First Synthesis of Novel Pentaheterocyclic Ring System of 1,2,4-Triazolo[2″,3″:6′,1′]pyrimido [4′,5′ :2,3]pyrido[1,2-a]benzimidazole

Article abstract of DOI:10.1002/jhet.5570410222

Reaction of 1-amino-3-arylpyrido[1,2-a] benzimidazole-2,4-dicarbonitrile (1) with dimethylformamide-dimethylacetal (DMF-DMA) gave 1-[N,N -(dimethylaminomethylene)amino]-3-arylpyrido[1,2-a]benzimidazole-2, 4-dicarbonitrile (2). Compounds (1) reacted with triethylorthoformate yielding 1-[N-(ethoxymethylene)amino] -3-arylpyrido[1,2-a]benzimidazole-2,4-dicarbonitrile (3). 3-Amino-4-imino-5-aryl-6-cyanopyrimido[5′,4′:5,6]pyrido[1,2-a] benzimidazole (4) was synthesized via condensation of either (2) or (3) with hydrazine hydrate. Reactions of (4) with acetic anhydride, ethyl chloroformate or aryl isothiocyanate yielded the respective derivative of the new ring system namely 1,2,4-triazolo[2″,3″:6′,1′]pyrimido[4′ ,5′:2,3]pyrido[1,2-a]benzimidazole (5-7).

Full text of DOI:10.1002/jhet.5570410222

Mar-Apr 2004
281
First Synthesis of Novel Pentaheterocyclic Ring System of 1,2,4-
Triazolo[2",3":6',1']pyrimido[4',5':2,3]pyrido[1,2-a]benzimidazole
Nehal M. Elwan
Department of Chemistry, Faculty of Science, Cairo University, Giza, Egypt
Received October 9, 2003
Reaction of 1-amino-3-arylpyrido[1,2-a]benzimidazole-2,4-dicarbonitrile (1) with dimethylformamide-
dimethylacetal (DMF-DMA) gave 1-[N,N-(dimethylaminomethylene)amino]-3-arylpyrido[1,2-a]benz-
imidazole-2,4-dicarbonitrile (2). Compounds (1) reacted with triethylorthoformate yielding 1-[N-(ethoxy-
methylene)amino]-3-arylpyrido[1,2- a]benzimidazole-2,4-dicarbonitrile (3). 3-Amino-4-imino-5-aryl-6-
cyanopyrimido[5',4':5,6]pyrido[1,2-a] benzimidazole (4) was synthesized via condensation of either (2) or
(3) with hydrazine hydrate. Reactions of (4) with acetic anhydride, ethyl chloroformate or aryl isothio-
cyanate yielded the respective derivative of the new ring system namely 1,2,4-triazolo[2",3":6',1']pyrim-
ido[4',5':2,3]pyrido[1,2-a]benzimidazole (5-7).
J. Heterocyclic Chem., 41, 281 (2004).
Introduction.
spectra showed, in each case, the following signals: a triplet
at δ 1.5 (3H, J=7Hz, OCH2CH3), a quartet at δ 4.4 (2H,
J=7Hz, OC H2CH3) and singlet signal at δ 8.5 (1H, N=C H) .
By condensation of 2a-d with NH2NH2 in ethanol at room
temperature afforded 3-amino-4-imino-5-aryl-6-cyano-
pyrimido[5', 4':5, 6]pyrido[1, 2- a]benzimidazoles 4a-d,
respectively. The assigned structure 4 for the latter products
In continuation of our previous work in the synthesis of
a variety of heterocycles from the readily available inex-
pensive starting materials [1-5], I report herein the utility
of pyrido[1,2-a]benzimidazole derivatives (1a-d) as build-
ing blocks for the synthesis of new ring system namely
1,2,4- triazolo[2",3":6',1']pyrimido[4',5':2,3]pyrido[1,2-a]-
benzimidazole of potential biological activity. The chem-
istry of pyrido[1,2-a]benzimidazole is now receiving con-
siderable interest [6,7]. Also, utility of heterocyclic enam-
inonitriles is now receiving considerable interest [8].
However, to my knowledge, no trial has ever been made to
utilize pyrimido[5',4':5,6]pyrido[1,2- a]benzimidazole as
precursor for 1,2,4-triazolo[2",3":6',1']pyrimido[4',5':2,3]-
pyrido[1,2-a]benzimidazole.
1
followed their elemental and spectral data (IR, H NMR)
(see Table 2) and their alternative synthesis. Thus treatment
of 1-[N-(ethoxymethylene)amino]-3-arylpyrido[1,2-a]benz-
imidazole-2,4-dicarbonitrile 3a-d with hydrazine hydrate in
Results and Discussion.
My initial attention was directed toward synthesis of such
new ring system namely 1,2,4-triazolo[2",3":6',1']pyrimido-
[4',5':2,3]pyrido[1,2-a]benzimidazole 5-7 (Scheme 1). For
this purpose 1-amino-3-arylpyrido[1,2-a]benzimidazole-
2,4-dicarbonitriles 1a-d each was treated with dimethylfor-
mamide-dimethylacetal (DMF-DMA) in dioxane under
reflux. The reaction furnished the corresponding 1-[N,N-
(dimethylaminomethylene)amino]-3-arylpyrido[1,2-a]ben-
zimidazole-2,4-dicarbonitrile 2a-d in good yields, respec-
tively. The assignment of structure 2a-d is compatible with
1
its spectral data. For example, the H-NMR spectra of 2a
revealed the presence of singlet signals in the region δ 3.3-
3.4 ppm assignable to the two methyl groups. Treatment of
1a-d with triethylorthoformate in acetic anhydride at reflux
yielded the respective 1-[N-(ethoxymethylene)amino]-3-
arylpyrido[1,2- a]benzimidazole-2,4-dicarbonitrile 3a-d
respectively in good yield. The structures of the latter deriv-
atives were confirmed by their analytical and spectroscopic
analyses (Table 1, 2). For example, the IR spectra of 3a-d
showed the absence of NH2 bands. Instead, they revealed
the presence of three bands at ν 2230 (CN), 1640
1
(N=CHOEt) and 1620 (ring C=N) cm-1. Their H NMR

282
N. M. Elwan
Vol. 41
ethanol at room temperature (Scheme 1) gave products iden-
tical with compounds 4 in all respects (mp., mixed mp.).
By refluxing each of 4a-d with acetic anhydride resulted
in cyclization to afford the corresponding 14-aryl-13-
c y a n o - 2 - m e t h y l - 1 , 2 , 4 - t r i a z o l o [ 2 " , 3 " : 6 ' , 1 ' ] p y r i m i d o -
[4',5':2,3]pyrido[1,2-a]benzimidazoles 5a-d (Scheme 1).
The formation of the triazole ring involving both amino
and imino groups was evidenced by the absence of absorp-
tion bands due to these groups in the IR spectrum of 5a-d.
Also, the 1H NMR spectrum of 5a revealed the following
signals at δ 2.5 (s, 3H, CH3), 7.5-8.4 (m, 9H, ArH) and
10.1 (s, 1H, pyrimidine-CH) ppm. In the mass spectrum of
Table 1
Chemical and Physical Properties of Prepared Compounds 2 – 7
Comp.
Yield
%
Mp °C
solvent
Molecular
Formula
Analysis (%)
Calcd./ Found m/z
Mass Spectra
(%)
C
H
N
+
2a
2b
2c
2d
3a
3b
3c
3d
85
82
80
83
80
78
79
77
282
DMF
261
DMF
293
DMF
320
DMF
390
DMF
280
AcOH
243
AcOH
250
AcOH
C
H
N
72.51
72.60
70.03
70.00
73.00
72.83
66.25
66.02
72.31
72.60
69.86
70.10
72.81
72.63
66.08
66.30
4.43
4.31
4.60
4.85
4.79
4.95
3.79
3.64
4.14
4.25
4.33
4.14
4.52
4.71
3.53
3.33
23.07
23.22
21.31
21.08
22.21
22.52
21.07
21.21
19.17
19.40
17.71
17.90
18.46
18.21
17.52
17.50
364 (M , 100), 322 (16), 182 (10.4)
22 16
6
(364.4)
N O
+
C
H
395 (M+1, 27), 394 (M , 100), 352 (13),
307 (10), 197 (13)
379 (M+1, 26), 378 (M , 100), 336 (12),
334 (16), 189 (11), 84 (18)
23 18
6
(394.42)
+
C
H
N
23 18
6
(378.42)
ClN
C
C
C
H
400 (M+2, 34), 399 (M+1, 28), 398
22 15
6
+
(398.84)
N O
(M , 100), 358 (14), 199 (10)
+
H
365 (M , 30), 309 (100), 141 (20),
22 15
5
(365.38)
N O
5 2
151 (25), 77 (18)
+
H
395 (M , 80), 339 (100), 269 (60), 65 (32)
23 17
(395.41)
N O
+
C
H
379 (M , 100), 323 (98), 322 (34),
23 17
5
(379.41)
ClN O
140 (12), 102 (12), 65 (77)
401 (M+2, 22), 400 (M+1, 25), 399
(M , 86), 343 (100), 308 (21),
C
H
22 14
5
+
(399.82)
157 (13), 102 (30), 63 (28)
+
4a
4b
4c
4d
82
81
84
80
295
Dioxane
292
Dioxane
275
Dioxane
290
Dioxane
C
H
N
68.37
68.51
66.13
66.09
69.03
69.30
62.23
62.35
3.73
3.80
3.96
4.11
4.14
4.06
3.14
3.40
27.91
28.21
25.71
25.52
26.83
27.00
25.41
25.13
351 (74), 333 (M , 100), 167 (23),
20 13
7
(351.35)
N O
102 (18), 77 (20), 51 (27)
381 (M , 100), 363 (69), 183 (14), 161 (20)
+
C
H
21 15
7
(381.38)
+
C
H
N
365 (M , 69), 347 (100), 174 (27),
140 (12), 102 (16), 65 (17)
387 (M+2, 33), 386 (M+1, 28), 385
(M , 100), 367 (69), 334 (28)
21 15
7
(365.38)
ClN
C
H
20 12
7
+
(385.80)
333 (35), 167 (16), 75 (18)
+
5a
5b
5c
5d
6a
6b
6c
6d
7a
7b
7c
7d
73
72
75
74
78
77
80
76
82
85
83
80
367
DMF
330
DMF
365
DMF
390
DMF
380
DMF
355
AcOH
415
DMF
420
DMF
410
DMF
348
DMF
350
DMF
390
DMF
C
H
N
70.39
70.21
68.14
68.30
70.94
70.73
64.47
64.66
66.84
66.95
64.86
65.01
67.51
67.23
61.25
61.43
64.11
64.31
62.40
62.61
64.85
65.03
58.94
58.83
3.49
3.60
3.73
3.92
3.88
3.92
2.95
3.03
2.94
2.70
3.22
3.42
3.35
3.61
2.45
2.26
2.82
3.01
3.09
3.21
3.22
3.05
2.36
2.53
26.12
26.08
24.19
24.01
25.18
25.35
23.92
24.15
25.98
25.79
24.07
24.00
25.05
25.20
23.81
24.01
24.92
24.79
23.16
23.35
24.07
24.23
22.92
22.71
375 (M , 100), 333 (30), 153 (11),
22 13
7
(375.37)
N O
306 (10), 167 (10), 51 (9)
+
C
H
405 (M , 100), 347 (17), 335 (10), 321 (10)
23 15
7
(405.39)
+
C
H
N
389 (M , 100), 375 (14), 347 (38),
23 15
7
(389.39)
ClN
(409.82)
174 (13), 161 (13)
C
C
C
H
411 (M+2, 20), 410 (M+1, 40),
22 12
7
+
409 (M , 100), 102 (25), 63 (15)
+
H
N O
377 (M , 16), 361 (100), 333 (42),
21 11
(377.35)
7
306 (10) 181 (12)
+
H
N O
407 (M , 100), 406 (61), 363 (12),
22 13
7
2
(407.37)
N O
321 (23), 161 (11)
+
C
H
391 (M , 81), 349 (100), 321 (16),
22 13
7
(391.37)
ClN O
102 (10), 77 (12)
413 (M+2, 46), 411 (M , 100), 167 (27),
102 (20), 50 (21)
394 (M+1, 29), 393 (M , 100), 335 (90),
+
C
H
21 10
7
(411.79)
N S
+
C
H
21 11
7
(393.41)
N SO
333 (17), 167 (28), 51 (16)
+
C
H
423 (M , 24), 286 (91), 269 (100), 134
22 13
7
(423.43)
N S
(32), 51 (24)
408 (M+1, 27), 407 (M , 100), 349 (74),
174 (39), 161 (30), 102 (16), 51 (14)
429 (M+2, 40), 428 (M+1, 33), 427 (M ,
86), 369 (25), 368 (38), 334 (100), 167
(33), 166 (15), 102 (17), 50 (16)
+
C
H
22 13
7
(407.43)
N ClS
+
C
H
21 10
7
(427.86)

Mar-Apr 2004
1,2,4-Triazolo[2",3":6',1']pyrimido[4',5':2,3]pyrido[1,2-a]benzimidazole
283
5a the molecular ion peak at m/z 375 (Table 1) was
observed. These data along with the elemental analysis
data are consistent with molecular formula C22H13N7.
Similarly, reaction of 4a-d with ethyl chloroformate,
yielded the corresponding 1,2,4-triazolo[2",3":6',1']-
pyrimido[4',5':2,3]pyrido[1,2-a]benzimidazol-2(1H) o n e s
6a-d (Scheme 1). The IR spectrum of the product 6a
showed characteristic bands at 3355, 2229 and 1697
assignable to the NH, nitrile and amidecarbonyl group
afforded were identical in all respects (mp., mixed mp., spec-
tra) with 7a-d obtained by using aryl isothiocyanate with 4a-
d (Scheme 1). Both IR and 1H NMR spectral data of the iso-
lated products 14-aryl-13-cyano-2-thioxo-1,2,4-triazolo-
[2",3":6',1']pyrimido[4',5':2,3]pyrido[1,2-a]benzimidazole
7a-d (Table 2) are compatible with their assigned structures.
EXPERIMENTAL
1
respectively. It's H NMR spectrum showed a multiplet
All melting points were determined on a Stuart melting point
apparatus and are uncorrected. Elemental analyses were carried out
at the microanalytical center, University of Cairo, Giza, Egypt.
Infrared spectra (KBr) were recorded on a Pye Unicam SP-300
signal at δ 7.2-9 (ArH), a singlet at δ 9.1 (pyrimidine-CH)
and a singlet at δ 9.3 (NH) ppm (see Table 2) .
Next, the reaction of 4a-d with phenyl isothiocyanate was
studied in ethanol under reflux and it was found that in each
case a single product was obtained. On the basis of their ele-
mental analyses and the spectral data (IR, 1H NMR, MS), the
products isolated were assigned the structure 7 a - d.
Repetition of the reaction between 4a-d using p-methyl
phenyl isothiocyanate gave also the same product 7a-d
which were identical in all respects (mp., mixed mp., spectra)
with that obtained by using phenyl isothiocyanate. The pres-
ence of sulphur in compounds 7a-d confirms that the reac-
tion proceeds via elimination of the arylamine moiety
(Scheme 1). The assigned structures 7a-d were also substan-
tiated by their alternative synthesis by refluxing 6a-d with
phosphorus pentasulfide in dry dioxane. The products
1
infrared spectrophotometer. H NMR spectra were determined on a
Varian Gemini 200 spectrometer (200 MHz) in deuterated DMSO
with TMS as an internal standard. Mass spectra were recorded on a
GCMS-QP 1000-Ex, Schimadzu, Japan. The starting 1-amino-3-
arylpyrido[1,2-a]benzimidazole-2,4-dicarbonitrile 1a-d [9] was pre-
pared as previously described. The physical constants with the spec-
tral data of new synthesized compounds are listed in Tables 1 and 2.
1-[ N,N-(dimethylaminomethylene)amino]-3-arylpyrido[1,2-a]-
benzimidazole-2,4-dicarbonitrile (2a-d).
A mixture of 1a-d (5 mmoles) and dimethylformamide-
dimethylacetal (DMF-DMA) (0.71 g, 6 mmoles) was refluxed for
4 h in dioxane (40 mL). After cooling, the solid that precipitated
was collected and crystallized from the proper solvent (Table 1)
to give products 2a-d.
Table 2
-1
1
Spectral Data of 2– 7 IR (ν/cm ) H NMR (δ/ppm)
1
IR
ν/cm
H NMR (d -DMSO)
6
-1
(δ/ppm)
2a
2b
2210 (CN)
3.34 (s, 3H, Me), 3.37 (s, 3H, Me), 7.4-8.7 (m, 10H, Ar and olefinic-H)
3.33 (s, 3H, Me), 3.36 (s, 3H, Me), 3.88 (s, 3H, OMe), 7.14-8.7 (m, 9H,
Ar and olefinic-H)
2.5 (s, 3H, Me), 3.33 (s, 3H, Me), 3.36 (s, 3H, Me), 7.2-8.6 (m, 9H, Ar
and olefinic-H)
2214 (CN)
2214 (CN)
2214 (CN)
2c
2d
3a
3b
3.33 (s, 3H, Me), 3.37 (s, 3H, Me), 7.3-8.7 (m, 9H, Ar and olefinic-H)
1.5 (t, 3H, Me), 4.6 (q, 2H, CH ), 7.4-8.7 (m, 10H, Ar and olefinic-H)
2
2214 (CN), 1643 (N=CHOEt), 1612 (ring C=N)
2221 (CN), 1643 (N=CHOEt), 1612 (ring C=N)
1.5 (t, 3H, Me), 3.9 (s, 3H, OMe), 4.2 (q, 2H, CH ), 7.2-8.8 (m, 9H, Ar
2
and olefinic-H)
3c
3d
4a
4b
2214 (CN), 1640 (N=CHOEt), 1612 (ring C=N)
2214 (CN), 1643 (N=CHOEt), 1612 (ring C=N)
1.5 (t, 3H, Me), 2.4 (s, 3H, Me), 4.5 (q, 2H, CH ), 7.3-8.7 (m, 9H, Ar and olefinic-H)
2
1.5 (t, 3H, Me), 4.5 (q, 2H, CH ), 7.3-8.7 (m, 9H, Ar and olefinic-H)
2
2221 (CN), 3340, 3301, 3055 (NH, NH )
3.5 (s, 2H, NH ), 6.4 (s, 1H, NH), 7.1-8.6 (m, 9H, pyrimid-H), 9.0 (s, 1H, pyrimid-H)
2
2
2229(CN), 3448, 3294, 3209 (NH, NH )
3.5 (s, 2H, NH ), 3.9 (s, 3H, OMe), 6.4 (s, 1H, NH), 7.1-8.5 (m, 8H, Ar),
2
2
9.1 (s, 1H, pyrimid-H)
4c
4d
5a
5b
5c
5d
6a
6b
6c
6d
7a
7b
7c
7d
2229(CN), 3448, 3294, 3047 (NH, NH )
2.4 (s, 3H, Me), 3.5 (s, 2H, NH ), 7.3-8.5 (m, 9H, Ar and NH), 9.0 (s, 1H, pyrimid-H)
2
2
2220 (CN), 3440, 3300, 3060 (NH, NH )
3.4 (s, 2H, NH ), 6.3 (s, 1H, NH), 7.0-8.5 (m, 8H, Ar), 9.0 (s, 1H, pyrimid-H)
2
2
2207 (CN)
2221 (CN)
2220 (CN)
2229 (CN)
1697 (CO), 2229 (CN), 3355 (NH)
1697 (CO), 2229 (CN), 3394 (NH)
1690 (CO), 2229 (CN), 3402 (NH)
1697 (CO), 2229 (CN), 3400 (NH)
2221 (CN)
2.5 (s, 3H, Me), 7.5-8.4 (m, 9H, Ar), 10.1 (s, 1H, pyrimid-H)
2.5 (s, 3H, Me), 3.9 (s, 3H, OMe), 7.1-8.5 (m, 8H, Ar), 10.0 (s, 1H, pyrimid-H)
2.4 (s, 3H, Me), 2.6 (s, 3H, Me), 7.3- 8.6 (m, 8H, Ar), 10.0 (s, 1H, pyrimid-H)
2.5 (s, 3H, Me), 7.1-8.4 (m, 8H, Ar), 10.1 (s, 1H, pyrimid-H)
7.2-9.0 (m, 9H, Ar), 9.1 (s, 1H, pyrimid-H), 9.3 (s, 1H, NH)
3.8 (s, 3H, OMe), 7.1-8.9 (m, 8H, Ar), 9.1 (s, 1H, pyrimid-H), 9.5 (s, 1H, NH)
2.3 (s, 3H, Me), 7.3-8.0 (m, 8H, Ar), 8.9 (s, 1H, pyrimid-H), 9.3 (s, 1H, NH)
7.4-8.9 (m, 8H, Ar), 9.0 (s, 1H, pyrimid-H), 9.3 (s, 1H, NH)
7.2-8.1 (m, 9H, Ar), 9.1 (s, 1H, pyrimid-H), 10.1 (s, 1H, NH)
2221 (CN)
2221 (CN)
2221 (CN)
3.8 (s, 3H, OMe), 7.3-8.3 (m, 8H, Ar), 9.0 (s, 1H, pyrimid-H), 10.0 (s, 1H, NH)
2.4 (s, 3H, Me), 7.1-8.2 (m, 8H, Ar), 9.4 (s, 1H, pyrimid-H), 10.1 (s, 1H, NH)
7.0-8.3 (m, 8H, Ar), 9.1 (s, 1H, pyrimid-H), 10.1 (s, 1H, NH)

284
N. M. Elwan
Vol. 41
1 - [N-(ethoxymethylene)amino]-3-arylpyrido[1,2-a] benzimida-
zole-2,4-dicarbonitrile (3a-d).
14-Aryl-13-cyano-2-thioxo-1,2,4-triazolo[2",3":6',1']pyrimido-
[4',5':2,3]pyrido[1,2-a]benzimidazole (7 a - d) .
To a solution of compound 1a-d (50 mmoles) in acetic anhy-
dride (30 mL), triethyl orthoformate (5.8 g, 50 mmoles) was
added. The mixture was refluxed for 5 h; the excess acetic anhy-
dride was distilled off under reduced pressure. The crude product,
obtained by cooling, was crystallized from the proper solvent
(Table 1) to give 3a-d.
Method A.
A mixture of compound 4a-d (5 mmoles) and phenyl isothio-
cyante (0.6, 5 mmoles) in ethanol (20 mL) was refluxed for 3 h
and then cooled. The solid that precipitated was collected and
crystallized from the proper solvent (Table 1) to give 7a-d.
Method B.
3-Amino-4-imino-5-aryl-6-cyanopyrimido[5',4':5,6]pyrido[1,2-a]-
benzimidazole(4 a - d).
As method A except using p-methylphenyl isothiocyante
instead of phenyl isothiocyanate. The compounds prepared are
identical with 7a-d which were obtained by method A.
Method A.
A mixture of compound 2a-d (50 mmoles) and hydrazine
hydrate (d=1.029) (5 mL) was stirred for 8 h in ethanol (20 mL)
at room temperature. The solid that separated was collected by
filtration and crystallized from dioxane to give products 4a-d.
Method C.
A mixture of compound 6a-d and phosphorus pentasulfide (5
mmoles each) in dry dioxane (20 mL) was refluxed for 2 h in an
oil bath (115-120 °C) and then cooled. The solid that precipitated
was collected and crystallized from suitable solvent to give 7a-d
(Table 1).
Method B.
Equimolecular quantities of 3a-d and hydrazine hydrate (50
mmoles each) in ethanol (20 mL) were stirred for 30 min and
then left at room temperature for 24 h. The solid that separated
was collected by filtration and crystallized from dioxane to give
products identical in all respects with compounds 4a-d which
obtained by Method A.
REFERENCES AND NOTES
[1] H. M. Hassaneen, A. S. Shawali, M. S. Algharib and N. M.
Elwan, Arch. Pharm. Res., 16, 75 (1993).
14-Aryl-13-cyano-2-methyl-1,2,4-triazolo[2",3":6',1']pyrimido-
[4',5':2,3]pyrido[1,2-a]benzimidazole (5a-d).
[2] N. M. Elwan, A. A. Fahmy, T. A. Abdallah and H. M.
Hassaneen, Sulfur Lett., 18, 9 (1994).
[3] N. M. Elwan, H. A. Abdelhadi, T. A. Abdallah and H. M.
Hassaneen, Tetrahedron, 52, 3451 (1996).
A solution of 4a-d (5 mmoles) in acetic anhydride (20 mL)
were refluxed for 3 h and cooled. The solid that formed were col-
lected and crystallized from a suitable solvent (Table 1) to give
5a-d.
[4] E. M. Awad, N. M. Elwan, H. M. Hassaneen, A. Linden and
H. Heimgartner, Helv. Chim. Acta., 84, 1172 (2001).
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H. Heimgartner, Helv. Chim. Acta., 85, 320 (2002).
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Chapat and Y. Blache, Heterocycl. Commun., 7, 23 (2001).
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23 (1998); Chem. Abstr., 132, 194375p (2000).
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Res. S., 1, 13 (2000).
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Chemie, 335, 279 (1993).
14-Aryl-13-cyano-1,2,4-triazolo[2",3":6',1']pyrimido[4',5':2,3]-
pyrido[1,2-a]benzimidazol-2(1H)one (6a-d).
To a solution of compound 4a-d (5 mmoles) in pyridine (20 mL),
ethyl chloroformate (0.5 mL, 5 mmoles) was added. The mixture
was stirred for 6 h at room temperature. The solid that formed
were collected and crystallized from the proper solvent (Table 1)
to give 6a-d.