Thermal decomposition products of methyl 1,5-diphenyl- and 5-methyl-1-phenyl-2,3-diazabicyclo[3.1.0]hex-2-ene-6-exo-carboxylates

Article abstract of DOI:10.1134/S1070428013070038

Methyl 1,5-diphenyl- and 5-methyl-1-phenyl-2,3-diazabicyclo[3.1.0]hex-2- ene-6-exo-carboxylates at 138 C undergo decomposition via elimination of nitrogen molecule with formation in each case of five products. Two products are methyl 1,3-diphenyl(or 1-met

Full text of DOI:10.1134/S1070428013070038

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 7, pp. 974–978. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © V.V. Razin, M.E. Yakovlev, V.A. Vasin, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49, No. 7, pp. 990–994.
Thermal Decomposition Products of Methyl 1,5-Diphenyl-
and 5-Methyl-1-phenyl-2,3-diazabicyclo[3.1.0]hex-2-ene-
6-exo-carboxylates
V. V. Razina, M. E. Yakovleva, and V. A. Vasinb
a St. Petersburg State University, Universitetskii pr. 26, St. Petersburg, 198504 Russia
b Ogarev Mordovia State University, Bol’shevistskaya ul. 68, Saransk, 430005 Republic of Mordovia, Russia
Received July 4, 2012
Abstract—Methyl 1,5-diphenyl- and 5-methyl-1-phenyl-2,3-diazabicyclo[3.1.0]hex-2-ene-6-exo-carboxylates
at 138°C undergo decomposition via elimination of nitrogen molecule with formation in each case of five
products. Two products are methyl 1,3-diphenyl(or 1-methyl-3-phenyl)bicyclo[1.1.0]butane-2-endo- and -exo-
carboxylates, and the three others are derivatives of buta-1,3-diene, methyl (Z)-2-benzylidene-3-phenyl(or
3-methyl)but-3-enoate and methyl (E)- and (Z)-3,4-diphenyl(or 4-methyl-3-phenyl)penta-2,4-dienoates. The
formation of these products may be rationalized assuming intermediacy of substituted allylcarbene which
undergoes both intramolecular cycloaddition and rearrangements involving 1,2-hydride and 1,2-vinyl shifts.
DOI: 10.1134/S1070428013070038
It is known [1–8] that substituted 2,3-diazabicyclo-
[3.1.0]hex-2-enes undergo thermal decomposition with
elimination of nitrogen molecule to produce buta-1,3-
diene and bicyclo[1.1.0]butane derivatives. The ratio
of the decomposition products, in particular the frac-
tion of bicyclobutane derivative, strongly depends on
the substitution pattern in the initial compound. In
order to elucidate this dependence, it is necessary to
study thermal decomposition of a wider series of sub-
strates. As such substrates we selected methyl 1,5-di-
phenyl- and 5-methyl-1-phenyl-2,3-diazabicyclo-
[3.1.0]hex-2-ene-6-exo-carboxylates I and II which
were used by us previously as pyridazine precursors
[9]. Komendantov et al. [2] reported that the thermol-
ysis of ester I yields endo-bicyclobutane IIIa as the
only product. We examined the thermal decomposition
of I in more detail with a view to thoroughly determine
the product composition and compare it with the com-
position of the thermolysis products of II.
more complex than it was reported in [2]. In each case,
two diastereoisomeric bicyclobutane derivatives (IIIa
and IIIb from I and IVa and IVb from II) and three
buta-1,3-diene derivatives (Va, VIa, and VIb from I
and VIIa, VIIIa, and VIIIb from II) were formed. The
compositions of the thermolysis products, determined
by 1H NMR, are given in Table 1. All compounds were
isolated as individual substances by chromatography.
Bicyclobutane IIIa was described previously [2, 10];
COOMe
COOMe
Ph
R
Ph
R
IIIa, IVa
IIIb, IVb
R
R
H2C
Ph
H2C
COOMe
COOMe
Va, VIIa
Ph
VIa, VIIIa
COOMe
It was found that the decomposition patterns of
compounds I and II are essentially similar and much
R
N
H2C
COOMe
R
N
Ph
VIb, VIIIb
Ph
I, II
IIIa, IIIb, Va, VIa, VIb, R = Ph; IVa, IVb, VIIa,
VIIIa, VIIIb, R = Me.
I, R = Ph; II, R = Me.
974

THERMAL DECOMPOSITION PRODUCTS OF METHYL 1,5-DIPHENYL- ...
975
Table 1. Composition of the thermolysis products of com-
pounds I and II
compound IIIb was synthesized in [11] by thermal
isomerization of IIIa. Bicyclobutanes IVa and IVb
1
were identified on the basis of their H and 13C NMR
Compound I
Compound II
spectra which were compared with the spectra of IIIa
and IIIb. As expected, similarity in the chemical shifts
of the 2-H and 4-H protons and C1 (C3), C2, and C4
carbon nuclei was observed for bicyclobutanes
with similar configuration (IIIa/IVa and IIIb/IVb)
(Table 2). The above proton signals of IIIa and IIIb
were displaced downfield relative to the corresponding
signals of IVa and IVb.
product
fraction, %
product
fraction, %
IIIa
IIIb
Va
71.2
05.3
05.9
12.7
04.9
IVa
53.5
17.1
13.3
07.0
09.1
IVb
VIIa
VIIIa
VIIIb
VIa
VIb
The key point in the determination of configuration
of stereoisomers IIIa/IIIb and IVa/IVb was splitting
of the exo-2-H and exo-4-H proton signals in the spec-
tra of IIIa and IVa due to long-range W-coupling [12]
which is possible only in the endo isomers. An addi-
tional evidence in support of structure IVb may be
similarity of the 2-H and C2 chemical shifts with those
characteristic of model dimethyl 1-methyl-3-phenylbi-
cyclobutane-2-exo,4-exo-dicarboxylate (IX) (δ 1.68,
δC 41.0 ppm). All signals from the ring protons in exo
isomers IIIb and IVb and from endo-4-H in endo
isomers IIIa and IVa appeared as singlets or weakly
split doublets due to small (0–1.4 Hz) geminal cou-
pling constant typical of bicyclobutanes and the lack of
long-range spin–spin coupling.
(Z,Z)-3,4-diphenylhexa-2,4-dienedioates Xa and Xb.
The structure of VIb was also confirmed by similarity
of the chemical shifts of 2-H in Vb (δ 6.47 ppm) and
Xb (δ 6.60 ppm). Likewise, the chemical shifts of 2-H
in VIa (δ 5.97 ppm) and Xa (δ 5.80 ppm) indicated
their similar configurations.
The structure of diene Va as stereoisomer of methyl
(E)-2-benzylidene-3-phenylbut-3-enoate (Vb) reported
in [13] followed from the position of the PhCH=
proton signal (δ 6.69 ppm), which was similar to the
position of the corresponding signal of model diene
VIIa (δ 6.70 ppm) but appreciably different from that
observed for isomer Vb (δ 7.67 ppm).
It should be noted that neither diene Vb nor its
analog VIIb [17] (which are characterized by ano-
malously large chemical shift of the olefinic proton in
the benzylidene fragment, δ 7.67 and 7.47 ppm,
respectively) was detected among the thermolysis
products of compounds I and II.
There were no problems in the structure assignment
of three known buta-1,3-diene derivatives VIIa
[13, 14], VIIIa [13, 15], and VIIIb [13] which were
1
identified by comparing their H NMR spectra with
published data.
Dienes Va, VIa, and VIb were not reported previ-
ously. However, ethyl ester analog of VIa was de-
scribed in [16], and compound VIa was identified on
the basis of the observed similarity in the chemical
shifts of 2-H and 5-H in these esters. The structure of
Some authors believe [1, 3, 18] that thermal
decomposition of 2,3-diazabicyclo[3.1.0]hex-2-enes
involves intermediate formation of diazo compound A
which generates allylcarbene B. Isomerization of the
latter may follow either intramolecular cycloaddition
pattern with formation of bicyclobutane structure or
1
diene VIb was determined by comparing its H NMR
spectrum with those of related dimethyl (E,E)- and
Scheme 1.
R
Ph
H
H
MeOC(O)
COOMe
N
N
H2C
N
N
COOMe
COOMe
Ph
Me
COOMe
Ph
H2C
Ph
Vb, VIIb
X
R
R
I, II
A
Ph
Ph
COOMe
MeOC(O)
COOMe
R
COOMe
Ph
Ph
MeOC(O) Ph
··
Xa
Xb
CH2
V, R = Ph; VII, R = Me.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 7 2013
B

RAZIN et al.
976
Table 2. Chemical shifts of selected protons and carbon nuclei in bicyclobutanes IIIa, IIIb, IVa, and IVb
Chemical shifts δ, ppm (J, Hz)
Compound no.
2-H
exo-4-H
endo-4-H
C1, C3
C2
C4
IIIa
IVa
IIIb
IVb
4.04 d (4.3)
3.26 d (4.3)
2.21 s
2.96 d.d (4.3, 1.4)
2.18 d.d (4.3, 1.0)
2.12 s
2.70 d (1.4)
2.32 br.s
1.32 s
31.4
24.6
28.8
22.7
46.7
49.1
44.9
43.4
35.1
33.7
33.2
32.5
1.78 s
1.59 s
0.92 s
1,2-hydride and/or 1,2-vinyl shifts with formation of
buta-1,3-diene derivatives (Scheme 1). As applied to
our case, the above mechanism rationalizes formation
of all detected thermolysis products of compounds I
and II. However, the absence of dienes Vb and VIIb
among the products and hence the statement of strict
stereoselectivity of the 1,2-hydride shift in carbene B,
in contrast to non-stereoselective 1,2-vinyl shift,
requires special discussion.
respectively, using CDCl3 as solvent. Analytical thin-
layer chromatography was performed on Silufol UV-
254 plates using petroleum ether–diethyl ether (4:1) as
eluent; spots were developed by treatment with iodine
vapor. Silica gel L (40–100 μm) was used for column
chromatography; eluent petroleum ether–diethyl ether.
Compounds I and II were synthesized according to the
procedure described in [9].
Thermolysis of methyl 1,5-diphenyl-2,3-diazabi-
cyclo[3.1.0]hex-2-ene-6-carboxylate (I). a. Prepara-
tive experiment. Ester I, 1.0 g, was added in one
portion to 5 ml of boiling p-xylene (bp 138°C), and the
solution was heated for 15 min under reflux in
an argon atmosphere. The mixture was cooled to 20°C,
the solvent was removed under reduced pressure, and
the residue, 910 mg of a light yellow viscous oily
material, was dissolved on heating in 10 ml of petro-
leum ether–diethyl ether (5:1). The solution was kept
for a long time at –5°C, and 140 mg of crystalline
bicyclobutane IIIa was filtered off. The mother liquor
was subjected to column chromatography on silica gel
to isolate an additional portion (343 mg) of IIIa and
compounds IIIb, Va, VIa, and VIb.
The large fraction of bicyclobutane derivatives
(76.5 and 70.6%, respectively) in the thermolysis
products of compounds I and II is a specific feature of
the substitution pattern in these 2,3-diazabicyclo-
[3.1.0]hex-2-ene derivatives bearing a phenyl group in
the bridgehead position (C1) and exo-oriented me-
thoxycarbonyl group on C6. Presumably, substituted
phenyl(allyl)carbene B appears to be fairly stable,
which ensures intramolecular cyclopropanation. On the
other hand, the presence of a methoxycarbonyl group
in the α-position with respect to the carbene center in
intermediate B favors its rearrangement to butadiene
derivatives. The latter assumption is supported by the
data of [7], according to which thermal decomposition
of an analog of I with a different substituent on C6,
1,5-diphenyl-6-exo-(phenylselanylmethyl)-2,3-diaza-
bicyclo[3.1.0]hex-2-ene, yields only the corresponding
bicyclobutane derivative. The ratio of stereoisomers
IIIa and IIIb formed by thermolysis of 2,3-diazabi-
cyclo[3.1.0]hex-2-ene (I) corresponds to the thermody-
namic equilibrium (~13.5:1) [11], whereas the ratio
IVa/IVb (3:1) in the transformation of 2,3-diazabicy-
clo[3.1.0]hex-2-ene II is determined by the kinetic fac-
tor, for compounds IVa and IVb, unlike their analogs
IIIa and IIIb, are not interconvertible up to 170°C.
Methyl 1,3-diphenylbicyclobutane-2-endo-car-
boxylate (IIIa). Yield 483 mg (53%), Rf 0.25, mp 74–
75°C (from hexane); published data [2]: mp 75°C. The
1H and 13C NMR spectra of IIIa were identical to
those reported in [10] (Table 2).
Methyl 1,3-diphenylbicyclobutane-2-exo-carbox-
ylate (IIIb). Yield 35 mg (4%), colorless oily sub-
1
stance, Rf 0.30. The H and 13C NMR spectra of IIIb
were identical to those reported in [10] (Table 2).
Methyl (Z)-2-benzylidene-3-phenylbut-3-enoate
(Va). Yield 38 mg (4%), colorless oily substance,
1
Rf 0.28. H NMR spectrum, δ, ppm: 3.75 s (3H,
EXPERIMENTAL
CO2CH3), 5.42 s and 5.45 s (1H each, =CH2), 6.69 s
(1H, =CH), 7.24–7.36 m (10H, Ph). 13C NMR spec-
trum, δC, ppm: 52.1, 116.8, 127.9, 128.2, 128.3,
128.35, 128.4, 128.45, 133.8, 135.3, 135.6, 139.6,
146.7, 167.6. Found, %: C 81.59; H 6.33. C18H16O2.
Calculated, %: C 81.79; H 6.10.
The elemental compositions were determined on
a Hewlett Packard HP-185B CHN analyzer. The
1H and 13C NMR spectra were measured on a Bruker
DPX-300 spectrometer at 300.130 and 75.468 MHz,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 7 2013

THERMAL DECOMPOSITION PRODUCTS OF METHYL 1,5-DIPHENYL- ...
977
Methyl (E)-3,4-diphenylpenta-2,4-dienoate
(VIa). Yield 73 mg (8%), colorless oily substance,
Rf 0.26. H NMR spectrum, δ, ppm: 3.57 s (3H,
49.1 (C2), 51.5 (OCH3), 125.3 (2C), 125.6, 128.3 (2C),
136.7, 171.7 (C=O). Found, %: C 78.09; H 5.64.
C13H11O2. Calculated, %: C 78.37; H 5.57.
1
CO2CH3), 5.23 s and 5.56 s (1H each, =CH2), 5.97 s
(1H, =CH), 7.31–7.49 m (10H, Ph). 13C NMR spec-
trum, δC, ppm: 51.2, 120.1, 122.9, 127.75, 127.8,
127.9, 128.3, 128.6, 128.7, 137.9, 140.0, 151.0. 156.5,
166.6. Found, %: C 81.62; H 6.29. C18H16O2. Calculat-
ed, %: C 81.79; H 6.10.
Methyl 1-methyl-3-phenylbicyclobutane-2-exo-
carboxylate (IVb). Yield 79 mg (12%), colorless oily
substance, Rf 0.36. H NMR spectrum, δ, ppm: 0.92 s
1
(1H, endo-4-H), 1.59 s (1H, exo-4-H), 1.78 s (1H,
endo-2-H), 1.79 s (3H, CH3), 3.69 s (3H, CO2CH3),
7.20–7.27 m (3H) and 7.28–7.36 m (2H) (Ph).
13C NMR spectrum, δC, ppm: 7.3 (CH3), 22.5 (C1),
22.7 (C3), 32.5 (C4), 43.4 (C2), 51.3 (OCH3), 126.1,
127.7 (2C), 128.1 (2C), 134.2, 168.2 (C=O). Found,
%: C 78.31; H 5.59. C13H11O2. Calculated, %: C 78.37;
H 5.57.
Methyl (Z)-3,4-diphenylpenta-2,4-dienoate
(VIb). Yield 26 mg (3%), colorless oily substance,
1
Rf 0.24. H NMR spectrum, δ, ppm: 3.65 s (3H,
CO2CH3), 5.25 s and 5.92 s (1H each, =CH2), 6.47 s
(1H, =CH), 7.26–7.34 m (3H), 7.36–7.42 m (3H),
7.44–7.52 m (2H), 7.57–7.66 m (2H). 13C NMR spec-
trum, δC, ppm: 51.2, 115.2, 118.0, 126.3, 127.5, 127.7,
128.4, 128.6, 129.5, 138.6, 138.7. 146.2, 156.0, 166.3.
Found, %: C 81.69; H 6.24. C18H16O2. Calculated, %:
C 81.79; H 6.10.
Methyl (Z)-2-benzylidene-3-methylbut-3-enoate
1
(VIIa). H NMR spectrum, δ, ppm: 2.07 s (3H, CH3),
3.76 s (3H, CO2Me), 5.09 s and 5.22 s (1H each,
=CH2), 6.70 s (1H, =CH), 7.25–7.37 m (5H, Ph).
Methyl (Z)-4-methyl-3-phenylpenta-2,4-dienoate
(VIIIa). 1H NMR spectrum, δ, ppm: 2.06 s (3H, CH3),
3.56 s (3H, CO2Me), 4.88 s and 5.37 s (1H each,
=CH2), 6.09 s (1H, =CH), 7.21–7.46 m (5H, Ph).
b. Analytical experiment. Compound I, 50 mg, was
added in one portion to 1.0 ml of boiling p-xylene, and
the mixture was heated for 15 min under reflux in
an argon atmosphere. The solvent was removed under
reduced pressure to leave 45 mg of a light yellow
Methyl (E)-4-methyl-3-phenylpenta-2,4-dienoate
(VIIIb). Yield 42 mg (6.4%), colorless oily substance,
1
1
viscous oily material which was analyzed by H NMR
Rf 0.31. H NMR spectrum, δ, ppm: 1.97 s (3H, CH3),
spectroscopy to reveal five compounds at a ratio
indicated in Table 1.
3.76 s (3H, CO2Me), 4.92 s and 5.27 s (1H each,
=CH2), 6.15 s (1H, =CH), 7.27–7.56 m (5H, Ph).
Found, %: C 78.49; H 5.34. C13H11O2. Calculated, %:
C 78.37; H 5.57.
b. Analytical experiment. Compound II, 50 mg, was
added in one portion to 1.0 ml of boiling p-xylene, and
the solution was heated for 30 min under reflux in
an argon atmosphere. The solvent was removed under
reduced pressure, and the light yellow viscous oily
residue was analyzed by 1H NMR (Table 1).
Thermolysis of methyl 5-methyl-1-phenyl-2,3-
diazabicyclo[3.1.0]hex-2-ene-6-carboxylate (II).
a. Preparative experiment. Ester II, 750 mg, was
added in one portion to 7.5 ml of boiling p-xylene. The
solution was heated for 30 min under reflux, the
solvent was removed under reduced pressure, and the
light yellow oily residue, 660 mg, was subjected to
chromatographic separation on silica gel to isolate
individual compounds IVa, IVb, and VIIIb. In addi-
tion, a fraction containing dienes VIIa and VIIIa at
a ratio of ~2:1 was isolated [Rf 0.34, colorless oily
substance, yield 102 mg (16%). Found, %: C 78.19;
H 5.64. C13H11O2. Calculated, %: C 78.37; H 5.57].
Signals of each components were identified in the
1H NMR spectrum of that fraction.
Dimethyl 1-methyl-3-phenylbicyclo[1.1.0]-
butane-2,4-dicarboxylate (IX) was synthesized
1
according to the procedure described in [19]. H NMR
spectrum, δ, ppm: 1.68 s (2H, endo-2-H, endo-4-H),
1.98 s (3H, CH3), 3.60 s (6H, CO2CH3), 7.28–7.40 m
(3H, Ph), 7.48–7.58 (2H, Ph). 13C NMR spectrum, δC,
ppm: 4.2 (CH3), 24.3 (C1), 29.2 (C3), 41.0 (C2, C4),
51.4 (OCH3), 127.8 (2C), 127.85 (2C), 129.6, 131.0,
167.4.
Methyl 1-methyl-3-phenylbicyclobutane-2-endo-
carboxylate (IVa). Yield 245 mg (37%), colorless oily
1
Dimethyl (E,E)-3,4-diphenylhexa-2,4-dienedi-
oate (IXa) was synthesized according to the procedure
substance, Rf 0.33. H NMR spectrum, δ, ppm: 1.40 s
2
4
(3H, CH3), 2.18 d.d (1H, exo-4-H, J = 1.0, J =
4.3 Hz), 2.32 br.s (1H, endo-4-H), 3.26 d (1H, exo-2-
H, J = 4.3 Hz), 3.71 s (3H, CO2CH3), 7.20–7.30 m
(2H, Ph), 7.32–7.42 m (3H, Ph). 13C NMR spectrum,
δC, ppm: 12.3 (CH3), 20.5 (C1), 24.6 (C3), 33.7 (C4),
1
described in [20]. H NMR spectrum, δ, ppm: 3.50 s
(6H, CO2CH3), 5.80 s (2H, 2-H, 5-H), 7.22–7.30 (4H)
and 7.40–7.50 (6H) (Ph). 13C NMR spectrum, δC, ppm:
51.3, 125.3, 128.2, 128.24, 128.6, 136.7, 155.9, 166.0.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 7 2013

RAZIN et al.
978
9. Razin, V.V., Yakovlev, M.E., Shataev, K.V., and
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Dimethyl (Z,Z)-3,4-diphenylhexa-2,4-dienedioate
(IXb) was synthesized as described in [21]. H NMR
spectrum, δ, ppm: 3.64 s (6H, CO2CH3), 6.60 s (2H,
2-H, 5-H), 7.33–7.40 (6H) and 7.53–7.60 (4H) (Ph).
13C NMR spectrum, δC, ppm: 51.3, 116.7, 127.0,
128.7, 129.6, 137.6, 154.4, 165.4.
1
12. Barfield, M. and Chakrabarti, B., Chem. Rev., 1969,
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