4-Dimethylaminoacetophenone O-vinyloxime: Synthesis and steric structure

Article abstract of DOI:10.1134/S1070428008100163

4-Dimethylaminoacetophenone oxime was synthesized from 4- dimethylaminoacetophenone and hydroxylamine hydrochloride. Its reaction with acetylene in the system KOH-DMSO gave previously unknown 4- dimethylaminoacetophenone O-vinyloxime as the major product.

Full text of DOI:10.1134/S1070428008100163

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 10, pp. 1497–1503. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © L.N. Sobenina, A.P. Demenev, A.I. Mikhaleva, Yu.Yu. Rusakov, L.I. Larina, N.V. Istomina, L.B. Krivdin, 2008, published in Zhurnal
Organicheskoi Khimii, 2008, Vol. 44, No. 10, pp. 1521–1526.
Dedicated to Full Member of the Russian Academy of Sciences
B.A. Trofimov on his 70th anniversary
4-Dimethylaminoacetophenone O-Vinyloxime:
Synthesis and Steric Structure
L. N. Sobenina, A. P. Demenev, A. I. Mikhaleva, Yu. Yu. Rusakov, L. I. Larina,
N. V. Istomina, and L. B. Krivdin
Favorskii Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
e-mail: sobenina@irioch.irk.ru
Received June 19, 2008
Abstract—4-Dimethylaminoacetophenone oxime was synthesized from 4-dimethylaminoacetophenone and
hydroxylamine hydrochloride. Its reaction with acetylene in the system KOH–DMSO gave previously un-
known 4-dimethylaminoacetophenone O-vinyloxime as the major product. According to the experimental data
and quantum-chemical calculations, 4-dimethylaminoacetophenone O-vinyloxime is formed as the only E
isomer with preferential s-trans conformation of the vinyloxy group, which is characterized by essentially non-
planar structure.
DOI: 10.1134/S1070428008100163
O-Vinyloximes attract persistent interest as prom-
ising monomers and intermediate products, especially
since the development of a procedure for their syn-
thesis via vinylation of oximes with acetylene [1–5].
The presence in O-vinyloxime molecules of a double
bond contiguous to two heteroatoms (CH2=CH–O–N=)
endows them with some specific properties which
make such compounds interesting models for
theoretical and spectral studies [6–8]. However, a seri-
ous obstacle hampering studies on O-vinyl oximes is
their chemical and thermal instability. It is known that
ketone O-vinyloximes having a methylene group in the
α-position with respect to the oxime moiety are key
intermediates in the synthesis of pyrroles from oximes
and acetylene (Trofimov reaction) [1, 2]. Alkyl aryl
ketone O-vinyloximes, especially those containing
electron-withdrawing substituents in the aromatic ring
are more prone to undergo cyclization to pyrroles, as
compared to their aliphatic analogs [4]. It might be ex-
pected that acetophenone O-vinyloximes having elec-
tron-donating groups in the benzene ring should be
more stable than unsubstituted acetophenone O-vinyl-
oxime and that such derivatives could be isolated as
individual substances.
Scheme 1.
CH2
OH
O
O
N
N
(1) NH2OH·HCl
(2) NaOH
HC CH, KOH–DMSO
≡
Me
Me
Me
Me2N
Me2N
Me2N
I
II
N
N
+
+
H
CH2
Me2N
Me2N
III
IV
1497

SOBENINA et al.
1498
1°
51°
1°
49°
3°
2°
s-trans-Z (1.9 kcal/mol)
s-cis-Z (2.1 kcal/mol)
4°
35°
31°
0°
3°
2°
s-trans-E (0.0 kcal/mol)
s-cis-E (0.2 kcal/mol)
Fig. 1. Equilibrium conformations of the E and Z isomers of model 4-aminoacetophenone O-vinyloxime, optimized by the
MP2/6-311G** method. The relative total energies are given in parentheses, and arrows show angular deviations of the phenyl and
vinyl group from the plane of the oxime fragment.
1H-pyrrole (0.8%) [4]. We succeeded in raising the
yield of vinyl oxime II to 85% by carrying out the
reaction of 4-dimethylaminoacetophenone oxime with
acetylene in pentane which favored removal of the
product from the reaction zone. In this case, the only
by-product was pyrrole (III, yield 5%).
In fact, 4-dimethylaminoacetophenone oxime (I)
prepared in 90% yield from 4-dimethylaminoaceto-
phenone and hydroxylamine hydrochloride reacted
with acetylene in the system KOH–DMSO (80°C, 1 h,
acetylene pressure 15 atm) to give mainly 4-dimethyl-
aminoacetophenone O-vinyloxime (II) in 70% yield.
Apart from compound II, the reaction mixture con-
tained 2-(4-dimethylaminophenyl)pyrrole (III, 6%)
and its N-vinyl derivative IV (12%) (Scheme 1). It
should be noted for comparison that vinylation of
acetophenone oxime under analogous conditions leads
to a mixture of acetophenone O-vinyloxime (4.5%),
2-phenyl-1H-pyrrole (53.4%), and 2-phenyl-1-vinyl-
Heating of O-vinyloxime II in DMSO at 120°C
promoted its rearrangement into pyrrole III (89%); the
latter was synthesized previously in 48% yield by
palladium-catalyzed cross coupling of pyrrolyl anion
with 4-bromo-N,N-dimethylaniline [9] or by photolysis
of 4-chloro-N,N-dimethylaniline in the presence of
pyrrole (yield 64%) [10]. The rearrangement of II into
Scheme 2.
CH2
O
N
DMSO, 120°C, 1 h
N
Me
H
Me2N
Me2N
II
III
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 10 2008

4-DIMETHYLAMINOACETOPHENONE O-VINYLOXIME:
1499
Calculateda (SOPPA CCSD) and experimental 13C–13C and 13C–1H coupling constants (Hz) of 4-dimethylaminoacetophenone
O-vinyloxime (II)
HX
O
HA
HB
α
β
N
2
1
Me2N
3 Me
Coupling
constant
Conforma-
tion
Isomer
JDSO
JPSO
JSD
JFC
J
Jexp
1J(C1,C2)
1J(C2,C3)
1J(Cα,Hβ)
1J(Cα,HX)
1J(Cβ,HA)
1J(Cβ,HB)
Z
s-trans
s-cis
0.36
0.35
0.34
0.35
0.26
0.26
0.27
0.27
0.18
0.18
0.18
0.18
1.00
0.96
0.99
0.94
0.57
0.59
0.56
0.59
0.61
0.66
0.60
0.66
–1.47
–1.45
–1.67
–1.68
–1.04
–1.07
–1.12
–1.14
–8.06
–7.96
–8.07
–7.98
–0.22
–0.10
–0.22
–0.09
–0.76
–0.76
–0.75
–0.74
–0.66
–0.52
–0.67
–0.51
0.67
0.66
0.79
0.76
0.71
0.71
0.69
0.69
3.24
3.08
3.25
3.11
0.26
0.18
0.26
0.19
0.37
0.36
0.37
0.36
0.35
0.41
0.35
0.40
054.34
053.94
062.68
062.53
051.46
051.39
043.33
043.30
085.75
084.29
085.71
084.48
182.36
179.56
183.10
179.82
160.64
159.03
160.98
159.13
157.03
162.38
156.78
162.63
053.90
053.50
062.14
061.96
051.39
051.29
043.17
043.12
081.11
079.59
081.07
070.79
183.40
180.60
184.13
180.86
162.34
160.74
162.66
160.82
158.65
163.97
158.40
164.20
060.9
E
Z
E
Z
E
Z
E
Z
E
Z
E
s-trans
s-cis
s-trans
s-cis
041.8
080.7
185.0
162.0
158.5
s-trans
s-cis
s-trans
s-cis
s-trans
s-cis
s-trans
s-cis
s-trans
s-cis
s-trans
s-cis
s-trans
s-cis
s-trans
s-cis
s-trans
s-cis
a
The calculations were performed for 4-aminoacetophenone O-vinyloxime to reduce computational expenses.
III was accompanied by side formation of 4-dimethyl-
aminoacetophenone, presumably as a result of decom-
position of initial O-vinyloxime II (Scheme 2) [4].
This rearrangement required more prolonged heating
(1 h) than did analogous transformation of ethyl me-
sityl ketone O-vinyloxime into the corresponding pyr-
role [11], which was complete in 5 min. These findings
provide an additional support to thermal stability of
O-vinyloxime II.
methylaminoacetophenone O-vinyloxime (II), in par-
ticular configuration of the C=N bond and predomi-
nant conformation related to internal rotation of the
vinyloxy group.
The results of quantum-chemical calculations per-
formed at the MP2/6-311G** level of theory showed
that the E isomer of model 4-aminoacetophenone
O-vinyloxime in the gas phase is more stable than the
Z isomer by ~2 kcal/mol and that each isomer gives
rise to two conformers due to internal rotation of the
vinyloxy group, s-cis and s-trans, with as small energy
difference as 0.2 kcal/mol (Fig. 1). Presumably, the Z
Taking into account stereoselectivity of intramolec-
ular cyclization of O-vinyloximes [1, 2], it seemed
very important to determine the steric structure of 4-di-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 10 2008

SOBENINA et al.
1500
isomer is less stable owing to strong steric interaction
between protons in the ortho positions of the benzene
ring and the azomethine fragment. This follows from
considerable deviation of the phenyl ring from the
CH=N plane: the corresponding dihedral angle reaches
35–50° (Fig. 1). The results of calculations allowed us
to presume that the only formed isomer of 4-dimethyl-
aminoacetophenone O-vinyloxime (II) has E configu-
ration at the C=N bond; however, preferential con-
formation of that conformer cannot be determined on
the basis of the above data.
It is known that 13C–13C coupling constants display
pronounced dependence on the orientation of lone
electron pair (LEP) on the nitrogen atom in oximes and
their derivatives [12]. The lone electron pair on the
imino nitrogen atom provides a positive through-space
contribution to the 13C–13C coupling constant for the
neighboring carbon–carbon bond in the cis position
(Jcis) with respect to the LEP; on the other hand, un-
paired electron density transfer from the C=N nitrogen
atom to the antibonding orbital of the neighboring
carbon–carbon bond in the trans position reduces the
corresponding 13C–13C coupling constant (Jtrans), i.e.,
the contribution of the nitrogen LEP to that constant is
negative. The nature of this effect was studied in detail
in [13]. Thus the effect of LEP strongly differentiates
the 13C–13C coupling constants Jcis and Jtrans, so that
they can be used to unambiguously assign configura-
tion of not only oximes and their derivatives but also
various Schiff bases (see [14] and references therein).
If 13C–13C coupling constants could be determined
experimentally for both isomers (Jcis and Jtrans), their
assignment is obvious; if only one value (Jcis or Jtrans
)
could be measured, it is necessary to calculate 13C–13C
coupling constants for both isomers by quantum-chem-
ical method and compare the calculated value with the
experimental one. According to the GLC and 13C NMR
data, compounds I and II exist as a single isomer. First
of all, we measured the corresponding 13C–13C cou-
pling constants from the position of 13C satellites of
the C=N carbon (C2) signal in the 13C NMR spectrum
of 4-dimethylaminoacetophenone O-vinyloxime (II)
(Fig. 2), and the 13C–13C and 13C–1H coupling con-
stants for both isomers were calculated with account
taken of their conformation (see table).
The 13C–13C coupling constants for compound II
were calculated in terms of the second-order polariza-
tion propagator approximation (SOPPA) with coupled
cluster singles and doubles amplitudes (CCSD), which
was proposed for the first time in [15]. We used special
Dunning’s correlation-consistent basis sets [16] ex-
tended by correlating functions and optimized for the
calculation of 13C–13C and 13C–1H coupling constants
as described in [17]. The total 13C–13C and 13C–1H cou-
C2
CH2
N
O
1
2
Me2N
3 Me
1J(C1,C2)
1J(C2,C3)
157.6
157.5
157.4
157.3
157.2
157.1
157.0
156.9
δC, ppm
Fig. 2. Satellites of the 13C signal from the azomethine carbon atom in the downfield region of the 13C NMR spectrum (101.61 MHz)
of 4-dimethylaminoacetophenone O-vinyloxime (II) in CDCl3.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 10 2008

4-DIMETHYLAMINOACETOPHENONE O-VINYLOXIME:
1501
pling constants were calculated with account taken of
four contributions: Fermi-contact (JFC), spin–dipole
(JSD), diamagnetic spin–orbital (JDSO), and paramag-
netic spin–orbital (JPSO). It is seen that the calculated
either standard basis sets or those modified by the
authors (for details, see [20]).
The reaction mixtures and products were analyzed
by thin-layer chromatography on Silufol UV-254
plates using hexane–diethyl ether (1 :1 or 1:3) as
eluent. 4-Dimethylaminoacetophenone was synthe-
sized by alkylation of 4-aminoacetophenone with
paraformaldehyde in the presence of formic acid
(Leuckart–Wallach reaction) according to the proce-
dure described in [21].
1
1
total coupling constants J(C1,C2) and J(C2,C3) are
determined almost completely by the Fermi-contact
contribution. As might be expected, their values for
the E and Z isomers of 4-dimethylaminoacetophenone
O-vinyloxime (II) differ by more than 10 Hz (see
1
1
above). The calculated J(C1,C2) and J(C2,C3) values
for the E isomer of II approach those found experi-
mentally (the difference is within the experimental
4-Dimethylaminoacetophenone oxime (I). A mix-
ture of 2.00 g (12.3 mmol) of 4-dimethylaminoaceto-
phenone, 1.45 g (20.8 mmol) of hydroxylamine hydro-
chloride, 40 ml of ethanol, and 4 ml of water was
stirred for 15 min at room temperature. Pelletized
sodium hydroxide, 2.73 g (68.2 mmol), was then added
over a period of 0.5 h, and the mixture was stirred for
1 h at room temperature and for 1 h at 50°C, cooled,
and neutralized with 10% hydrochloric acid. The pre-
cipitate was filtered off, washed with water (3×50 ml),
dried in air, and recrystallized from chloroform. Yield
2.14 g (98%), light yellow crystals, mp 203°C. IR
spectrum, ν, cm–1: 3220, 2904, 2820, 1607, 1552,
1528, 1484, 1447, 1412, 1373, 1363, 1319, 1233,
1201, 1176, 1132, 1086, 1067, 1002, 947, 914, 819,
error). The calculated J(C1,C2) value for the Z isomer
1
is lesser than the experimental value by more than
1
10 Hz, whereas the calculated J(C2,C3) value exceeds
the experimental coupling constant by more than
10 Hz. These data unambiguosuly indicate that both
4-dimethylaminoacetophenone O-vinyloxime (II) and
its precursor, 4-dimethylaminoacetophenone (I), are E
isomers with respect to the C=N bond. It should be
1
specially emphasized that the constants J(C1,C2) and
1J(C2,C3) are not sensitive to conformational behavior
related to internal rotation of the vinyloxy group (see
table). This means that the described method can be
used to determine configuration of conformationally
heterogeneous O-vinyloximes.
1
764, 727, 583, 556, 512, 485, 436. H NMR spectrum
On the other hand, comparison of the experimental
and calculated coupling constants 1J(Cβ,HA), 1J(Cβ,HB),
1J(Cα,HX), and 1J(Cα,Cβ), which strongly depend on the
orientation of the vinyloxy group (see table), allowed
us to unambiguously assign preferential s-trans con-
formation to both isomers of 4-dimethylaminoaceto-
phenone O-vinyloxime (II).
(DMSO-d6), δ, ppm: 2.08 s (3H, Me), 2.91 s (6H, Me),
6.68 d (2H, Harom, J = 8.9 Hz), 7.47 d (2H, Harom, J =
8.9 Hz), 10.68 br.s (1H, OH). 15N NMR spectrum
(DMSO-d6), δN, ppm: –23.5 (NOH), –329.1 (NMe2).
Found, %: C 67.64; H 8.21; N 15.49. C10H14N2O. Cal-
culated, %: C 67.39; H 7.92; N 15.72.
4-Dimethylaminoacetophenone O-vinyloxime
(II). a. A 250-ml steel rotating high-pressure reactor
was charged with 1.00 g (5.61 mmol) of oxime I,
0.314 g (5.61 mmol) of KOH, and 40 ml of DMSO.
The mixture was saturated with acetylene to a pressure
of 15 atm and heated for 1 h at 80°C. After cooling, the
mixture was diluted with 150 ml of water and ex-
tracted with diethyl ether (5×50 ml). The combined
extracts were washed with water (2×50 ml), dried over
MgSO4, and evaporated, and the residue was subjected
to column chromatography on Al2O3 using diethyl
ether–hexane (1:1) as eluent. Yield 0.80 g (70%), light
gray crystals, mp 51°C.
EXPERIMENTAL
The IR spectra (400–4000 cm–1) were recorded in
KBr on a Bruker IFS-25 spectrometer. The H, 13C,
1
and 15N NMR spectra were measured on a Bruker DPX
400 instrument at 400.13, 100.61, and 40.56 MHz,
respectively. The chemical shifts were determined
relative to tetramethylsilane (1H, 13C) or nitromethane
(15N). The 13C–13C coupling constants were determined
from the positions of 13C satellites in the 13C NMR
spectrum of 4-dimethylaminoacetophenone O-vinyl-
oxime (II) with native concentration of 13C isotope; the
spectrum was recorded on a Bruker Avance-400 spec-
trometer (101.61 MHz) from a concentrated solution in
CDCl3 (accumulation time 12 h).
b. The reaction was performed in a similar way
using 1.00 g (5.61 mmol) of oxime I, 0.314 g
(5.61 mmol) of KOH, 40 ml of DMSO, and 40 ml of
pentane. After cooling, the pentane layer was separat-
Quantum-chemical calculations were performed
using GAMESS [18] and DALTON software [19] with
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 10 2008

SOBENINA et al.
1502
4. Trofimov, B.A., Mikhaleva, A.I., Vasiltsov, A.M.,
Schmidt, E.Yu., Tarasova, O.A., Morozova, L.V.,
Sobenina, L.N., Preiss, Th., and Henkelman, J.,
Synthesis, 2000, p. 1125.
ed, washed with water, and dried over magnesium
sulfate. Removal of the solvent gave 0.54 g (47%) of
oxime II. The dimethyl sulfoxide solution was treated
as described above in a to isolate 0.44 g (38%) of
oxime II and 0.05 g (5%) of pyrrole III. IR spectrum
of II, ν, cm–1: 2922, 2862, 2820, 1639, 1609, 1546,
1524, 1481, 1443, 1369, 1319, 1283, 1231, 1202,
1183, 1076, 1003, 969, 947, 881, 845, 821, 787, 724,
5. Vasil’tsov, A.M., Shmidt, E.Yu., Mikhaleva, A.I., Zai-
tsev, A.B., Tarasova, O.A., Afonin, A.V., Toryashino-
va, D.-S.D., Il’icheva, L.N., and Trofimov, B.A., Russ.
J. Org. Chem., 2001, vol. 37, p. 334.
6. Sohlberg, K., Leary, S.P., Owen, N.L., and Trofi-
1
689, 583, 558, 506, 483. H NMR spectrum (CDCl3),
δ, ppm: 2.25 s (3H, Me), 2.96 s (6H, Me), 4.11 d (1H,
HB, JBX = 15.0 Hz), 4.64 d (1H, HA, JAX = 7.4 Hz),
mov, B.A., Vibr. Spectrosc., 1997, vol. 13, p. 227.
7. Shagun, V.A., Sinegovskaya, L.M., Toryashinova, D.-
S.D., Tarasova, O.A., and Trofimov, B.A., Izv. Ross.
Akad. Nauk, Ser. Khim., 2001, p. 732.
6.65 d (2H, Harom, J = 8.9 Hz), 6.99 d.d (1H, HX, JAX
=
7.4 Hz, JBX = 15.0 Hz), 7.57 d (2H, Harom, J = 8.9 Hz).
13C NMR spectrum (CDCl3), δC, ppm: 12.5, 40.2, 87.8,
111.5, 122.5, 128.2, 151.1, 152.8, 156.8. 15N NMR
spectrum (CDCl3), δN, ppm: –15.0 (NO), –328.4
(NMe2). Found, %: C 70.74; H 8.00; N 13.55.
C12H16N2O. Calculated, %: C 70.56; H 7.89; N 13.71.
8. Afonin, A.V., Ushakov, I.A., Zinchenko, S.V., Taraso-
va, O.A., and Trofimov, B.A., Magn. Reson. Chem.,
2000, vol. 38, p. 994.
9. Rieth, R.D., Mankad, N.P., Calimano, E., and
Salighi, J.P., Org. Lett., 2004, vol. 6, p. 3981.
10. Guizzardi, B., Mella, M., Fagnoni, M., and Albini, A.,
Tetrahedron, 2000, vol. 56, p. 9383.
2-(4-Dimethylaminophenyl)-1H-pyrrole (III).
A solution of 0.52 g (2.55 mmol) of O-vinyloxime II
in 30 ml of DMSO was heated for 1 h at 120°C. The
mixture was cooled to room temperature and diluted
with 150 ml of water, and the precipitate was filtered
off, dried in air, and purified by sublimation. Yield
0.42 g (89%), light yellow crystals, mp 180°C. IR
spectrum, ν, cm–1: 3420, 2921, 2887, 2801, 1614,
1597, 1517, 1481, 1441, 1323, 1227, 1193, 1168, 1125,
1062, 1033, 947, 881, 818, 789, 711, 589, 546.
1H NMR spectrum (CDCl3), δ, ppm: 2.93 s (6H, Me),
6.24 d.d (1H, 4-H, J = 2.4, 6.0 Hz), 6.33 m (1H, 3-H),
6.71 d (2H, Harom, J = 8.9 Hz), 6.75 m (1H, 5-H),
7.33 d (2H, Harom, J = 8.9 Hz), 8.33 br.s (1H, NH).
13C NMR spectrum (CDCl3), δC, ppm: 40.6, 103.8,
109.6, 112,8, 117.4, 121.8, 125.0, 132.7, 149.0. Found,
%: C 77.14; H 7.36; N 14.97. C12H14N2. Calculated, %:
C 77.38; H 7.58; N 15.04.
11. Zaitsev, A.B., Meallet-Renault, R., Schmidt, E.Yu., Mi-
khaleva, A.I., Badre, S., Dumas, C., Vasiltsov, A.M.,
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This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 08-03-00021).
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