Unexpected formation of 2-phenyloxazolo[3,2-α]benzimidazole from 2-chloro-1-phenacylbenzimidazole and an example of its transformation into 3-phenyl-1,4-dihydro-1,2,4-triazino-[4,3-α]benzimidazole by the action of hydrazine hydrate [4]

Full text of DOI:10.1023/A:1013208522951

Chemistry of Heterocyclic Compounds, Vol. 37, No. 9, 2001
UNEXPECTED FORMATION OF
a
2-PHENYLOXAZOLO[3,2- ]BENZIMIDAZOLE
FROM 2-CHLORO-1-PHENACYLBENZIMIDAZOLE
AND AN EXAMPLE OF ITS TRANSFORMATION
INTO 3-PHENYL-1,4-DIHYDRO-1,2,4-TRIAZINO-
a
[4,3- ]BENZIMIDAZOLE BY THE ACTION
OF HYDRAZINE HYDRATE
M. V. Povstyanoi, V. P. Kruglenko, and V. M. Povstyanoi
Keywords: 2-chloro-1-phenacylbenzimidazole, 2-phenyloxazolo[3,2-a]benzimidazole, hydrazine
hydrate, ring expansion, 1,4-dihydro-3-phenyl-1,2,4-triazino[4,3-a]benzimidazole.
We have found that heating 2-chloro-1-phenacylbenzimidazole (1) in DMF at reflux with
aminoguanidine for 2 h leads to 3-phenyl-1,4-dihydro-1,2,4-triazino[4,3-a]benzimidazole (2), which is identical
to the product of the reaction of ketone 1 with hydrazine hydrate [1].
The
reaction
of
the
compound
1
with
acetophenone
aminoguanylhydrazone
H2NCH(=NH)NHN=C(Me)Ph under the same conditions proceeds differently and gives previously unreported
2-phenyloxazolo[3,2-a]benzimidazole (3). Product 3 was also obtained in 76% yield by heating ketone 1 with
sodium benzoate in DMF at reflux for 2 h. This method is analogous to the synthesis of oxazolotheophylline
from 8-bromo-7-phenacyltheophylline [2].
At heating of the compound 3 with hydrazine hydrate in DMF at reflux for 4 h the expansion of the
oxazole ring to a 1,2,4-triazine ring has been observed for the first time, triazinobenzimidazole 2 being formed
in the reaction.
Ph
N
N
N
2
N
H
Ph
N
C
O
N
Cl
1
N
N
3
O
Ph
__________________________________________________________________________________________
Kherson State Technical University, Kherson 73008, Ukraine, e-mail: lvi@tlc.kherson.ua,
kstu@tlc.kherson.ua. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1284-1285,
September, 2001. Original article submitted March 8, 2001, submitted after revision June 19, 2001.
0009-3122/01/3709-1179$25.00©2001 Plenum Publishing Corporation
1179

a
was obtained in 86% yield;
3-Phenyl-1,4-dihydro-1,2,4-triazino[4,3- ]benzimidazole (2)
mp 305-307°C (aq. DMF) (306-308°C [1]). Mass spectrum, m/z (Irel, %): 249 (24) [M + 1]+, 248 (100) M+,
145 (43) [M - PhCN]+, 144 (29), 119 (10), 118 (36) [M - PhCN - HCN]+, 91 (10) [M - PhCN - 2HCN]+, 77 (11)
Ph+.
a
was obtained in 49% yield; mp 235-237°C (aq. DMF).
2-Phenyloxazolo[3,2- ]benzimidazole (3)
IR spectrum (KBr): vC–O–O 1080, benzimidazole fragment 1490, 1150, 995, 850 cm-1 (see [3]). Mass spectrum,
m/z (Irel, %): 236 (6) [M + 1]+, 234 (100) M+, 233 (14), 206 (34) [M - CO]+, 205 (50) [M - COH]+, 118 (32)
CH
PhC
; C7H4N2 116 (14), 89 (19), 77 (25) Ph+ (see data on the fragmentation of oxazole derivatives [4]).
O
Found, %: C 77.20; H 4.22; N 12.12. C15H10N2O. Calculated, %: C 76.91; H 4.30; N 11.96.
REFERENCES
1.
2.
M. V. Povstyanoi, E. V. Logachev, and P. M. Kochergin, Khim. Geterotsikl. Soedin., 1287 (1975).
S. N. Garmash, B. A. Priimenko, N. A. Klyuev, N. I. Romanenko, V. A. Golets, and T. A. Kozik, Khim.
Geterotsikl. Soedin., 534 (1988).
G. A. Shvekhgeimer and G. A. Mikheichev, Khim. Geterotsikl. Soedin., 820 (1974).
P. B. Terent'ev and A. P. Stankyavichius, Mass-spectrometric Analysis of Biologically Active Bases
[in Russian], Mokslas, Vilnius (1987), p. 161.
3.
4.
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