Synthesis of 3,3′-bi-1,2,4-Triazolo[4,5-a]-benzimidazole, 5,5′-bi-1,3,4-Thiadiazole, and Thiazolo[3,2-a]benzimidazole Derivatives

Article abstract of DOI:10.1081/SCC-120026349

A series of novel 3,3′-bi-1,2,4-triazolo[4,5-a]benzimidazole and thiazolo[3,2-a]-benzimidazole derivatives were synthesized via the reaction of bis-hydrazonoyl chlorides with 2-methylthiobenzimidazole and with benzimidazol-2-thiol, respectively. A direct synthesis of 5,5′ -bi-1,3,4-thiadiazole and 4,5-bis-phenylhydrazono-2,3,4,5-tetrahydrothiazole derivatives is also described.

Full text of DOI:10.1081/SCC-120026349

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Synthesis of 3,3′-bi-1,2,4-Triazolo[4,5-a]-
benzimidazole, 5,5′-bi-1,3,4-Thiadiazole, and
Thiazolo[3,2-a]benzimidazole Derivatives
Kamal M. Dawood a , Mohamed A. Raslan b & Ahmad M. Farag a
a Faculty of Science, Department of Chemistry, Cairo University, Giza, Egypt
b Faculty of Science, Department of Chemistry, Aswan, Egypt
Published online: 16 Aug 2006.
To cite this article: Kamal M. Dawood , Mohamed A. Raslan & Ahmad M. Farag (2003): Synthesis of 3,3′-bi-1,2,4-Triazolo[4,5-
a]- benzimidazole, 5,5′-bi-1,3,4-Thiadiazole, and Thiazolo[3,2-a]benzimidazole Derivatives, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 33:23, 4079-4086
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 23, pp. 4079–4086, 2003
Synthesis of 3,30-bi-1,2,4-Triazolo[4,5-a]-
benzimidazole, 5,50-bi-1,3,4-Thiadiazole, and
Thiazolo[3,2-a]benzimidazole Derivatives
Kamal M. Dawood,1 Mohamed A. Raslan,2
and Ahmad M. Farag1,
*
1Faculty of Science, Department of Chemistry,
Cairo University, Giza, Egypt
2Faculty of Science,
Department of Chemistry, Aswan, Egypt
ABSTRACT
A
series of novel 3,30-bi-1,2,4-triazolo[4,5-a]benzimidazole and
thiazolo[3,2-a]-benzimidazole derivatives were synthesized via the
reaction of bis-hydrazonoyl chlorides with 2-methylthiobenzimida-
zole and with benzimidazol-2-thiol, respectively. A direct synthesis
of 5,50-bi-1,3,4-thiadiazole and 4,5-bis-phenylhydrazono-2,3,4,5-
tetrahydrothiazole derivatives is also described.
*Correspondence: Ahmad M. Farag, Faculty of Science, Department of
Chemistry, Cairo University, Giza 12613, Egypt; Fax: 02-5676501; E-mail:
afarag@main-scc.cairo.edu.eg.
4079
DOI: 10.1081/SCC-120026349
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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4080
Dawood, Raslan, and Farag
Key Words: bis-Hydrazonoyl chlorides; Biheterocycles; Thiazoles;
Benzothiazoles; Benzimidazoles.
Bi-heterocycles are commonly used as chelating agents, in coordi-
nation, organometallic and analytical chemistry. They have also been used
as subunits in molecular hosts such as macrocycles and supermolecular
species.[1] Moreover, some bi-heterocycles such as 2,20-bi-1,3,4-thiadiazole
derivatives exhibit interesting photoluminescence and electroluminescence
and are used as thermotropic liquid crystals.[2,3] In addition, 3.30-bis-1,2,4-
triazoles have proved to possess bactericidal, fungicidal, and anthelmintic
activities.[4]
In the course of our investigations, we have found that bis-
hydrazonoyl chlorides 1a,b are highly versatile and useful building
blocks for the synthesis of a wide variety of bi-heterocyclic systems
such as 3,30-bi-1,2,4-triazole,[5,6] 3,30-bipyrazole,[6–8] 2,20-bi-1,3,4-thiadia-
zole,[9] and 2,20-bi-1,3,4-selenadiazole[10] derivatives.
As part of our ongoing program to explore the utility of bis-
hydrazonoyl chlorides 1 as reactive precursors in heterocyclic synthesis,
we now report a convenient route to some 3,30-bi-(1,2,4-triazolo[4,5-a]-
benzimidazoles) 4, 2,3-bis-arylhydrazonothiazolo-[3,2-a]benzimidazoles
8, 5,50-bi-1,3,4-thiadiazoles 15 and 2,3-bis-arylhydrazonothiazoles 18.
Thus, when bis-hydrazonoyl chlorides 1 were allowed to react with
2-methyl-thiobenzimidazole (2) in 1:2 molar ratio in refluxing ethanol, in
the presence of triethylamine, they furnished in each case, only one
isolable product. The structure of the reaction products was established
as 1,10-diaryl-3,30-bi-(1,2,4-triazolo[4,5-a]-benzimidazoles) 3 on the basis
of their elemental and spectral analyses (Sch. 1).
On the other hand, when compound 1a was treated with benzimida-
zole-2-thiol (4) in 1:2 molar ratio under the same experimental conditions,
it afforded a high yield of an intense yellow product. Elemental analyses
and spectral data showed that the reaction product is 1:1 instead of
the expected 1:2 cyclocondensation product. This result was confirmed
by carrying out the same reaction using 1:1 molar ratio of the starting
substrates, where the same product was obtained. The structure of
the isolated product was identified as 2,3-bis-phenylhydrazono-2,3,4,5-
tetrahydrothiazolo[3,2-a]-benzimidazole (5a) (Sch. 1). The expected 1:2
adduct 3a, which could be formed via loss of two molecules of hydrogen
sulfide and hydrogen chloride, was not detected in the crude reaction
product as examined by TLC. Similar results were obtained when com-
pound 1b was treated with benzimidazole-2-thiol (4) (see experimental
part).

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Synthesis of Benzimidazole Derivatives
4081
Cl
Cl
2
4
- 2 HCl
1:2
- 2MeSH
Ar HN
N
N
NH Ar
1:1
- 2 HCl
1a,b
N
Ar
N
N
4
N
N
1:2
N
S
N
N
N
N NH Ar
Ar HN N
- 2 HCl
-2 H2S
N
Ar
5a,b
3a,b
N
1,3,5
Ar
C6H5
4-ClC6H4
N
a
SMe
N
H
N
H
SH
b
4
2
Scheme 1.
Next, the behavior of bis-hydrazonoyl chlorides 1 towards the
reactive sulfur nucleophiles 7, 10, and 12 was investigated. Thus, when
compounds 1a,b were allowed to react with the nonisolable intermediate
7 (formed in situ from the reaction of 2-cyanomethybenzothiazole (6)
with phenylisothiocyanate in the presence of potassium hydroxide), in
each case, solely 1:2 cyclocondensation product was formed as evidenced
by elemental analyses and mass spectrometry. Two possible isomeric
structures 8 and 9 can be postulated for the reaction products (Sch. 2).
The mass spectra of the isolated products displayed, in each case, a
fragment ion corresponding to Mþ/2 in addition to the molecular ion
peak Mþ. This finding provides a firm support for the 5,50-bi-1,3,4-thia-
diazole structure 8 rather than the other possible fused heterocyclic
system 9. The structures 11a,b that can be formed via 1:1 cyclocondensa-
tion of 1a,b with 7 were not detected in the crude reaction products.
However, compounds 8a,b were obtained as minor products when
the bis-hydrazonoyl chlorides 1a,b were treated with the thioacetanilide
derivative 10 in refluxing ethanol in the presence of triethylamine. The
major products of this reaction were found to be 4,5-bis-arylhydrazo-
nothiazole derivatives 11a,b (Sch. 2). The structures of the latter products
were established on the basis of their elemental analyses and spectral data
(cf. Experimental part).
Most noteworthy is to report that, when the bis-hydrazonoyl
chlorides 1a,b were treated with the methyldithioacetal derivative 12, in

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4082
Dawood, Raslan, and Farag
N
N
CS2
MeI
1a,b
8a,b
CN
CN
S
S
- 2HCl
- 2MeSH
6
HS
SMe
12
PhNCS / KOH
N
N
N
N
CN
CN
S
CN
S
S
S
HCl
1a,b
S
+ K-
Ph
+ 8a,b
PhNH
PhNH
10
S
7
Ar HN
N
N
NH Ar
11a,b
1a,b
CN
Ar
- 2 PhNH2
N
S
N
N
S
S
S
N
N
N
Ar
NC
8a,b
8,9,11
a
b
Ar
CN
S
N
S
Ar
C6H5 4-ClC6H4
N
N
N
N
N
S
S
Ar
CN
9a,b
Scheme 2.
ethanolic triethylamine solution under reflux, they furnished products
identical in all respects (TLC, m.p., mixed m.p., and spectral data) with
compounds 8a,b.
EXPERIMENTAL
Melting points were measured with a Gallenkamp apparatus and are
uncorrected. Infrared spectra were recorded on Shimadzu FT-IR 8101
PC infrared spectrophotometer. The 1H NMR spectra were determined in
DMSO-d6 at 300 MHz on a Varian Mercury VX 300 NMR spectrometer
using TMS as an internal standard. Mass spectra were measured on a
GCMS-QP1000 EX spectrometer at 70 eV. Elemental analyses were
carried out at the Microanalytical center of Cairo University.
Bis-hydrazonoyl chlorides 1a,b,[8,9] 2-methylthiobenzimidazole (2),[11]
benzimidazole-2-thiol (4),[12] and 2-cyanomethylbenzothiazole (6) and its
derivatives 7, 10 and 12,[13] were prepared as reported in literature.

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Synthesis of Benzimidazole Derivatives
4083
Synthesis of 1,10-Diaryl-3,30-bi-
(1,2,4-triazolo[4,5-a]benzimidazoles) 3a,b
A mixture of the appropriate bis-hydrazonoyl chloride 1a,b (1 mmol)
and 2-methylthiobenzimidazole (2) (2 mmol) in ethanol (20 mL) was
refluxed for 1 h, then left to cool to room temperature. The brown-
colored precipitate was filtered off, washed with ethanol and dried.
Recrystallization from dimethylformamide (DMF) afforded the corre-
sponding 3,30-bi-1,2,4-triazolo[4,5-a]benzimidazoles 3a,b.
1,10-Diphenyl-3,30-bi-(1,2,4-triazolo[4,5-a]benzimidazole) (3a). Yield
61%. M.p.: 298–300ꢀC. IR (KBr): ꢀ 1615 (C ¼ N) cmꢁ1
.
1H NMR
[DMSO-d6] ꢁ 7.12–8.23 (m, 14H, ArH), 8.3 (d, 2H, J ¼ 9.0 Hz), 8.75 (d,
2H, J ¼ 8.1 Hz). MS, m/z (%) 467 (Mþ þ 1, 10.3), 466 (Mþ, 19.8), 363
(14.4), 259 (16.4), 233 (Mþ/2, 10.3), 207 (20.9), 77 (100). Calcd. for
C28H18N8: C, 72.09; H, 3.89; N, 24.02. Found: C, 71.83; H, 3.81;N, 23.77.
1,10-Di-(4-chlorophenyl)-3,30-bi-(1,2,4-triazolo[4,5-a]benzimidazole)
(3b). Yield 74%. M.p.>300ꢀC. IR (KBr) ꢀ 1627, 1608 (C ¼ N) cmꢁ1
.
1H NMR [DMSO-d6] ꢁ 7.16–8.69 (m, ArH). MS, m/z (%) 537 (Mþþ3,
11.7), 536 (Mþ þ 2, 26.9), 535 (Mþ þ 1, 35.0), 534 (Mþ, 46.4), 466 (38.0),
465 (40.3), 293 (20.3), 268 (Mþ þ 1/2, 6.8), 267 (Mþ/2, 7.4), 206 (39.4),
113 (37.4%), 111 (100), 75 (34.5). Calcd. for C28H16Cl2N8: C, 62.81; H,
3.01; N, 20.93. Found: C, 62.70; H, 3.19; N, 20.61.
2,3-bis-Arylhydrazono-2,3,4,5-tetrahydrothiazolo[3,2-a]-
benzimidazoles 5a,b
These compounds were prepared by the same procedure used in the
synthesis of compounds 3a,b using benzimidazole-2-thiol (4) instead of
2-methylthiobenzimidazole (2).
2,3-bis-phenylhydrazono-2,3,4,5-tetrahydrothiazolo[3,2-a]benzimidazole
(5a.) Yield 77%. M.p.: 253–255ꢀC (DMF). IR (KBr): ꢀ 3205, 3178 (2NH),
1598 (C ¼ N)cmꢁ1. 1H NMR [DMSO-d6] ꢁ 6.95 (t, 1H, J ¼ 7.2 Hz), 7.03 (t,
1H, J ¼ 7.2 Hz), 7.25–7.47 (m, 10H, ArH), 7.69 (d, 1H, J ¼ 7.2 Hz), 8.12
(d, 1H, J ¼ 7.2 Hz), 10.57 (s, 1H, NH), 11.03 (s, 1H, NH). MS, m/z (%)
385 (Mþ þ 1, 8.6), 384 (Mþ, 24.1), 293 (13.0), 186 (4.6), 143 (8.3), 105
(27.5), 92 (18.3), 77 (100). Calcd. for C21H16N6S: C, 65.61; H, 4.19; N,
21.86; S, 8.34. Found: C, 65.77; H, 4.18; N, 21.58; S, 8.46.
2,3-bis-(4-chlorophenylhydrazono)-2,3,4,5-tetrahydrothiazolo[3,2-a]-
benzimidazole (5b). Yield 90%. M.p.: 266–268ꢀC (DMF). IR (KBr): ꢀ
1
3215, 3180 (2NH), 1601 (C ¼ N) cmꢁ1. H NMR [DMSO-d6] ꢁ 7.27–7.48
(m, 10H, ArH), 7.68 (d, 1H, J ¼ 7.2 Hz), 8.10 (d, 1H, J ¼ 7.2 Hz), 10.66

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4084
Dawood, Raslan, and Farag
(s, 1H, NH), 10.97 (s, 1H, NH). MS, m/z (%) 454 (Mþ þ 2, 13.6), 453
(Mþ þ 1, 18.8), 452 (Mþ, 22.4), 327 (30.4), 326 (32.4), 186 (8.1), 175
(14.9), 139 (47.9), 126 (28.4), 111 (100), 90 (29.3), 75 (31.6). Calcd. for
C21H14Cl2N6S: C, 55.64; H, 3.11; N, 18.54; S, 7.07. Found: C, 55.72; H,
3.05; N, 18.29; S, 7.25.
5,50-Bi-[3-Aryl-2-(benzothiazol-2-yl)cyanomethylene-
2,3-dihydro-1,3,4-thiadiazoles] 8a,b
Method A. To a stirred solution of potassium hydroxide (0.11 g,
2 mmol) in DMF (20 mL) was added 2-benzothiazoleacetonitrile (6)
(0.348 g, 2 mmol). The mixture was stirred for 30 min, then phenyl-
isothiocyanate (0.27 g, 2 mmol) was added, and the stirring was continued
for 6 h. The appropriate bis-hydrazonoyl chloride 1a,b (1 mmol) was
added portion wise and the resulting reaction mixture was stirred for
further 12 h, during which the bis-hydrazonoyl chlorides 1 dissolved
and an orange-red product precipitated. The solid product was filtered
off, washed with water and ethanol, dried and finally recrystallized from
DMF to afford the corresponding 5,50-bi-1,3,4-thiadiazole derivatives
8a,b in 66 and 71% yields, respectively.
Method B. A mixture of the appropriate bis-hydrazonoyl chloride
1a,b (1 mmol) and 2-(benzothiazol-2-yl)cyanothioacetanilide (10)
(0.618 g, 2 mmol) in ethanol (20 mL), in the presence of triethylamine,
was refluxed for 1 h, during which the starting materials were dissolved
and a heavy solid product was precipitated. TLC proved that the reaction
affords in all cases a mixture of two products. The so-formed precipitate
was filtered off, washed with ethanol, and dried. Partial crystallization
from DMF afforded compounds 8a,b in 35 and 27% yields, respectively.
Dilution of the mother-liquor with water resulted in the formation of
solid preciptate which was filtered off, dried and recrystallized from
DMF/water to give the 3,4-bis-arylhydrazonothiazole derivatives 11a,b
in 45 and 60% yields, respectively.
Method C. A procedure similar to that in method B using the methyl
dithioacetal derivative 12 instead of thioacetanilde derivative 10 was
conducted. 5,50-bi-1,3,4-thiadiazoles 8a,b were obtained in 83 and 90%
yields, respectively.
5,50-Bi-[3-phenyl-2-(benzothiazol-2-yl)cyanomethylene-2,3-dihydro-
1,3,4-thiadiazole] (8a). Yield 83%. M.p.: >300ꢀC. IR (KBr): ꢀ 2192
(C ꢂ N), 1622, 1593 (2C ¼ N) cmꢁ1
.
1H NMR [DMSO-d6] ꢁ 7.21–8.55
(m, ArH). MS, m/z (%) 666 (Mþ, 8.4), 611 (4.3), 586 (14.3), 536 (3.3),
509 (100), 450 (6.0), 393 (6.3), 359 (44.6), 307 (40.4), 248 (13.2), 135

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Synthesis of Benzimidazole Derivatives
4085
(33.8), 91 (47.8), 77 (89.7). Calcd. for C34H18N8S4: C, 61.24; H, 2.72;
N, 16.81; S, 19.23. Found: C, 61.39; H, 2.66; N, 16.63; S, 19.27.
5,50-Bi-[3-(4-chlorophenyl)-2-(benzothiazol-2-yl)cyanomethylene-2,3-
dihydro-1,3,4-thiadiazole] (8b). Yield 90%. M.p.: >300ꢀC. IR (KBr): ꢀ
2195 (C ꢂ N), 1624, 1585 (2C ¼ N) cmꢁ1
.
1H NMR. Insoluble in the
common solvents. MS, m/z (%) 736 (Mþ þ 2, 4.8), 735 (Mþ þ 1, 6.9),
734 (Mþ, 13.2), 521 (2.4), 520 (15.3), 394 (100), 393 (51.3), 367 (4.6),
307 (65.9), 271 (28.3), 204 (22.6), 160 (64.2), 127 (81.0), 111 (64.4), 90
(34.3), 75 (81.0). Calcd. for C34H16Cl2N8S4: C, 55.51; H, 2.19; N, 15.23;
S, 17.43. Found: C, 55.42; H, 2.26; N, 14.97; S, 17.28.
4,5-Di-(phenylhydrazono)-2-(benzothiazol-2-yl)cyanomethylene-3-phenyl-
2,3,4,5-tetrahydrothiazole (11a). Yield 45%. M.p.: 238–240ꢀC. IR (KBr): ꢀ
3228 (br., 2NH), 2193 (C ꢂ N), 1599 (C ¼ N) cmꢁ1. 1H NMR [DMSO-d6] ꢁ
7.15–8.23 (m, 19H, ArH), 9.07 (br. s, 1H, NH), 10.92 (br. s, 1H, NH). MS,
m/z (%) 544 (Mþ þ 1, 13.3), 543 (Mþ, 18.5), 478 (23.1), 359 (37.6), 307
(27.6), 275 (17.8), 178 (12.5), 146 (12.4), 109 (13.0), 77 (100). Calcd. for
C30H21N7S2: C, 66.28; H, 3.89; N, 18.03; S, 11.80; Found: C, 66.04; H,
3.81; N, 17.78; S, 11.83.
4,5-Di-(4-chlorophenylhydrazono)-2-(benzothiazol-2-yl)cyanomethylene-
3-phenyl-2,3,4,5-tetrahydrothiazole (11b). Yield (60%). M.p.: 259–261ꢀC.
IR (KBr): ꢀ 3230, 3159 (2NH), 2194 (C ꢂ N), 1602 (C ¼ N) cmꢁ1
.
1H NMR [DMSO-d6] ꢁ 7.12–8.33 (m, 17H, ArH), 10.71 (br., s, 1H,
NH), 11.20 (br., s, 1H, NH). MS, m/z (%) 614 (Mþ þ 2, 10.3), 613
(Mþ þ 1, 18.5), 612 (Mþ, 27.2), 486 (23.7), 343 (26.3), 275 (14.2), 204
(12.5), 160 (12.4), 126 (28.0), 111 (100), 77 (63.6). Calcd. for
C30H19Cl2N7S2: C, 58.82; H, 3.13; N, 16.01; S, 10.47. Found: C, 58.61;
H, 3.45; N, 16.33; S, 10.41.
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Received in Poland April 8, 2003