Nitriles in organic synthesis: A convenient route to some heterocycles incorporating a benzothiazole moiety

Article abstract of DOI:10.1080/10426500500542828

2-(Benzo[d]thiazol-2-yl)-4-chloro-3-oxobutanenitrile (2) was utilized for the synthesis of several new benzothiazole derivatives. Compound 2 reacted with aniline, hydrazine hydrate, ethanolamine, and ethyl glycinate hydrochloride to yield benzothiazole de

Full text of DOI:10.1080/10426500500542828

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Nitriles in Organic Synthesis:
A Convenient Route to Some
Heterocycles Incorporating a
Benzothiazole Moiety
a
b
b
M. E. A. Zaki , A. A. Fadda , K. Samir & F. A.
a
Amer
a
Photochemistry Department, National Research
Center, Dokki, Cairo, Egypt
b
Chemistry Department, Mansoura University,
Mansoura, Egypt
Version of record first published: 01 Feb 2007.
To cite this article: M. E. A. Zaki , A. A. Fadda , K. Samir & F. A. Amer (2006): Nitriles
in Organic Synthesis: A Convenient Route to Some Heterocycles Incorporating a
Benzothiazole Moiety, Phosphorus, Sulfur, and Silicon and the Related Elements,
181:8, 1815-1823
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Phosphorus, Sulfur, and Silicon, 181:1815–1823, 2006
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500500542828
Nitriles in Organic Synthesis: A Convenient Route to
Some Heterocycles Incorporating a Benzothiazole Moiety
M. E. A. Zaki
Photochemistry Department, National Research Center,
Dokki, Cairo, Egypt
A. A. Fadda
K. Samir
F. A. Amer
Chemistry Department, Mansoura University, Mansoura, Egypt
2-(Benzo[d]thiazol-2-yl)-4-chloro-3-oxobutanenitrile (2) was utilized for the synthe-
sis of several new benzothiazole derivatives. Compound 2 reacted with aniline,
hydrazine hydrate, ethanolamine, and ethyl glycinate hydrochloride to yield ben-
zothiazole derivatives 3–6, respectively.
Keywords Benzothiazole; chloroactyl chloride; 2-cyanomethylbenzothiazole
INTRODUCTION
Benzothiazole derivatives have attracted a great deal of inter-
1
,2
3
4
est due to their antiviral,
antibacterial, antimicrobial, and
5
6
fungicidal activites. They are also useful as antiallergic, anti-
7
8
9
inflammatory and anthelmintic agents and as appetite depressants,
antihypertensives,10 antineurodegenerative diseases,
11
for treat-
12
13−16
ment circulatory organ diseases,
plant protectants, histamine H2 antagonists, and photographic
sensitizers. In continuation of our interest in the synthesis of het-
erocycles containing a benzothiazole moiety,
intermediates for dyes,
17
18
1
9
2
0,21
we report here on a
facile route to the synthesis of some new benzothiazole derivatives.
Received August 1, 2005; accepted September 22, 2005.
Address correspondence to A. A. Fadda, Chemistry Department, Faculty of Science,
Mansoura University, Mansoura, Egypt. E-mail: afadda2@yahoo.com
1815

1
816
M. E. A. Zaki et al.
RESULTS AND DISCUSSION
As a part of a program aimed at the synthesis of novel benzoth-
iazole derivatives, which could be useful for biological and phar-
macological screening, we have investigated the possible utility of
2-cyanomethylbenzothiazole (1) for the synthesis of some heterocyclic
compounds. It has been found that the reaction of 1 with chloroacetyl
chloride in the presence of triethylamine afforded 2-(benzo[d]thiazol-
2
-yl)-4-chloro-3-oxobutanenitrile (2) in a high yield (Scheme 1).22 The
structure of 2 was established based on both elemental and spectral
data.
SCHEME 1
−
1
The IR spectrum showed strong absorption bands at 2199 cm and
−1
1
1
625 cm due to CN and (C N), respectively. The H NMR spectrum
of 2 revealed two singlet signals at δ 4.50 and 4.72 ppm of CH2 and
CH respectively, and an aromatic multiplet at δ 7.45–8.22 ppm, while
+
its mass spectroscopic measurement showed m/z: 250 (M ), 215, 201
(
100% base peak), 189, 173, 147, 108, and 107.
The latter 2-(benzo[d]thiazol-2-yl)-4-chloro-3-oxobutanenitrile
2) allowed a fruitful, one step synthesis of several heterocyclic
(
rings via its reaction with aniline, hydrazine hydrate, ethanolamine,
and ethyl glycinate hydrochloride to yield 5-amino-4-(benzo-
[
d]thiazol-2-yl)-1-phenyl-1H-pyrrol-3-ol (3), 2-amino-3-chloroacetyl
pyra zollo[5,1-b]benzothiazole (4), 4-(benzo[d]thiazol-2-yl)-5-(2-hydrox-
yethylimino)pyrrolidin-3-one (5), and ethyl 3-amino-4-(benzo[d]thiazol-
2
-yl)-5-oxo-1,4,5,6-tetrahydropyridine-2-carboxylate (6), respectively,
in high yield, as shown in Scheme 2.
The reaction of compound 2 with aniline in refluxing dimethylfor-
mamide afforded a single product 3.23 The structure of the compound
was established on the basis of both the elemental analysis and IR
spectrum of the reaction product.
−
−
1
1
The IR spectrum showed absorption bands at 3339 and 3406 cm
due to the NH2 group, in addition to bands at 3381 and 3163 cm
due to the OH and tautomeric NH groups, respectively, it and showed
−
1
no bands in the region of cyano group around 2200 cm . However,
1
H-NMR spectroscopy together with the mass fragmentation pattern
provided conclusive evidence of the proposed structure. Thus, a broad

Nitriles in Organic Synthesis
1817
SCHEME 2
signal D2O-exchangeable proton observed at δ 4.48 ppm was attributed
to the amino group, a singlet signal at δ 8.5 ppm due to an OH proton,
and a multiplet at δ 7.3–8.1 ppm for aromatic protons.
The structure of 3 was confirmed also by its mass spectroscopic mea-
+
surement, which showed m/z the molecular ion peak at 307 (M , base
peak).
We thought to extend this synthetic approach by allowing 2 to react
with hydrazine hydrate to yield a compound that was identical with
product 4, where the elemental analysis and mass spectroscopy con-
2
4
firmed that the product 4 was formed by a loss of ammonia.
This derivative was thus assumed to be formed via an initial addition
of a hydrazine molecule to the cyano group in compound 2 to yield
the intermediate (A) that cylices into product 4 by a loss of ammonia
molecule, as shown in Scheme 3.

1
818
M. E. A. Zaki et al.
SCHEME 3
The structure of 4 was established by chemical tests and spectral
data. The element test showed the presence of a chlorine atom, indi-
cating that chlorine was not involved in the reaction. The IR spectrum
showed no absorption band of a cyano group around the region 2150–
−
1
2
300 cm , indicating that the cyano group was involved in the reaction.
−
1
In addition, the IR spectrum showed a band at 1718 cm due to the
carbonyl group. Moreover the H NMR showed a singlet signal at δ
1
4
.52 ppm assigned to the CH2 and a D2O-exchangable broad signal at
δ 5.64 ppm assignable to NH2besides an aromatic multiplet at δ 7.20–
.01 ppm. The mass spectrum showed a molecular ion peak at m/e 266
7%), which indicated that the intermediate was cyclized by a loss of an
8
(
ammonia molecule.
The mass spectrum also showed the fragments 189 (15%), 173 (13%),
57 (10%), and 73 (100% base peak).
1
In a different manner to the behavior of aniline and hydrazine,
ethanol amine reacted with 2 in refluxing dimethylformamide to yield 5.
The structure of 5 was determined on the basis of its spectral data as
well as the elemental analysis. The element test showed the absence of
a chlorine atom, indicating that it was lost during the cyclization step.
Thus, the mass spectrum of 5 revealed a molecular ion peak at m/z = 275
with 100% relative abundance corresponding to the molecular formula
C13H13N3O2S. Its IR spectrum showed absorption peaks corresponding
to the presence of OH and NH functions at 3896 and 3128, respectively,
besides the disappearance of absorption bands due the NH2 and C≡N
groups.
1
In its H NMR spectrum (DMSO-d6), two types of D2O-exchangeable
protons at δ 8.3 (s, 1H) and 8.68 (s, 1H) ppm corresponding to NH and
OH functions, respectively, were detected in addition to the aromatic
1
multiplet. Also, the H NMR showed a multiplet band for four protons
(
CH2CH2 ) at δ 3.6–3.7, a singlet at δ 4.0 for two protons ( CH2 ),
and a singlet band at δ 5.06 for the CH proton.

Nitriles in Organic Synthesis
1819
2
reacts with ethyl glycinate hydrochloride in DMF to yield the pyri-
dine derivatives 6. The structure of 6 was confirmed by its IR spec-
trum, which showed the absence of a spectrum band in the region of
−
1
2
220 cm , which indicated that, the CN group was involved in the cy-
−
1
clization process; it also showed bands at 1715 cm ( COOEt), 3189,
and 3416 cm due to NH and OH (enolized), respectively, and at 3252
and 3398 cm due to the NH2 function. The H NMR (DMSO-d6)
showed a triblet band at δ 1.2 ppm due to CH3 protons, a singlet at
δ 2.8 ppm due to CH2 protons, a quartet broad band in the region 3.5–
−1
−
1
1
3
.85 ppm due to CH2 and NH2 protons, a singlet band at δ 4.6 ppm due
to NH, and a multiplet band at δ 7.4–8.4 ppm due to aromatic protons.
+
+
Mass spectrum showed m/z at 317 (M ), 245 (19.8% M -COOEt), 214
15.6%), 213 (5.9%), 201 (18.3%), 174 (100%), 134, and 108 (31.5%).
All attempts to cyclize compound 5 by heating in it DMF in the pres-
(
ence of different bases to obtain the pyrrolo[2,1-b]benzothiazole deriva-
tive (7) failed.
SCHEME 4
On the other hand, it was found that refluxing compound 2 in
boiling pyridine yielded a single product, which analyzed correctly
for C16H12N3SOCl. This product was formulated as 1-[3-cyano-3-
(
benzothiazol-2-yl]acetonyl]-pyridinium chloride (8).
SCHEME 5
1
1
The structure of 8 was proved by IR and H NMR spectra. Its H NMR
DMSO-d6) spectrum revealed a singlet band at δ 4.7 ppm due to a
(
CH proton, δ 5.8 ppm attributable to the CH2 protons, and a multiplet
band at δ 7.1–7.8 ppm for four aromatic protons of benzothiazole ring,
in addition to a multiplet at δ 8.2–9.0 ppm due to aromatic protons of
the pyridine ring.

1
820
M. E. A. Zaki et al.
In addition, its IR spectrum showed absorption frequency at
220 cm due to the C N group while the carbonyl absorption function
−1
2
was not observed, which may explain that compound 8 may be exist in
the enol form in a solid state.
The thiazoline heterocyclic ring incorporating a benzothiazole moi-
ety was prepared directly from compound 1. Thus, the treatment of
1
with sulfur metal and phenylisothiocyanate in the presence of an
25−26
excess of triethylamine
afforded the corresponding 4-amino-5-
(
benzo[d]thiazol-2-yl)-3-phenylthiazole-2(3H)-thione (9).
SCHEME 6
The structure of 9 could be established for the reaction product
based on the IR spectrum, which showed absorption bands at 3482
−1
1
and 3395 cm (NH2). Its H NMR (DMSO-d6) spectrum revealed a
D2O-exchangable proton at δ 6.12 ppm due to NH2 protons besides a
multiplet at δ 7.22–8.16 ppm due to 9 aromatic protons.
EXPERIMENTAL
Melting points were uncorrected. Elemental analysis was carried out
in the Microanalytical Unit Faculty of Science, Cairo University, Cairo,
−
1
Egypt. IR spectra were recorded on a Pye Unicam SP-1000 cm spec-
1
trometer using a KBr wafer technique. H NMR spectra were deter-
mined on Varian Gemini 200 MHz NMR spectrometers using TMS as
an internal standard with δ = 0 ppm. Mass spectra were determined
on a GC-MS.QP-100 EX Schimadzye (Japan).
The Synthesis of 2-(Benzo[d]thiazol-2-yl)-4-chloro-
3-oxobutanenitrile (2)
In a mixture of 1 (0.01 mole) in absolute ethanol (25 mL) containing
a catalytic amount of triethylamine (6 drops) and chloroacetyl chlo-
ride (0.01 mole), the mixture was heated over a water bath for 10 min.
The obtainable solid product was collected by filtration and crystallized
from chloroform-ethanol (1:1) to give compound 2. Compound 2: Light
◦
−1
brown crystals; yield (96%); m.p. 249 C; IR(cm )(KBr) 1625 (C N),

Nitriles in Organic Synthesis
1821
1
2
199 (CN); H NMR: (DMSO-d6): δ=4.5 (s, 2H, CH2), 4.72 (s, 1H, CH)
+
and 7.45–8.22 (m, 4H, Ar-H); MS: m/z 250 (M ), 215, 201 (100% base
peak), 189, 173, 147, 108, 107. Anal. calcd. for C11H7N2OSCl: C, 52.45;
H, 2.78; N, 11.03. Found: C, 52.70; H, 2.81; N, 11.17.
The Synthesis of 5-Amino-4-(benzo[d]thiazol-2-yl)-
1-phenyl-1H-pyrrol-3-ol (3)
To a solution of 2 (0.01 mole) in dimethylformamide (25 mL) a freshly
distillated aniline (0.01 mole) was added. The reaction mixture was
refluxed for 4 and left to cool at r.t., and poured onto ice cold water
(
100 mL). The solid product was collected by filtration and recrystal-
lized from dimethylformamide-ethanol (1:1) to obtain (3). Compound
3
(
2
◦
−1
: white crystals; yield (65%); m.p. 230 C; IR(cm )(KBr) 3339, 3406
1
NH2), 3381(OH) and 3163 (NH); H NMR: (DMSO-d6): δ = 4.48 (br,
+
H, NH2), 7.3–8.1 (m, 10H, Ar-H), 8.5 (s, 1H, OH); MS: m/z 307 (M ,
base peak), 306, 279, 230, 174, 173, 106. Anal. calcd. for C17H13N3OS:
C, 66.45; H, 4.12; N, 13.43. Found: C, 66.43; H, 4.26; N, 13.67.
The Synthesis of 2-Amino-3-chloroacetyl
Pyrazolo[5,1-b]benzothiazole (4)
A mixture of 5 (0.01 mole) and hydrazine hydrate (0.012 mole) in
dimethylformamide (20 mL) was refluxed for 3 hs. The reaction mixture
after cooling was evaporated under reduced pressure, and the residue
was triturated with ethanol. The resulting material was collected by fil-
tration and recrystallized from ethanol to give (4). Compound 4: white
◦
−1
crystals; yield (48%); mp 165 C; IR(cm )(KBr) 3339, 3406 (NH2), 1718
1
(
C O), 3345, 3478 (NH2); H NMR: (DMSO-d6): δ = 4.52 (s, 2H, CH2),
+
5
.64 (br, 2H, NH2) 7.20–8.01 (m, 4H, Ar-H),; MS: m/z 266 (M ). Anal.
calcd. for C11H8ClN3OS: C, 49.64; H, 2.98; N, 15.76. Found: C, 49.72; H,
.03; N, 15.81.
3
The Synthesis of 4-(benzo[d]thiazol-2-yl)-5-(2-
hydroxyethylimino)pyrrolidin-3-one (5)
To a solution of 2 (0.01 mol) in dimethylformamide (20 mL)
ethanolamine (0.6 mL, 0.01 mole) was added. The reaction mixture
was refluxed for 5 h, left to cool at r.t., and poured onto ice cold water.
The solid product was collected by filtration and recrystallized from
dimethylformamide-ethanol (1:2) to give (5). Compound 5: orange crys-
◦
−1
tals; yield (74%); mp 244 C; IR(cm )(KBr) 1704(C O), 3128, 3896

1
822
M. E. A. Zaki et al.
1
(
NH and OH respectively); H NMR: (DMSO-d6):δ = 3.6–3.7 (m, 4H,
CH2CH2), 4.0 (s, 2H, CH2), 5.06 (s, 1H, CH), 7.0–8.0 (m, 4H, Ar-H),
+
8
.3(br, 1H, NH) and 8.68 (s, 1H, OH): MS (M = 275). Anal. calcd. for
C13H13N3O2S: C, 57.01; H, 4.69; N, 15.16. Found: C, 56.71; H, 4.76; N,
5.26.
1
The Synthesis of Ethyl 3-Amino-4-(benzo[d]thiazol-2-yl)-
-oxo-1,4,5,6-tetrahydropyridine-2-carboxylate (6)
5
A mixture of 2 (0.01 mole), ethyl glycinate hydrochloride (0.01 mol),
and sodium acetate (0.82 g, 0.01 mole) in dimethylformamide (25 mL)
was refluxed for 6 h. The reaction mixture was left to cool at r.t., and
then poured onto ice cold water (100 mL). The precipitated product was
collected by filtration and crystallized from dimethylformamide-ethanol
◦
(
1:1) to yield (6). Compound 6: white crystals; yield (62%); mp 247 C;
−1
IR(cm ) (KBr) 1715 (-COOEt), 3189, 3416 (NH, OH respectively) and
1
3
252, 3398 (NH2); H NMR: (DMSO-d6):δ = 1.2 (t, 3H, CH3), 2.8 (s, 2H,
CH2), 3.5–3.8 (br, q, 4H, CH2 and NH2), 5.3 (s, 1H, CH), 7.4–8.4 (m, 4H,
Ar-H). Anal. calcd. for C15H15N3O3S: C, 56.76; H, 4.80; N, 13.19. Found:
C, 56.77; H, 4.76; N, 13.24.
The Synthesis of 1-[3-Cyano-3-(benzothiazol-2-yl)-
acetonyl]pyridium Chloride (8)
Compound 2 (0.01 mol) was refluxed for 30 min in dry pyridine. The
resulting solid product was separated as white crystals, collected by
filtration, dried well, and recrystallized from pyridine to give (8). Com-
◦
−1
pound 8: white crystals; yield (89%); mp 272 C; IR(cm )(KBr); 2220
(
1
CN) H NMR: (DMSO-d6):δ = 4.7(s, 1H, CH), 5.8 (s, 2H, CH2), 2.8 (s,
2
(
H), 7.1–7.8 (m, 4H, benzene-H), 8.2–9.0 (m, 4H, pyridine-H); MS 317
+
+
M , 12%), 245 (M -COOEt), 214 (15.6%), 213 (5.9%), 201 (18.3%), 174
100%), 134, 108 (31.5%).
(
Anal. calcd. for C16H12ClN3OS: C, 58.27; H, 3.67; N, 12.74. Found: C,
8.42; H, 3.59; N, 12.68.
5
The Synthesis of 4-Amino-5-(benzo[d]thiazol-2-yl)-
-phenylthiazole-2(3H)-thione (9)
3
A stirred mixture of 1 (0.01 mol), elementary sulfur (0.32 g, 0.01 mol)
and phenylisothiocyanate (1.2 mL, 0.01 mol) in dimethylformamide
◦
(
6.0 mL) was added to triethylamine (6.0 mL) dropwise at 50 C. The
reaction mixture was stirred at this temperature for 3 h, and then

Nitriles in Organic Synthesis
1823
cooled to r.t. The resulting crystals were obtained by the addition of
a water-acetone mixture (5:1), collected by filtration, and recrystallized
from acetic acid to give (9). Compound 9: brown crystals; yield (58%); mp
◦
−1
−1
1
2
6
26 C; IR(cm )(KBr); 3482, 3395 cm (NH2); H NMR: (DMSO-d6):δ =
+
.12 (br, 2H, NH2), 7.22–8.16 (m, 9H, Ar-H); MS (M = 341). Anal. calcd.
for C16H11N3S3: C, 56.09; H, 3.10; N, 12.29. Found: C, 56.28; H, 3.25; N,
12.31.
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