 118.4, 118.2, 110.9,
56.0; IR (KBr) ṽ (cm−1): 2066, 1636, 1570, 1348, 685; HRMS (ESI) calcd for C17H12NO6,
[M+H]+ 326.0665, found: 326.0663.
6-Bromo-3-(4-Bromobenzoyl)-2H-chromen-2-one (2ad): Following the general procedure A,
2ad was obtained after flash chromatography (EtOAc/Hex = 1/8) as a white solid (73% yield,
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2.978 g). Rf 0.48 (EtOAc/Hex = 1/8); m.p.: 261.3-262.7 °C; H NMR (400 MHz, DMSO-d6)
δ/ppm: 8.40 (s, 1H), 8.11 (s, 1H), 7.94-7.83 (m, 3H), 7.77 (d, J = 8.7 Hz, 2H), 7.48 (d, J = 8.7 Hz,
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1H); C NMR (100 MHz, DMSO- d6) δ/ppm: 190.5, 157.5, 153.2, 144.4, 135.8, 134.9, 131.7,
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131.6, 131.4, 128.1, 126.8, 120.1, 118.5, 116.2; IR (KBr) ṽ (cm−1): 1750, 1732, 1606, 1234, 932,
767; HRMS (ESI) calcd for C16H9Br2O3, [M+H]+ 406.8918, found: 406.8914.
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was obtained after flash chromatography (EtOAc/Hex = 1/6) as a white solid (78% yield, 3.182
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g). Rf 0.52 (EtOAc/Hex = 1/6); m.p.: 265.6-266.3 °C; H NMR (400 MHz, d6-DMSO) δ/ppm:
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8.40 (s, 1H), 8.13 (d, J = 9.0 Hz, 2H),7.92 (dd, J = 20.3, 7.7 Hz, 3H), 7.58-7.43 (m, 2H); C
NMR (400 MHz, d6-DMSO) δ/ppm: 190.3, 157.5, 153.4, 144.7, 138.1, 136.5, 135.9, 131.9,
131.7, 130.9, 128.4, 126.8, 122.0, 120.2, 118.6, 116.2; IR (KBr) ṽ (cm−1): 2068, 1636, 608;
HRMS (ESI) calcd for C16H8Br2O3Na, [M+Na]+ 428.8742, found: 428.8738.
6-Bromo-3-(2-Bromobenzoyl)-2H-chromen-2-one (2af): Following the general procedure A, 2af
was obtained after flash chromatography (EtOAc/Hex = 1/6) as a pale yellow solid (24% yield,
0.979 g). Rf 0.52 (EtOAc/Hex = 1/6); m.p.: 142.4-143.1 °C; 1H NMR (400 MHz, CDCl3) δ/ppm:
8.28 (s, 1H), 7.78 (d, J = 2.0 Hz, 1H) , 7.72 (dd, J = 8.8, 2.1 Hz, 1H), 7.59 (d, J = 7.9 Hz, 1H),
7.51 (d, J = 7.5 Hz, 1H), 7.44 (t, J = 7.4 Hz, 1H), 7.37 (t, J = 8.0 Hz, 1H), 7.26 (d, J = 8.8 Hz,
1H); 13C NMR (400 MHz, CDCl3) δ/ppm: 191.3, 157.2, 154.0, 145.9, 139.8, 136.9, 133.1, 132.4,
131.9, 129.9, 127.6, 126.5, 119.8, 119.6, 118.6, 117.4; IR (KBr) ṽ (cm−1): 1750, 1732, 1606,
1234, 932, 767; HRMS (ESI) calcd for C16H9Br2O3, [M+H]+ 406.8918, found: 406.8917.
3-(2-Naphthoyl)-6-bromo-2H-chromen-2-one (2ag): Following the general procedure A, 2ag
was obtained after flash chromatography (EtOAc/Hex = 1/6) as a white solid (61% yield, 2.313
g). Rf 0.46 (EtOAc/Hex = 1/6); m.p.: 205.8-206.8 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 8.33
(s, 1H), 8.01 (s, 1H), 7.99-7.85 (m, 4H), 7.79-7.69 (m, 2H),7.62 (t, J = 7.3 Hz, 1H) ,7.54 (t, J =
7.5 Hz, 1H), 7.31 (d, J = 9.4 Hz, 1H); 13C NMR (400 MHz, CDCl3) δ/ppm: 191.0, 157.8, 153.6,
143.6, 136.2, 136.1, 133.3, 132.3, 132.1, 131.3, 129.7, 129.1, 128.7, 128.4, 127.9, 127.0, 124.5,
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119.7, 118.7, 117.6; IR (KBr) ṽ (cm−1): 1627, 1362, 1195, 657; HRMS (ESI) calcd for
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C20H12BrO3, [M+H]+ 378.9970, found: 378.9972.
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6-Bromo-3-(Thiophene-2-carbonyl)-2H-chromen-2-one (2ah): Following the general procedure
A, 2ah was obtained after flash chromatography (EtOAc/Hex = 1/3) as a white solid (49% yield,
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1.642 g). Rf 0.58 (EtOAc/Hex = 1/3); m.p. 205.1-206.1 C; 1H NMR (400 MHz, CDCl3, 25 oC)
δ/ppm: 8.00 (s, 1H), 7.78 (d, J = 4.1 Hz, 1H), 7.77-7.68 (m, 3H), 7.31 (d, J = 9.7 Hz, 1H), 7.17 (s,
1H); 13C NMR (100 MHz, CDCl3, 25 oC) δ/ppm: 182.4, 157.5, 153.4, 143.1, 142.6, 136.3, 136.0,
135.3, 131.2, 128.4, 127.9, 119.5, 118.7, 117.6; IR (ATR): ṽ (cm-1) 2116, 1623, 1272, 696;
HRMS (ESI) for C14H7BrO3SNa [M+Na]+ calc.: 356.9197, found: 356.9196.
6-Bromo-3-(Cyclohexanecarbonyl)-2H-chromen-2-one (2ai): Following the general procedure A,
2ai was obtained after flash chromatography (EtOAc/Hex = 1/12) as a white solid (28% yield,
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0.938 g). Rf 0.54 (EtOAc/Hex = 1/12); m.p.: 237.1-238.5 °C; H NMR (400 MHz, CDCl3)
δ/ppm: 8.29 (s, 1H), 7.76 (d , J = 1.8 Hz, 1H), 7.72 (d , J = 8.80 Hz, 1H), 7.27 (d , J = 2.8 Hz,
1H), 3.62-3.45 (m, 1H), 1.99-1.64 (m, 5H), 1.47-1.15 (m, 5H); 13C NMR (400 MHz, CDCl3)
δ/ppm: 201.2, 158.2, 153.9, 145.7, 136.6, 131.9, 126.2, 119.9, 118.4, 117.4, 48.2, 28.5, 25.9,
25.6; IR (KBr) ṽ (cm−1): 2066, 1635, 694; HRMS (ESI) calcd for C16H16BrO3, [M+H]+
335.0283, found: 335.0285.
Ethyl 6-methoxy-2-oxo-2H-chromene-3-carboxylate (2dj): Following the general procedure A,
2dj was obtained after flash chromatography (EtOAc/Hex = 2/5) as a pale yellow solid (37%
yield, 0.918 g). Rf 0.25 (EtOAc/Hex = 1/3); m.p.: 145.1-146.3 °C; 1H NMR (400 MHz, CDCl3)
δ/ppm: 8.41 (s, 1H), 7.23-7.12 (m, 2H) , 6.95 (d, J = 2.8 Hz, 1H), 4.34 (q, J = 7.1 Hz, 2H), 3.40
(s, 3H), 1.34 (t, J = 7.0 Hz, 3H); 13C NMR (400 MHz, CDCl3) δ/ppm: 162.9, 156.7, 156.1, 149.5,
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148.2, 122.4, 118.2, 117.9, 117.6, 110.5, 61.7, 55.7, 14.0; IR (KBr) ṽ (cm−1): 1750 (s), 1380 (w),
1300 (w), 796 (w); HRMS (ESI) calcd for C13H12O5, [M+Na]+ 271.0582, found: 271.0586.
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General procedure B for the synthesis of Michael addition product 3:
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A mixture of DABCO (0.02 mmol), α,β-unsaturated γ-butyrolactam 1 (0.12 mmol, 21.9 mg) and
3-acylcoumarin 2 (0.1 mmol) in 0.2 mL of anhydrous THF was stirred at 30 °C until the
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completion of the reaction (monitored by H NMR). Then the solvent was removed under
reduced pressure and the residue was purified by column chromatography over silica gel using
hexane/EtOAc as eluent to give the desired product 3.
tert-Butyl
3-(3-Benzoyl-6-bromo-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate (3aa): Prepared according to the general procedure B using 3-benzoyl-6-bromo-2H-
chromen-2-one 2aa and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1. Purification
by column chromatography (EtOAc/Hex = 2/5) furnished the desired product 3aa as a white
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solid (99% yield, 50.7 mg). Rf 0.34 (EtOAc/Hex = 1/3); m.p.: 186.2-187.1 °C; H NMR (500
MHz, CDCl3) δ/ppm: 8.23 (d, J = 7.6 Hz, 2H), 7.64 (t, J = 7.6 Hz, 1H), 7.54 (t, J = 7.6 Hz, 2H),
7.48 (dd, J = 8.7 Hz, 2.4 Hz, 1H), 7.16 (d, J= 2.4 Hz, 1H), 7.10 (d, J = 8.7 Hz, 1H), 6.51-6.50 (m,
1H), 5.29 (d, J = 2.3 Hz, 1H), 4.45-4.42 (m, 1H), 4.29 (pseudo dt, J = 20.3 Hz, 1.9 Hz, 1H), 4.23
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(pseudo dt, J = 20.3 Hz, 2.2 Hz, 1H), 1.58 (s, 9H); C NMR (100 MHz, CDCl3) δ/ppm: 192.6,
167.7, 163.8, 150.6, 149.0, 141.1, 137.5, 134.6, 133.4, 133.0, 131.0, 129.5, 129.2, 121.7, 119.1,
117.7, 83.8, 52.5, 50.0, 37.5, 28.0; IR (KBr) ṽ (cm−1): 1781, 1718, 1480, 1325, 1154, 537;
HRMS (MALDI) calcd for C25H22BrNO6Na, [M+Na]+ 534.0528, found: 534.0531.
tert-Butyl
3-(3-Benzoyl-6-chloro-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate (3ba): Prepared according to the general procedure B using 3-benzoyl-6-chloro-2H-
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chromen-2-one 2ba and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1. Purification
by column chromatography (EtOAc/Hex = 1/3) furnished the desired product 3ba as a white
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solid (82% yield, 38.3 mg). Rf 0.5 (EtOAc/Hex = 1/3); m.p.: 190.7-191.8 °C; H NMR (400
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MHz, CDCl3) δ/ppm: 8.23 (d, J = 7.4 Hz, 2H), 7.64 (t, J = 7.5 Hz, 1H), 7.54 (t, J = 7.6 Hz, 2H),
7.34 (dd, J = 8.7 Hz, 2.5 Hz, 1H), 7.15 (d, J= 8.7 Hz, 1H), 7.01 (d, J = 2.4 Hz, 1H), 6.54-6.47 (m,
1H), 5.30 (d, J = 2.5 Hz, 1H), 4.46-4.40 (m, 1H), 4.29 (pseudo dt, J = 20.4 Hz, 1.7 Hz, 1H), 4.23
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(pseudo dt, J = 20.4 Hz, 2.2 Hz, 1H), 1.58 (s, 9H); C NMR (100 MHz, CDCl3) δ/ppm: 192.8,
167.9, 164.1, 150.3, 149.2, 141.4, 137.6, 134.8, 133.6, 130.5, 130.2, 129.7, 129.4, 128.4, 121.5,
119.0, 84.1, 52.7, 50.2, 37.8, 28.3; IR (KBr) ṽ (cm−1): 1766, 1688, 1478, 1360, 1154, 684;
HRMS (ESI) calcd for C25H21NO6Cl, [M-H]- 466.1057, found: 466.1058.
tert-Butyl
3-(3-Benzoyl-6,8-dichloro-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate (3ca): Prepared according to the general procedure B using 3-benzoyl-6,8-dichloro-
2H-chromen-2-one 2ca and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1.
Purification by column chromatography (EtOAc/Hex = 1/3) furnished the desired product 3ca as
a yellow solid (91% yield, 45.7 mg). Rf 0.49 (EtOAc/Hex = 1/3); m.p.: 184.4-185.0 °C; 1H NMR
(400 MHz, CDCl3) δ/ppm: 8.21 (d, J = 7.6 Hz, 2H), 7.65 (t, J = 7.4 Hz, 1H), 7.54 (t, J = 7.8 Hz,
2H), 7.44 (d, J= 2.4 Hz, 1H), 6.95 (d, J = 2.3 Hz, 1H), 6.63-6.55 (m, 1H), 5.33 (d, J = 2.5 Hz,
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1H), 4.49-4.44 (m, 1H), 4.35-4.20 (m, 2H), 1.58 (s, 9H); C NMR (100 MHz, CDCl3) δ/ppm:
192.1, 167.6, 162.7, 148.9, 146.3, 141.3, 136.8, 134.7, 133.3, 130.4, 130.1, 129.5, 129.2, 126.6,
123.4, 122.7, 83.9, 52.1, 50.1, 37.8, 28.0; IR (KBr) ṽ (cm−1): 1757, 1645, 1449, 1288, 1158, 692;
HRMS (ESI) calcd for C25H21NO6Cl2Na, [M+Na]+ 524.0644, found: 524.0654.
tert-Butyl
3-(3-Benzoyl-6-methoxy-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate (3da): Prepared according to the general procedure B using 3-benzoyl-6-methoxy-
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2H-chromen-2-one 2da and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1.
Purification by column chromatography (EtOAc/Hex = 2/5) furnished the desired product 3da as
a yellow solid (98% yield, 45.4 mg). Rf 0.23 (EtOAc/Hex = 1/3); m.p.: 188.0-189.1 °C; 1H NMR
(400 MHz, CDCl3) δ/ppm: 8.24 (d, J = 7.4 Hz, 2H), 7.63 (t, J = 7.4 Hz, 1H), 7.53 (t, J = 7.4 Hz,
2H), 7.14 (d, J = 9.0 Hz, 1H), 6.88 (dd, J= 9.0 Hz, 3.0 Hz, 1H), 6.51 (d, J = 3.0 Hz, 1H), 6.50-
6.49 (m, 1H), 5.24 (d, J = 2.2 Hz, 1H), 4.42-4.39 (m, 1H), 4.27 (pseudo dt, J = 20.3 Hz, 1.8 Hz,
1H), 4.20 (pseudo dt, J = 20.3 Hz, 2.1 Hz, 1H), 3.73 (s, 3H) , 1.58 (s, 9H); 13C NMR (100 MHz,
CDCl3) δ/ppm: 192.9, 168.0, 164.7, 156.6, 149.0, 145.3, 141.0, 138.0, 134.3, 133.6, 129.5, 129.1,
120.3, 118.2, 114.9, 113.3, 83.7, 55.6, 53.0, 50.0, 38.0, 28.0; IR (KBr) ṽ (cm−1): 1763, 1723,
1677, 1475, 1317, 1169; HRMS (MALDI) calcd for C26H25NO7Na, [M+Na]+ 486.1529, found:
486.1538.
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tert-Butyl 3-(3-Benzoyl-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate (3ea):
Prepared according to the general procedure B using 3-benzoyl-2H-chromen-2-one 2ea and tert-
butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1. Purification by column chromatography
(EtOAc/Hex = 2/5) furnished the desired product 3ea as a yellow solid (89% yield, 38.6 mg). Rf
0.33 (EtOAc/Hex = 1/3); m.p.: 155.4-156.1 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 8.24 (d, J =
8.0 Hz, 2H), 7.63 (t, J = 7.4 Hz, 1H), 7.53 (t, J = 7.8 Hz, 2H), 7.42-7.34 (m, 1H), 7.22 (d, J= 8.1
Hz, 1H), 7.11 (td, J = 7.1 Hz, 1.0 Hz, 1H), 7.00 (d, J = 7.6, 1.2 Hz, 1H), 6.48-6.44 (m, 1H), 5.28
(d, J=2.2 Hz, 1H), 4.50-4.44 (m, 1H), 4.27 (pseudo dt, J = 20.2 Hz, 1.8 Hz, 1H), 4.20 (pseudo dt,
J = 20.2 Hz, 1.8 Hz, 1H), 1.58 (s, 9H); 13C NMR (100 MHz, CDCl3) δ/ppm: 192.9, 168.0, 164.6,
151.5, 149.0, 141.0, 138.1, 134.4, 133.5, 130.0, 129.5, 129.1, 128.3, 125.2, 119.4, 117.4, 83.7,
53.1, 50.0, 37.7, 28.0; IR (KBr) ṽ (cm−1): 1773, 1720, 1460, 1355, 1156; HRMS (MALDI) calcd
for C25H23NO6Na, [M+Na]+ 456.1423, found: 456.1416.
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3-(3-(4-Methoxybenzoyl)-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-1-
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carboxylate (3eb): Prepared according to the general procedure B using 3-(4-methoxybenzoyl)-
2H-chromen-2-one 2eb and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1.
Purification by column chromatography (EtOAc/Hex = 2/5) furnished the desired product 3eb as
a white solid (74% yield, 34.3 mg). Rf 0.23 (EtOAc/Hex = 1/3); m.p.: 119.6-120.9 °C; 1H NMR
(400 MHz, CDCl3) δ/ppm: 8.24 (d, J = 8.9 Hz, 2H), 7.36 (t, J = 8.0 Hz, 1H), 7.21 (d, J = 8.0 Hz,
1H), 7.10 (t, J = 7.5 Hz, 1H), 7.02-6.97 (m, 3H), 6.45-6.43 (m, 1H), 5.22 (d, J= 2.2 Hz, 1H),
4.45-4.42 (m, 1H), 4.27 (pseudo dt, J = 20.3 Hz, 1.8 Hz, 1H), 4.20 (pseudo dt, J = 20.3 Hz, 2.2
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Hz, 1H), 3.88 (s, 3H), 1.58 (s, 9H); C NMR (100 MHz, CDCl3) δ/ppm: 191.2, 168.1, 164.7,
164.5, 151.6, 149.0, 140.9, 138.3, 131.9, 129.9, 128.3, 126.5, 125.1, 119.6, 117.3, 114.3, 83.7,
55.5, 52.9, 50.0, 37.9, 28.0; IR (KBr) ṽ (cm−1): 1774, 1726, 1675, 1601, 1459, 1320, 1156;
HRMS (MALDI) calcd for C26H25NO7Na, [M+Na]+ 486.1523, found: 486.1529.
tert-Butyl
3-(3-(4-Nitrobenzoyl)-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate (3ec): Prepared according to the general procedure B using 3-(4-nitrobenzoyl)-2H-
chromen-2-one 2ec and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1. Purification by
column chromatography (EtOAc/Hex = 2/5) furnished the desired product 3ec as a yellow solid
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(83% yield, 39.7 mg). Rf 0.32 (EtOAc/Hex = 1/3); m.p.: 192.1-192.8 °C; H NMR (400 MHz,
CDCl3) δ/ppm: 8.49-8.34 (m, 4H), 7.40 (t, J = 7.8 Hz, 1H), 7.23 (d, J = 7.7 Hz, 1H), 7.15 (t, J =
7.5 Hz, 1H), 7.00 (d, J = 7.6 Hz, 1H), 6.52-6.48 (m, 1H), 5.34 (d, J = 2.5 Hz, 1H), 4.44-4.39 (m,
1H), 4.30 (pseudo dt, J = 20.4 Hz, 1.7 Hz, 1H), 4.24 (pseudo dt, J = 20.4 Hz, 2.1 Hz, 1H), 1.59 (s,
9H); 13C NMR (100 MHz, CDCl3) δ/ppm: 191.7, 168.0, 163.6, 151.3, 151.0, 148.9, 141.6, 138.0,
137.5, 130.6, 130.2, 128.2, 125.5, 124.2, 118.9, 117.5, 84.0, 53.1, 50.1, 37.4, 28.0; IR (KBr) ṽ
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(cm−1): 1772, 1718, 1522, 1458, 1359, 1320, 1155; HRMS (ESI) calcd for C25H22N2O8, [M]+
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478.1376, found: 478.1378.
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3-(6-Methoxy-3-(4-Methoxybenzoyl)-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-
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pyrrole-1-carboxylate (3db): Prepared according to the general procedure B using 6-methoxy-3-
(4-methoxybenzoyl)-2H-chromen-2-one 2db and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate 1. Purification by column chromatography (EtOAc/Hex = 1/2) furnished the desired
product 3db as a yellow solid (96% yield, 47.4 mg). Rf 0.14 (EtOAc/Hex = 1/3); m.p.: 123.7-
123.9 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 8.24 (d, J = 9.0 Hz, 2H), 7.13 (t, J = 9.0 Hz, 1H),
7.00 (t, J = 9.0 Hz, 2H), 6.88 (dd, J = 9.0 Hz, 3.0 Hz, 1H), 6.51 (d, J= 3.0 Hz, 1H), 6.50-6.46 (m,
1H), 5.17 (d, J = 2.2 Hz, 1H), 4.40-4.36 (m, 1H), 4.27 (pseudo dt, J = 20.2 Hz, 1.8 Hz, 1H), 4.20
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(pseudo dt, J = 20.2 Hz, 2.2 Hz, 1H), 3.88 (s, 3H), 3.72 (s, 3H), 1.58 (s, 9H); C NMR (100
MHz, CDCl3) δ/ppm: 191.2, 168.1, 164.9, 164.5, 156.6, 149.0, 145.4, 140.9, 138.1, 132.0, 126.5,
120.4, 118.1, 114.9, 114.3, 113.3, 83.6, 55.6, 55.5, 52.8, 50.0, 38.1, 28.0; IR (KBr) ṽ (cm−1):
1772, 1672, 1599, 1457, 1320, 1157; HRMS (ESI) calcd for C27H26NO8, [M-H]- 492.1658,
found: 492.1674.
tert-Butyl 3-(6-Methoxy-3-(4-Nitrobenzoyl)-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-
1-carboxylate (3dc): Prepared according to the general procedure B using 6-methoxy-3-(4-
nitrobenzoyl)-2H-chromen-2-one 2dc and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate 1. Purification by column chromatography (EtOAc/Hex = 1/3) furnished the desired
product 3dc as a yellow solid (73% yield. 37.1 mg). Rf 0.43 (EtOAc/Hex = 1/3); m.p.: 180.9-
181.4 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 8.49-8.33 (m, 4H), 7.15 (d, J = 9.0 Hz, 1H), 6.91
(dd, J = 9.0 Hz, 3.0 Hz, 1H), 6.56-6.52 (m, 1H), 6.50 (d, J = 3.0 Hz, 1H), 5.30 (d, J = 2.6 Hz,
1H), 4.39-4.34 (m, 1H), 4.30 (pseudo dt, J = 20.5 Hz, 1.9 Hz, 1H), 4.24 (pseudo dt, J = 20.5 Hz,
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2.2 Hz, 1H), 3.74 (s, 3H), 1.58 (s, 9H); 13C NMR (100 MHz, CDCl3) δ/ppm: 191.7, 168.0, 163.8,
156.8, 151.0, 149.0, 145.1, 141.6, 138.0, 137.3, 130.7, 124.2, 119.8, 118.4, 115.1, 113.3, 84.0,
55.6, 53.1, 50.1, 37.6, 28.1; IR (KBr) ṽ (cm−1): 1765, 1720, 1599, 1526, 1437, 1359, 1327, 1196;
HRMS (ESI) calcd for C26H23N2O9, [M-H]- 507.1404, found: 507.1403.
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tert-Butyl
3-(6-Bromo-3-(4-Methoxybenzoyl)-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-
pyrrole-1-carboxylate (3ab): Prepared according to the general procedure B using 6-bromo-3-(4-
methoxybenzoyl)-2H-chromen-2-one 2ab and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate 1. Purification by column chromatography (EtOAc/Hex = 1/2) furnished the desired
product 3ab as a yellow solid (80% yield, 43.4 mg). Rf 0.18 (EtOAc/Hex = 1/3); m.p.: 172.4-
173.2 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 8.23 (d, J = 8.9 Hz, 2H), 7.48 (dd, J = 8.8 Hz, 2.3
Hz, 1H), 7.15 (d, J = 2.3 Hz, 1H), 7.10 (d, J = 8.7 Hz, 1H), 7.00 (d, J= 8.9 Hz, 2H), 6.50-6.46 (m,
1H), 5.22 (d, J = 2.2 Hz, 1H), 4.43-4.37 (m, 1H), 4.29 (pseudo dt, J = 20.3 Hz, 1.7 Hz, 1H), 4.22
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(pseudo dt, J = 20.3 Hz, 2.2 Hz, 1H), 3.89 (s, 3H), 1.58 (s, 9H); C NMR (100 MHz, CDCl3)
δ/ppm: 190.9, 167.8, 164.7, 164.1, 150.7, 149.0, 141.0, 137.7, 132.9, 132.0, 131.1, 126.3, 121.8,
119.1, 117.6, 114.4, 83.9, 55.6, 52.4, 50.0, 37.7, 28.1; IR (KBr) ṽ (cm−1): 1780, 1723, 1602,
1478, 1357, 1154, 538; HRMS (MALDI) calcd for C26H24BrNO7Na, [M+Na]+ 564.0634, found:
564.0612.
tert-Butyl 3-(6-Bromo-3-(4-Nitrobenzoyl)-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate (3ac): Prepared according to the general procedure B using 6-bromo-3-(4-
nitrobenzoyl)-2H-chromen-2-one 2ac and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate 1. Purification by column chromatography (EtOAc/Hex = 2/5) furnished the desired
product 3ac as a yellow solid (66% yield, 36.8 mg). Rf 0.34 (EtOAc/Hex = 1/3); m.p.: 178.2-
179.0 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 8.47-8.32 (m, 4H), 7.52 (dd, J = 8.7 Hz, 2.3 Hz,
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1H), 7.16 (d, J = 2.2 Hz, 1H), 7.12 (d, J = 8.7 Hz, 1H), 6.57-6.53 (m, 1H), 5.35 (d, J = 2.6 Hz,
1H), 4.41-4.37 (m, 1H), 4.33 (pseudo dt, J = 20.5 Hz, 1.7 Hz, 1H), 4.26 (pseudo dt, J = 20.5 Hz,
2.0 Hz, 1H), 1.59 (s, 9H); 13C NMR (100 MHz, CDCl3) δ/ppm: 191.4, 167.8, 162.9, 151.1, 150.4,
148.9, 141.8, 137.8, 136.8, 133.3, 131.0, 130.7, 124.3, 121.1, 119.3, 118.0, 84.1, 52.6, 50.1, 37.2,
28.0; IR (KBr) ṽ (cm−1): 1173, 1525, 1479, 1358, 1157; HRMS (MALDI) calcd for
C25H21BrN2O8, [M]+ 556.0481, found: 556.0467.
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tert-Butyl 3-(6-Bromo-3-(4-Bromobenzoyl)-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-
1-carboxylate (3ad): Prepared according to the general procedure B using 6-bromo-3-(4-
bromobenzoyl)-2H-chromen-2-one 2ad and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate 1. Purification by column chromatography (EtOAc/Hex = 2/5) furnished the desired
product 3ad as a yellow solid (73% yield, 43.1 mg). Rf 0.33 (EtOAc/Hex = 1/3); m.p.: 166.1-
166.5 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 8.12 (d, J = 7.6 Hz, 2H), 7.68 (d, J = 8.6 Hz, 2H),
7.49 (dd, J = 8.7 Hz, 2.3 Hz, 1H), 7.15 (d, J = 2.3 Hz, 1H), 7.10 (d, J = 8.7 Hz, 1H), 6.52-6.48
(m, 1H), 5.24 (d, J = 2.2 Hz, 1H), 4.41-4.35 (m, 1H), 4.30 (pseudo dt, J = 20.5 Hz, 1.7 Hz, 1H),
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4.23 (pseudo dt, J = 20.5 Hz, 2.1 Hz, 1H), 1.59 (s, 9H); C NMR (100 MHz, CDCl3) δ/ppm:
191.7, 167.7, 163.4, 150.5, 148.9, 141.3, 137.2, 133.1, 132.6, 132.1, 131.0, 131.0, 130.2, 121.4,
119.2, 117.8, 84.0, 52.4, 50.1, 37.4, 28.0; IR (KBr) ṽ (cm−1): 1773, 1722, 1477, 1357, 1156, 537;
HRMS (ESI) calcd for C25H20NO6Br2, [M-H]- 587.9657, found: 587.9655.
tert-Butyl 3-(6-Bromo-3-(3-Bromobenzoyl)-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-
1-carboxylate (3ae): Prepared according to the general procedure B using 6-bromo-3-(3-
bromobenzoyl)-2H-chromen-2-one 2ae and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate 1. Purification by column chromatography (EtOAc/Hex = 1/3) furnished the desired
product 3ae as a white solid (80% yield, 47.3 mg). Rf 0.57 (EtOAc/Hex = 1/3); m.p.: 136.3-137.6
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°C; H NMR (400 MHz, CDCl3) δ/ppm: 8.33 (d, J = 7.8 Hz, 1H), 8.21 (s, 1H), 7.76 (d, J = 8.0
Hz, 1H), 7.76-7.52 (m, 2H), 7.16 (s, 1H), 7.10 (dd, J = 8.6 Hz, 2.0 Hz, 1H), 6.55-6.50 (m, 1H),
5.25 (d, J = 1.7 Hz, 1H), 4.42-4.38 (m, 1H), 4.30 (pseudo dt, J = 20.1 Hz, 1.3 Hz, 1H), 4.24
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(pseudo dt, J = 20.1 Hz, 1.1 Hz, 1H), 1.58 (s, 9H); C NMR (100 MHz, CDCl3) δ/ppm: 191.4,
167.7, 163.3, 150.4, 148.9, 141.5, 137.4, 137.1, 135.1, 133.1, 132.1, 131.0, 130.8, 128.3, 123.5,
121.4, 119.2, 117.8, 83.9, 52.3, 50.0, 37.3, 28.0; IR (KBr) ṽ (cm−1): 1772, 1723, 1477, 1357,
1156; HRMS (ESI) calcd for C25H20Br2NO6, [M-H]- 587.9657, found: 587.9677.
tert-Butyl
3-(3-(2-Naphthoyl)-6-Bromo-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate (3ag): Prepared according to the general procedure B using 3-(2-naphthoyl)-6-
bromo-2H-chromen-2-one 2ag and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1.
Purification by column chromatography (EtOAc/Hex = 1/3) furnished the desired product 3ag as
a white solid (85% yield, 47.8 mg). Rf 0.49 (EtOAc/Hex = 1/3); m.p.: 180.9-181.4 °C; 1H NMR
(400 MHz, CDCl3) δ/ppm: 9.02 (s, 1H), 8.15 (d, J = 8.0 Hz, 1H), 8.09 (dd, J = 8.7 Hz, 1.7 Hz,
1H), 7.92 (d, J = 8.7 Hz, 1H), 7.88 (d, J = 8.0 Hz, 1H), 7.65 (t, J= 7.5 Hz, 1H), 7.59 (t, J = 7.5
Hz, 1H), 7.49 (dd, J = 8.6 Hz, 2.4 Hz, 1H), 7.15-7.09 (m, 2H), 6.54-6.49 (m, 1H), 5.45 (d, J =
2.6 Hz, 1H), 4.56-4.50 (m, 1H), 4.31 (pseudo dt, J = 20.3 Hz, 1.7 Hz, 1H), 4.24 (pseudo dt, J =
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20.3 Hz, 2.1 Hz, 1H), 1.60 (s, 9H); C NMR (100 MHz, CDCl3) δ/ppm: 192.5, 167.8, 163.9,
150.6, 149.0, 141.2, 137.5, 136.1, 133.0, 132.5, 132.4, 131.0, 130.5, 130.4, 129.4, 129.0, 127.7,
127.0, 124.0, 121.7, 119.1, 117.7, 83.8, 52.7, 50.0, 37.8, 28.0; IR (KBr) ṽ (cm−1): 1773, 1723,
1676, 1477, 1357, 1154, 539; HRMS (ESI) calcd for C29H23BrNO6, [M-H]- 560.0709, found:
560.0721.
tert-Butyl
3-(6-Bromo-2-oxo-3-(Thiophene-2-carbonyl)chroman-4-yl)-2-oxo-2,5-dihydro-1H-
pyrrole-1-carboxylate (3ah): Prepared according to the general procedure B 6-bromo-3-
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(thiophene-2-carbonyl)-2H-chromen-2-one 2ah and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate 1. Purification by column chromatography (EtOAc/Hex = 1/3) furnished the desired
product 3ah as a white solid (85% yield, 44.0 mg). Rf 0.43 (EtOAc/Hex = 1/3); m.p.: 169.7-
170.2 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 8.51 (d, J = 3.7 Hz, 1H), 7.76 (d, J = 5.4 Hz, 1H),
7.49 (dd, J = 8.7 Hz, 2.2 Hz, 1H), 7.23 (t, J = 4.4 Hz, 1H), 7.21 (d, J= 2.2 Hz, 1H), 7.09 (d, J =
8.7 Hz, 1H), 6.54-6.48 (m, 1H), 5.13 (d, J = 2.2 Hz, 1H), 4.50-4.44 (m, 1H), 4.29 (pseudo dt, J =
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21.0 Hz, 1.8 Hz, 1H), 4.23 (pseudo dt, J = 21.0 Hz, 2.7 Hz, 1H), 1.58 (s, 9H); C NMR (100
MHz, CDCl3) δ/ppm: 185.0, 167.7, 163.2, 150.6, 149.0, 141.2, 140.7, 137.4, 136.4, 135.9, 133.0,
131.1, 129.1, 121.6, 119.1, 117.8, 83.9, 53.1, 50.0, 38.0, 28.0; IR (KBr) ṽ (cm−1): 1774, 1720,
1655, 1479, 1357, 1155, 528; HRMS (ESI) calcd for C23H19BrNO6S, [M-H]- 516.0116, found:
516.0108.
(E)-tert-Butyl 3-(6-Bromo-3-(Cyclohexyl(Hydroxy)methylene)-2-oxochroman-4-yl)-2-oxo-2,5-
dihydro-1H-pyrrole-1-carboxylate (3ai): Prepared according to the general procedure B using 6-
bromo-3-(cyclohexanecarbonyl)-2H-chromen-2-one 2ai and tert-butyl 2-oxo-2,5-dihydro-1H-
pyrrole-1-carboxylate 1. Purification by column chromatography (EtOAc/Hex = 1/3) furnished
the desired product 3ai as a white solid (59% yield, 30.6 mg). Rf 0.47 (EtOAc/Hex = 1/3); m.p.:
1
155.4-156.1 °C; H NMR (400 MHz, CDCl3) δ/ppm: 13.58 (s, 1H), 7.65 (d, J = 2.3 Hz, 1H),
7.35 (dd, J = 8.8 Hz, 2.3 Hz, 1H), 6.94 (d, J = 8.8 Hz, 1H), 6.79-6.76 (m, 1H), 4.88 (s, 1H), 4.23
(pseudo dt, J = 20.2 Hz, 1.6 Hz, 1H), 4.15 (pseudo dt, J = 20.2 Hz, 2.0 Hz, 1H), 2.52 (t, J = 11.0
Hz, 1H), 1.89-1.62 (m, 5H), 1.55 (s, 9H), 1.47-1.19 (m, 5H); 13C NMR (100 MHz, CDCl3)
δ/ppm: 185.8, 169.5, 167.3, 149.3, 148.9, 142.8, 138.2, 131.8, 131.6, 124.8, 118.8, 117.4, 91.5,
83.4, 49.5, 40.7, 33.2, 29.5, 29.0, 28.1, 25.6, 25.5, 25.4; IR (KBr) ṽ (cm−1): 3453, 1766, 1653,
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tert-Butyl 3-(6-Bromo-3-(Ethoxycarbonyl)-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate (3aj): Prepared according to the general procedure B using ethyl 6-bromo-2-oxo-
2H-chromene-3-carboxylate 2aj and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1.
Purification by column chromatography (EtOAc/Hex = 2/5) furnished the desired product 3aj as
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a white solid (70% yield, 33.6 mg). Rf 0.30 (EtOAc/Hex = 1/3); m.p.: 72.4-73.2 °C; H NMR
(400 MHz, CDCl3) δ/ppm: 7.46 (dd, J = 8.6 Hz, 2.3 Hz, 1H), 7.41 (d, J = 2.3 Hz, 1H), 7.01 (d, J
= 8.6 Hz, 1H), 6.65-6.64 (m, 1H), 4.55-4.52 (m, 1H), 4.27 (pseudo dt, J = 21.0 Hz, 1.8 Hz, 1H),
4.22 (pseudo dt, J = 21.0 Hz, 1.6 Hz, 1H), 4.14 (m, 3H),1.56 (s, 9H), 1.15 (t, J = 7.1 Hz, 3H);
13C NMR (100 MHz, CDCl3) δ/ppm: 166.7, 165.5, 162.7, 150.1, 149.3, 140.6, 136.7, 132.7,
131.5, 122.8, 118.9, 117.9, 83.7, 62.7, 49.7, 49.7, 36.2, 28.0, 13.8; IR (KBr) ṽ (cm−1): 1774,
1736, 1477, 1368, 1155, 585; HRMS (MALDI) calcd for C21H22BrNO7Na, [M+Na]+ 502.0477,
found: 502.0460.
tert-Butyl 3-(3-(Ethoxycarbonyl)-6-methoxy-2-oxochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-
1-carboxylate (3dj): Prepared according to the general procedure B using ethyl 6-methoxy-2-
oxo-2H-chromene-3-carboxylate 2dj and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate
1. Purification by column chromatography (EtOAc/Hex = 1/2) furnished the desired product 3dj
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as a white solid (91% yield, 39.2 mg). Rf 0.19 (EtOAc/Hex = 1/3); m.p.: 134.4-135.1 °C; H
NMR (400 MHz, CDCl3) δ/ppm: 7.05 (d, J = 8.9 Hz, 1H), 6.85 (dd, J = 8.9 Hz, 3.0 Hz, 1H),
6.78 (d, J = 3.0 Hz, 1H), 6.63-6.60 (m, 1H), 4.53-4.49 (m, 1H), 4.28-4.06 (m, 5H), 3.78 (s, 3H),
1.56 (s, 9H), 1.05 (t, J = 7.1 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ/ppm: 167.0, 165.9, 163.7,
156.7, 149.4, 144.8, 140.4, 137.2, 121.7, 118.0, 115.1, 113.4, 83.5, 62.5, 55.7, 50.2, 49.7, 36.6,
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[M-H]- 430.1502, found: 430.1501.
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3-(3-Benzoyl-2-oxothiochroman-4-yl)-2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate
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(3ea’): Prepared according to the general procedure B using 3-benzoyl-2H-thiochromen-2-one
2ea’ and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1. Purification by column
chromatography (EtOAc/Hex = 2/5) furnished the desired product 3ea’ as a white solid (94%
yield, 42.2 mg). Rf 0.40 (EtOAc/Hex = 1/3); m.p.: 100.8-101.5 °C; 1H NMR (400 MHz, CDCl3)
δ/ppm: 8.13 (d, J = 7.7 Hz, 2H), 7.60 (t, J = 7.4 Hz, 1H), 7.49 (t, J = 7.7 Hz, 2H), 7.35-7.27 (m,
2H), 7.18 (t, J= 7.2 Hz, 1H), 7.03 (d, J = 7.7 Hz, 1H), 6.57-6.52 (m, 1H), 5.28 (d, J = 2.6 Hz,
1H), 4.63-4.58 (m, 1H), 4.28 (pseudo dt, J = 20.2 Hz, 1.5 Hz, 1H), 4.18 (pseudo dt, J = 20.2 Hz,
2.4 Hz, 1H), 1.58 (s, 9H); 13C NMR (100 MHz, CDCl3) δ/ppm: 195.5, 193.3, 168.3, 149.1, 141.3,
136.2, 134.4, 133.9, 131.2, 130.0, 129.7, 129.2, 128.9, 128.6, 127.7, 127.1, 83.5, 58.9, 49.9, 42.5,
28.0; IR (KBr) ṽ (cm−1): 1774, 1722, 1670, 1476, 1357, 1156; HRMS (ESI) calcd for
C25H22NO5S, [M-H]- 448.1219, found: 448.1205.
General Procedure C for the synthesis of hydrolyisis/decarboxylation product 4:
A mixture of DABCO (0.04 mmol), α,β-unsaturated γ-butyrolactam 1 (0.12 mmol), 3-
acylcoumarin 2 (0.1 mmol) and H2O (0.04 mmol) in 0.2 mL of EtOAc was stirred at 30 °C until
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the completion of the reaction (monitored by H NMR). Then the solvent was removed under
reduced pressure and the residue was purified by column chromatography to give the desired
product 4.
tert-Butyl
3-(1-(2-Hydroxyphenyl)-3-oxo-3-phenylpropyl)-2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate (4ea): Prepared according to the general procedure C using 3-benzoyl-2H-chromen-
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2-one 2ea and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1. Purification by column
chromatography (EtOAc/Hex = 2/5) furnished the desired product 4ea as a white solid (86%
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yield, 35.0 mg). Rf 0.40 (EtOAc/Hex = 1/3); m.p.: 69.1-70.0 °C; H NMR (400 MHz, CDCl3)
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δ/ppm: 7.96 (m, 3H), 7.56 (m, 1H), 7.44 (t, J = 8.0 Hz, 2H), 7.18 (dd, J = 7.8 Hz, 1.8 Hz, 1H),
7.11 (m, 1H), 6.94 (m, 2H), 6.88 (td, J = 7.6 Hz, 1.1 Hz, 1H), 4.77 (t, J = 6.7 Hz, 1H), 4.23 (m,
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2H), 3.93 (dd, J = 17.5 Hz, 8.1 Hz, 1H), 3.67 (dd, J = 17.6 Hz, 6.5 Hz, 1H), 1.53 (s, 9H); C
NMR (100 MHz, CDCl3) δ/ppm: 198.1, 170.4, 154.3, 149.3, 141.5, 138.0, 136.3, 133.5, 128.7,
128.4, 128.1, 128.0, 121.1, 118.9, 83.5, 50.1, 41.5, 31.8, 28.0; IR (KBr) ṽ (cm−1): 3433, 2064,
1635, 1361, 1268, 1157, 750; HRMS (ESI) calcd for C24H25NO5Na, [M+Na]+ 430.1630, found:
430.1632.
tert-Butyl
3-(1-(5-Bromo-2-hydroxyphenyl)-3-oxo-3-phenylpropyl)-2-oxo-2,5-dihydro-1H-
pyrrole-1-carboxylate (4aa): Prepared according to the general procedure C using 3-benzoyl-6-
bromo-2H-chromen-2-one 2aa and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1.
Purification by column chromatography (EtOAc/Hex = 1/2) furnished the desired product 4aa as
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a white solid (82% yield, 39.9 mg). Rf 0.38 (EtOAc/Hex = 1/2); m.p.: 79.2-80.0 °C; H NMR
(400 MHz, CDCl3) δ/ppm: 8.22 (s, 1H), 7.98 (d, J = 7.4 Hz, 2H), 7.59 (t, J = 7.3 Hz, 1H), 7.47 (t,
J = 7.7 Hz, 2H), 7.23 (d, J = 2.4 Hz, 1H), 7.21 (dd, J= 8.5 Hz, 2.4 Hz, 1H), 6.96-6.91 (m, 1H),
6.85 (d, J = 8.5 Hz, 1H), 4.72 (t, J = 6.8 Hz, 1H), 4.35-4.19 (m, 2H), 3.91 (dd, J = 17.7 Hz, 8.3
Hz, 1H), 3.63 (dd, J = 17.7 Hz, 6.0 Hz, 1H), 1.54 (s, 9H); 13C NMR (100 MHz, CDCl3) δ/ppm:
197.5, 170.3, 153.7, 149.1, 141.2, 138.1, 136.2, 133.6, 131.3, 130.5, 130.4, 128.7, 128.2, 125.3,
121.0, 113.1, 83.6, 50.2, 41.3, 31.5, 28.0; IR (KBr) ṽ (cm−1): 3447, 1768, 1677, 1363, 1156, 469;
HRMS (MALDI) calcd for C24H24BrNO5Na, [M+Na]+ 508.0736, found: 508.0730.
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tert-Butyl
3-(1-(5-Chloro-2-hydroxyphenyl)-3-oxo-3-phenylpropyl)-2-oxo-2,5-dihydro-1H-
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pyrrole-1-carboxylate (4ba): Prepared according to the general procedure C using 3-benzoyl-6-
chloro-2H-chromen-2-one 2ba and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1.
Purification by column chromatography (EtOAc/Hex = 1/2) furnished the desired product 4ba as
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a white solid (94% yield, 41.5 mg). Rf 0.40 (EtOAc/Hex = 1/2); m.p.: 79.1-80.6 °C; H NMR
(400 MHz, CDCl3) δ/ppm: 8.22 (s, 1H), 7.97 (d, J = 7.6 Hz, 2H), 7.57 (t, J = 7.2 Hz, 1H), 7.45 (t,
J = 4.7 Hz, 2H), 7.08 (d, J = 2.6 Hz, 1H), 7.03 (dd, J = 8.6 Hz, 2.6 Hz, 1H), 6.95 (s, 1H), 6.85 (d,
J = 8.8 Hz, 1H), 4.74 (t, J = 7.0 Hz, 1H), 4.27 (d, J = 1.4 Hz, 2H), 3.85 (dd, J = 17.7 Hz, 8.3 Hz,
1H), 3.63 (dd, J = 17.7 Hz, 6.2 Hz, 1H), 1.53 (s, 9H); 13C NMR (100 MHz, CDCl3) δ/ppm:
197.5, 170.3, 153.1, 149.1, 141.1, 138.1, 136.1, 133.6, 129.9, 128.7, 128.3, 128.2, 127.6, 125.7,
120.4, 83.6, 50.2, 41.3, 31.5, 28.0; IR (KBr) ṽ (cm−1): 3436, 2076, 1635, 1375, 1299, 1158, 991,
775, 685; HRMS (ESI) calcd for C24H24NO5ClNa, [M+Na]+ 464.1241, found: 464.1241.
tert-Butyl 3-(1-(3,5-Dichloro-2-hydroxyphenyl)-3-oxo-3-phenylpropyl)-2-oxo-2,5-dihydro-1H-
pyrrole-1-carboxylate (4ca): Prepared according to the general procedure C using 3-benzoyl-6,8-
dichloro-2H-chromen-2-one 2ca and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-carboxylate 1.
Purification by column chromatography (EtOAc/Hex = 2/5) furnished the desired product 4ca as
a white solid (98% yield, 46.7 mg). Rf 0.32 (EtOAc/Hex = 1/3); m.p.: 197.5-198.3 °C; 1H NMR
(400 MHz, CDCl3) δ/ppm: 7.97 (d, J = 8.0 Hz, 2H), 7.57 (t, J = 7.3 Hz, 1H), 7.45 (t, J = 7.6 Hz,
2H), 7.22 (d, J = 2.2 Hz, 1H), 7.14 (d, J = 2.0 Hz, 1H), 7.09 (s, 1H), 6.94 (s, 1H), 4.80 (t, J = 7.0
Hz, 1H), 4.29-4.21 (m, 2H), 3.90 (dd, J = 17.6 Hz, 7.6 Hz, 1H), 3.62 (dd, J = 17.6 Hz, 6.7 Hz,
1H), 1.54 (s, 9H); 13C NMR (100 MHz, CDCl3) δ/ppm: 197.3, 169.1, 149.4, 148.5, 139.9, 139.2,
136.2, 133.5, 130.4, 128.7, 128.1, 127.7, 127.3, 125.5, 122.6, 83.4, 49.8, 40.7, 32.8, 28.0; IR
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(KBr) ṽ (cm−1): 3419, 1633, 1464, 1268, 757; HRMS (ESI) calcd for C24H23Cl2NO5Na,
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[M+Na]+ 498.0851, found: 498.0852.
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3-(1-(2-Hydroxyphenyl)-3-(4-Methoxyphenyl)-3-oxopropyl)-2-oxo-2,5-dihydro-1H-
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pyrrole-1-carboxylate (4eb): Prepared according to the general procedure C using 3-(4-
methoxybenzoyl)-2H-chromen-2-one 2eb and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate 1. Purification by column chromatography (EtOAc/Hex = 2/3) furnished the desired
product 4eb as a yellow solid (74% yield, 32.4 mg). Rf 0.40 (EtOAc/Hex = 2/3); m.p.: 77.8-78.5
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°C; H NMR (400 MHz, CDCl3) δ/ppm: 8.05 (s, 1H), 7.95 (d, J = 8.8 Hz, 2H), 7.17 (d, J = 7.6
Hz, 1H), 7.10 (t, J = 7.4 Hz, 1H), 6.98-6.83 (m, 5H), 4.75 (t, J = 6.9 Hz, 1H), 4.30-4.15 (m, 2H),
3.90-3.80 (m, 4H), 3.62 (dd, J = 17.3 Hz, 6.5 Hz, 1H), 1.53 (s, 9H); 13C NMR (100 MHz, CDCl3)
δ/ppm: 196.7, 170.3, 163.8, 154.2, 149.3, 141.5, 138.1, 130.5, 129.3, 128.3, 128.2, 128.0, 121.0,
118.8, 113.8, 83.3, 55.5, 50.0, 41.2, 31.9, 28.0; IR (KBr) ṽ (cm−1): 3418, 2924, 2076, 1633, 1356,
1260, 1169, 757; HRMS (ESI) calcd for C25H27NO6Na, [M+Na]+ 460.1736, found: 460.1736.
tert-Butyl
3-(1-(5-Bromo-2-hydroxyphenyl)-3-(4-Methoxyphenyl)-3-oxopropyl)-2-oxo-2,5-
dihydro-1H-pyrrole-1-carboxylate (4ab): Prepared according to the general procedure C using 6-
bromo-3-(4-methoxybenzoyl)-2H-chromen-2-one 2ab and tert-butyl 2-oxo-2,5-dihydro-1H-
pyrrole-1-carboxylate 1. Purification by column chromatography (EtOAc/Hex = 2/3) furnished
the desired product 4ab as a white solid (80% yield, 41.3 mg). White solid; Rf 0.40 (EtOAc/Hex
= 2/3); m.p.: 55.5-56.5 °C; 1H NMR (400 MHz, CDCl3) δ/ppm: 8.30 (s, 1H), 7.95 (d, J = 8.9 Hz,
2H), 7.24-7.12 (m, 2H), 6.97-6.88 (m, 3H), 6.81 (t, J = 9.9 Hz, 1H), 4.71 (t, J = 7.0 Hz, 1H),
4.34-4.19 (m, 2H), 3.89-3.73 (m, 4H), 3.57 (dd, J = 17.4 Hz, 6.3 Hz, 1H), 1.52 (s, 9H); 13C
NMR (100 MHz, CDCl3) δ/ppm: 196.2, 170.2, 163.9, 153.7, 149.2, 141.0, 138.4, 131.3, 130.6,
130.5, 129.3, 120.6, 113.9, 112.8, 83.5, 55.5, 50.1, 41.1, 31.7, 28.0; IR (KBr) ṽ (cm−1): 1780,
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1723, 1602, 1478, 1357; HRMS (MALDI) calcd for C25H26BrNO6Na, [M+Na]+ 538.0836, found:
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538.0840.
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3-(1-(5-Bromo-2-hydroxyphenyl)-3-(Naphthalen-2-yl)-3-oxopropyl)-2-oxo-2,5-
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dihydro-1H-pyrrole-1-carboxylate (4ag): Prepared according to the general procedure C using 3-
(2-naphthoyl)-6-bromo-2H-chromen-2-one 2ag and tert-butyl 2-oxo-2,5-dihydro-1H-pyrrole-1-
carboxylate 1. Purification by column chromatography (EtOAc/Hex = 1/2) furnished the desired
product 4ag as a white solid (80% yield, 42.9 mg). Rf 0.40 (EtOAc/Hex = 1/2); m.p.: 112.3-
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113.6 °C; H NMR (400 MHz, CDCl3) δ/ppm: 8.53 (s, 1H), 8026 (s, 1H), 8.05-7.93 (m, 2H),
7.93-7.78 (m, 2H), 7.61 (td, J = 6.8 Hz, 1.3 Hz, 1H), 7.56 (td, J = 5.6 Hz, 1.3 Hz, 1H), 7.29 (d, J
= 2.3 Hz, 1H), 7.20 (dd, J = 8.6 Hz, 2.2 Hz, 1H), 6.97 (d, J = 1.0 Hz, 1H), 6.85 (d, J = 8.6 Hz,
1H), 4.79 (t, J = 7.0 Hz, 1H), 4.35-4.21 (m, 2H), 4.03 (dd, J = 17.6 Hz, 8.2 Hz, 1H), 3.76 (dd, J =
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17.6 Hz, 6.0 Hz, 1H), 1.54 (s, 9H); C NMR (100 MHz, CDCl3) δ/ppm: 197.5, 170.4, 153.7,
149.2, 141.2, 138.3, 135.8, 133.5, 132.5, 131.3, 130.6, 130.5, 130.1, 129.7, 128.8, 128.7, 127.8,
127.0, 123.7, 120.9, 113.1, 83.7, 50.2, 41.4, 31.7, 28.0; IR (KBr) ṽ (cm−1): 3419, 2083, 1631,
1268, 757; HRMS (ESI) calcd for C28H26BrNO5Na, [M+Na]+ 558.0892, found: 558.0895.
General procedure D for the synthesis of 9aa:
A mixture of DABCO (0.02 mmol), α-angelica lactone 8 (0.12 mmol) and 3-benzoyl-6-bromo-
2H-chromen-2-one 2aa in 0.5 mL of anhydrous THF was stirred at 30 °C until the completion of
the reaction (monitored by 1H NMR). Then the solvent was removed under reduced pressure and
the residue was purified by column chromatography to give the desired product 9aa as a mixture
of diastereomers (A small amount of pure diastereomer could be obtained after repeated column
chromatography, which was used to record the analytical data).
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