Substituted 5-dinitromethyl-3-phenyl-1,2,4-oxadiazoles in reactions with arylethenes

Article abstract of DOI:10.1023/B:RUJO.0000003170.40693.36

Reactions of substituted 5-dinitromethyl-3-phenyl-1,2,4-oxadiazoles with arylethenes of various nucleophilicity, number and position of substituents attached to the double bond give rise to nitroalkenes and secondary products resulting from α-nitroketones or nitroalcohols O-alkylation. The direction of transformations in the arising ion pair is governed predominantly by steric effects.

Full text of DOI:10.1023/B:RUJO.0000003170.40693.36

Russian Journal of Organic Chemistry, Vol. 39, No. 6, 2003, pp. 890 892. Translated from Zhurnal Organicheskoi Khimii, Vol. 39, No. 6, 2003,
pp. 939 941.
Original Russian Text Copyright
2003 by Tyrkov.
Substituted 5-Dinitromethyl-3-phenyl-1,2,4-oxadiazoles
in Reactions with Arylethenes
A. G. Tyrkov
Astrakhan State Pedagogical University, Astrakhan, 414056 Russia
Received February 23, 2001
Abstract Reactions of substituted 5-dinitromethyl-3-phenyl-1,2,4-oxadiazoles with arylethenes of various
nucleophilicity, number and position of substituents attached to the double bond give rise to nitroalkenes and
secondary products resulting from -nitroketones or nitroalcohols O-alkylation. The direction of transforma-
tions in the arising ion pair is governed predominantly by steric effects.
A specific character of dual reactivity of tetra-
nitromethane [1], halotrinitromethanes [2], or tri-
nitroacetonitrile [3] with arylalkenes originates from
intermediate formation of ambidental anions of tri-
nitromethane or dinitrocyanoacetate which depending
on the nature of the reacting partner are capable of
nucleophilic addition either at carbon (C-alkylation)
or oxygen (O-alkylation) atom. At the same time the
data on reactions with alkenes of polynitromethanes
possessing an oxadiazole moiety are scanty. The only
known example of reaction between 5-trinitromethyl-
3-phenyl-1,2,4-oxadiazole with phenylethene resulted
in denitration of azole and furnished -nitroketones
or 1-methyl-2-nitro-1-phenyl-1-ethanol [4]. Aiming at
revealing the main rules governing the reactions of
substituted 5-trinitromethyl-3-phenyl-1,2,4-oxazoles
with arylalkenes we studied under comparable condi-
tions the reactions between 5-trinitromethyl-3-phenyl-
1,2,4-oxadiazole (I) and its analog, substituted ester
II with a series of arylethenes of various nucleophili-
city, number and position of substituents attached to
the double bond. The structure and some spectral
characteristics of compounds I, II are similar to those
of trinitromethane; therefore it is reasonable to expect
that their electrophilic addition to arylalkenes would
proceed through formation of a -complex which
transforms into a reactive ion pair -nitrocarbocation
ambidentete anions of 5-dinitromethyl-3-phenyl-1,2,4-
oxadiazole or ethyl 3-phenyl-1,2,4-oxadiazol-5-
ylnitroacetate followed by conversion into the final
products. In the reaction of nitroalkanes I, II with
substituted 1,1-diphenylethenes the arising nitro-
carbocations A because of significant shielding effect
of two benzene rings are incapable to react with
anions B and undergo stabilization by ejecting a
proton and affording conjugated nitroalkenes III V.
I, VI, R4 = NO2; II, VII, R4 = CO2C2H5; III, R1 = R2 = Ph, R3 = H; IV, R1 = R2 = 4-CH3OC6H4, R3 = H; V,
R1 R2 4-Me2NC6H4, R2
Me.
=
=
=
From the reaction mixture were additionally isolat-
ed the products of decomposition of the initial
reagents: 5-dinitromethyl-3-phenyl-1,2,4-oxadiazole
(VI) from compound I or ethyl nitro(oxadiazolyl)-
acetate (VII) from compound II. The structure of
nitroalkenes III V was established by means of IR
spectra and confirmed by comparison of their
physical constants with the published data.
Reactions of oxadiazoles with arylalkenes where
the number of bulky phenyl substituents did not
exceed one at each carbon atom of the multiple bond
had more complicated pattern and depending on the
number and position of alkyl groups attached to the
double bond afforded -nitroketones or nitroalcohols.
This is due to reduction of steric hindrances at the
reaction site of the intermediate -nitrocarbocations A
1070-4280/03/3906-0890$25.00 2003 MAIK Nauka/Interperiodica

SUBSTITUTED 5-DINITROMETHYL-3-PHENYL-1,2,4-OXADIAZOLES
891
I, VI, XIV, R4 = NO2; II, VII, XV, R4 = CO2Et; VIII XI, XVI, R2 = R3 = H; VIII, Ar = Ph; IX, Ar =
4-MeC6H4; X, Ar = 4-BrC6H4; XI, Ar = 4-CH3OC6H4; XII, Ar = 4-CH3OC6H4, R2 = R3 = Me; XIII, Ar = Ph,
R2 = H, R3 = Ph; XIV, XV, R1 = H; XVI, Ar = Ph, R1 = Me; XVII, Ar = Ph, R1 = R2 = Me, R3 = H.
making possible their interaction with anions B.
For instance, the reaction of nitroalkanes I and II
with arylethenes disregarding the extent of their
nucleophilicity in the presence of a hydrogen in the
-position to the double bond gives rise to O-alkyl-
ated products, -nitroketones VIII XIII and oximes
XIV, XV.
addition to the initial alkene due to steric hindrances
created by the presence of a bulky heterocycle. There-
fore they suffer decomposition along the mechanism
of intramolecular oxidation reduction [5] into -nitro-
ketones VIII XIII. We proved the lack of formation
of the product originating from 1,3-dipolar addition
(the respective isoxalidine) by the method of
chemical trap : carrying out reaction of compound I
with 1-(4-methoxyphenyl)ethene in solution of active
dipolarophile, acrylonitrile. The formation of nitro-
alcohols XVI, XVII within the framework of the
assumed scheme may be rationalized as resulting from
hydration of intermediates A with water present in
the reaction mixture [6]. It should be noted that nitro-
alkane II unlike compound I is inert in reaction with
1,1- and 1,2-diphenylethenes apparently due to its
lower dipolarophile activity than that of compound I.
The structure of nitroketones was established from
their IR spectra, by comparison of the physical con-
stants with the published data, and also by preparation
of the corresponding 2,4-dinitrophenylhydrazones.
The reaction between nitroalkanes and arylethenes
having a methyl group instead of a hydrogen in the
-position to the multiple bond provides nitroalcohols
XVI, XVII and products of compounds I, II decom-
position (oxadiazoles VI, VII). The structure of nitro-
alcohols was established using IR and 1H NMR
spectra, and also by comparison of their physical
constants with the published data. In none of the
reactions under study products of C-alkylation were
obtained. The single pathway taken by reaction of
oxadiazolenitroalkanes I, II with arylalkenes evid-
ences that the intermediate anions are prone to
O-alkylation with the arising nitrocarbocations. Inte-
rmediately forming nitron esters C in all cases studied
evidently are not able to undergo 1,3-dipolar cyclo-
EXPERIMENTAL
IR spectra were recorded on spectrophotometer
IKS-29 from solutions in chloroform. 1H NMR
spectra were registered on spectrometer Tesla BS-
487C980 MHz) in acetone-d6, internal reference
HMDS. Compounds I and II were synthesized as in
[7], arylalkenes were prepared from appropriate
carbonyl compounds and alkylmagnesium halides
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 6 2003

892
TYRKOV
1
with isolation of alcohols followed by their dehydra-
tion [8]. Physical constants of arylethenes were in
agreement with the published values.
cm : 1720 (C=O). 1H NMR spectrum, , ppm:
7.75 m (C6H5); 4.50 q (CH2); 1.30 t (CH3). Found, %:
C 55.06; H 4.14; N 16.02. C12H11N3O4. Calculated,
%: C 55.17; H 4.22; N 16.09.
Reaction of 5-R-dinitromethyl-3-phenyl-1,2,4-
oxadiazoles I, II with arylethenes. To a solution of
5 mmol of compound I or II in 10 ml of anhydrous
ethyl ether at 0 5 C was added 5 mmol of arylethene
ethereal solution. The reaction mixture was maintain-
ed for 10 days at 25 C, the solvent was evaporated,
and the residue was subjected to chromatography on
a column (10 250 mm) packed with activated silica
gel of Silicagel 100/400 brand. Eluent for com-
pounds VIII X, XII, XIII, XVI, XVII C6H6, for
compounds III V, XI CHCl3, for compounds VI,
VII, XIV, XV ethyl ether.
1-Methyl-2-nitro-1-phenyl-1-ethanol
(XVI).
Yield 52%, n 20 1.5190 [16].
D
1,2-Dimethyl-2-nitro-1-phenyl-1-ethanol (XVII).
Yield 54%, nD20 1.5216. IR spectrum, , cm :
1
1
3550 (OH); 1560, 1350 (NO2). H NMR spectrum, ,
ppm: 7.24 m (C6H5); 5.47 s (OH); 4.54 q (CH);
1.70 d (CH3); 1.63 s (CH3). Found, %: C 61.46;
H 6.58; N 7.06. C10H13NO3. Calculated, %:
C 61.54; H 6.67; N 7.18.
REFERENCES
1,1-Diphenyl-2-nitroethene (III). Yield 48%,
mp 88 C [9].
1. Altukhov, K.V. and Perekalin, V.V., Zh. Org. Khim.,
1967, vol. 3, p. 2003.
1,1-Bis(4-methoxyphenyl)-2-nitroethene (IV).
Yield 55%, mp 114 C [10].
2. Tartakovskii, V.A., Fainzil,berg, A.A., Gulev-
skaya, V.I., and Novikov, S.S., Izv. Akad. Nauk
SSSR, Ser. Khim., 1968, p. 621.
1,1-Bis(4-dimethylaminophenyl)-2-methyl-2-
nitroethene (V). Yield 57%, mp 142 143 C [11].
3. Ratsino, E.V., Andreeva, L.M., Altukhov, K.V., and
Perekalin, V.V., Zh. Org. Khim., 1974, vol. 10, p. 728.
4. Tyrkov, A.G. and Kosova, Yu.V., Zh. Org. Khim.,
2000, vol. 36, p. 1879.
5-Dinitromethyl-3-phenyl-1,2,4-oxadiazole (VI).
Yield 10%, mp 83 84 C [4].
Ethyl 3-phenyl-1,2,4-oxadiazol-5-ylnitro-acetate
5. Tartakovskii, V.A., Ioffe, S.L., and Novikov, S.S.,
Zh. Org. Khim., 1967, vol. 3, p. 628.
6. Altukhov, K.V. and Perekalin, V.V., Usp. Khim.,
1976, vol. 45, p. 2050.
1
(VII). Yield 10%, mp 115 C. IR spectrum, , cm :
1
1775 (C=O); 1590, 1380 (NO2). H NMR spectrum,
, ppm: 7.62 m (C6H5); 6.84 s (CH); 4.52 q (CH2);
1.32 t (CH3). Found, %: C 51.83; H 3.85; N 15.04.
C12H11N3O5. Calculated, %: C 51.99; H 3.97;
N 15.16.
7. Ladyzhnikova, T.D., Altukhov, K.V., and Solov,-
ev, N.A., Zh. Org. Khim., 1986, vol. 22, p. 2618.
8. Agronomov, A.E. and Shabarov, Yu.S., Laborator-
nye raboty v organicheskom praktikume (Students
Works in Organical Laboratory), Moscow: Khimiya,
1974, p. 145.
2-Nitro-1-phenyl-1-ethanone (VIII). Yield 55%,
mp 105 C [12].
2-Nitro-1-(4-t°lyl)-1-ethanone (IX). Yield 57%,
mp 144 145 C [13].
9. Wieland, W. and Rahn, F., Ber., 1921, vol. 54,
p. 1770.
10. Altukhov, K.V., Ratsino, E.V., and Perekalin, V.V.,
Zh. Org. Khim., 1973, vol. 9, p. 269.
11. Dornow, A. and Lupfel, S., Chem. Ber., 1957,
vol. 90, p. 1780.
1-(4-Bromophenyl)-2-nitro-1-ethanone
Yield 52%, mp 177 178 C [13].
(X).
1-(4-Methoxyphenyl)-2-nitro-1-ethanone (XI).
Yield 56%, mp 153 154 C [14].
12. Fujise, S., Takenchio, O., Kamoika, T., and Tiba, K.,
Ber., 1935, vol. 68, 1272.
2-Methyl-1-(4-methoxyphenyl)-2-nitro-1-etha-
13. Zheved,, T.D., Cand. Sci. (Chem.) Dissertation,
Leningrad, 1978.
none (XII). Yield 61%, nD20 1.5545 [15].
1,2-Diphenyl-2-nitro-1-ethanone (XIII). Yield
48%, mp 64 C [13].
14. Tyrkov, A.G., Ladyzhnikova, T.D., and Altu-
khov, K.V., Zh. Org. Khim., 1990, vol. 26, p. 1134.
15. Ratsino, E.V., Altukhov, K.V., and Perekalin, V.V.,
Zh. Org. Khim., 1972, vol. 8, p. 523.
16. Sitkin, A.I., Cavmulina, O.Z., Fridman, A.L., and
Zakharova, L.I., Khim. i Khim. Tekhnol., Kuzbass:
Kuzbass. Gos. Univ., 1974, no. 69, p. 158.
Nitro(3-phenyl-1,2,4-oxadiazol-5-yl)methanal
oxime (XIV). Yield 10%, mp 97 98 C [4].
Ethyl (3-phenyl-1,2,4-oxadiazol-5-yl)acetate
oxime (XV). Yield 12%, mp 154 C. IR spectrum, ,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 6 2003