Synthesis and structure of nitrocyclohexenylcarboxylates

Article abstract of DOI:10.1134/S1070363211090180

The diene condensation of 3-nitro- and 3-bromo-3-nitroacrylates with 2,3-dimethyl-1,3-butadiene and isoprene obtained under the reaction condition from 3-methyl-3-thiolene-1,1-dioxide was investigated. The formed 6-nitro-3-cyclohexenylcarboxylates were subjected to the intramolecular transformation (dehydration and dehydrohalogenation) to give the corresponding nitrocyclohexadienyl- and arylcarboxylates. The structure of the obtained compounds was established from the IR, ¹H NMR spectra and independent synthesis.

Full text of DOI:10.1134/S1070363211090180

ISSN 1070-3632, Russian Journal of General Chemistry, 2011, Vol. 81, No. 9, pp. 1845–1852. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © N.A. Anisimova, A.A. Kuzhaeva, G.A. Berkova, V.M. Berestovitskaya, 2011, published in Zhurnal Obshchei Khimii, 2011, Vol. 81,
No. 9, pp. 1507–1514.
Synthesis and Structure of Nitrocyclohexenylcarboxylates
N. A. Anisimova, A. A. Kuzhaeva, G. A. Berkova, and V. M. Berestovitskaya
Herzen Russian State Pedagogical University, nab. r. Moiki 48, St. Petersburg, 191186 Russia
e-mail: kohrgpu@yandex.ru
Received March 30, 2011
Abstract—The diene condensation of 3-nitro- and 3-bromo-3-nitroacrylates with 2,3-dimethyl-1,3-butadiene
and isoprene obtained under the reaction condition from 3-methyl-3-thiolene-1,1-dioxide was investigated. The
formed 6-nitro-3-cyclohexenylcarboxylates were subjected to the intramolecular transformation (dehydration
and dehydrohalogenation) to give the corresponding nitrocyclohexadienyl- and arylcarboxylates. The structure
of the obtained compounds was established from the IR, 1H NMR spectra and independent synthesis.
DOI: 10.1134/S1070363211090180
The cyclohexane ring is very common in the nature
as a structural fragment of vitamins, terpenes, hor-
mones, alkaloids, and other practically important
substances [1, 2]. The interest in natural compounds
containing cyclohexene or cyclohexadiene ring is due
to the importance of their functions (enzyme inhibitors
[3, 4]) and the possibility of their use as key
compounds in the synthesis of drugs possessing
anticancer [5], narcotic [6, 7], and antiviral [8, 9]
activity as well as a promising therapeutic means in the
AIDS treatement [10].
(prolonged heating in a pressure reactor) [16, 17]. The
introduction of the second electro-withdrawing
substituent (CO2R, CCl3, SO2Ph) into the β-position of
nitroalkenes regularly makes the reaction conditions
milder [11, 12].
Previously, a 3-nitroacrilate was found to react
successfully with some open-chain [18] and cyclic
dienes [19], as well as with the diene systems of
heterocyclic structure [20–22]. Note that the 3-bromo-
3-nitroacrylate was not introduced into the diene
condensation before our research.
One of convenient and accessible methods of the
synthesis of functionalized cyclohexenes is the Diels–
Alder reaction involving as a dienophile the vicinal
substituted nitroalkenes containing the second easily
modifiable group (CO2R, SO2Ph) [11, 12]. These
dienophiles are used for the synthesis of the bio-
logically active compounds, including natural analgesic
epibatidine [13, 14], morphine derivatives [15], and
conduritols [10].
In this work we studied the reaction of 3-nitro- and
3-bromo-3-nitroacrylates I and II with 2,3-dimethyl-
1,3-butadiene and isoprene. The reaction of the
nitroalkene I with 2,3-dimethyl-1,3-butadiene occurs
in a boiling benzene in 1 h and affords the correspond-
ing 3,4-dimethyl-6-nitro-3-cyclohexen-1-ylcarboxylate
III in 90% yield (Table 1). The reaction of bromo-
nitroalkene II with the same diene proceeds only at
boiling the reaction mixture in benzene for 2 h. Ethyl
4,5-dimethyl-2-nitrophenylcarboxylate V was isolated
along with cyclohexene IV in a low yield (5%).
According to the literature, nitroalkenes enter the
condensation with dienes usually in rigid conditions
O
O
H2
H1
O
CH2
CH2
H3C
H
C
C
H3C
H3C
H3C
H3C
C
C
C
C
C
2
5
6
OC2H5
Δ, C6H6
OC2H5
5
4
OC2H5
3
1
6
1
2
+
+
X
4
3
NO2
NO2
O2N
H3C
X
H2
III, IV
H1
I, II
V
X = H (I, III), Br (II, IV).
1845

1846
ANISIMOVA et al.
Table 1. Yields, Rf, and elemental analysis data for nitrocyclohexenes III, IV, VIa, VIIa, VIIb, nitrocyclohexadienes IX, XI,
XVI, XVII, and nitroarenes V, XII, XIII
Found, %
H
Calculated, %
Yield,
%
Comp. no.
Rf
Formula
C11H17NO4
C11H16BrNO4
C11H13NO4
C10H15NO4
C10H14BrNO4
C10H13NO4
C10H11NO4
C11H15NO4
C
N
C
H
N
90
91
25
33
62
6
0.33
0.48
0.29
0.43
58.01
58.06
43.16
43.19
59.21
59.24
56.36
56.39
41.13
41.15
56.88
56.91
57.45
57.49
58.69
58.71
7.07
7.09
5.28
5.30
5.85
5.88
7.06
7.09
4.81
4.84
6.19
6.21
5.30
5.35
6.65
6.69
6.04
6.12
4.61
4.65
6.30
6.35
6.61
6.63
4.83
4.84
6.67
6.70
6.65
6.68
6.30
6.35
58.15
7.49
6.17
III
IV
V
43.14
59.19
56.34
41.10
56.87
57.42
58.67
5.23
5.83
7.04
4.79
6.16
5.26
6.67
4.58
6.28
6.57
4.79
6.64
6.70
6.22
VIa
0.38
0.45
0.37
0.45
0.39
0.48
0.18
0.24
VIIа,
VIIb
IX,
XI
12
30
XII,
XIII
XVI,
XVII
The condensation of nitroalkenes I and II with 3-
methyl-3-thiolene-1,1-dioxide was carried out under
more rigid conditions (reflux for 13 h in p-xylene) due
to preliminary desulfonylation of the reagent and
isoprene formation in situ directly under the reaction
conditions. According to the literature [11, 12, 23], the
reaction of nitroalkenes with asymmetric 1,3-dienes
affords the regioisomeric cyclohexenes. In the
simultaneous presence of nitro- and an other electron-
withdrawing groups (SO2Ph, C≡N, CO2R) in the
dienophile it is the nitro moiety that defines the cyclo-
addition regioselectivity. This fact was also observed
O
O
O
C
O
C
C1
Me
H''
H''
H'
H'
OEt
H
OEt
C
2
OEt
OEt
Me
2
2
5
H2C
C
C
3
4
Δ , п-xelene
3
4
1
6
1
6
+
+
X
+
X
CH3
5
S
O2
Me
NO2
NO2
X
O2N
H''
O2N
H'
H'
X
H''
I, II
XIV, XV
1,4-VIa, VIIa
1,3-VIb, VIIb
O
C
O
O
Me
Me
Me
OEt
C
OEt
C OEt
6
3
6
6
1
2
5
4
1
2
5
4
5
4
1
2
3
3
NO2
NO2
NO2
1,4-VIII
1,3-Х
1,4-IX
1,3-XI
1,4-XII
1,3-XIII
X = H (I, VIа, VIb, XIV), Br (II, VIIа, VIIb, XV).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 9 2011

1847
SYNTHESIS AND STRUCTURE OF NITROCYCLOHEXENYLCARBOXYLATES
in our case [24]. Isoprene formed in situ reacts with
nitroalkenes I and II to form a mixture of regioisomers
VIa, VIb and VIIa, VIIb with the methyl substituents
in the 3 and 4 positions of the cyclohexene ring with
respect to the nitro group. The yields of cyclohexenes
VIa, VIb and VIIa, VIIb were 52 and 62%,
respectively.
The structure of the obtained nitrocyclohexenes III,
IV, VIa, VIb, VIIa, VIIb was established from the IR
and 1H NMR spectra (Table 2), as well as by
comparing their spectral characteristics with those in
the spectra of the structurally similar compounds
described in [18, 24, 26].
The IR spectra of nitrocyclohexenes III, IV, VIa,
VIb and VIIa, VIIb contain the characteristic bands of
all functional groups. The ester group vibrations
appear as strong bands in the regions of 1735–1745
(C=O), 1025–1030, and 1090–1195 cm–1 (C–O–C).
The two bands of moderate and high intensity
correspond to the symmetric (1350–1340 cm–1) and
antisymmetric (1570–1560 cm–1) vibrations of the
nitro groups. A weak band at 1620 cm–1 in the spectra
of compounds VIa, VIb and VIIa, VIIb corresponds
to the double bond of the cyclohexene ring. This band
is absent in the spectra of compounds III, IV with the
symmetrically substituted C=C bond.
The formation of regioisomeric cyclohexenes VIa,
VIb and VIIa, VIIb is confirmed by the double set of
1
signals of the ring and methyl protons in the H NMR
spectra. The ratio of 1,4- (VIa, VIIa) and 1,3-isomers
1
(VIb, VIIb) was determined from the the H NMR
spectra: VIa:VIb = 4:1, VIIa: VIIb = 3:1. Only the
1,4-isomer VIa was individually isolated by the
column chromatography (Table 1).
The rigid conditions of the isoprene condensation
with nitroalkenes I and II promote further intramole-
cular transformation of the formed nitrocyclohexenes
1
VIa, VIb and VIIa, VIIb. In the H NMR spectra of
1
the reaction mixtures along with the signals of
compounds VIa, VIb and VIIa, VIIb, there are the
proton signals of the conjugated and nonconjugated
cyclohexadienes and substituted benzenes. The
reaction is complicated because each nitrocyclohexene
regioisomer suffers intramolecular transformations,
hence, 1,4- and 1,3-isomers each react to form a pairs
of the corresponding nitrocyclohexadienes and
nitroarenes, respectively. The reaction of nitroalkene I
with isoprene formed from 3-methyl-3-thiolene-1,1-
dioxide affords not only nitrocyclohexenes VIa and
VIb, but also the dehydration and aromatization
products: 1,4 - and 2,4-cyclohexadienes VIII–XI and
2-nitrophenylcarboxylates XII and XIII, respectively.
According to the H NMR spectroscopy (Table 2),
compounds III, IV, VI, VII are sterically uniform. The
formation of two 1,4- (VIa, VIIa) and 1,3-
regioisomers (VIb, VIIb) is proved by a double set of
the methyl group signals at 1.70 and 1.88 ppm (VIa,
VIb), 1.70 and 1.72 ppm (VIIa, VIIb), and of cyclic
protons H1 at 3.21 and 3.50 ppm (VIa, VIIa), 3.29 and
3.70 ppm (VIb, VIIb) and H6 at 4.88 (VIa) and
4.70 ppm (VIb). The methylene protons at the atom C2
in the spectra of nitrocyclohexenes III, IV, VIa, VIb
and VIIa, VIIb appear as multiplets at 2.10–2.65 ppm.
Owing to the effect of NO2-group, the signals of
methylene protons H5 are shifted downfield (2.32–
3.45 ppm) in comparison with the signals of H2 (2.10–
2.65 ppm). The chemical shift values are close to those
in the published spectra of analogs [12, 24].
The formation of the conjugated and nonconjugated
cyclohexadienes VIII, IX and X, XI, and the
substituted benzenes XII and XIII in the case of the
reaction of nitroalkenes I, II with 2,3-dimethyl-1,3-
butadiene and isoprene can be described as the
simultaneous or successive processes of dehydrohalo-
genation and dehydrogenation.
The presence of the bromine atom at the gem-
position to the NO2 group in the molecules of
compounds IV, VIIa, and VIIb causes a downfield
shift of the methylene protons (H2, H5) signals at 0.23
and 0.65 ppm, respectively. The methyne protons H1
give rise in the spectra of compounds III, VIa, VIb to
a multiplet in the range of 3.05–3.29 ppm. In the case
of the compounds IV, VIIa, VIIb this signal is shifted
downfield to 3.50–3.70 due to the influence of the
bromine atom. A multiplet at 4.70–4.88 ppm in the
spectra of compounds III, VIa, and VIb belongs to the
methine proton H6. The signals of the ring olefin
protons in the spectra of compounds VIa, VIb, VIIa,
VIIb appear at 5.39 and 5.45 ppm (H3), 5.65 and
In addition to the compounds mentioned above, β-
nitro- and β-bromo-β-nitropropanoate XIV, XV were
isolated from the reaction mixture, whose formation
can result from the hydrogenation of the carbon-carbon
double bond of nitroalkenes I, II unreacted or formed
in a retrodiene process. A similar example of the
nitroalkenes hydrogenation with
a
hydrogen
eliminating from the formed reaction product was
noted in [24, 25].
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 9 2011

1848
ANISIMOVA et al.
Table 2. 1Н NMR spectral parameters for nitrocyclohexenylcarboxylates III, IV, VIa, VIb, VIIa, VIIb
δ, ppm (CDCl3), J (Hz)
Comp.
C2H
C5H
СO2Et
OCH2
С3Н
С4Н
H1
H6
no.
H2'
H2''
H5'
H5''
Mе
(СН3)
(СН3)
(1.52 s)
1.52 s
2.30
2.10 m
2.55
2.32
3.05
4.70
4.25 q
1.30 t
III
JH1 2' 5.1
J H1 2'' 12.0
JH6 5' 9.5
JH6 5'' 7.0
JH1 2' 5.1
JH5' 6 9.5
H
H
H
H
H
H
JH2' 2'' 13.6
JH5' 5'' 14.0
JH1 2'' 12.0
JH5'' 6 7.0
H
H
H
H
JH1 6 10.2
Н
(1.68 s)
(1.70 s)
1.68 s
5.65
2.65
2.36
3.25
3.04
3.70 d.d
–
4.19 q
4.16 q
1.32 t
1.24 t
IV
JH1 2' 6.25
JH1 2' 8.75
JH5' 5'' 18.0
JH1 2' 6.25
H
H
H
H
2.25
2.21
2.80
2.70
3.21
4.88
VIа
JH4 5' 1.2
JH1 2' 5.9
JH1 2' 9. 5
JH5' 6 11.5 JH5'' 6 6.6
JH1 2' 5.9
JH6 5' 11.5
H
H
H
H
H
H
H
JH4 5'' 1.0
JH2' 2' 13.5
JH5' 4 1.2
JH5'' 4 1.0
JH1 2'' 9.5
JH6 5' 6.6
H
H
H
H
H
H
JH5' 5'' 16.0
JH1 6 10.0
H
H
5.39
(1.88 s)
2.42
2.38
2.50
JH5' 6 8.0
2.41
3.29
4.70
4.32 q
1.36 t
VIb
JH3 2' 1.6
JH1 2' 6.4
JH1 2'' 7.0
JH5'' 6 7.3
JH1 2' 6.4
JH6 5 8.0
H
H
H
H
H
H
JH3 2'' 1.2
JH2' 2'' 16.0
JH5' 5'' 10.0
JH1 2'' 7.0
JH6 5'' 7.3
H
H
H
H
H
JH1 6 12.8
H
(1.70 s)
5.45
5.70
2.58 m
2.65 m
3.45 m
3.35 m
3.50 m
3.70 m
–
–
4.35 q
4.30 q
1.25 t
1.27 t
VIIа
(1.72 s)
VIIb
5.70 ppm (H4). Depending on the compound structure
the signals of methyl groups are differently located in
the spectrum. For example, the methyl group signals in
the spectra of compounds III and IV containing two
methyl substituents are shifted more upfield (chemical
shifts 1.52 and 1.68 ppm), compared with the
compounds VIa, VIb and VIIa, VIIb containing only
one methyl substituent (1.70–1.88 ppm).
ring we have considered the spin-spin coupling constant
of the vicinal protons H1 and H6. For the studied com-
pounds its value lies in the range of 3J1,6 10.0–12.8 Hz
(Table 2), which corresponds to the dihedral angle
between the vicinal protons (~180°C) or axial arrange-
ment of vicinal protons [27, 28]. Consequently, the
molecules of the compounds III, VIa, VIb contain a
six-membered ring in a semi-chair form with the
equatorial location of the bulky substituents (NO2 and
CO2C2H5) and anti-orientation of the vicinal protons
along the C1–C6 bond, as shows the Newman
projection.
To reveal the relative position of the nitro and ester
groups in the nitrocyclohexenylcarboxylate molecule
and conformational characteristics of the six-membered
O
H
H6
6
H
O2N
H
C2H5O
C
5
H
H
(3)
4
(1)
4
3
5
2
H
6
2
1
O2N
H
COC2H5
H1
H
O
To determine the structure of nitrocyclohexadienyl-
and nitroarylcarboxylates isolated from the products
mixture obtained by the Diels–Alder reaction an
attempt was made of their synthesis directly from the
bromonitrocyclohexene IV by the dehydrohalogena-
tion. The halonitrocyclohexene IV was found to
eliminate HBr already at boiling in benzene and to
convert into a mixture of the nitro-containing 1,4 - and
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 9 2011

1849
SYNTHESIS AND STRUCTURE OF NITROCYCLOHEXENYLCARBOXYLATES
1
Table 3. Н NMR spectral parameters for nitrocyclohexadienylcarboxylates VIII–XI, XVI, XVII and nitroarylcarboxylates
V, XII, XIII
δ, ppm (CDCl3), J (Hz)
Comp. no.
С1Н
С3Н
С4Н, (СН3)
С5Н, (СН3)
С6Н
OCH2
СН3
Nitrocyclohexadienes
–
2.40 m
8.00 m
2.30 m
7.92
5.50 m
7.35 m
(2.30 s)
(2.40 s)
(1.75 s)
(2.35 s)
(1.70 s)
2.35 m
2.45 m
2.40 m
2.50 m
2.10 m
2.80 m
4.20 q
4.20 q
4.30 q
4.30 q
4.15 q
4.25 q
1.30 t
1.30 t
1.30 t
1.30 t
1.30 t
1.30 t
VIII
IX
3.25 m
–
(1.75 s)
5.30 m
7.45 m
(1.70 s)
(2.28 s)
X
3.25 m
–
XI
2.28 m
7.50 m
XVI
XVII
3.45 m
Nitroarenes
–
–
–
7.70 s
8.20 m
8.15 m
(2.38 s)
7.15 m
(2.45 s)
(2.35 s)
(2.20 s)
7.25
7.50 m
6.50 m
6.70 m
4.36 q
4.40 q
4.40 q
1.34 t
1.40 t
1.40 t
V
XII
XIII
2,4-cyclohexadienes XVI and XVII and aromatic
derivative V. The dehydrohalogenation of bromonitro-
cyclohexene IV in the presence of triethylamine leads
to the formation of nitroarene V in a 62% yield.
Me
CO2Et
CO2Et
Me
Me
CO2Et
Br
Me
CO2Et
N(C2H5)3
_HBr
+
+
NO2
Me
Me
Me
NO2
Me
NO2
NO2
V
IV
XVI
XVII
The structure of the synthesized nitroaromatic
compounds V, XII, XIII was established on the basis
of the spectral characteristics in comparison with the
The assignement of nitrocyclohexadienylcarbo-
xylates to the conjugate (IX, XI, XVII) and
nonconjugated (VIII, X, XVI) systems were carried
out on the basis of analysis of their 1H NMR spectra, as
well as by comparison with the corresponding
characteristics of the model nitrocyclohexadienes [12].
For the nonconjugated cyclohexadienes VIII, X, XVI
the 1H NMR spectrum is characteristed by the presence
of the methylene protons signals at the atoms C3, C6
(2.10–2.40 ppm) and of the olefin protons of the
isolated C=C bond at 5.30–5.50 ppm. This is
consistent with the corresponding parameters of the
structurally identical compounds [12, 29] (Table 3).
The presence of two conjugated C=C bonds in the six-
membered ring causes a downfield shift of the signals
of methylene and olefin protons compared with those
of the similar protons in the corresponding initial
cyclohexenes and nonconjugated cyclohexadienes.
1
structurally identical compounds [24]. In the H NMR
spectra of these compounds the proton signal of C6H is
observed in the range of 6.50–7.50 ppm, and the signal
of the C3H proton is shifted downfield (~7.70–
8.20 ppm) due to the effect of an electron-withdrawing
nitro group (Table 3).
The IR spectra of nitroarylcarboxylates V, XII,
XIII contain characteristic absorption bands
corresponding to the functional groups present in the
molecule: to the ester group belong three bands in the
range of 1745–1750 (νC=O), 1025–1035 and 1055–
1110 cm–1 (νC–O–C), and two bands at 1550–1560 and
1360–1380 cm–1 correspond to the conjugated nitro
groups.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 81 No. 9 2011

1850
ANISIMOVA et al.
Thus, in the 1H NMR spectrum of cyclohexadienes IX,
XI and XVII the olefin proton at C3H appears at 7.50–
8.00 ppm, the signals of the methylene and ring
protons appear at 2.45–2.80 ppm (Table 3).
EXPERIMENTAL
The IR spectra were obtained on an Infralum FT-02
spectrometer (chloroform, c 0.1–0.001 M). The H
NMR spectra were registered on a Bruker AC-200
spectrometer (200 MHz) from solutions in CDCl3. The
chemical shifts were determined relative to external
standard (HMDS) accurate to ±0.5 Hz.
1
An important criterion in the structural analysis of
the compounds is the value of chemical shift of the
methyl protons. The signal of the CH3 groups at C=C
bond in the nonconjugated dienes VIII, X, XVI has
chemical shift in the range of 1.70–1.75 ppm. In the
spectra of the conjugated (IX, XI, XVII) and aromatic
(V, XII, XIII) structures it is shifted downfield (2.20–
2.45 ppm).
The individual compounds were isolated by the
column chromatography on a Chemapol 100\200 silica
gel and aluminum oxide. The compounds individuality
and the reaction progress were monitored by the TLC
on Silufol-254 plates in hexane–acetone mixture (3:2)
detecting with iodine vapor. The compounds ratio was
The 1,4- and 1,3-isomers of methylnitrocyclo-
hexadienes were identified by considering the methyl
groups signal. The downfield signal δ(CH3) 2.30–
2.40 ppm corresponds to the mutual location of the
methyl and nitro groups in the 1,3-isomers (X, XI). In
the spectrum of 1,4-isomers (VIII, IX) the methyl
group signal appears in a stronger field (1.70–
1.75 ppm) due to the weaker electron-withdrawing
effect of the nitro group.
1
determined by the H NMR spectroscopy after the
column chromatography.
The starting nitro- and gem-bromonitroacrylates I
and II were prepared according to the procedures
[33, 34], respectively.
Ethyl 3,4-dimethyl-6-nitro-3-cyclohexen-1-ylcar-
boxylate (III). To a solution of 0.86 g of ethyl 3-nitro-
acrylate I in 5 ml of benzene was added 0.1 g of
hydroquinone and 1.1 ml of 2,3-dimethyl-1,3-buta-
diene. The reaction mixture was boiled for 1 h. The
solvent was removed on a rotary evaporator, and the
residue was chromatographed on alumina. From the
fraction eluted with carbon tetrachloride was isolated
1.22 g (90%) of compound III as a yellow oil, Rf 0.33.
The spectral (IR and 1H NMR) characteristics of β-
nitro- and β-bromo-β-nitropropanoates XIV, XV
1
conform fully the proposed structures. Thus, in the H
NMR spectrum of compound XIV the methylene
protons appear at 4.50 (C2H2) and 4.80 ppm (C3H2).
The presence of Br atom in compound XV contributes
to the downfield shift of the signals of C3H2. The
signals appear at 4.85 ppm, and the methine proton
C3H resonates at 5.20 ppm
Ethyl
6-bromo-3,4-dimethyl-6-nitro-3-cyclo-
hexen-1-ylcarboxylate (IV), ethyl 4,5-dimethyl-2-
nitrophenylcarboxylate (V). To a solution of 0.8 g of
ethyl 3-bromo-3-nitroacrylate II in 5 ml of benzene
was added 0.1 g of hydroquinone and 0.84 ml of 2,3-
dimethyl-1,3-butadiene in 1 ml of benzene. The
reaction mixture was boiled for 2 h. The solvent was
removed on a rotary evaporator, and the residue was
chromatographed on alumina. From the fraction eluted
with carbon tetrachloride was isolated 1.0 g (91%) of
compound IV as a yellow oil, Rf 0.48. From the
fraction eluted with benzene was obtained 0.05 g (5%)
of compound V, Rf 0.29.
Thus, as a result of our study the reaction
conditions of 3-nitro- and 3-bromo-3-nitroacrylates
with 2,3-dimethyl-1,3-butadiene, as well as with 3-
methyl-3-thiolene-1,1-dioxide,
a
source of the
synthetic 1,3-alkadiene, were found. The nitro- and
gem-bromonitrocyclohexenes are shown to exhibit an
increased tendency to the intramolecular trans-
formations under the conditions of their synthesis
(dehydrobromination, dehydrogenation, aromatization).
The largest mobility is characteristic of the bromine-
containing nitrocycloalkenylcarboxylates.
Ethyl 3(4)-methyl-6-nitro-3-cyclohexen-1-yl-car-
boxylate (VIa, VIb), ethyl 5(4)-methyl-2-nitro-1,4-
cyclohexadien-1-ylcarboxylates (VIII, X), ethyl-
5(4)-methyl-2-nitro-2,4-cyclohexadien-1-ylcarboxy-
lates (IX, XI), ethyl 5(4)-methyl-2-nitrophenyl-
carboxylates (XII, XIII), ethyl 3-nitropropanoate
(XIV). To a solution of 0.8 g of ethyl 3-nitroacrylate I
in 5 ml of p-xylene was added 0.1 g of hydroquinone
The Diels–Alder reaction involving 3-nitroacrylates
and acyclic 1,3-alkadienes can be considered as an
accessible preparative method for the synthesis of
nitrocyclohexenylcarboxylates, the nitro precursors of
the potentially biologically active compounds and, in
particular, cyclohexane β-amino acids [30–32].
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1851
SYNTHESIS AND STRUCTURE OF NITROCYCLOHEXENYLCARBOXYLATES
1
and 1.46 g of 3-methyl-3-thiolene-1,1-dioxide. The
reaction mixture was boiled for 13 h. The solvent was
removed on a rotary evaporator, and the residual oil
was chromatographed on a silica gel. From the fraction
eluted with benzene was obtained 0.12 g of a yellow
oil as a mixture of compounds VIII–XI in a 2:1:2:1
ratio. From the first chloroform portion (~100 ml) was
obtained 0.25 g of a yellow oil as a mixture of
compounds IX, XI, XIV in a 3:2:2 ratio. From the
second chloroform portion (~150 ml) was obtained
0.61 g (52%) of a yellow oil as a mixture of
compounds VIa and VIb in a 2:1 ratio, Rf 0.43, 0.33.
The compounds VIII–XI were registered spectrally.
1030, 1080 (С–O–C). H NMR spectrum (CDCl3), δ,
ppm: 4.85 m (2Н, СН2СО2R), 5.20 m (1Н, CHNO2),
4.20 q (2Н, ОСН2), 1.18 t (3Н, СН3). Found, %: С
26.58, 26.61; Н 3.60, 3.58; N 6.25, 6.28. С5Н8BrNО4.
Calculated, %: С 26.55; Н 3.54; N 6.19.
The repeated chromatographing compounds VIII,
IX, and XI mixture with benzene gave 0.05 g (6%) of
a yellow oil as a mixture of compounds IX and XI in a
3:2 ratio, Rf 0.45, 0.37.
The repeated chromatographing compounds IX,
XII and XIII mixture with benzene gave 0.05 g (7%)
of a mixture of compounds XII and XIII in a 2:1 ratio,
Rf 0.39, 0.48. The spectra of compounds VIII and X
were recorded.
The repeated chromatographing compounds VIa
and VIb mixture with benzene gave 0.39 g (33%) of
compound VIa as an oil, Rf 0.43. From the first ether
portion (~100 ml) was obtained 0.14 g (12%) of a
mixture of compounds XII and XIII in a 2:1 ratio, Rf
0.39, 0.48. From the second ether portion (~150 ml)
was obtained 0.07 g (9%) of compound XIV, Rf 0.42.
IR spectrum (CHCl3), ν, cm–1: 1570, 1375 (NO2), 1740
(С=О), 1030, 1090 (С–O–C). 1H NMR spectrum
(CDCl3), δ, ppm: 4.50 m (2Н, СН2СО2R), 4.80 m (2Н,
CH2NO2), 4.25 q (2Н, ОСН2), 1.15 t (3Н, СН3).
Found, %: С 40.85, 40.89; Н 6.15, 6.16; N 9.58, 9.61.
С5Н9NО4. Calculated, %: С 40.82; Н 6.12; N 9.52.
Ethyl 6-bromo-3,4-dimethyl-6-nitro-3-cyclohexen-
1-ylcarboxylate (IV), ethyl 4,5-dimethyl-2-nitro-
phenylcarboxylate (V), ethyl 4,5-dimethyl-2-nitro-
1,4-cyclohexadien-1-ylcarboxylate (XVI), ethyl 4,5-
dimethyl-2-nitro-2,4-cyclohexadien-1-ylcarboxylate
(XVII). а. To a solution of 0.8 g of ethyl 3-bromo-3-
nitroacrylate II in 5 ml of benzene was added 0.1 g of
hydroquinone and 0.84 ml of 2,3-dimethyl-1,3-
butadiene in 1 ml of benzene. The reaction mixture
was refluxed for 15 h. The solvent was removed on a
rotary evaporator, and the residue was chromato-
graphed on alumina. From the fraction, eluted with
carbon tetrachloride was isolated 0.5 g of a mixture of
compounds IV, XVI and XVII in a 1:2:1 ratio,
respectively, and from the benzene fraction was
obtained 0.9 g of a mixture of compounds V, XVI, and
XVII. The repeated chromatographing compounds IV,
XVI, and XVII mixture gave 0.31 g (30%) of a mixture
of compounds XVI and XVII (eluent – benzene) in a
1:2 ratio, Rf 0.18, 0.24.
Ethyl 6-bromo-3(4)-methyl-6-nitro-3-cyclohexen-
1-ylcarboxylates (VIIа, VIIb), ethyl 5(4)-methyl-2-
nitro-1,4-cyclohexadien-1-ylcarboxylates (VIII, X),
ethyl 5(4)-methyl-2-nitro-2,4-cyclohexadien-1-ylcar-
boxylates (IX, XI), ethyl 5(4)-methyl-2-nitro-
phenylcarboxylates (XII, XIII), ethyl 3-bromo-3-
nitropropanoate (XV). To a solution of 0.8 g of ethyl
3-bromo-3-nitroacrylate II in 5 ml of p-xylene was
added 0.1 g of hydroquinone, 0.48 g of 3-methyl-3-
thiolene-1,1-dioxide, and the reaction mixture was
boiled for 13 h. After removing the solvent, the residue
was chromatographed on a silica gel. From the first
benzene portion (~150 ml) was obtained 0.06 g of a
yellow oil as a mixture of compounds VIII, IX, XI in
a 1:2:1 ratio. From the second benzene portion
(~150 ml) was obtained 0.15 g of a yellow oil as a
mixture of compounds IX, XII, XIII in a 1:2:1 ratio.
From chloroform was obtained 0.65 g (62%) of a
yellow oil as a mixture of compounds VIIa, VIIb in a
3:1 ratio, Rf 0.38, 0.45.
The repeated chromatographing the compounds V,
XVI, and XVII mixture with benzene gave 0.27 g
(25%) of compound V as a yellow oil, Rf 0.29.
b. To a solution of 0.80 g of compound IV in 4 ml
of benzene was added 0.20 ml of triethylamine, and
the reaction mixture was boiled for 20 h. The triethyl-
amine hydrobromide was filtered off. The filtrate was
diluted with 20 ml of benzene and washed with water.
Benzene extract was dried over anhydrous magnesium
sulfate, evaporated, and chromatographed on alumina.
From the benzene fraction was obtained 0.67 g (62%)
of compound V as a yellow oil, Rf 0.29.
From the ether fraction was obtained 0.1 g (12%) of
compound XV as a yellow oil, Rf 0.51. IR spectrum
(CHCl3), ν, cm–1: 1560, 1370 (NO2), 1735 (С=О),
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1852
ANISIMOVA et al.
19. Barco, A., Benetti, S., Pollini, G., Spalluto, G., and
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