Reactions of 3-nitro- and 3-bromo-3-nitroacrylates with 1,3-cyclohexadiene

Full text of DOI:10.1134/S1070363212120213

ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 12, pp. 2013–2016. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © N.A. Anisimova, A.A. Kuzhaeva, G.A. Berkova, V.M. Berestovitskaya, 2012, published in Zhurnal Obshchei Khimii, 2012, Vol. 82,
No. 12, pp. 2061–2064.
LETTERS
TO THE EDITOR
Reactions of 3-Nitro- and 3-Bromo-3-nitroacrylates
with 1,3-Cyclohexadiene
N. A. Anisimova, A. A. Kuzhaeva, G. A. Berkova, and V. M. Berestovitskaya
Herzen Russian State Pedagogical University, Moika emb. 48, St. Petersburg, 191186 Russia
e-mail: kohrgpu@yandex.ru
Received July 27, 2012
DOI: 10.1134/S1070363212120213
Nitroacrylates and their derivatives are known to be
active dienophiles in the Diels–Alder reaction with
acyclic [1, 2] and cyclic {cyclopentadiene [3, 4], furan
[5, 6], β-furylnitroethene [7], β-(2-nitrovinyl)indole
[8]} 1,3-dienes. In this work we investigate the
reaction of the nitro- and gem-bromonitroacrylates I, II
with 1,3-cyclohexadiene. The study of these reactions
is of interest for the development of convenient
methods of the synthesis of functionalized bicycle-
octenes, which are important intermediates in the syn-
thesis of fragments of the natural compounds (hor-
mones, vitamin D3, etc.) [1, 9].
a quantitative yield [3, 4]. In contrast to cyclo-
pentadiene the reaction of 1,3-cyclohexadiene occurs
in more rigid conditions (boiling the reaction mixture
in benzene for 36 h) and results in a mixture of endo-
and exo-isomers of ethyl 3-nitrobicyclo[2.2.2]-5-octen-
2-ylcarboxylate IIIa, IIIb in 87% yield. The endo-
isomer IIIa was isolated in pure form by the repeated
chromatography of the bicyclooctene isomers mixture.
Bromonitroacrylate II reacts with cyclohexadiene
under similar conditions (benzene, 80°C, 40 h) to
afford a mixture of the difficultly separable products,
from which by the column chromatography the endo-
IVa and exo-IVb isomers of ethyl 3-bromo-3-nitro-
bicyclo[2.2.2]-5-octen-2-ylcarboxylate in the ratio of
6:1 with an overall yield of 45%, and the products of
Cyclopentadiene is known to react with nitro-
acrylate I at 0°C to give a mixture of endo- and exo-
diastereomers of the corresponding nitronorbornene in
7
7
COOEt
H
COOEt
H
C6H6, 80oC
8
8
1
1
+
+
6
COOEt
NO2
6
2
2
36−40 h
4
H
X
4
3
3
O2N
X
5
5
I, II
NO2
endo-
IIIa, IVa
X
exo-
IIIb, IVb
−HBr
7
6
8
1
1
2
COOEt
NO2
COOEt
5
6
2
4
4
3
5
3
NO2
VI
V
X = H (I, IIIa, IIIb), Br (II, IVa, IVb).
2013

2014
ANISIMOVA et al.
their intramolecular transformations: ethyl 3-nitro-
bicyclo[2.2.2]-2 ,5-octadien-2-ylcarboxylate V and
ethyl 2-nitrophenylcarboxylate VI were isolated.
stereomers endo-(NO2)-IIIa, IVa and exo-(NO2)-IIIb,
IVb.
In accordance with [17, 18], the criteria used to
determine the stereochemical nature of the bicyclic
systems (norbornenes) were applied to bicyclooctenes.
One of the criteria for the substituted bicyclooctenes
can be a difference between the chemical shifts of the
ring С5Н and С6Н protons. In the endo-isomer a
difference between the chemical shifts of these protons
is greater due to the steric closeness with the
substituent on the rear part of the molecule (in this
case, NO2-group). In the exo-isomer the effect of a
nitro group is weakened, and the chemical shifts of the
olefinic protons differ less that can be seen by
comparing the corresponding parameters of the endo-
and exo-isomers of bicyclooctenes IIIa, IVa and IIIb,
IVb. So, for these compounds the С5Н and С6Н
protons signals are close for exo-isomers IIIb, IVb (Δδ
0.15–0.20 ppm) and are separated from each other for
endo-isomers IIIa, IVa (Δδ 0.45–0.48 ppm). For
example, in the spectrum of endo-IIIa with the signals
of the protons at 5.98 (H5) and 5.50 ppm (H6) Δδ is
0.48 ppm, and in the spectrum of exo-IIIb this value is
Δδ 0.15 ppm [5.85 (H5) and 5.70 ppm (H6)].
According to this parameter (Δδ 0.48 ppm), the stereo-
homogeneous nitrobicyclooctenylcarboxylate IIIa is of
the endo-configuration. Analyzing the integral in-
tensities of the non-overlapping signals of the olefinic
protons at 5.50–5.98 ppm and the upfield signals of the
The lower yield of bicyclooctene IV (45%)
compared to bicyclooctene III (87%) seems to
originate from a greater steric strain of the unsaturated
bicyclic system with three electron-withdrawing groups
(COOR, NO2, Br) and from a greater susceptibility of
IV to intramolecular transformations under the rigid
conditions. The presence of a good leaving nucleofuge
halogen atom gem-positioned relative to the nitro
group and the labile hydrogen atom at the COOR
function obviously contributes to the dehydrohalo-
genation process and to the formation of the cor-
responding bicyclooctadiene V. The possibility of
producing the substituted bicyclooctadienes from the
diene synthesis adducts have been discussed by us [10]
and other authors [11, 12] for the condensation of 1,3-
cyclohexadiene with various dienophiles. The
instability of V is, probably, due to a forced cis
location of the ester and nitro groups at the C=C bond
(steric factor) [13]. As a result, the ethane bridge
destruction and the formation of aromatic structure VI
occurs. The presence of compound VI in the reaction
mixture is confirmed by the presence of the charac-
teristic signals of aromatic protons at 7.70–8.80 ppm in
the 1H NMR spectrum.
The formation of aromatic products in a significant
yield (80–92%) in the Diels–Alder reaction involving
1,3-cyclohexadiene was also observed by other authors
[12, 14, 15], for example, in the case of the reaction of
cyclohexadiene with acetylenic dienophiles or β-halo-
nitroalkenes [10]. The formation of the benzene ring
Petrzilka et al. [11] and Wolinsky et al. [12] associated
with the bridge destruction in the intermediate
bicyclooctadiene by removing ethylene.
1
bridge protons at 1.10–2.22 ppm in the H NMR
spectra of a mixture of compounds IVa and IVb, it is
possible to conclude that the ratios of the endo/exo-
stereoisomers IIIа:IIIb and IVа:IVb equal 5:1 and
6:1, respectively.
1
The H NMR spectrum of compound VI contains
the signals of aromatic protons in the range of 6–9 ppm
[19, 20]. The signal at 8.20 ppm belongs to the С6Н
proton. The C3H proton experiencing the greatest
impact from an electron-withdrawing nitro group
resonates in a weaker field at 8.80 ppm. The signals of
the С4Н and С5Н protons appear at 7.75 and 7.70 ppm,
respectively, which is consistent with the spectra of the
structurally similar compounds [10, 21].
Bicyclooctadiene V we detected only spectrally. In
1
the H NMR spectra there are multiplets of the С1Н
and С4Н protons at 3.40 and 3.55 ppm, respectively.
They are regularly observed in a weaker field
compared with those of the original bicyclooctene IV.
The structure of nitrobicyclooctenes IIIa, IVa,
IVb, and arene VI was established by the NMR spec-
tra analysis and their comparison with the cor-
responding parameters of the structuraly similar
compounds described in the literature [10, 16]. In the
1H NMR spectra of bicyclooctenes III, IV there are a
doubling of the signals of all the ring protons, which
indicates the existence of a mixture of two dia-
Ethyl 3-nitrobicyclo[2.2.2]-5-octen-2-ylcarboxy-
lates (IIIa, IIIb). To a solution of 0.72 g (0.005 mol)
of ethyl 3-nitroacrylate I in 5 ml of anhydrous benzene
was added 0.1 g of hydroquinone and 0.47 ml
(0.005 mol) of 1,3-cyclohexadiene. The reaction mix-
ture was boiled for 36 h with the continuous stirring.
After the solvent removal, the residue was chro-
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REACTIONS OF 3-NITRO- AND 3-BROMO-3-NITROACRYLATES
2015
matographed eluting with benzene. Yield 0.73 g
(87%), yellow oily substance, which is a mixture of
endo- and exo-isomers in a ratio of 5:1, Rf 0.62, 0.65.
1Н NMR spectrum, δ, ppm: IIIа, 2.32–2.37 m (1Н,
Н1), 3.33–3.36 m (1Н, Н2), 5.02–5.07 m (1Н, Н3),
3.38–3.44 m (1Н, Н4), 5.96–5.99 m (1Н, Н5), 5.48–
5.52 m (1Н, Н6), 1.20–1.40 m (2Н, СН27), 1.60–1.80 m
(2Н, СН28), 1.30–1.38 m (3Н, СН3), 4.15–4.34 m (2Н,
ОСН2); IIIb, 2.50–2.55 m (1Н, Н1), 3.68–3.72 m (1Н,
Н2), 4.82–4.88 m (1Н, Н3), 3.63–3.68 m (1Н, Н4),
5.83–5.86 m (1Н, Н5), 5.68–5.71 m (1Н, Н6), 1.10–
1.20 m (2Н, СН27), 1.60–1.80 m (2Н, СН28), 1.15–1.34
m (3Н, СН3), 4.10–4.28 m (2Н, ОСН2). Found, %: С
58.60, 58.71; Н 6.71, 6.74; N 6.26, 6.27. C11H15NO4.
Calculated, %: С 58.67; Н 6.67; N 6.22.
(2Н, СН27), 2.07–2.15 m (2Н, СН28), 1.20–1.42 m (3Н,
СН3), 4.10–4.38 m (2Н, ОСН2). Found, %: С 43.47,
43.48; Н 4.63, 4.66; N 4.58, 4.62. C11H14BrNO4.
Calculated, %: С 43.42; Н 4.61; N 4.61.
The IR spectra were registered on an InfraLUM FT
02 instrument for the samples in a chloroform solution
1
(c 0.1–0.001 M). The Н NMR spectra were recorded
on a Bruker АС-200 instrument (200 MHz) in CDCl3
relative to external HMDS with accuracy up to ±0.5 Hz.
The purification and isolation of the individual
substances was performed by the column chromato-
graphy on silica gel Chemapol 100/200 or on alumina
using a Trappe series of the solvents [22]. The
individuality of the substances obtained and the reac-
tion progress were monitored by the thin layer chro-
matography (TLC) on Silufol-254 plates eluting with a
hexane–acetone mixture (3:1) and detecting with
iodine vapor. The starting nitro- and gem-bromo-
nitroacrylates I, II were prepared as in [23, 24].
The endo-isomer IIIa was isolated individually by
the repeated chromatography of the mixture in a yield
of 65% (eluent chloroform). IR spectrum, ν, cm–1:
1379, 1575 (NO2), 1735 (C=O), 1045, 1195 (C–O–C).
Found, %: N 6.20, 6.22. C11H15NO4. Calculated, %: N
6.22.
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