Reaction products of methyl tricyclo[4.1.0.02,7]heptane-1- carboxylate and tricyclo[4.1.0.02,7]hept-1-yl phenyl sulfone with dinitrogen tetraoxide

Article abstract of DOI:10.1134/S1070428008040076

The reaction of methyl tricyclo[4.1.0.0^2,7]hepatne-1-carboxylate with dinitrogen tetraoxide in diethyl ether at -10 to 0°C, followed by treatment of the reaction mixture with methanol, gave approximately equal amounts of methyl exo,syn-6,7-dinitro-and exo-6-hydroxy-syn-7-nitrobicyclo[3.1. 1]heptane-endo-6-carboxylates. Tricyclo[4.1.0.0^2,7]hept-1-yl phenyl sulfone reacted with dinitrogen tetraoxide under analogous conditions to produce a mixture of diastereoisomeric exo,syn-and endo,syn-6,7-dinitro-6- phenylsulfonylbicyclo-[3.1.1]heptanes and 6,6-dimethoxy-endo-7-nitrobicyclo[3.1. 1]heptane at a ratio of 4.5:2:1. Probable factors responsible for the different stereoselectivities in the addition of N₂O₄ at the central C¹-C⁷ bond of the initial tricycloheptane compounds were discussed. The structural parameters of the dinitro ester and related dinitro sulfone were compared on the basis of the X-ray diffraction data.

Full text of DOI:10.1134/S1070428008040076

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 4, pp. 511–515. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © V.A. Vasin, S.G. Kostryukov, I.Yu. Bolusheva, V.V. Razin, 2008, published in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 4,
pp. 516–520.
Reaction Products of Methyl Tricyclo[4.1.0.02,7]heptane-
1-carboxylate and Tricyclo[4.1.0.02,7]hept-1-yl Phenyl Sulfone
with Dinitrogen Tetraoxide
V. A. Vasina, S. G. Kostryukova, I. Yu. Bolushevaa, and V. V. Razinb
a Ogarev Mordovian State University, ul. Bol’shevistskaya 68, Saransk, 430000 Russia
e-mail: vasin@mrsu.ru
b St. Petersburg State Institute of Technology, Moskovskii pr. 26, St. Petersburg, 190013 Russia
Received June 26, 2007
Abstract—The reaction of methyl tricyclo[4.1.0.02,7]heptane-1-carboxylate with dinitrogen tetraoxide in di-
ethyl ether at –10 to 0°C, followed by treatment of the reaction mixture with methanol, gave approximately
equal amounts of methyl exo,syn-6,7-dinitro- and exo-6-hydroxy-syn-7-nitrobicyclo[3.1.1]heptane-endo-6-car-
boxylates. Tricyclo[4.1.0.02,7]hept-1-yl phenyl sulfone reacted with dinitrogen tetraoxide under analogous con-
ditions to produce a mixture of diastereoisomeric exo,syn- and endo,syn-6,7-dinitro-6-phenylsulfonylbicyclo-
[3.1.1]heptanes and 6,6-dimethoxy-endo-7-nitrobicyclo[3.1.1]heptane at a ratio of 4.5:2:1. Probable factors
responsible for the different stereoselectivities in the addition of N2O4 at the central C1–C7 bond of the initial
tricycloheptane compounds were discussed. The structural parameters of the dinitro ester and related dinitro
sulfone were compared on the basis of the X-ray diffraction data.
DOI: 10.1134/S1070428008040076
a source of electrophilic nitrosyl cation, leading to the
formation of 3-ethoxycyclobutanone oxime which then
undergoes hydrolysis to 3-ethoxycyclobutanone. These
data led us to conclude that the presence of an elec-
tron-withdrawing substituent in the bridgehead posi-
tion is likely to favor addition of N2O4 at the central
bicyclobutane bond.
In the present communication we give more detailed
data on the reaction of ester I with N2O4, as well as on
the nitration of one more tricycloheptane compound
having an electron-withdrawing group in the bridge-
head position, sulfone II. The reactions were carried
out using dinitrogen tetraoxide preliminarily dried by
distillation over phosphoric anhydride [7].
Addition reactions of dinitrogen tetraoxide to
olefins provide a convenient synthetic route to nitro-
substituted hydrocarbons [1]. The high strain energy of
bicyclo[1.1.0]butane and olefin-like character of the
central carbon–carbon bond therein [2] suggest that
addition of N2O4 at the C1–C7 bond of bicyclo[1.1.0]-
butane is possible. We previously [3] were the first to
present experimental proofs for the above assumption:
The reaction of methyl tricyclo[4.1.0.02,7]heptane-1-
carboxylate (I) (which may be regarded as a bridged
bicyclo[1.1.0]butane derivative) with dinitrogen tetra-
oxide gave dinitro compound III which was formed
just via addition of N2O4 at the central bicyclobutane
bond. The structure of III was proved by X-ray anal-
ysis [4]. Later on, Archibald et al. [5] reported on the
synthesis of ethyl 1,3-dinitrocyclobutane-1-carboxylate
by reaction of dinitrogen tetraoxide with ethyl bicyclo-
[1.1.0]butane-1-carboxylate which is structurally relat-
ed to ester I. The reaction of parent bicyclo[1.1.0]-
butane with dinitrogen tetraoxide in diethyl ether at
–78°C gave no nitrogen-containing compounds; in-
stead, 3-ethoxycyclobutanone was obtained as the only
product [6]. It was presumed [6] that dinitrogen tetra-
oxide in the reaction with bicyclo[1.1.0]butane acts as
The reaction of tricycloheptane I with excess liquid
N2O4 was carried out in diethyl ether at –10°C. After
treatment of the reaction mixture with methanol, we
detected (GLC, NMR) norpinane derivatives III and
IV at a ratio of ~1.1:1 (Scheme 1).
Compounds III and IV were isolated as individual
substances by column chromatography on aluminum
oxide, and their structure was confirmed by the IR and
13
1H and C NMR spectra. In particular, the configura-
tion of substituent on C7 in each of compounds III and
511

VASIN et al.
512
Scheme 1.
(1) N2O4
(2) MeOH
+
O2N
COOMe
NO2
O2N
COOMe
COOMe
OH
I
III
IV
IV is determined by the presence of a triplet signal
from 7-H in the H NMR spectrum [8, 9]. Taking into
The structure of compounds V–VII was confirmed
1
by the IR and NMR spectra. The nitro groups in their
molecules gave rise to two strong absorption bands in
the IR spectra at ~1385 and ~1535 cm–1; the bands at
1165 and 1335 cm–1 were assigned to the sulfonyl
group. Ketones VIa and VIb characteristically dis-
played a strong absorption band at 1790 cm–1 due to
stretching vibrations of the carbonyl group [11]. The
configuration at C7 unambiguously followed from the
account that the structure of norpinane derivative III
was unambiguously established previously by X-ray
analysis, the endo orientation of the methoxycarbonyl
group in molecule IV was assigned on the basis of the
1
observed similarity in the chemical shifts of H and
13C in the trimethylene fragments of III and IV.
The reactions of sulfone II with liquid N2O4 were
carried out at –10 to 0°C in diethyl ether or methylene
chloride using excess reagent; the reaction mixtures
were then treated with water or methanol. In the first
case we obtained stereoisomeric dinitro sulfones Va
and Vb and nitro ketone VIa at a ratio of 2.9:1:3.5
1
presence of a triplet signal from 7-H in the H NMR
spectra of nitro derivatives Va, Vb, VIa, and VII or
a singlet from the same proton in the spectrum of VIb
[8, 9]. The strong difference between the chemical
shifts of 7-H in stereoisomeric dinitro sulfones Va and
Vb allowed us to assign configuration at C6 in their
molecules with account taken of known stronger long-
range deshielding effect of sulfo group as compared to
nitro group [12]. The structure of dinitro sulfone Va
was finally proved by X-ray analysis (see figure).
The dihedral angle between the C1C2C4C5 and
C2C3C4 planes in molecule Va is about 165°, and the
C3 atom deviates from the C1C2C4C5 plane by 0.211 Å
toward C7. The corresponding dihedral angle in the
molecule of ester III [4] is equal to 178.2°, i.e., the
trimethylene bridge is almost planar. Both nitro groups
in Va are oriented almost orthogonally to the plane
passing through the C3, C6, and C7 atoms. The C1–C7
1
(according to the H NMR data), while in the second
case a mixture of dinitro sulfones Va and Vb and nitro
dimethyl acetal VII at a ratio of 4.5:2:1 was formed
(Scheme 2).
Compounds Va, VIa, and VII were isolated as indi-
vidual substances by column chromatography on silica
gel. The stereochemical purity of dinitro sulfone Vb
was 90%. Chromatographic separation on aluminum
oxide of the product mixture obtained after treatment
of the reaction mixture with water gave dinitro sul-
fones Va and Vb and nitro ketone VIb. Presumably,
the latter was formed by epimerization of VIa over
aluminum oxide as catalyst [10].
Scheme 2.
(1) N2O4
(2) H2O
+
+
O2N
SO2Ph
NO2
O2N
NO2
O2N
O
SO2Ph
Va
Vb
VIa
SO2Ph
(1) N2O4
(2) MeOH
II
Va
+ Vb +
O2N
OMe
OMe
VII
O
NO2
VIb
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REACTION PRODUCTS OF METHYL TRICYCLO[4.1.0.02,7]HEPTANE-1-CARBOXYLATE
513
O2
and C5–C7 bonds (average length 1.537 Å) in the
cyclobutane fragment of Va are shorter than the C1–C6
and C5–C6 bonds (average length 1.546 Å; cf. 1.536
and 1.553 Å, respectively, in molecule III); the di-
hedral angle between the C6C1C5 and C7C1C5 planes in
Va is 136.4° (cf. 139.7° in III).
O1
C3
C8
C9
C4
C13
C12
S1
C5
C6
C2
C7
C10
C11
C1
O3
O4
We believe that the addition of dinitrogen tetra-
oxide to bicyclobutane derivatives I and II follows
a radical chain mechanism. As might be expected on
the basis of published data [13], N-nitro radical gen-
erated by decomposition of N2O4 attacks the central
C1–C7 bond in the substrate at the β-position with
respect to the electron-withdrawing substituent with
strict endo selectivity. As a result, the corresponding
norpinanyl radical is formed. In the second chain pro-
pagation step dinitrogen tetraoxide acts as carrier of
nitro and nitrosyl groups which are transferred to nor-
pinanyl radical, yielding dinitronorpinane derivative
and nitronorpinanyl nitrite [14]. The latter is converted
into nitronorpinanol IV (in the reaction with ester I) or
into nitronorpinanone VIa or its acetal VII (in the
reaction with sulfone II) upon treatment of the reaction
mixture with water or methanol.
O5
N1
N2
O6
Structure of the molecule of exo-6,syn-7-dinitro-endo-6-
phenylsulfonylbicyclo[3.1.1]heptane (Va) according to the
X-ray diffraction data (one of the two crystallographically
independent molecules is shown).
Analogous difference in the stereoselectivities of
radical addition of benzenethiol and benzenesulfonyl
bromide to the same tricycloheptane substrates (anti
addition to ester I and syn addition to sulfone II) was
reported previously [15, 16]; a similar patter was also
typical of nucleophilic addition (e.g., of sodium
methoxide and sodium methanethiolate) to compounds
I and II [10, 17, 18].
EXPERIMENTAL
Special comments should be given to the observed
difference in the stereochemistry of addition to tri-
cycloheptane derivatives I and II. This difference is
determined by stereoselectivity of the second step of
the process, transfer of nitro or nitrosyloxy group to
the reaction center in intermediate norpinan-6-yl radi-
cal, and is likely to be related to specific structure of
the latter in each case. Initially, the intermediate
always has conformation A, and it can undergo revers-
ible isomerization into conformer B (Scheme 3).
The elemental compositions were determined on
an HP-185B CHN analyzer. The 1H and 13C NMR spec-
tra were measured on a Bruker DPX-300 spectrometer
at 300.130 and 75.468 MHz, respectively, from solu-
tions in CDCl3. The IR spectra were recorded in KBr
on an InfraLYuM FT-02 instrument with Fourier trans-
form. GLC analysis was performed on a Chrom-41
chromatograph equipped with a flame ionization
detector and a glass column, 1200×3 mm, packed with
3% of OV-17 on Inerton N-Super (0.125–0.160 mm);
carrier gas nitrogen, flow rate 40 ml/min; oven tem-
perature 140°C, injector temperature 210°C. The com-
ponents were quantitated by the internal normalization
technique; the calibration factors for all components
were assumed to be equal to unity. Analytical thin-
layer chromatography was performed using Silufol
UV-254 plates (hexane–diethyl ether, 1:1; develop-
ment with iodine vapor). Aluminum oxide of activity
grade II and silica gel L (40–100 μm) were used for
column chromatography; eluent light petroleum ether–
diethyl ether, 2:1 to 3:1.
Scheme 3.
X
O2N
O2N
X
A
B
X = CO2Me, SO2Ph.
Presumably, the anti-stereoselectivity of the nitra-
tion decreases in going from ester I to sulfone II due to
increased barrier to inversion in intermediate A (X =
SO2Ph), which is stabilized by participation of d-or-
bitals on the sulfur atom. The inversion of radical A
(X = CO2Me) requires less energy, and radical B thus
formed is more reactive due to the lack of steric
shielding of the reaction center by the C3H2 fragment.
Compounds I [17] and II [19] were synthesized by
known methods.
Reaction of methyl tricyclo[4.1.0.02,7]heptane-1-
carboxylate (I) with dinitrogen tetraoxide. A solu-
tion of 0.73 g (4.8 mmol) of compound I in 10 ml of
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 4 2008

VASIN et al.
514
anhydrous diethyl ether was cooled to –10°C, and a so-
lution of 1.13 g (12.3 mmol) of dinitrogen tetraoxide
(prepared according to [7] and purified by distillation
over P2O5) in 10 ml of the same solvent was slowly
added under stirring. The mixture was stirred for
30 min on cooling and treated with 5 ml of methanol.
The solvent was removed under reduced pressure
(water-jet pump) to obtain a greenish–yellow semi-
pounds Va, Vb, and VII at a ratio of 4.5:2:1. By col-
umn chromatography on silica gel we isolated 1.92 g
(32%) of dinitro sulfone Va, 0.72 g (12%) of dinitro
sulfone Vb, and 0.18 g (5%) of nitro acetal VII.
b. The reaction was carried out as described above
in a, but the mixture was treated with 3 ml of water.
The organic layer was separated, the aqueous layer
was extracted with methylene chloride (3×5 ml), the
extracts were combined with the organic phase and
dried over calcium chloride, and the solvent was re-
1
crystalline material. According to the H NMR and
GLC data, the product was a mixture of compounds III
and IV at a ratio of 1.1:1 with a small impurity of two
other compounds whose structure was not determined
[presumably, substituted norpinanes, δ(anti-7-H) 5.07
and 5.19 ppm]. By column chromatography on alumi-
num oxide we isolated 0.62 g (52%) of dinitro ester III
and 0.24 g (23%) of hydroxy nitro ester IV.
1
moved. According to the H NMR data, the residue
contained compounds Va, Vb, and VIa at a ratio of
2.9:1:3.5. By column chromatography on silica gel we
isolated 0.14 g (7%) of nitro ketone VIa, 1.74 g (29%)
of dinitro sulfone Va, and 0.93 g (16%) of dinitro sul-
fone Vb. In an analogous experiment, chromatographic
separation of the crude product in a column charged
with aluminum oxide gave 0.11 g (5.2%) of nitro
ketone VIb.
Methyl exo-6,syn-7-dinitrobicyclo[3.1.1]heptane-
endo-6-carboxylate (III). mp 119–120°C (from
CH2Cl2–hexane), Rf 0.58, Rt 8.1 min. IR spectrum, ν,
cm–1: 540 m, 665 m, 814 m, 1061 m, 1123 s, 1167 s,
1386 s (NO2, asym.), 1456 s, 1553 v.s (NO2, sym.),
exo-6,syn-7-Dinitro-endo-6-phenylsulfonylbicy-
clo[3.1.1]heptane (Va). mp 155–156°C (from MeOH),
Rf 0.46. IR spectrum, ν, cm–1: 555 m, 606 s, 687 m,
721 m, 760 m, 1165 s, 1335 s, 1450 m, 1551 v.s,
1553 v.s. 1H NMR spectrum, δ, ppm: 1.36–1.51 m and
1.86–2.03 m (1H each, 3-H), 2.52–2.68 m and 2.92–
3.08 m (2H each, 2-H, 4-H), 4.03 br.s (2H, 1-H, 5-H),
4.33 t (1H, anti-7-H, J = 5.5 Hz), 7.58–7.67 m (2H)
and 7.75–7.87 (3H) (Ph). 13C NMR spectrum, δC, ppm:
12.0 (C3), 22.5 (C2, C4), 51.1 (C1, C5), 73.3 (C7), 102.7
(C6); 129.3, 129.6, 134.6, 135.6 (Carom). Found, %:
C 47.92; H 4.44; N 8.47. C13H14N2O6S. Calculated, %:
C 47.85; H 4.32; N 8.58.
1
1759 v.s (C=O). H NMR spectrum, δ, ppm: 1.32–
1.59 m (2H, 3-H), 2.45 br.t (4H, 2-H, 4-H, J = 7 Hz),
3.78 br.d (2H, 1-H, 5-H, J = 5.9 Hz), 3.87 s (3H,
OMe), 4.89 t (1H, anti-7-H, J = 5.9 Hz). 13C NMR
spectrum, δC, ppm: 11.4 (C3), 22.4 (C2, C4), 48.7 (C1,
C5), 53.6 (OMe), 74.0 (C7), 90.0 (C6), 162.5 (C=O).
Found, %: C 44.52; H 5.01; N 11.50. C9H12N2O6. Cal-
culated, %: C 44.27; H 4.95; N 11.47.
Methyl exo-6-hydroxy-syn-7-nitrobicyclo[3.1.1]-
heptane-endo-6-carboxylate (IV). mp 86–87°C (from
CH2Cl2–hexane), Rf 0.21, Rt 6.2 min. IR spectrum, ν,
cm–1: 557 m, 814 m, 1060 m, 1385 s (NO2, asym.),
1553 v.s (NO2, sym.), 1734 br.s (C=O), 3449 m (OH).
1H NMR spectrum, δ, ppm: 1.21–1.56 m (2H, 3-H),
2.25 br.t (4H, 2-H, 4-H, J = 7 Hz), 2.96 br.s (1H, OH),
3.12 br.d (2H, 1-H, 5-H, J = 5.9 Hz), 3.86 s (3H,
OMe), 5.10 t (1H, anti-7-H, J = 5.9 Hz). 13C NMR
spectrum, δC, ppm: 12.1 (C3), 22.3 (C2, C4), 50.0 (C1,
C5), 52.4 (OMe), 74.3 (C7), 76.5 (C6), 169.9 (C=O).
Found, %: C 50.12; H 6.14; N 6.37. C9H13NO5. Cal-
culated, %: C 50.23; H 6.09; N 6.51.
Reaction of phenyl tricyclo[4.1.0.02,7]hept-1-yl
sulfone (II) with dinitrogen tetraoxide. a. A solution
of 4.3 g (18.4 mmol) of compound II in 20 ml of
methylene chloride was cooled to –15°C, and a solu-
tion of 7.45 g (81.5 mmol) of dinitrogen tetraoxide in
10 ml of the same solvent was slowly added under
stirring. The mixture was stirred for 15 min and treated
with 5 ml of methanol. The solvent was distilled off to
obtain a semicrystalline material which contained com-
endo-6,syn-7-Dinitro-exo-6-phenylsulfonylbi-
cyclo[3.1.1]heptane (Vb). mp 173–178°C (from
acetone–pentane), Rf 0.38, stereochemical purity 90%.
1H NMR spectrum, δ, ppm: 1.25–1.40 m (2H, 3-H),
2.22–2.38 m and 2.42–2.56 m (2H each, 2-H, 4-H),
3.77 br.d (2H, 1-H, 5-H, J = 5.7 Hz), 5.49 t (1H, 7-H,
J = 5.7 Hz), 7.59–7.72 m (2H) and 7.75–7.93 (3H)
(Ph). 13C NMR spectrum, δC, ppm: 10.3 (C3), 22.4 (C2,
C4), 48.1 (C1, C5), 70.6 (C7), 100.6 (C6); 129.6, 130.2,
135.6, 136.0 (Carom). Found, %: C 47.90; H 4.53;
N 8.68. C13H14N2O6S. Calculated, %: C 47.85; H 4.32;
N 8.58.
6,6-Dimethoxy-endo-7-nitrobicyclo[3.1.1]hep-
tane (VII). mp 68–69°C (from pentane), Rf 0.78.
1H NMR spectrum, δ, ppm: 1.16–1.34 m and 1.47–
1.64 m (1H each, 3-H), 1.96–2.10 m and 2.12–2.26 m
(2H each, 2-H, 4-H), 3.10 br.s (2H, 1-H, 5-H), 3.24 s
and 3.28 s (3H each, OMe), 4.55 t (1H, 7-H, J =
13
5.9 Hz). C NMR spectrum, δC, ppm: 12.8 (C3), 22.2
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REACTION PRODUCTS OF METHYL TRICYCLO[4.1.0.02,7]HEPTANE-1-CARBOXYLATE
515
(C2, C4), 46.2 (C1, C5), 49.5 and 50.2 (OMe), 75.0
(C7), 98.3 (C6). Found, %: C 53.68; H 7.60; N 6.87.
C9H15NO4. Calculated, %: C 53.72; H 7.51; N 6.96.
ically independent molecules with similar structures.
The complete set of crystallographic data for com-
pound Va was deposited to the Cambridge Crystallo-
graphic Data Center (entry no. CCDC 295617).
endo-7-Nitrobicyclo[3.1.1]heptan-6-one (VIa).
mp 112–113°C (from hexane–diethyl ether), Rf 0.69.
IR spectrum, ν, cm–1: 459 w, 783 w, 806 w, 1389 m,
1451 m, 1536 v.s, 1539 s, 1782 s, 2886 w, 2951 m,
2978 m. 1H NMR spectrum, δ, ppm: 1.52–1.79 m (2H,
3-H), 2.34–2.49 m and 2.65–2.81 m (2H each, 2-H,
4-H), 3.47 br.d (2H, 1-H, 5-H, J = 6.1 Hz), 4.95 t (1H,
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7-H, J = 6.1 Hz). C NMR spectrum, δC, ppm: 14.7
(C3), 30.0 (C2, C4), 60.0 (C1, C5), 71.6 (C7), 205.8 (C6).
Found, %: C 53.98; H 5.88; N 8.91. C7H9NO3. Calcu-
lated, %: C 54.19; H 5.85; N 9.03.
exo-7-Nitrobicyclo[3.1.1]heptan-6-one (VIb).
mp 71–72°C (from hexane–diethyl ether), Rf 0.54. IR
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1369 m, 1450 m, 1542 v.s, 1547 v.s, 1558 v.s, 1797 s.
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2.53 br.t (4H, 2-H, 4-H, J = 5.8 Hz), 3.59 br.s (2H,
1-H, 5-H), 4.79 s (1H, 7-H). 13C NMR spectrum, δC,
ppm: 15.7 (C3), 33.3 (C2, C4), 63.7 (C1, C5), 82.1 (C7),
205.3 (C6). Found, %: C 54.22; H 5.96; N 9.15.
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7. Handbuch der präparativen anorganischen Chemie,
X-Ray diffraction study of compound (Va).
Transparent scaly single crystals, 0.50×0.35×0.20 mm.
Total of 5039 reflections were measured at 293 K on
a Siemens P3/PC automatic four-circle diffractometer
(graphite monochromator, MoKα irradiation, λ =
0.71073 Å, θ–2θ scanning, 2θmax = 50.12°, spherical
segment –1 ≤ h ≤ 13, 0 ≤ k ≤ 23, 0 ≤ l ≤ 31). Averaging
of equivalent reflections gave 4918 independent reflec-
tions (Rint = 0.0437), which were used in the structure
solution and refinement. Rhombic crystals with the
following unit cell parameters: a = 11.060(10), b =
19.444(16), c = 26.58(2) Å; V = 5716(9) Å3; M 652.64;
Z = 16; dcalc = 1.517 g/cm3; μ = 0.259 mm–1; F(000) =
2720; space group Pbca. The structure was solved by
the direct method. All atoms were localized by succes-
sive syntheses of electron density. The refinement was
performed with respect to F2hkl in anisotropic approxi-
mation for non-hydrogen atoms and isotropic approx-
imation for hydrogen atoms. The final divergence
factors were R1 = 0.0659 [from 2785 reflections with
I > 2σ(I), Fhkl] and wR2 = 0.1797 (from all 4918 reflec-
tions involved in the refinement procedure, F2hkl).
Number of refined parameters 505, goodness of fit
1.019. The residual electron density from the Fourier
difference series was 0.248 and –0.269 e Å–3. No cor-
rection for absorption was introduced. All calculations
were performed using SHELXTL ver. 5.1 software
package [20]. A unit cell contained two crystallograph-
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 4 2008