Synthesis of non-racemic dihydrofurans via Ni(II)-catalyzed asymmetric Michael addition

Article abstract of DOI:10.1016/j.tet.2021.132029

A highly efficient strategy for the enantio- and diastereoselective synthesis of 4,5-dihydrofuran derivatives was developed. Addition of carbonyl compounds which contain bulky adamantyl substituent and β-keto or phosphonate group to conjugated α-bromonitroolefins in the presence of a chiral Ni(II) complex gave corresponding non-racemic products of Michael reaction. These adducts were used for intramolecular cyclization leading to trans-4,5-dihydrofurans with two stereocenters. Resulting trans-4,5-dihydrofurans were obtained in good yields with moderate to high enantioselectivities (84–99% ee) and excellent diastereoselectivities (dr >99%).

Full text of DOI:10.1016/j.tet.2021.132029

Tetrahedron 84 (2021) 132029
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of non-racemic dihydrofurans via Ni(II)-catalyzed
asymmetric Michael addition
,
Dmitry S. Nikerov a *, Maria A. Ashatkina a, Vadim A. Shiryaev a, Ilya M. Tkachenko a,
Victor B. Rybakov b, Alexander N. Reznikov a, Yuri N. Klimochkin a
a Department of Organic Chemistry, Samara State Technical University, Molodogvardeyskaya Str., 244, 443100, Samara, Russian Federation
b Department of Chemistry, Moscow State University, Leninskie Gory, 1, 119991, Mosсow, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
A highly efficient strategy for the enantio- and diastereoselective synthesis of 4,5-dihydrofuran de-
Received 10 December 2020
Received in revised form
11 February 2021
Accepted 14 February 2021
Available online 19 February 2021
rivatives was developed. Addition of carbonyl compounds which contain bulky adamantyl substituent
and b-keto or phosphonate group to conjugated a-bromonitroolefins in the presence of a chiral Ni(II)
complex gave corresponding non-racemic products of Michael reaction. These adducts were used for
intramolecular cyclization leading to trans-4,5-dihydrofurans with two stereocenters. Resulting trans-
4,5-dihydrofurans were obtained in good yields with moderate to high enantioselectivities (84e99% ee)
and excellent diastereoselectivities (dr >99%).
Keywords:
© 2021 Elsevier Ltd. All rights reserved.
Asymmetric catalysis
Michael addition
2,3-Dihydrofurans
Cyclization
Pyrrole
Chiral Ni(II) complex
1. Introduction
precursors for broad range of useful compounds with diverse
pharmacological properties.
Dihydrofurans and their derivatives are often key building
blocks in organic syntheses. Such heterocycle moiety is present in
numerous natural products, agrochemicals and pharmaceuticals:
The pioneer work of Dauzonne and co-workers for the one-pot
preparation of racemic dihydrofurans includes the Michael reaction
as a key stage [11]. Asymmetric synthesis of such dihydrofurans has
attracted extensive attention. A number of synthetic strategies have
been developed in recent years, including rearrangement [12],
cheimonophyllal (nematicidal activity) [1], jiadifenlactone
A
(antiviral activity) [2], colletofragarones A1 (germination self-
inhibitors from the fungus) [3] and inoscavin A (antioxidative ac-
tivity) [4] (Fig. 1).
ꢀ
cycloaddition [13] and modified FeistꢀBenary reaction [14]. The
application of these methods is limited by their relatively narrow
substrate scope and comparatively poor enantioselectivity. It is
highly desirable to develop an efficient pathway to chiral dihy-
drofurans. Several non-racemic 4,5-dihydrofurans could be ob-
tained using organocatalysis [6a,15]. However this method requires
the use of a large amount of organocatalyst (ꢁ10 mol %). In addition,
organocatalysts, such as сinchona alkaloids-derived thioureas and
squaramides are expensive and have low synthetical access which
reduces the practical value of these methods. Therefore, a syn-
thetically available and inexpensive nickel complex 3, successfully
applied in the construction of chiral substrates by the Michael re-
action [16], was used in this work.
Non-racemic dihydrofurans represents important subunits of
different biologically active compounds and precursors for the
preparation of some biologically active tetrahydrofurans. For
example, deoxy-C-nucleosides (potential therapeutic agents and
Biochemical probes) [5], virgatusin (antifungal) [6] and nymphone
(cytotoxin) [6a,7] are prepared directly from non-racemic dihy-
drofurans. Some xyloketals, exhibiting a broad range of biological
activity (Fig. 2) could be obtained from dihydrofurans [8].
Dihydrofurans readily react with electrophiles [9] and nucleo-
philes [10]. Thus, dihydrofurans represents an excellent synthetic
The presence of the dihydrofuran subunits and lipophilic ada-
manate scaffold could be presubposition to some interesting bio-
logical properties [17]. This will allow the use of these chemical
* Corresponding author.
E-mail address: d.nikerov@mail.ru (D.S. Nikerov).
https://doi.org/10.1016/j.tet.2021.132029
0040-4020/© 2021 Elsevier Ltd. All rights reserved.

D.S. Nikerov, M.A. Ashatkina, V.A. Shiryaev et al.
Tetrahedron 84 (2021) 132029
Fig. 1. Biologically active substances based on the dihydrofurans.
Scheme 1. Synthesis of chiral precursors of 4,5-dihydrofurans by the asymmetric
Michael reaction catalyzed by a Ni(II)-complex.
used in the asymmetric addition of 1,3-dicarbonyl compounds [19],
b
-keto phosphonates [16c,20] and
olefins. In a number of cases, these reactions proceeded enantio-
and diastereoselectively. The reaction with -bromonitroolefins in
b-ketosulfones [16d] to nitro-
a
most cases led to the formation of four diastereomers according to
1H and 31P NMR (Table 1). However, in some experiments forma-
tion of only two diastereoisomers was observed. Subsequent
recrystallization of Michael adducts led to some diastereomeric
enrichment.
The stereocenter at 3 position of the resulting nitroketones 4a-i
can be attributed to the (S)-configuration according to absolute
configuration of the previously reported cyclization product 5
а
[15e].
At the next step the obtained adducts 4a-i were subjected to
cyclization with the formation of 4,5-dihydrofurans 5a-i. Initially,
the cyclization of 3-(2-bromo-2-nitro-1-phenylethyl) pentane-2,4-
dione (4a) was chosen as a model reaction to find the optimal re-
action conditions. The cyclization product 5а was previously ob-
tained using reaction conditions for one-pot Michael addition/I2-
mediated cyclization sequence [15e]. The cyclization of compound
Fig. 2. Some examples of biologically active compounds derived from dihydrofurans.
4
а
in the presence of potassium carbonate (1.0 equiv.) gave 4,5-
dihydrofuran 5 in 85% yield. The configuration 5a (4R,5R) is the
а
same as of 4,5-dihydrofuran obtained by Zhang et al. [15e].
However, the synthesis of 4,5-dihydrofuran 5b from adamantyl
containing compound 4b wasn’t successful when the same
objects in the drug development. The use of atom-efficient
methods of asymmetric catalysis for the synthesis of such com-
pounds is extremely relevant. The transition metal catalyzed [16] or
organocatalyzed [18] asymmetric Michael reaction is one of the
most important synthetic tools for the asymmetric formation of a
CeC bond. A possibility to create one stereocenter with a given
configuration during the catalytic process could be the starting
point of complex enantioselective syntheses of compounds with
several new stereocenters. Our work reports the synthesis of non-
racemic adamantyl 4,5-dihydrofurans via Ni(II)-catalyzed asym-
Table 1
The yields of the products 4a-i and their diastereomeric ratio.
Entry
1
2
Product 4
Yieldb of 4, %
dr of 4c
1
2
3
4
5
6
7
8
9
1a
1b
1b
1b
1b
1c
1d
1e
1b
2a
2a
2b
2c
2d
2a
2a
2a
2e
4a
4b
4c
4d
4e
4f
4g
4h
4i
95
56
70
71
64
40
58
58
40
1.1:1.0
5.0:1.0
1.6:1.0
3.7:2.4:1.1:1.0
4.1:3.9:2.1:1.0
1.6:1.0
23:22:3:1
1.3:1.0
metric Michael addition of
b-diketone, b-ketoester or b-keto
phosphonate to conjugated -bromonitroolefins, where bromide is
a
a good leaving group which promote subsequent intramolecular
cyclization.
1.5:1.0
2. Results and discussion
aReaction conditions: carbonyl compounds 1a-e (2.2 mmol),
a
-bromonitroolefins
2a-e (2.2 mmol), toluene (2 mL), Ni(II) complex 3 (0.044 mmol), rt, 24 h.
The Michael addition of 1,3-dicarbonyl compounds to
monitroolefins was carried out in the presence of 2 mol % Ni(II)
complex 3 (Scheme 1). This complex was previously successfully
a-bro-
b
After recrystallization from MeOH (entries 2,3,6), toluene (entry 8) or purifica-
tion by column chromatography on silica gel (eluent CCl4, entries 1,4,5,7,9).
c
Determined by 1H NMR.
2

D.S. Nikerov, M.A. Ashatkina, V.A. Shiryaev et al.
Tetrahedron 84 (2021) 132029
conditions were used. For this reason, further optimization of the
cyclization was required for adamantyl Michael adducts (Table 2).
The cleavage of
b-diketone moiety was observed while using
aqueous NaOH leading to 6 (entry 4). When DMAP was used as a
base in acetonitrile cyclization product 5b was formed after 24 h in
74% yield.
The structure 5b was confirmed by 1H, 13C NMR, NOESY, HMQC
and HMBC spectra. The vicinal spin-spin coupling constants of two
methine protons compound 5b is 1.2 Hz. Vicinal coupling constants
of two methine protons in cis-dihydrofuran are Jcis 7e10 Hz [21],
while in trans-dihydrofurans vicinal coupling constants are Jtrans
2.5e7.5 Hz [22]. In the NOESY spectrum, there are no cross peaks
between H-4 and H-5 of the dihydrofuran ring. These facts also
prove the trans configuration of substituents at the 4 and 5 posi-
tions of the dihydrofuran ring.
Non-racemic 4,5-dihydrofurans 5a-e,h,i were obtained using
optimized reaction conditions (Scheme 2). Compounds 5a-e,h,i
were obtained as trans-isomer in 50e85% yields and 84e99% ee
(Table 3). The vicinal spin-spin coupling constants for the com-
pounds 5a-e,h,i are Jtrans 1.0e2.0 Hz between H-4 and H-5 of the
dihydrofuran ring. The configuration of trans-4,5-dihydrofurans 5a-
e,h,i was suggested analogically to 5b.
It is noteworthy that reaction of nitroketoester 4f leads to 4,5-
dihydrofuran 5f, despite steric hindrance of adamantly group.
Compound 5f was obtained as trans-isomer in 60% yield and >99%
ee (Scheme 3). The vicinal spin-spin coupling constants for the
compound 5f between H-4 and H-5 of the dihydrofuran ring is Jtrans
1.2 Hz.
Unfortunately, we were unable to grow a single crystal of
phosphorylated dihydrofuran 5g, therefore we could’t establish the
absolute configuration of this compound using X-ray structural
analysis. However, we succeed in growing a single crystal of the
compound 5f that was suitable for X-ray determination of the
relative configuration of 4,5-dihydrofuran 5f. An X-ray diffraction
study of the 4,5-dihydrofuran 5f showed its trans-configuration
(Fig. 3) [23]. The relative configurations of dihydrofurans 5a-i were
assigned by analogy.
Scheme 2. Synthesis of non-racemic 4,5-dihydrofurans by the reaction of intra-
molecular cyclization from Michael adducts.
Table 3
The yields of the products 5a-e,h,i and their diastereomeric ratio, enantiomeric
excessesa.
Entry
Product
Yield, %
drb
eed
1
2
3
4
5
6
7
5a
5b
5c
5d
5e
5h
5i
56
77
57
61
56
85
50
1/-
94
99
89
92
90
96
84e
1/-
1/-c
1/-c
1/-
1/-
9.0:1.0
a
Reaction conditions: compounds 4a-e,h,i (0.94 mmol), DMAP (0.94 mmol),
MeCN (5 mL), rt, 24 h.
b
Determined by 1H NMR.
Two diastereomers according to HPLC analysis. The second diastereomer is
c
formed by epimerization in a chromatographic column.
d
ee of products 5a-e,h,i was determined by HPLC; eee of major diastereomer 5i.
Therefore, to determine the absolute configuration of the com-
pound 5f, we selected a method that is based on correlation of
computed specific rotation with experimental values. This method
analysis showed high rigidity of this molecule. The optimization of
geometry and calculation of specific rotation were performed using
the 6e311þþG(2d,2p)/B3LYP basis set with solvation model
IEFPCM in chloroform. The obtained results showed a correlation of
the sign of specific rotation and the behavior of ORD curve of
allows the absolute configuration of molecules having [a] more
than 25ꢂ to be correlated [24]. The calculations were performed for
the trans-isomer of dihydrofuran (4R,5R)-5f. The conformational
Table 2
Optimization of the conditions of intramolecular cyclization reaction with substance 4ba.
Entry
Base
Phase- transfer catalystc
Solvent
tоС
time, h
Yield of 5b, %
Yield of 6, %
1
2
2
3
4
5
6
K2CO3
KOH
e
THF
benzene
H2O
MeCN
H2O
CH2Cl2
MeCN
20
20
70
20
20
20
20
24
36
6
5
6
e
e
18-crown-6
TBAB
KI/18-crown-6
e
e
e
e
e
NaOAc
K2CO3
NaOHb
DMAP
DMAP
e
e
e
e
e
50d
e
72
24
74d
74d
e
a
Reaction conditions: compound 4b (0.94 mmol), base (0.94 mmol), solvent (5 mL).
NaOH (2.10 mmol).
Phase-transfer catalyst (0.094 mmol).
b
c
d
After recrystallization from MeOH.
3

D.S. Nikerov, M.A. Ashatkina, V.A. Shiryaev et al.
Tetrahedron 84 (2021) 132029
(Table 5, entries 2e4). The structure 5g was confirmed by 1H, 13
C
NMR, NOESY, HMQC and HMBC spectra. The vicinal spin-spin
coupling constants of two methine protons compound 5g is
1.6 Hz. In the NOESY spectrum, there are no cross peaks between H-
4 and H-5 of the dihydrofuran ring, indicating the trans-isomer of
dihydrofuran 5g.
To improve the method of obtaining 4,5-dihydrofurans, we have
developed a Ni-catalyzed one-pot procedure, with a base additive,
avoiding the isolation of the Michael adduct (Scheme 4). The
application of this procedure to simple starting compound, such as
acetylacetone and 1,3-diphenylpropane-1,3-dione, allows to obtain
Scheme 3. Synthesis of non-racemic 4,5-dihydrofuran 5f by the reaction of intra-
molecular cyclization from nitroketoester 4f.
4,5-dihydrofurans 5а,h. Unfortunately, shift to more complex
adamantyl-containing 1,3-diketones and, especially, ketophosph-
onates lead to the formation of numerous byproducts. Therefore, in
the case of sterically hindered substrates there is needed to isolate
the Michael adducts before their cyclization to 4,5-dihydrofurans.
Pyrroles are an important class of compounds in the pharma-
ceutical [25] and material sciences [26]. In the course of our study,
polysubstituted pyrrole 7 was obtained in 90% yield from dihy-
drofuran 5а by reduction with H2 on Pd/C (10%) catalyst (Scheme 5).
3. Conclusions
In summary, a convenient protocol for the synthesis of non-
racemic trans-4,5-dihydrofurans was developed. Synthetic strat-
egy consist of asymmetric Michael addition in the presence of
readily available Ni(II) complex and subsequent intramolecular
cyclization of enantioenriched adducts. The applicability of the
method was shown through the synthesis of novel enantioenriched
adamantyl-substituted dihydrofurans using the Ni(II) complex as a
catalyst at the key step. DMAP-promoted cyclization of interme-
diate bromonitroketones leads to formation of trans-isomers in
good yields and moderate to high enantioselectivities (84e99% ee).
The obtained 4,5-dihydrofurans also could be used as precursors of
aromatic pyrroles and furans.
Fig. 3. ORTEP diagram of (4R,5R)-5f.
(4R,5R)-5f with experimental values that allow this configuration
to be confirmed (Table 4). Therefore, the absolute configuration of
the compound 5f is (4R,5R). The absolute configurations of the
other dihydrofurans 5a-i are similar.
The cyclization of adduct 4g using optimal reaction conditions
leads to formation of non-racemic phosphoryl-substituted 4,5-
dihydrofuran 5g in 90% yield after 24 h (Table 4, entry 1) despite
the poor solubility of phosphonate 4g in acetonitrile. Other com-
binations of bases and solvents leads to significant decrease in yield
4. Experimental section
4.1. General methods
All commercially obtained reagents were used without further
purification. All solvents were distilled prior to use.
a-Bromoni-
troalkenes [27], dimethyl (2-oxo-2-phenylethyl)phosphonate [16c],
1-(adamantan-1-yl)butane-1,3-dione [28], ethyl 3-(adamantan-1-
yl)-3-oxopropanoate [29] were obtained according to reported
Table 4
Experimental and calculated values for the specific rotation of (4R,5R)-5f.
procedures.
k
Bis[(1R,2R)-N,N՚-dibenzylcyclohexane-1,2-diamine-
2N,N՚](dibromo)nickel was obtained according to a reported pro-
cedure [19a]. Melting points were measured with an OptiMelt
automated melting point system. All the reactions were monitored
by TLC, performed on precoated silica gel plates (Sorbfil); (display
with iodine vapour). 1H, 13C, 19F and 31P NMR spectra were recorded
with a JEOL JNM-ECX400 spectrometer at 399.78, 100.53, 376.17
and 161.83 MHz, respectively, in CDCl3 solution. Elemental analysis
was performed with an EuroVector EA-3000 analyzer. Optical ro-
tations were measured with Rudolph Research Analytical (Autopol
V Plus Automatic Polarimeter). The enantiomeric purity of the
products was determined by HPLC analysis on Shimadzu Promi-
nence LC-20AD (Spd-20auv vis detector, Cto-20a column over, Dgu-
20a degasing unit) equipped with a chiral stationary phase column
(ChiralPAK AD-3) with hexane/2-propanol as eluent. Column
chromatography was performed on Silica gel 60, Merck (230e400
mesh). The X-ray studies were fulfilled using a STOE STADI VARI
PILATUS-100K diffractometer.
20
Wavelength,
l
(nm)
(4R,5R)-5f [
a
]
exp.
(4R,5R)-5f [a]
20 calc.
365
405
436
546
589
633
ꢀ817.40
ꢀ491.80
ꢀ368.00
ꢀ174.90
ꢀ140.50
ꢀ115.70
ꢀ1559.96
ꢀ883.60
ꢀ623.47
ꢀ274.92
ꢀ218.28
ꢀ178.16
The initial modelling of structure was performed with Avogadro
1.1.1 [30] in force field MMFF94s, optimization of structure and
4

D.S. Nikerov, M.A. Ashatkina, V.A. Shiryaev et al.
Tetrahedron 84 (2021) 132029
Table 5
Optimization of the conditions of intramolecular cyclization reaction with substance 4ga.
Entry
Base
Phase- transfer catalystb
Solvent
tоС
time, h
Yieldc of 5g, %
drd
eee
1
2
DMAP
KOH
e
MeCN
benzene:toluene
2:1
20
0
24
36
90
40
1/-
1/-
98
98
18-crown-6
3
4
KOH
NaOAc
18-crown-6
TBAB
benzene
H2O
20
70
36
7
51
42
1/-
1/-
98
97
a
Reaction conditions: compound 4g (1.10 mmol), base (1.10 mmol), solvent (9 mL).
Phase-transfer catalyst (0.11 mmol).
b
c
After purification by column chromatography on silica gel (eluent e petroleum ether: ethyl acetate 5:1).
d
e
determined by 1H NMR.
ee of product 5g was determined by HPLC.
diastereomer, Me), 2.32 (s, 3H e second diastereomer, Me), 4.35
(dd, 3JHH ¼ 10.4, 5.6 Hz, 1H e first diastereomer, CHPh), 4.55e4.66
3
(m, 3H, CHC(O), CHPh), 6.39 (d, JHH ¼ 5.6 Hz, 1H e first diaste-
3
reomer, CHBr), 6.52 (d, JHH ¼ 5.6 Hz, 1H e second diastereomer,
CHBr), 7.12e7.31 (m, 5H e first diastereomer, 5H e second diaste-
reomer, aromatic); 13C NMR (101 MHz, CDCl3):
d
¼ 29.4 (Me, first
diastereomer), 29.5 (Me, second diastereomer), 30.5 (Me, first
diastereomer), 30.7 (Me, second diastereomer), 48.2 (CHPh, first
diastereomer), 50.1 (CHPh, second diastereomer), 70.5 (CHC(O),
first diastereomer), 71.9 (CHC(O), second diastereomer), 83.1 (CHBr,
first diastereomer), 86.2 (CHBr, second diastereomer), 127.3 (aro-
matic), 129.0 (aromatic), 129.1 (aromatic), 129.2 (aromatic), 129.4
(aromatic), 129.5 (aromatic), 129.6 (aromatic), 131.9 (aromatic),
132.9 (aromatic), 199.9 (C]O), 200.6 (C]O), 201.1 (C]O), 201.5
(C]O). Anal. calcd for C13H14BrNO4: C, 47.58; H, 4.30; N, 4.27.
Found: C, 47.64; H, 4.33; N, 4.36.
Scheme 4. One-Pot synthesis of non-racemic 4,5-dihydrofurans 5а,h.
Scheme 5. Synthesis of pyrrole 7 by reduction from 4,5-dihydrofuran 5а.
4.2.2. 1-(Adamantan-1-yl)-2-[(1S)-2-bromo-2-nitro-1-
phenylethyl]butane-1,3-dione (4b)
Yield: 0.55 g (56%), white crystals [mixture of diastereomers dr
optical rotation calculations were performed with Gaussian G.09
Rev A.02 [31] in 6e311þþG(2d,2p) basis set with solvation model
IEFPCM in chloroform.
20
5:1], mp 156e157 ꢂC (methanol), [
a
]
¼ e 39.8 (c 1.0.
D
d
CHCl3). 1H NMR (400 MHz, CDCl3):
¼ 1.48e1.66 (m, 12H e first
diastereomer, 12H e second diastereomer, Ad), 1.93 (br s, 3H e first
diastereomer, 3H e second diastereomer, Ad), 2.29 (s, 3H e first
diastereomer, 3H e second diastereomer, Me), 4.30e4.31 (m, 1H e
second diastereomer, CHPh), 4.58e4.62 (m, 1H e first diastereomer,
CHPh), 4.83 (d, 3JHH ¼ 10.4 Hz,1H - first diastereomer, CHC(O)), 4.95
4.2. General procedure for the preparation of adducts Michael
A mixture of
phonate 1d (2.2 mmol),
bis[(1R,2R)-N,N՚-dibenzylcyclohexane-1,2-diamine-
b
-diketone 1a,b,e,
-bromonitroalkene 2a-e (2.2 mmol) and
2N,N՚](di-
b-ketoester 1c or b-keto phos-
a
3
(d, JHH ¼ 10.0 Hz, 1H e second diastereomer, CHC(O)), 6.34 (d,
k
3JHH ¼ 5.2 Hz, 1H e first diastereomer, CHBr), 6.44 (d, 3JHH ¼ 6.4 Hz,
1H - second diastereomer, CHBr), 7.17e7.33 (m, 5H e first diaste-
reomer, 5H e second diastereomer, aromatic); 13C NMR (101 MHz,
bromo)nickel (3) (0.044 mmol) in 2 mL of toluene was stirred at rt
for 24 h. The formed crystalline compounds 4b,c,f were filtered and
recrystallized from MeOH, and the crystalline compound 4h
filtered and recrystallized from toluene. If no precipitate was
formed, then the solvent was distilled off under reduced pressure,
and the compounds 4a,d,e,g,i were purified by column chroma-
tography on silica gel (eluent CCl4).
CDCl3):
d
¼ 27.7 (Ad, first diastereomer), 27.8 (Ad, second diaste-
reomer), 29.3 (Me, first diastereomer), 30.5 (Me, second diaste-
reomer), 36.1 (Ad, first diastereomer), 36.3 (Ad, second
diastereomer), 38.1 (Ad, fist diastereomer), 38.4 (Ad, second dia-
stereomer), 48.1 (Ad, second diastereomer), 48.3 (Ad, first diaste-
reomer), 50.2 (CHPh, first diastereomer), 52.7 (CHPh, second
diastereomer), 64.4 (CHC(O), second diastereomer), 65.3 (CHC(O),
first diastereomer), 82.3 (CHBr, second diastereomer), 85.2 (CHBr,
first diastereomer), 128.7 (aromatic), 128.9 (aromatic), 129.2 (aro-
matic), 129.7 (aromatic), 129.9 (aromatic), 133.2 (aromatic), 133.7
(aromatic), 201.3 (C]O, first diastereomer), 201.7 (C]O, second
diastereomer), 207.2 (C]O, first diastereomer), 208.3 (C]O,
4.2.1. 3-[(1S)-2-Bromo-2-nitro-1-phenylethyl]pentane-2,4-dione
(4a)
Yield: 0.68 g (95%), colorless oil [mixture of diastereomers dr
20
1:1], [
a]
¼ þ126.1 (c 1.0, CHCl3).
D
1H NMR (400 MHz, CDCl3):
Me), 1.91 (s, 3H - first diastereomer, Me), 2.31 (s, 3H e second
d
¼ 1.89 (s, 3H - first diastereomer,
5

D.S. Nikerov, M.A. Ashatkina, V.A. Shiryaev et al.
Tetrahedron 84 (2021) 132029
second diastereomer). Anal. calcd for C22H26BrNO4: C, 58.94; H,
5.85; N, 3.12. Found: C, 58.99; H, 5.91; N, 3.21.
diastereomer), 38.5 (Ad, second diastereomer.), 48.1 (Ad, third
diastereomer), 48.3 (Ad, fourth diastereomer), 48.6 (Ad, second
diastereomer), 48.7 (Ad, first diastereomer), 48.8 (MeO, first dia-
stereomer), 49.6 (MeO, third diastereomer), 50.7 (MeO, second
diastereomer), 51.9 (MeO, fourth diastereomer.), 55.3 (СНAr), 64.3
(CHC(O), third diastereomer), 64.7 (CHC(O), second diastereomer),
65.3 (CHC(O), fourth diastereomer), 66.0 (CHC(O), first diaste-
reomer), 82.4 (CHBr, third diastereomer), 83.6 (CHBr, second dia-
stereomer), 85.6 (CHBr, fourth diastereomer), 86.8 (CHBr, first
diastereomer), 114.0 (aromatic), 114.4 (aromatic), 114.4 (aromatic),
123.0 (aromatic, first diastereomer), 124.0 (aromatic, second dia-
stereomer), 124.9 (aromatic, first diastereomer), 125.2 (aromatic,
fourth diastereomer), 130.9 (aromatic), 131.0 (aromatic), 160.0 (ar-
omatic, fourth diastereomer.), 160.1 (aromatic, third diastereomer),
160.2 (aromatic, second diastereomer), 160.3 (aromatic, first dia-
stereomer), 200.5 (C]O, first diastereomer), 201.4 (C]O, second
diastereomer), 201.5 (C]O, fourth diastereomer), 201.9 (C]O,
third diastereomer), 207.2 (C]O, fourth diastereomer), 208.6 (C]
O, third diastereomer), 208.8 (C]O, first diastereomer), 209.2 (C]
O, second diastereomer). Anal. calcd for C23H28BrNO5: C, 57.75; H,
5.90; N, 2.93. Found: C, 57.82; H, 5.93; N, 3.08.
4.2.3. 1-(Adamantan-1-yl)-2-[(1S)-2-bromo-2-nitro-1-(4-
methylphenyl)ethyl]butane-1,3-dione (4c)
Yield: 0.71 g (70%), white crystals [mixture of diastereomers dr
20
1.6:1], mp 95.1e96.4 ꢂC (CCl4), [
a
]
¼ e 20.2 (c 1.0, CHCl3).
D
1H NMR (400 MHz, CDCl3):
d
¼ 1.67e1.73 (m, 12H, Ad), 1.79 (s,
3H e second diastereomer, Me), 1.82 (s, 3H e first diastereomer,
Me), 1.86e1.89 (m, 12H, Ad), 2.07 (br s, 3H e first diastereomer, 3H
e second diastereomer, Ad), 2.29 (s, 3H e first diastereomer, Me),
3
2.30 (s, 3H e second diastereomer, Me), 4.32 (dd, JHH ¼ 10.3,
5.0 Hz, 1H e first diastereomer, CHAr), 4.65 (dd, 3JHH ¼ 11.2, 4.0 Hz,
1H e second diastereomer, CHAr), 4.79 (d, 3JHH ¼ 11.0 Hz, 1H e first
3
diastereomer, CHC(O)), 4.92 (d, JHH ¼ 10.3 Hz, 1H e second dia-
stereomer, CHC(O)), 6.24e6.27 (m, 1H e first diastereomer, 1H e
second diastereomer, CHBr), 7.04e7.13 (m, 4H e first diastereomer,
4H e second diastereomer, aromatic); 13C NMR (101 MHz, CDCl3):
d
¼ 21.3 (Me), 27.9 (Ad, first diastereomer), 28.0 (Ad, second dia-
stereomer), 28.2 (Me, first diastereomer), 28.6 (Me, second dia-
stereomer), 36.2 (Ad, first diastereomer), 36.3 (Ad, second
diastereomer), 38.4 (Ad, first diastereomer), 38.6 (Ad, second dia-
stereomer), 48.6 (Ad, second diastereomer), 48.7 (Ad, first diaste-
reomer), 49.2 (CHAr, first diastereomer), 51.1 (CHAr, second
diastereomer), 64.7 (CHC(O), second diastereomer), 66.0 (CHC(O),
first diastereomer), 83.5 (CHBr, second diastereomer), 86.6 (CHBr,
first diastereomer), 128.2 (aromatic, first diastereomer), 129.3 (ar-
omatic, second diastereomer), 129.6 (aromatic), 129.7 (aromatic),
129.8 (aromatic), 139.3 (aromatic), 139.4 (aromatic), 200.5 (C]O,
first diastereomer), 201.4 (C]O, second diastereomer), 208.8 (C]
O, first diastereomer), 209.2 (C]O, second diastereomer). Anal.
calcd for C23H28BrNO4: C, 59.75; H, 6.10; N, 3.03. Found: C, 59.83; H,
6.15; N, 3.18.
4.2.5. 1-(Adamantan-1-yl)-2-[(1S)-2-bromo-1-(4-fluorophenyl)-2-
nitroethyl]butane-1,3-dione (4e)
Yield: 0.66 g (64%), white crystals [mixture of diastereomers dr
20
4.1:3.9:2.1:1], mp 60e61 ꢂC (CCl4), [
a
]
¼ e 5.3 (c 1.0.
D
CHCl3). 1H NMR (400 MHz, CDCl3):
d
¼ 1.49e1.77 (m, 12H e first
diastereomer, 12H e second diastereomer, 12H e third diaste-
reomer, 12H e fourth diastereomer, Ad), 1.81 (s, 3H e fourth dia-
stereomer, Me), 1.83 (s, 3H e third diastereomer, Me), 1.85 (br s, 3H
e second diastereomer, Ad), 1.88 (br s, 3H e third diastereomer,
Ad), 1.95 (br s, 3H e first diastereomer, Ad), 2.07 (br s, 3H e fourth
diastereomer, Ad), 2.28 (br s, 3H e second diastereomer, Me), 2.30
(br s, 3H e first diastereomer, Me), 4.27e4.33 (m, 1H e first dia-
3
4.2.4. 1-(Аdamantan-1-yl)-2-[(1S)-2-bromo-1-(4-
methoxyphenyl)-2-nitroethyl]butane-1,3-dione (4d)
stereomer, 1H e fourth diastereomer, CHAr), 4.60 (dd, JHH ¼ 10.8,
3
4.8 Hz, 1H e second diastereomer, CHAr), 4.66 (dd, JHH ¼ 10.8,
Yield: 0.75 g (71%), yellow oil [mixture of diastereomers dr
4.0 Hz, 1H e first diastereomer, CHAr), 4.74e4.79 (m, 1H e first
diastereomer, 1H e third diastereomer, CHC(O)), 4.90e4.93 (m, 1H
e second diastereomer, 1H e fourth diastereomer, CHC(O)), 6.25 (d,
3JHH ¼ 4.0 Hz, 1H e third diastereomer, CHBr), 6.28e6.31 (m, 1H e
first diastereomer, 1H e fourth diastereomer, CHBr), 6.40 (d,
3JHH ¼ 6.8 Hz, 1H e second diastereomer, CHBr), 6.95e7.02 (m, 8H,
aromatic), 7.15e7.20 (m, 4H, aromatic), 7.25e7.29 (m, 4H, aro-
1
20
3.7:2.4:1.1:1], [
a]
¼ e 2.2 (c 1.0, CHCl3). H NMR (400 MHz.
D
CDCl3):
d
¼ 1.50e1.56 (m, 12H e second diastereomer, Ad),
1.63e1.76 (m, 12H e first diastereomer, Ad), 1.79 (s, 3H e second
diastereomer, Me), 1.82 (s, 3H e first diastereomer, Me), 1.85e1.88
(m, 12H e third diastereomer, 12H e fourth diastereomer, Ad), 1.94
(br s, 3H e third diastereomer, 3H e fourth diastereomer, Ad), 2.07
(br s, 3H e third diastereomer, 3H e fourth diastereomer, Ad), 2.25
(s, 3H e fourth diastereomer, Me), 2.28 (s, 3H e third diastereomer,
Me), 3.75e3.76 (m, 3H e first diastereomer, 3H e second diaste-
reomer, 3H e third diastereomer, 3H e fourth diastereomer, MeO),
4.21e4.26 (m, 1H e third diastereomer, CHAr), 4.30 (dd, 3JHH ¼ 10.8,
matic); 13C NMR (101 MHz, CDCl3):
d
¼ 27.7 (Ad, first diastereomer),
27.8 (Ad, second diastereomer), 27.8 (Ad, third diastereomer), 27.9
(Ad, fourth diastereomer), 28.2 (Me, third diastereomer), 28.7 (Me,
fourth diastereomer), 29.3 (Me, first diastereomer), 30.5 (Me, sec-
ond diastereomer), 36.1 (Ad, first diastereomer), 36.2 (Ad, second
diastereomer), 36.3 (Ad, fourth diastereomer), 38.1 (Ad, first dia-
stereomer), 38.4 (Ad, third diastereomer), 38.5 (Ad, second dia-
stereomer), 38.5 (Ad, fourth diastereomer), 48.1 (Ad, second
diastereomer), 48.2 (Ad, first diastereomer), 48.6 (Ad, fourth dia-
stereomer), 48.7 (CHAr, second diastereomer), 49.5 (CHAr, first
diastereomer), 50.7 (CHAr, fourth diastereomer), 51.9 (CHAr, third
diastereomer), 64.1 (CHC(O), second diastereomer), 64.5 (CHC(O),
fourth diastereomer), 65.3 (CHC(O), first diastereomer), 65.9
(CHC(O), third diastereomer), 82.1 (CHBr, second diastereomer),
83.1 (CHBr, fourth diastereomer), 85.2 (CHBr, first diastereomer),
86.4 (CHBr, third diastereomer), 115.8 (d, 2JСF ¼ 42.9 Hz, aromatic),
3
4.8 Hz, 1H e second diastereomer, CHAr), 4.55 (dd, JHH ¼ 10.8,
3
5.2 Hz, 1H e fourth diastereomer, CHAr), 4.63 (dd, JHH ¼ 10.8,
6.0 Hz, 1H e first diastereomer, CHAr), 4.75e4.80 (m, 1H e first
diastereomer, 1H e third diastereomer, 1H e fourth diastereomer,
CHC(O)), 4.90 (d, 3JHH ¼ 9.6 Hz, 1H e second diastereomer, CHC(O)),
6.24e6.25 (m, 1H e first diastereomer, 1H e second diastereomer,
CHBr), 6.29 (d, 3JHH ¼ 5.2 Hz, 1H e second diastereomer, CHBr), 6.39
3
(d, JHH ¼ 7.2 Hz, 1H e fourth diastereomer, CHBr), 6.78e6.89 (m,
4H e first diastereomer, aromatic), 7.07e7.12 (m, 4H e third dia-
stereomer, 4H e fourth diastereomer, aromatic), 7.17e7.19 (m, 4H e
second diastereomer, aromatic); 13C NMR (101 MHz, CDCl3):
2
d
¼ 27.7 (Ad), 27.8 (Ad), 27.9 (Ad), 28.0 (Me, first diastereomer), 28.6
116.0 (d, JСF ¼ 22 Hz, aromatic), 115.8 (aromatic), 127.2 (d,
(Me, second diastereomer), 29.2 (Me, third diastereomer), 30.4 (Me,
fourth diastereomer), 36.1 (Ad, fourth diastereomer), 36.2 (Ad, third
diastereomer), 36.3 (Ad, first diastereomer.), 36.4 (Ad, second dia-
stereomer), 38.1 (Ad, third diastereomer), 38.4 (Ad, first
4JСF ¼ 3.8 Hz, aromatic, third diastereomer), 128.1 (d, 4JСF ¼ 2.8 Hz,
4
aromatic, fourth diastereomer), 129.0 (d, JСF ¼ 2.8 Hz, aromatic,
4
third diastereomer), 129.4 (d, JСF ¼ 3.8 Hz, aromatic, second dia-
3
stereomer), 131.5 (d, JСF ¼ 7.6 Hz, aromatic second diastereomer),
6

D.S. Nikerov, M.A. Ashatkina, V.A. Shiryaev et al.
Tetrahedron 84 (2021) 132029
1
131.7 (d, 3JСF ¼ 9.5 Hz, aromatic, first diastereomer),131.6 (aromatic,
diastereomer), 50.7 (d, JCP ¼ 128 Hz, CHP(O), second diaste-
1
2
third diastereomer), 162.9 (d, JСF ¼ 247.9 Hz, aromatic, second
reomer), 53.3 (d, JCP ¼ 6.7 Hz, MeO, first diastereomer), 53.4 (d,
diastereomer), 163.1 (d, 1JСF ¼ 247 Hz, aromatic, first diastereomer),
163.3 (d, 1JСF ¼ 247.9 Hz, aromatic third diastereomer), 200.2 (C]O,
third diastereomer), 201.0 (C]O, first diastereomer), 201.2 (C]O,
fourth diastereomer), 201.5 (C]O, second diastereomer), 206.9
(C]O, first diastereomer), 208.3 (C]O, second diastereomer),
208.5 (C]O, third diastereomer), 209.0 (C]O, fourth diaste-
reomer); 19F NMR (376 MHz, CDCl3): ꢀ111.3 (third
diastereomer), ꢀ111.4 (fourth diastereomer), ꢀ111.7 (first
diastereomer), ꢀ111.8 (second diastereomer). Anal. calcd for
2JCP ¼ 6.7 Hz, MeO, first diastereomer), 53.8 (d, 2JCP ¼ 7.6 Hz, MeO,
2
second diastereomer), 54.4 (d, JCP ¼ 6.7 Hz, MeO, second diaste-
3
reomer), 86.9 (d, JCP ¼ 19.2 Hz, CHNO2, first diastereomer), 88.5
(CHNO2, second diastereomer), 128.4 (aromatic), 128.5 (aromatic),
128.8 (aromatic), 128.9 (aromatic), 129.0 (aromatic), 129.3 (aro-
matic), 129.4 (aromatic), 129.8 (aromatic), 130.0 (aromatic), 130.1
(aromatic), 132.2 (aromatic), 132.8 (aromatic), 132.9 (aromatic),
133.8 (aromatic), 134.1 (aromatic), 134.2 (aromatic), 136.8 (aro-
2
matic), 137.1 (aromatic), 192.8 (d, JCP ¼ 5.7 Hz, C(O), first diaste-
2
C
22H25BrFNO4: C, 56.66; H, 5.40; N, 3.00. Found: C, 56.71; H, 5.44;
reomer), 194.3 (d, JCP ¼ 5.7 Hz, C(O), second diastereomer); 31P
N, 3.19.
NMR (161 MHz, CDCl3):
d
¼ 22.3 (fourth diastereomer), 21.9 (first
diastereomer), 21.6 (third diastereomer), 21.3 (second diaste-
reomer). Anal. calcd for C18H19BrNO6P: C, 47.39; H, 4.20; N, 3.07.
Found: C, 47.44; H, 4.27; N, 3.18.
4.2.6. Ethyl (3S)-2-[(adamantane-1-carbonyl]-4-bromo-4-nitro-3-
phenylbutanoate (4f)
Yield: 0.4 g (40%), white crystals [mixture of diastereomers dr
20
1.6:1], mp 136e138 ꢂC (methanol), [
a
]
¼ e 19.6 (c 1.0.
4.2.8. [(1S)-2-Bromo-2-nitro-1-phenylethyl]-1,3-diphenylpropane-
1,3-dione (4h)
D
CHCl3). 1H NMR (400 MHz, CDCl3):
d
¼ 1.16 (t, 3JHH ¼ 6.8 Hz, 3H
3
Yield: 0.58 g (58%), white crystals [mixture of diastereomers dr
e second diastereomer, Me), 1.27 (t, JHH ¼ 6.8 Hz, 3H e first dia-
stereomer, Me), 1.51e1.65 (m, 12H e first diastereomer, 12H e
second diastereomer, Ad), 1.92 (s, 3H e first diastereomer, 3H e
second diastereomer, Ad), 4.06e4.09 (m, 2H e second diaste-
20
1.3:1], mp 163e164 ꢂC (toluene), [
a
]
¼ þ35.2 (c 1.0, CHCl3).
D
1H NMR (400 MHz, CDCl3):
d
¼ 4.67 (dd, 3JHH ¼ 8.4, 7.2 Hz, 1H e
first diastereomer, CHPh), 5.05 (dd, 3JHH ¼ 10.4, 5.2 Hz, 1H e second
3
3
reomer, OCH2), 4.23 (q, JHH ¼ 7.4 Hz, 2H e first diastereomer,
diastereomer, CHPh), 6.09 (d, JHH ¼ 10.4, 1H e second diaste-
3
OCH2), 4.24e4.28 (m, 1H e second diastereomer, CHPh), 4.61e4.62
(m, 1H e first diastereomer,1H e first diastereomer, CHPh, CHC(O)),
reomer, CHC(O)), 6.27 (d, JHH ¼ 8.8, 1H e first diastereomer,
3
CHC(O)), 6.80 (d, JHH ¼ 5.2 Hz, 1H e first diastereomer, 1H e sec-
3
4.73 (d, JHH ¼ 10.0 Hz, 1H e second diastereomer, CHC(O)),
ond diastereomer, CHBr), 7.28e7.48 (m, 10H e first diastereomer,
10H e second diastereomer, aromatic), 7.54e7.58 (m, 1H e first
diastereomer, 1H e second diastereomer, aromatic), 7.70e7.74 (m,
2H e first diastereomer, 2H e second diastereomer, aromatic), 7.98
(d, 3JHH ¼ 7.6, 2H e first diastereomer, aromatic), 8.04 (d, 3JHH ¼ 7.6,
2H e second diastereomer, aromatic); 13C NMR (101 MHz, CDCl3):
6.68e6.70 (m, 1H e first diastereomer, 1H e second diastereomer,
CHBr), 7.22e7.29 (m, 5H e first diastereomer, 5H e second dia-
stereomer, aromatic); 13C NMR (101 MHz, CDCl3):
d
¼ 13.9 (Me,
second diastereomer), 14.1 (Me, first diastereomer), 27.8 (Ad, sec-
ond diastereomer), 27.9 (Ad, first diastereomer), 36.2 (Ad, first
diastereomer), 36.3 (Ad, second diastereomer), 38.1 (Ad, first dia-
stereomer), 38.4 (Ad, second diastereomer), 47.7 (Ad), 49.4 (CHPh,
first diastereomer), 51.9 (CHPh, second diastereomer), 55.4
(CHC(O), second diastereomer), 55.9 (CHC(O), first diastereomer),
62.2 (OCH2, first diastereomer), 62.4 (OCH2, second diastereomer),
82.6 (CHBr, first diastereomer), 85.7 (CHBr, second diastereomer),
128.6 (aromatic, first diastereomer), 128.7 (aromatic, second dia-
stereomer), 129.0 (aromatic, second diastereomer), 129.1 (aromatic,
first diastereomer), 129.7 (aromatic, first diastereomer), 130.0 (ar-
omatic, second diastereomer), 133.3 (aromatic, first diastereomer),
133.7 (aromatic, second diastereomer), 167.1 (C(O)O, first diaste-
reomer), 167.4 (C(O)O, second diastereomer), 206.5 (C]O, first
diastereomer), 207.7 (C]O, second diastereomer). Anal. calcd for
d
¼ 50.3 (CHPh, second diastereomer), 52.2 (CHPh, first diaste-
reomer), 59.2 (CHC(O), first diastereomer), 61.1 (CHC(O), second
diastereomer), 83.0 (CHBr, first diastereomer), 85.9 (CHBr, second
diastereomer), 128.5 (aromatic), 128.6 (aromatic), 128.7 (aromatic),
128.8 (aromatic), 128.9 (aromatic), 129.0 (aromatic), 129.1 (aro-
matic), 129.1 (aromatic), 129.2 (aromatic), 129.8 (aromatic), 130.0
(aromatic), 132.4 (aromatic), 132.7 (aromatic), 133.7 (aromatic),
133.8 (aromatic), 134.2 (aromatic), 134.4 (aromatic), 135.9 (aro-
matic), 136.0 (aromatic), 136.3 (aromatic), 192.6 (C]O, second
diastereomer), 193.4 (C]O, second diastereomer), 193.9 (C]O, first
diastereomer), 194.1 (C]O, first diastereomer). Anal. calcd for
C
23H18BrNO4: C, 61.08; H, 4.01; N, 3.10. Found: C, 61.12; H, 4.05; N,
3.29.
C
23H28BrNO5: C, 57.75; H, 5.90; N, 2.93. Found: C, 57.84; H, 5.95; N,
3.01.
4.2.9. 1-(adamantan-1-yl)-2-((1S)-2-bromo-1-(5-bromofuran-2-
yl)-2-nitroethyl)butane-1,3-dione (4i)
4.2.7. Dimethyl [(3R)-4-bromo-4-nitro-1-oxo-1,3-diphenylbutan-
2-yl]phosphonate (4g)
Yield: 0.45 g (40%), yellow oil [mixture of diastereomers dr
20
1.5:1.0], [
a
]
¼ þ66.0 (c 1.0, CHCl3).
D
1H NMR (400 MHz, CDCl3):
d
¼ 1.66e1.86 (m, 12H e first dia-
Yield: 0.58 g (58%), white crystals [mixture of diastereomers dr
20
23:22:3:1], mp 136e138 ꢂC (methanol), [
a
]
¼ e 35.5 (c 1.0.
stereomer, 12H e second diastereomer, Ad), 1.95 (s, 3H e first
diastereomer, Me), 1.98 (s, 3H e second diastereomer, Me), 2.07 (br
s, 3H e first diastereomer, 3H e second diastereomer, Ad), 4.31 (dd,
D
CHCl3). NMR data are presented for two main diastereomers. 1H
3
NMR (400 MHz, CDCl3):
d
¼ 3.19 (d, JHP ¼ 11.2 Hz, 3H e first dia-
3
3
stereomer, MeO), 3.27 (d, JHP ¼ 11.2 Hz, 3H e first diastereomer,
MeO), 3.73 (d, 3JHP ¼ 11.2 Hz, 3H e second diastereomer, MeO), 3.86
(d, 3JHP ¼ 11.2 Hz, 3H e second diastereomer, MeO), 4.78e4.95 (m,
2H e first diastereomer, 2H e second diastereomer, CHP(O), CHPh),
6.44e6.48 (m, 1H e first diastereomer,CHNO2), 7.10e7.78 (m, 16H
aromatic, 1H e second diastereomer CHNO2), 7.79 (d, 3JHH ¼ 7.2 Hz,
3JHH ¼ 9.6 Hz, JHH ¼ 4.8 Hz, 1H e first diastereomer, CH(5-
bromofuran-2-yl)), 4.72e4.78 (m, 1H e second diastereomer,
CH(5-bromofuran-2-yl), 1H e second diastereomer, CHC(O)), 4.88
3
(d, JHH ¼ 9.6 Hz, 1H - first diastereomer, CHC(O)), 6.14 (d,
3JHH ¼ 3.2 Hz, 1H e first diastereomer, aromatic), 6.23e6.26 (m, 1H
e first diastereomer, CHBr, 2H e second diastereomer, aromatic),
3
3
1H e first diastereomer, aromatic), 8.10 (d, JHH ¼ 7.2 Hz, 1H e
7.25 (d, JHH ¼ 0.4 Hz, 1H e second diastereomer, CHBr); 13C NMR
second diastereomer, aromatic); 13C NMR (101 MHz, CDCl3):
(101 MHz, CDCl3):
d
¼ 27.7 (Ad, second diastereomer), 27.8 (Ad, first
2
d
¼ 48.4 (CHPh, first diastereomer), 48.8 (d, JCP ¼ 3.8 Hz, CHPh,
diastereomer), 28.8 (Me, second diastereomer), 29.4 (Me, first
diastereomer), 36.2 (Ad, second diastereomer), 36.3 (Ad, first
1
second diastereomer), 48.9 (d, JCP
¼
124 Hz, CHP(O), first
7

D.S. Nikerov, M.A. Ashatkina, V.A. Shiryaev et al.
Tetrahedron 84 (2021) 132029
diastereomer), 38.3 (Ad, second diastereomer), 38.4 (Ad, first dia-
stereomer), 44.5 (CH(5-bromofuran-2-yl, second diastereomer),
45.9 (CH(5-bromofuran-2-yl, first diastereomer), 48.1 (Ad, first
diastereomer), 48.3 (Ad, second diastereomer), 61.8 (CHC(O), first
diastereomer), 63.1 (CHC(O), second diastereomer), 80.8 (CHBr, first
diastereomer), 83.4 (CHBr, second diastereomer), 112.6 (aromatic,
second diastereomer), 112.7 (aromatic, first diastereomer), 114.7
(aromatic, second diastereomer), 115.0 (aromatic, first diaste-
reomer), 123.2 (aromatic, CBr, first diastereomer), 123.4 (aromatic,
CBr, second diastereomer), 148.0 (aromatic, second diastereomer),
148.1 (aromatic, first diastereomer), 199.8 (C]O, second diaste-
reomer), 200.6 (C]O, first diastereomer), 207.6 (C]O, second
diastereomer), 208.2 (C]O, first diastereomer). Anal. calcd for
NMR (101 MHz, CDCl3):
d
¼ 28.2 (Ad), 31.1 (Me), 36.6 (Ad), 37.4 (Ad),
37.6 (Ad), 57.8 (C-4), 108.6 (C-5), 113.0 (C-3), 127.2 (aromatic), 128.9
(aromatic), 129.8 (aromatic), 137.4 (aromatic), 175.1 (С-2), 193.8
(С ¼ О). Anal. calcd for C22H25NO4: C, 71.91; H, 6.86; N, 3.81. Found:
C, 71.97; H, 6.89; N, 3.99.
4.3.1.3. (Adamantan-1-yl)[(4R,5R)-2-methyl-5-nitro-4-(4-
methylphenyl)-4,5-dihydrofuran-3-yl]methanone (5c). Yield: 0.20 g
(57%), 89% ee (4R,5R). HPLC analysis (CHIRALPAK AD-3 column;
hexane/2-propanol, 97:3; flow rate 1.2 mL/min; wavelength
210 nm): tR ¼ 5.0 (4S,5R), 5.9 (4R,5S), 9.3 (4R,5R), 11.1 (4S,5S) min.
The HPLC chromatogram shows two diastereomers. The second
diastereomer is formed by epimerization in a chromatographic
1
20
C
20H23Br2NO5: C, 46.44; H, 4.48; N, 2.71. Found: C, 46.50; H, 4.52; N,
column. Yellow oil, [
CDCl3):
a
]
¼ e88.6 (c 1.0, CHCl3). H NMR (400 MHz,
D
2.73.
d
¼ 1.73e1.86 (m, 6Н, Ad), 1.90 (s, 3Н, Me), 2.05 (s, 3Н, Ad),
2.18 (s, 6Н, Ad), 2.35 (s, 3Н, Me), 4.59 (s, 1Н, H-4), 5.57 (d,
3JHH ¼ 1.6 Hz, 1H, H-5), 7.11 (d, 3JHH ¼ 8.0 Hz, 2H, aromatic), 7.20 (d,
3JHH ¼ 8.0 Hz, 2H, aromatic). 13C NMR (101 MHz, CDCl3): 21.2 (Me),
28.2 (Ad), 31.1 (Me), 36.6 (Ad), 37.6 (Ad), 38.4 (Ad), 57.5 (C-4), 108.8
(C-5), 113.6 (C-3), 127.1 (aromatic), 129.7 (aromatic), 134.4 (aro-
matic), 138.8 (aromatic), 174.9 (C-2), 193.9 (С ¼ О). Anal. calcd for
4.3. General procedure for the synthesis of 4,5-dihydrofurans
To a mixture of compound 4a-i (0.94 mmol) in 5 mL acetonitrile
was added (0.94 mmol). The reaction mixture was kept at rt for
24 h, then washed with a solution of ammonium chloride. The
aqueous layer was extracted with CHCl3 (3х20 mL). The organic
phase was separated, dried over Na2SO4. The solvent was distilled
off under reduced pressure. The residue was purified by column
chromatography on silica gel (eluent CCl4).
C
23H27NO4: C, 72.42; H, 7.13; N, 3.67. Found: C, 72.48; H, 7.20; N,
3.80.
4.3.1.4. (Adamantan-1-yl)[(4R,5R)-4-(4-methoxyphenyl)-2-methyl-
5-nitro-4,5-dihydrofuran-3-yl]methanone (5d). Yield: 0.23 g (61%),
92% ee (4R,5R). HPLC analysis (CHIRALPAK AD-3 column; hexane/2-
propanol, 97:3; flow rate 1.2 mL/min; wavelength 210 nm): tR ¼ 6.5
(4S,5R), 8.8 (4R,5S), 12.4 (4R,5R), 13.9 (4S,5S) min. The HPLC chro-
matogram shows two diastereomers. The second diastereomer is
4.3.1. One-pot procedure for the synthesis of 4,5-dihydrofurans 5a
and 5h
A mixture of
2a (2.2 mmol) and bis[(1R,2R)-N,N՚-dibenzylcyclohexane-1,2-
diamine-
2N,N՚](dibromo)nickel (3) (0.044 mmol) in 2 mL of
b-diketone 1a,e (2.2 mmol), a-bromonitroalkene
k
formed by epimerization in a chromatographic column. Yellow oil,
20
toluene was stirred at rt for 24 h. Then DMAP (2.2 mmol) was added
to this reaction medium and kept at rt for 24 h. The reaction
mixture was washed with a solution of ammonium chloride. The
aqueous layer was extracted with CHCl3 (3х20 mL). The organic
phase was separated, dried over Na2SO4. The solvent was distilled
off under reduced pressure. The residue was purified by column
chromatography on silica gel (eluent CCl4).
[
d
a
]
¼
e100.0 (c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3):
D
¼ 1.73e1.83 (m, 6Н, Ad), 1.90 (s, 3Н, Ad), 2.05 (s, 3Н, Ad), 2.17 (s,
3
6Н, Ad), 3.80 (s, 3Н, MeO), 4.58 (s, 1Н, H-4), 5.57 (d, JHH ¼ 1.2 Hz,
1H, H-5), 6.91 (d, 3JHH ¼ 8.8 Hz, 1H, aromatic), 7.14 (d, 3JHH ¼ 8.8 Hz,
1H, aromatic); 13C NMR (101 MHz, CDCl3): 27.9 (Ad), 31.1 (Me), 36.6
(Ad), 37.7 (Ad), 38.1 (Ad), 55.5 (OMe), 57.2 (C-4), 108.8 (C-5), 113.4
(C-3), 115.1 (aromatic), 128.4 (aromatic), 129.2 (aromatic), 159.9
(aromatic), 174.8 (C-2), 193.9 (С ¼ О). Anal. calcd for C23H27NO5: C,
69.50; H, 6.85; N, 3.52. Found: C, 69.58; H, 6.89; N, 3.64.
4.3.1.1. 1-[(4R,5R)-2-Methyl-5-nitro-4-phenyl-4,5-dihydrofuran-3-
yl]ethan-1-one (5a). General procedure: Yield: 0.13 g (56%), 94% ee
(4R,5R). One-pot procedure: Yield: 0.26 g (49%), 94% ee (4R,5R).
HPLC analysis (CHIRALPAK AD-3 column; hexane/2-propanol, 97:3;
4.3.1.5. (Adamantan-1-yl)[(4R,5R)-4-(4-fluorophenyl)-2-methyl-5-
nitro-4,5-dihydrofuran-3-yl]methanone (5e). Yield: 0.22 g (56%),
90% ee (4R,5R). HPLC analysis (CHIRALPAK AD-3 column; hexane/2-
propanol, 97:3; flow rate 1.2 mL/min; wavelength 210 nm): tR ¼ 9.5
(4R,5R), 11.1 (4S,5S) min. Yellow oil, [
NMR (400.
flow rate 1.2 mL/min; wavelength 210 nm): tR ¼ 9.8 (4R,5R), 10.4
20
(4S,5S). White crystals, mp 70.2e72.3 ꢂC (CCl4), [
a]
¼ e 199.4(c
D
1
20
D
1.0, CHCl3).
a]
¼ e 62.2 (c 1.0, CHCl3). H
1H NMR (400 MHz, CDCl3):
d
¼ 2.01 (s, 3H, Me), 2.52 (d,
3JHH ¼ 1.2 Hz, 3H, Me), 4.65 (s, 1H, H-4), 5.72 (d, 3JHH ¼ 2.0 Hz, 3H,
MHz, CDCl3):
d
¼ 1.73e1.83 (m, 6Н, Ad), 1.90 (s, 3Н, Me), 2.05 (s,
H-5), 7.21e7.26 (m, 2H, aromatic), 7.31e7.40 (m, 3H, aromatic); 13
C
3Н, Ad), 2.17 (br s, 6Н, Ad), 4.63 (s, 1Н, H-4), 5.57 (d, 3JHH ¼ 0.8 Hz,
NMR (101 MHz, CDCl3):
(C-5), 115.7 (C-3), 127.2 (aromatic), 128.8 (aromatic), 129.6 (aro-
d
¼ 14.6 (Me), 29.8 (Me), 56.4 (C-4), 109.6
1H, H-5), 7.08e7.12 (m, 2Н, aromatic), 7.20e7.25 (m, 2Н, aromatic);
13C NMR (101 MHz, CDCl3):
d
¼ 28.2 (Ad), 31.1 (Me), 36.5 (Ad), 37.3
matic), 137.6 (aromatic), 166.9 (C-2), 193.2 (C]O). Anal. calcd for
(Ad), 37.7 (Ad), 57.1 (C-4), 108.4 (C-5), 113.0 (C-3), 116.8 (d,
2JCF ¼ 22.0 Hz, aromatic), 129.0 (d, 3JCF ¼ 8.6 Hz, aromatic), 133.1 (d,
4JCF ¼ 3.8 Hz, aromatic),162.9 (d, 1JCF ¼ 247.9 Hz, aromatic),175.1 (C-
C
13H13NO4: C, 65.13; H, 5.30; N, 5.67. Found: C, 65.23; H, 5.33; N,
5.83.
2), 193.6 (С ¼ О); 19F NMR (376 MHz, CDCl3):
¼ ꢀ112.4. Anal. calcd
d
4.3.1.2. (Adamantan-1-yl)[(4R,5R)-2-methyl-5-nitro-4-phenyl-4,5-
dihydrofuran-3-yl])methanone (5b). Yield: 0.26 g (77%), 99% ee
(4R;5R). HPLC analysis (CHIRALPAK AD-3 column; hexane/2-
propanol, 97:3; flow rate 1.2 mL/min; wavelength 210 nm):
for C22H24FNO4: C, 68.56; H, 6.28; N, 3.63. Found: C, 68.61; H, 6.32;
N, 3.78.
4.3.1.6. Ethyl (4R,5R)-2-(adamantan-1-yl)-5-nitro-4-phenyl-4,5-
dihydrofuran-3-carboxylate (5f). Yield: 0.22
tR ¼ 10.8 (4R,5R), 12.4 (4S,5S) min. White crystals, mp 93.5e95.0 ꢂC
g (60%), >99% ee
¼ e 94.8 (c 1.0, CHCl3). 1H NMR (400 MHz, CDCl3):
20
(4R;5R). HPLC analysis (CHIRALPAK AD-3 column; hexane/2-
propanol, 92:8; flow rate 1.2 mL/min; wavelength 210 nm):
(CCl4), [
d
a
]
D
¼ 1.73e1.84 (m, 6H, Ad), 1.90 (s, 3H, Me), 2.06 (s, 3H, Ad), 2.18 (s,
tR ¼ 3.4 (4R,5R), 3.9 (4S,5S) min. White crystals, mp 125e126 ꢂC
6H, Ad), 4.63 (d, 3JHH ¼ 1.2 Hz,1H, H-4), 5.60 (d, 3JHH ¼ 1.2 Hz,1H, H-
5), 7.23e7.36 (m, 2H, aromatic), 7.38e7.43 (m, 3H, aromatic); 13C
20
(methanol), [
a
]
¼ e 140 (c 1.0, CHCl3).
D
8

D.S. Nikerov, M.A. Ashatkina, V.A. Shiryaev et al.
Tetrahedron 84 (2021) 132029
3
1H NMR (400 MHz, CDCl3):
d
¼ 1.04 (t, JHH ¼ 7.1 Hz, 3H, Me),
4.4. (3S)-1-(adamantan-1-yl)-4-bromo-4-nitro-3-phenylbutan-1-
one (6)
1.74e1.84 (m, 6Н, Ad), 2.07 (s, 3Н, Ad), 2.25 (s, 6Н, Ad), 3.98 (q,
3JHH ¼ 7.1 Hz, 2H, ОСН2), 4.61 (d, JHH ¼ 1.2 Hz, 1Н, H-4), 5.66 (d,
3
3JHH ¼ 1.2 Hz, 1Н, H-5), 7.18e7.20 (m, 2Н, aromatic), 7.28e7.37 (m,
A mixture of compound 4b (0.5 g, 1.12 mmol), sodium hydroxide
(0.1 g, 2.50 mmol) in 5 mL of water was stirred at rt for 6 h until
complete dissolution. Then the reaction mass was acidified with 5%
HCl solution, extracted with CHCl3 (3 ꢃ 20 mL). The organic phase
was separated, dried over Na2SO4. The solvent was distilled off
under reduced pressure. The formed crystalline product (6) was
filtered and recrystallized from MeOH. Yield: 0.24 g (50%), brown
crystals [mixture of diastereomers dr 1.0:0.4], mp 119.2e119.8 ꢂC
3Н, aromatic); 13C NMR (101 MHz, CDCl3):
d
¼ 13.9 (Me), 28.3 (Ad),
36.6 (Ad), 37.0 (Ad), 38.2 (Ad), 57.5 (C-4), 60.4 (ОСН2), 106.3 (C-3),
108.6 (C-5), 127.1 (aromatic), 128.3 (aromatic), 129.2 (aromatic),
138.4 (aromatic), 162.9 (C(O)O), 175.3 (С-2). Anal. calcd for
C
23H27NO5: C, 69.50; H, 6.85; N, 3.52. Found: C, 69.58; H, 6.89; N,
3.64. The single crystal of compound 5f was grown by slow evap-
oration of methanol. The compound crystallizes in the ortho-
rhombic crystal system, space group P212121, a ¼ 9.8066(3) Å,
(MeOH). 1H NMR (400 MHz, CDCl3):
d
¼ 1.62e1.73 (м, 12Н e first
b ¼ 13.2489(4) Å, c ¼ 16.3828(6) Å,
a
¼ 90ꢂ,
b
¼ 90ꢂ,
g
¼ 90ꢂ,
diastereomer, 12Н esecond diastereomer, Ad), 4.43 (br s, 3Н e first
V ¼ 2128.56(12) Å3, Z ¼ 4, dcalcd¼1.240 g/cm3, F(000) ¼ 848, Theta
diastereomer, 3Н e second diastereomer, Ad), 2.98 (d, 3JHH ¼ 5.6 Hz,
3
range 4.292e72.775ꢂ,
wR2 ¼ 0.1490.
R
indices (all data) R1
¼
0.0897
1Н e second diastereomer., СН2С(О)), 3.02 (d, JHH ¼ 6 Hz, 1H e
second diastereomer, СН2С(О)), 3.08e3.17 (m, 2Н efirst diaste-
reomer, СН2С(О)), 4.13e4.21 (m, 1Н e first diastereomer, 1Н e
3
second diastereomer, CHPh), 6.29 (d, JHH ¼ 8.8 Hz, 1Н e second
4.3.1.7. Dimethyl [(4S,5R)-5-nitro-2,4-diphenyl-4,5-dihydrofuran-3-
yl]phosphonate (5g). Yield: 0.37 g (90%), 98% ee (4S;5R). HPLC
analysis (CHIRALPAK AD-3 column; hexane/2-propanol, 93:7; flow
rate 1.2 mL/min; wavelength 210 nm): tR ¼ 25.0 (4R,5S), 28.8
diastereomer, СНBr), 6.38 (d, 3JHH ¼ 6.8 Hz, 1H e first diasteromer,
СНBr), 7.20e7.31 (m, 5H e first diastereomer, 5H e second dia-
stereomer, aromatic). 13C NMR (101 MHz, CDCl3):
d
¼ 27.9 (Ad), 36.5
1
20
(Ad), 37.9 (Ad, second diastereomer), 38.0 (Ad, first diastereomer),
38.6 (CH2, first diastereomer), 38.9 (CH2, second diastereomer), 39.3
(Ad), 45.9 (CHPh, first diastereomer), 46.5 (CHPh, second diaste-
reomer), 84.2 (CHBr, second diastereomer), 85.4 (CHBr, first dia-
stereomer), 127.5 aromatic, first diastereomer), 127.8 (aromatic,
second diastereomer),128.4 (aromatic, second diastereomer), 128.6
(aromatic, first diastereomer), 128.9 (aromatic, first diastereomer),
129.0 (aromatic, second diastereomer), 136.4 (aromatic, first dia-
stereomer), 136.6 (aromatic, second diastereomer), 211.4 (C]O,
first diastereomer), 211.6 (C]O, second diastereomer). Anal. calcd
for C20H24BrNO3: C, 59.12; H, 5.95; N, 3.45. Found: C, 59.20; H, 5.99;
N, 3.64.
(4S,5R) min. [
a
]
¼ e 38.5 (c 1.0, CHCl3). H NMR (400 MHz, CDCl3):
d
¼ 3.31 (d, 3DJHH ¼ 12.0 Hz, 3H, MeO), 3.39 (d, 3JHH ¼ 12.0 Hz, 3H,
3
3
MeO), 4.76 (dd, JHP ¼ 4.0 Hz, JHH ¼ 1.6 Hz, 1H, H-4), 5.91 (d,
3JHH ¼ 1.6 Hz, 1H, H-5), 7.34e7.40 (m, 5H, aromatic), 7.45e7.53 (m,
3H, aromatic), 8.04e8.07 (m, 2H, aromatic); 13C NMR (101 MHz,
CDCl3):
d
¼ 52.4 (d, 2JCP ¼ 4.8 Hz, MeO), 52.6 (d, 2JCP ¼ 4.8 Hz, MeO),
59.7 (d, 2JCP ¼ 10.5 Hz, C-4), 100.7 (d, 1JCP ¼ 213.5 Hz, C-3), 109.2 (d,
2JCP ¼ 10.5 Hz, C-5), 127.4 (aromatic), 127.6 (aromatic), 128.4 (aro-
matic), 128.8 (aromatic), 129.4 (aromatic), 129.6 (aromatic), 132.0
(aromatic), 137.4 (aromatic), 165.0 (d, 2JCP ¼ 25.7 Hz, C-2): 31P NMR
(161 MHz, CDCl3):
d
¼ 16.3. Anal. calcd for C18H18NO6P: C, 57.60; H,
4.83; N, 3.73. Found: C, 57.66; H, 4.86; N, 3.84.
4.5. General procedure for the preparation of 1-(2-methyl-4-
phenyl-1H-pyrrol-3-yl)ethan-1-one (7)
4.3.1.8. [(4R,5R)-5-nitro-2,4-diphenyl-4,5-dihydrofuran-3-
yl](phenyl)methanone (5h). General procedure: Yield: 0.21 g (61%),
96% ee (4R,5R). One-pot procedure: Yield: 0.54 g (67%), 96% ee
(4R,5R). HPLC analysis (CHIRALPAK AD-3 column; hexane/2-
propanol, 93:7; flow rate 1.2 mL/min; wavelength 210 nm):
To a solution of compound 5a (0.25 mg, 1.01 mmol) in methanol
(1.5 mL) was added 10% Pd/C (25 mg). The reaction mixture was
stirred under an atmosphere of H2 (5 bar) at rt for 4 days. The
solvent was distilled off under reduced pressure. The product was
filtered through a layer of silica gel (CHCl3).
tR ¼ 12.9 (4R,5R), 18.3 (4S,5S) min. White crystals, mp 77e78 ꢂC
20
(CCl4), [
a]
¼ e 124.3 (c 1.0.
D
CHCl3). 1H NMR (400 MHz, CDCl3):
d
¼ 4.94 (d, 3JHH ¼ 1.2 Hz, 1Н,
Yield: 0.18 g (90%), purple crystals, mp 151.2e152.6 ꢂC. 1H NMR
H-4), 5.98 (d, 3JHH ¼ 1.2 Hz, 1H, H-5), 7.10e7.51 (m, 15Н, aromatic);
(400 MHz, CDCl3):
d
¼ 2.06 (s, 3H, Me), 2.51 (s,3H, Me), 6.52 (d,
13C NMR (101 MHz, CDCl3):
d
¼ 59.2 (C-4), 109.3 (C-5), 114.4 (C-3),
3JHH ¼ 2.4 Hz, 1H, H-5), 7.29e7.36 (m, 5H, aromatic), 9.12 (s, 1H,
127.3 (aromatic), 127.8 (aromatic), 128.1 (aromatic), 128.2 (aro-
matic), 128.6 (aromatic), 129.2 (aromatic), 129.4 (aromatic), 129.7
(aromatic), 131.4 (aromatic), 132.4 (aromatic), 137.6 (aromatic),
162.9 (C-2), 191.4 (С ¼ О). Anal. calcd for C23H17NO4: C, 74.38; H,
4.61; N, 3.77. Found: C, 74.44; H, 4.65; N, 3.80.
NH); 13C NMR (101 MHz, CDCl3):
d
¼ 14.3 (Me), 30.9 (Me), 115.7 (C-
5), 120.8 (C-4), 126.8 (aromatic), 126.9 (C-3), 128.3 (aromatic), 129.6
(aromatic), 135.7 (C-2), 136.9 (aromatic), 197.7 (C]O). Anal. calcd
for C13H13NO: C, 78.36; H, 6.58; N, 7.03. Found: C, 78.41; H, 6.63; N,
7.15.
4.3.1.9. (Adamantan-1-yl)[(4S,5R)-2-methyl-5-nitro-4-(5-
Declaration of competing interest
bromofuran-2-yl)-4,5-dihydrofuran-3-yl]methanone
(5i). Yield:
0.21 g (50%), yellow oil [mixture of diastereomers dr 9.0:1.0], 84% ee
(4S;5R). HPLC analysis (CHIRALPAK AD-3 column; hexane/2-
propanol, 97:3; flow rate 1.2 mL/min; wavelength 210 nm):
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
1
20
tR ¼ 12.2 (4S,5R), 17.2 (4R,5S) min. [
a
]
¼ e 47.1 (c 1.0, CHCl3). H
D
NMR (400 MHz, CDCl3):
d
¼ 1.63e1.80 (m, 6H, Ad), 2.02 (s, 3H, Me),
Acknowledgments
2.04 (s, 3H, Ad), 2.11 (s, 6H, Ad), 4.74 (s, 1H, H-4), 5.75 (s, 1H, H-5),
3
3
6.17 (d, JHH ¼ 3.2 Hz, 1H, aromatic), 6.29 (d, JHH ¼ 3.2 Hz, 1H, ar-
The authors gratefully acknowledge the support of this work by
the Russian Science Foundation (project 18-13-00447), Russia.
Spectral and chromatographic analysis was performed by joint use
center « Research of physical and chemical properties of substances
and materials» with financial support of the Russian Ministry of
Science and Higher Education for a basic part of a research (project
omatic); 13C NMR (101 MHz, CDCl3):
d
¼ 28.1 (Ad), 30.7 (Me), 36.4
(Ad), 37.4 (Ad), 37.6 (Ad), 51.3 (C-4), 105.6 (C-5), 109.9 (C-3), 111.3
(aromatic), 112.7 (aromatic), 123.2 (aromatic, CBr), 151.9 (aromatic),
176.1 (С-2), 192.9 (С ¼ О). Anal. calcd for C20H22BrNO5: C, 55.06; H,
5.08; N, 3.21. Found: C, 55.10; H, 5.12; N, 3.25.
9

D.S. Nikerov, M.A. Ashatkina, V.A. Shiryaev et al.
Tetrahedron 84 (2021) 132029
(f) F.-L. Hu, Y. Wei, M. Shi, Chem. Commun. 50 (2014) 8912, https://doi.org/
10.1039/C4CC03479A;
(g) F.-L. Zhu, Y.-H. Wang, D.-Y. Zhang, J. Xu, X.-P. Hu, Angew. Chem. Int. Ed. 53
(2014) 10223, https://doi.org/10.1002/anie.201405857;
(h) Y. Zhou, F.-L. Zhu, Z.-T. Liu, X.-M. Zhou, X.-P. Hu, Org. Lett. 18 (2016) 2734,
https://doi.org/10.1021/acs.orglett.6b01192;
0778-2020-0005), Russia. The X-ray studies were fulfilled using a
STOE STADI VARI PILATUS-100K diffractometer purchased by MSU
Development Program.
Appendix A. Supplementary data
(i) Y. Cheng, Y. Han, P. Li, Org. Lett. 19 (2017) 4774, https://doi.org/10.1021/
acs.orglett.7b02144.
[14] (a) M.A. Calter, C. Zhu, Org. Lett.
ol0169978;
4 (2002) 205, https://doi.org/10.1021/
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tet.2021.132029.
(b) M.A. Calter, C. Zhu, R.J. Lachicotte, Org. Lett. 4 (2002) 209, https://doi.org/
10.1021/ol0169980;
(c) M.A. Calter, R.M. Phillips, C. Flaschenriem, J. Am. Chem. Soc. 127 (2005)
14566, https://doi.org/10.1021/ja055752d;
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