Novel synthesis of 3-amino-4-oxo-(2H)-pyrazolo[3′,4′:4,5]pyrimido-[2,1-b] benzothiazole and its 2- and 3-substituted derivatives

Article abstract of DOI:10.1002/jhet.5570400322

Reaction of 4H-pyrimido[2,1-b]benzothiazole-2-thiomethyl-3-cyano-4-one (1) with hydrazine hydrate/aryl hydrazine/heteryl hydrazine in the presence of anhydrous potassium carbonate and dimethyl formamide afforded 3-amino-4-oxo-(2H)/aryl/heteryl pyrazolo[3′,4′:4,5]pyrimido[2,1-b]benzothiazoles in good yield. These pyrazole derivatives on diazotization followed by replacement with hydroxy, chloro, bromo, iodo and on reduction gave the corresponding 3-substituted derivatives.

Full text of DOI:10.1002/jhet.5570400322

Novel Synthesis of 3-Amino-4-oxo-(2H)-pyrazolo[3',4':4,5]pyrimido-
[2,1-b]benzothiazole and its 2- and 3-Substituted Derivatives
K. G. Baheti
May-Jun 2003
547
Department of Pharmaceutical Chemistry, Nanded Pharmacy College, Nanded – 431 602 (India)
S. V. Kuberkar*
Post Graduate Research Centre, Department of Chemistry, Yeshwant College, Nanded - 431 602 (India)
Received November 27, 2001
Revised September 6, 2002
Reaction of 4H-pyrimido[2,1-b]benzothiazole-2-thiomethyl-3-cyano-4-one (1) with hydrazine
hydrate/aryl hydrazine/heteryl hydrazine in the presence of anhydrous potassium carbonate and dimethyl
formamide afforded 3-amino-4-oxo-(2H)/aryl/heteryl pyrazolo[3',4':4,5]pyrimido[2,1-b]benzothiazoles in
good yield. These pyrazole derivatives on diazotization followed by replacement with hydroxy, chloro,
bromo, iodo and on reduction gave the corresponding 3-substituted derivatives.
J. Heterocyclic Chem., 40, 547 (2003).
A literature survey reveals that very few references are
Since compounds (3a-f) prepared presently possess a reac-
tive amino group at the 3-position and could be replaced by
various substituents, it is surmised that they would become
best precursors for the synthesis of 3-substituted derivative
of compounds (3a-f). Compound 3a, 3b and 3c as they con-
tain a free amino group at 3-position, on diazotization at 0-5
°C with sodium nitrite and mineral acid gave the correspond-
ing diazonium salts (4a-c). On hydrolysis, treatment with
cuprous chloride, cuprous bromide and potassium iodide 4a-
c afforded 3-hydroxy (5a-c), 3-chloro (5d-f), 3-bromo (5g-i)
and 3-iodo (5j-l) derivatives respectively. 3-Hydrazino-4-
oxo-(2H)/phenyl/benzothiazolylpyrazolo[3',4':4,5] pyrim-
ido[2,1-b]benzothiazoles (5m,n,o) were prepared by reduc-
tion of diazonium salts (4a-c) with alkaline sodium sulphite.
(Scheme II). Structures of these derivatives were confirmed
on the basis of elemental analysis and spectral data. The ir
available on the synthesis of pyrazolo pyrimido benzothia-
zole [1-3]. Garin Javier et al. [1-2] reported synthesis of 1-
substituted derivatives of pyrazolo [3',4':4,5]pyrimido[2,1-
b]benzothiazole from respective diphenyl pyrazolo pyrim-
idine thione and N-chlorosuccinimide in sulphuric acid. In
continuation of our earlier work [4] on the synthesis of
fused heterocycles containing bridgehead nitrogen atom,
we report in this paper a convenient route for the synthesis
of 3-amino-4-oxo-(2H)/aryl/heteryl pyrazolo[3',4':4,5]-
pyrimido[2,1-b]benzothiazoles (3a-f) starting from 4H-
pyrimido[2,1-b]benzothiazole-2-thiomethyl-3-cyano-4-
one (1).
2-Amino benzothiazole in dimethyl formamide in the
presence of anhydrous potassium carbonate was refluxed
with ethyl-2-cyano-3,3-bismethylthio acrylate to get the
required starting compound (1) which contains reactive
thiomethyl group at the 2-position and a cyano group at the
3-position [4]. Compound (1) on heating independently
with hydrazine hydrate, phenyl hydrazine, 2-hydrazino
benzothiazole [5], 4-nitro phenyl hydrazine, 2,4-dinitro
phenyl hydrazine and 6-nitro-2-hydrazino benzothiazole
[5] in the presence of dimethyl formamide and a catalytic
amount of potassium carbonate afforded 3-amino-4-oxo-
(2H)/aryl/heteryl pyrazolo [3',4':4,5]pyrimido[2,1-b]ben-
zothiazoles(3a-f) respectively in 42-60% yield(Scheme I).
1
and H nmr spectra of these compounds showed the absence
of bands and peaks respectively due to NH group. Chemical
2
evidence also confirmed the structures of some derivatives.
3-Chloro derivatives (5d,e,f) were also obtained by heating
the corresponding 3-hydroxy derivatives (5a,b,c) with phos-
phoryl chloride for a period of 1-4 hours. The 3-hydrazino
derivatives (5m,n,o) were also obtained by heating 3-iodo
derivatives (5j,k,l) in methanol with 80% hydrazine hydrate
for a period of 1-4 hours(Scheme III).
3-Chloro derivatives (5d,e,f) and 3-hydrazino deriva-
tives(5m,n,o) prepared by two different routes, showed
undepressed mixed melting points and exhibited the same
Rf values in tlc.
EXPERIMENTAL
All melting points were determined in capillary tube and are
uncorrected. Infrared (ir) spectra were recorded in potassium
bromide pellets on a Bomen MB 104 FT Infrared spectropho-
tometer. Nuclear magnetic resonance (nmr) spectra were
obtained on a FT Gemini 60 (60MHz) spectrometer with tetram-
ethyl silane as an internal standard. Mass spectra (ms) were
recorded on a FT VG-7070 H Mass spectrophotometer using the
EI technique at 70 eV. Microanalysis was performed on a
No.
R
Mp
(°C)
Yield
(%)
3a
b
c
d
e
hydrogen
phenyl
2-benzothiazolyl
4-nitro phenyl
2,4-dinitro phenyl
6-nitro-2-benzothiazolyl
338
305
320
>360
>360
>360
60
51
57
44
42
50
f

548
Communication to the Editor
Vol. 40
3-Amino-4-oxo-2-phenylpyrazolo[3',4':4,5]pyrimido[2,1-b]ben-
zothiazole (3b).
This compound (1.7 g, 5.1 mmoles) was prepared from (1)
(2.73 g, 10 mmoles) and phenyl hydrazine (2.16, 20 mmoles) in
51% yield in a manner similar to that described for the prepara-
-1
tion of 3a, mp 305 °C; ir (potassium bromide): ν max cm 3490,
+
1
3410 (NH ), 1703 (C=O); ms: m/z 333 (M , 100%); H-nmr
2
(deuteriodimethyl sulfoxide): δ 6.5 (broad s, 2H, NH exchange-
2,
able with D O), 7.2-8.3 (m, 9H, aromatic-H).
2
Anal. Calcd. for C H N OS: C, 61.26; H, 3.30; N, 21.02.
17 11
5
Found C, 61.20; H, 3.32; N, 21.00.
No
R
R'
Yield(%)
3-Amino-4-oxo-2(2'-benzothiazolyl)pyrazolo[3',4':4,5]pyrim-
ido[2,1-b]benzothiazole(3c).
5a
b
c
d
e
hydrogen
phenyl
2-benzothiazolyl
hydrogen
phenyl
2-benzothiazolyl
hydrogen
phenyl
2-benzothiazolyl
hydrogen
phenyl
2-benzothiazolyl
hydrogen
OH
OH
OH
Cl
Cl
Cl
Br
Br
Br
I
40
41
43
27
34
39
29
36
39
28
33
36
40
35
38
This compound (2.25 g, 5.76 mmoles) was prepared from (1)
(2.73 g, 10 mmoles) and 2-hydrazino benzothiazole (1.65 g, 10
mmoles) in 57 % yield in a manner similar to that described for
the preparation of 3a, mp 320 °C; ir (potassium bromide): ν max
f
g
h
i
j
k
l
m
n
o
1
+
cm- 3470, 3400 (NH ), 1715 (C=O); ms: m/z 390 (M ,100%);
2
1
H-nmr (deuteriodimethyl sulfoxide): δ 5.2 (broad s, 2H, NH
2,
exchangeable with D O), 7.3-8.4 (m, 8H, aromatic-H).
2
I
I
Anal. Calcd. for C H N OS : C,55.38; H, 2.58; N, 21.52.
18 10
6
2
Found C, 55.40; H, 2.54; N, 21.56.
NHNH
NHNH
NHNH
2
2
2
3-Amino-4-oxo-2(4'-nitrophenyl)pyrazolo[3',4':4,5]pyrim-
ido[2,1-b]benzothiazole (3d).
phenyl
2-benzothiazolyl
This compound (1.6 g, 4.39 mmoles) was prepared from (1)
(2.73 g, 10 mmoles) and 4-nitro phenyl hydrazine (1.53 g, 10
mmoles) in 44 % yield in a manner similar to that described for
the preparation of 3a, mp >360 °C; ir (potassium bromide): ν
-1
+
max cm 3480, 3415 (NH ), 1695 (C=O); ms: m/z 378 (M ,
2
1
100%); H-nmr (deuteriodimethyl sulfoxide): δ 5.6 (broad s, 2H,
NH exchangeable with D O), 7.2-8.4 (m, 8H, aromatic-H).
2,
2
Anal. Calcd. for C H N O S: C, 53.96; H, 2.66; N, 22.21.
17 10
6 3
Found C, 53.90; H, 2.60; N, 22.19.
3-Amino-4-oxo-2(2',4'-dinitrophenyl)pyrazolo[3',4':4,5]pyrim-
ido[2,1-b]benzothiazole (3e).
This compound (1.75 g, 4.2 mmoles) was prepared from (1)
(2.73 g, 10 mmoles) and 2,4-dinitro phenyl hydrazine (1.98 g,
10 mmoles) in 42 % yield in a manner similar to that described
for the preparation of 3a, mp >360 °C; ir (potassium bromide):
Heraeus CHN-O Rapid analyzer. All the reactions were moni-
tored by thin layer chromatography (tlc), carried out on 0.2 mm
silica gel-G plate using iodine vapor for detection.
1
+
ν max cm- 3480, 3390 (NH ), 1700 (C=O); ms: m/z 423 (M ,
2
1
100%); H-nmr (deuteriodimethyl sulfoxide): δ 5.8 (broad s,
3-Amino-4-oxo-(2H)pyrazolo[3',4':4,5]pyrimido[2,1-b]benzoth-
iazole (3a).
2H, NH exchangeable with D O), 7.1-8.0 (m, 7H,
2,
2
aromatic-H).
Anal. Calcd. for C H N O S: C, 48.22; H, 2.14; N, 23.16.
Found C, 48.19; H, 2.08; N, 23.08.
A mixture of 2.73 g (10 mmoles) of 4H-pyrimido[2,1-b]ben-
zothiazole-2-thiomethyl-3-cyano-4-one (1) and 1.0 g (20
mmoles) of hydrazine hydrate (80%) was refluxed in the pres-
ence of a catalytic amount of anhydrous potassium carbonate and
25 ml of dimethylformamide for 3-4 hours. After cooling the
solid that appeared was collected by filtration and recrystallized
from dimethyl formamide to give 1.54 g (6 mmoles, 60%) of
17
9 7 5
3-Amino-4-oxo-2(6'-nitro-2'-benzothiazolyl)pyrazolo[3',4':4,5]-
pyrimido[2,1-b]benzothiazole (3f).
This compound (2.20 g, 5.05 mmoles) was prepared from (1)
(2.73 g, 10 mmoles) and 6-nitro-2-hydrazino benzothiazole (2.10
g, 10 mmoles) in 50 % yield in a manner similar to that described
for the preparation of 3a, mp >360 °C; ir (potassium bromide): ν
crystalline solid of 3a, mp 338 °C; ir (potassium bromide): ν max
-1
cm 3500, 3420 (NH ), 3310 (NH), 1715 (C=O); ms: m/z
2
1
+
+
1
max cm- 3470, 3410 (NH ), 1710 (C=O); ms: m/z 435 (M ,
257(M ,100%): H-nmr (deuteriodimethyl sulfoxide): δ 5.2
(broad s, 2H, NH exchangeable with D O), 10.9 (s, 1H, NH,
2
1
100%): H-nmr (deuteriodimethyl sulfoxide): δ 5.1 (broad s, 2H,
2,
2
NH exchangeable with D O), 6.9-7.9 (m, 7H, aromatic-H).
exchangeable with D O), 7.3-7.7 (m, 4H, aromatic-H).
2,
2
2
Anal. Calcd. for C H N O S : C,49.64;H, 2.08; N, 22.52.
Anal. Calcd. for C H N OS: C,51.36; H, 2.72; N, 27.23.
18
9 7 3 2
11
7 5
Found C, 51.34; H, 2.70; N, 27.25.
Found C, 49.60; H, 2.01; N, 22.50.

May-Jun 2003
Communication to the Editor
549
3-Hydroxy-4-oxo-(2H)-pyrazolo[3',4':4,5]pyrimido[2,1-b] ben-
zothiazole (5a).
Synthesis of 5d from 5a Using Phosphoryl Chloride.
A mixture of 0.129 g (0.5 mmoles) of 5a and 2 ml of phospho-
ryl chloride was refluxed for 1 hour. The mixture was poured on
crushed ice. The separated solid was filtered, washed with water
and recrystallized from ethanol to give 0.05 g (18%) of 5d, mp
240-242 °C.
Compound 3a (0.257 g, 1 mmole) was dissolved in 2 ml of
conc. sulphuric acid and 2 ml of water. The mixture was cooled
to 0-5 °C, diazotized by adding 0.069 g (1 mmole) of sodium
nitrite in 1 ml of water. A mixture of 5 ml of sulphuric acid and
5 ml of water was added to above mixture with stirring
Followed by heating on water bath for 30 minutes. The solid
that appeared was collected by filtration and recrystallized from
ethanol to give 0.105 g (0.4 mmoles, 40%) of crystalline solid
3-Chloro-4-oxo-2-phenylpyrazolo[3',4':4,5]pyrimido[2,1-b] ben-
zothiazole (5e).
This compound (0.120 g, 0.34 mmole) was prepared from 3b
(0.333 g, 1 mmole) in 34% yield in a manner similar to that
described for 5d, mp 220-225 °C; ir (potassium bromide): ν max
-1
of 5a, mp 152 °C; ir (potassium bromide): ν max cm 3475-
+
3375 (broad OH), 1693 (C=O); ms: m/z 258 (M , 100%);
-1
cm 1710(C=O); 710(C-Cl); ms: m/z 354(M+2,15%),
1
H-nmr (deuteriodimethyl sulfoxide): δ 4.6 (s, 1H, OH
,
+
1
352(M ,45%); H-nmr (deuteriochloroform): δ 7.1-8.1 (m, 9H,
exchangeable with D O), 11.0 (s, 1H, NH, exchangeable with
2
aromatic-H).
D O), 7.3-7.6 (m, 4H, aromatic-H).
2
Anal. Calcd. for C H N OSCl: C, 57.95; H, 2.55; N, 15.90.
17
9 4
Anal. Calcd. for C H N O S: C, 51.16; H, 2.30; N, 21.70.
11
6 4 2
Found C, 57.90; H, 2.50; N, 15.82.
Found C, 51.10; H, 2.25; N, 21.65.
Synthesis of 5e from 5b Using Phosphoryl Chloride.
3-Hydroxy-4-oxo-2-phenylpyrazolo[3',4':4,5]pyrimido[2,1-
b]benzothiazole (5b).
A mixture of 0.166 g (0.5 mmoles) of 5b and 2 ml of phospho-
ryl chloride was refluxed for 3 hours. The mixture was poured on
crushed ice. The solid separated was filtered, washed with water
and recrystallized from ethanol to give 0.06 g (34%) of 5e, mp
225 °C
This compound (0.14 g, 0.41mmole) was prepared from 3b
(0.333 g, 1 mmole) in 41% yield in a manner similar to that
described for 5a, mp 202 °C; ir (potassium bromide): ν max
-1
cm 3427-3360(broad, OH), 1698(C=O); ms: m/z
+
1
3-Chloro-4-oxo-2(2'-benzothiazolyl)pyrazolo[3',4':4,5]pyrim-
ido[2,1-b]benzothiazole (5f).
334(M ,100%); H-nmr (deuteriodimethyl sulfoxide): δ 5.4
(s, 1H, OH exchangeable with D O), 7.3-7.9 (m, 9H, aro-
,
2
matic-H).
Anal. Calcd. for C H N O S: C, 61.07; H, 2.99; N, 16.76.
Found C, 61.05; H, 2.92; N, 16.78.
This compound (0.16 g, 0.39 mmole) was prepared from 3c
(0.39 g, 1 mmole) in 39% yield in a manner similar to that
described for 5d, mp 260-265 °C; ir (potassium bromide): ν
17 10
4 2
-1
max cm 1720(C=O), 720(C-Cl); ms: m/z 411(M+2, 25%),
3-Hydroxy-4-oxo-2(2'-benzothiazolyl)pyrazolo[3',4':4,5]pyrim-
ido[2,1-b]benzothiazole (5c).
+
1
409(M , 75%); H-nmr (deuteriochloroform): δ 7.1-7.9 (m, 8H,
aromatic-H).
This compound (0.17 g, 0.43 mmole) was prepared from 3c
(0.39 g, 1 mmole) in 43% yield in a manner similar to that
Anal. Calcd. For C H N OS Cl: C, 52.81; H, 1.95; N, 17.11.
18
8
5
2
Found C, 52.78; H, 1.92; N, 17.08.
described for 5a, mp 230 °C; ir (potassium bromide): ν max
Synthesis of 5f from 5c Using Phosphoryl Chloride.
-1
cm
3400-3200(broad OH), 1703(C=O); ms: m/z
+
1
391(M ,100%); H-nmr (deuteriodimethyl sulfoxide): δ 6.1
A mixture of 0.179 g (0.5 mmoles) of 5c and 2 ml of phospho-
ryl chloride was refluxed for 4 hours. The mixture was poured on
crushed ice. The separated solid was collected by filtration,
washed with water and recrystallized from ethanol to give 0.06 g
(30%) of 5f, mp 258-260 °C.
(s, 2H, OH exchangeable with D O), 7.3-8.1 (m, 8H, aro-
,
2
matic-H).
Anal. Calcd. for C H N O S : C, 55.24; H, 2.30; N, 17.90.
18
9 5 2 2
Found C, 55.20; H, 2.28; N, 17.88.
3-Chloro-4-oxo-(2H)-pyrazolo[3',4':4,5]pyrimido[2,1-b] benzo-
thiazole (5d).
3-Bromo-4-oxo-(2H)-pyrazolo[3',4':4,5]pyrimido[2,1-b]ben-
zothiazole (5g).
Compound 3a (0.257 g, 1 mmoles) was dissolved in 2 ml of
conc. sulphuric acid and 2 ml of water. The mixture was cooled
to 0-5 °C, diazotized by adding 0.069 g (1 mmole) of sodium
nitrite in 1 ml of water. While diazotization was in progress,
the calculated amount of a mixture of cuprous chloride in conc.
hydrochloric acid was added with stirring. The mixture was
stirred for 15 minutes. Then the mixture was heated on water
bath for 30 minutes. The solid that appeared was collected by
filtration and recrystallized from ethanol to give 0.075 g (0.27
mmoles, 27%) of crystalline solid of 5d, mp 240-245 °C; ir
Compound 3a (0.257 g, 1 mmoles) was dissolved in 2 ml of
conc. sulphuric acid and 2 ml of water. The mixture was cooled
to 0-5 °C, diazotized by adding 0.069 g (1 mmole) of sodium
nitrite in 1 ml of water. While diazotization was in progress, the
calculated amount of a mixture of cuprous bromide in hydro-
bromic acid was added with stirring. The mixture was stirred
for 15 minutes. Then the mixture was heated on water bath for
30 minutes. The solid that appeared was collected by filtration
and recrystallized from ethanol to give 0.095 g (0.29 mmoles,
29%) of crystalline solid of 5g, mp 275-278 °C; ir (potassium
-1
1
(potassium bromide): ν max cm 3100(NH), 1716(C=O);
bromide): ν max cm- 3341(NH), 1734(C=O); 576(C-Br); ms:
+
1
+
1
690(C-Cl); ms: m/z 278(M+2,10%), 276(M , 30%); H-nmr
m/z 322(M+2, 67%), 320( M , 69%); H-nmr (deuterio-
(deuteriochloroform): δ 10.7(s, 1H, NH, exchangeable with
chloroform): δ 11.1(s, 1H, NH, exchangeable with D O), 7.2-
2
D O), δ 7.4-7.9 (m, 4H, aromatic-H).
7.7 (m, 4H, aromatic-H).
2
Anal. Calcd. for C H N OSBr:C, 41.25; H, 1.56; N, 17.50.
Anal. Calcd. for C H N OSCl:C,47.82;H,1.81;N, 20.28;
11
5 4
11
5 4
Found C, 41.20; H, 1.52; N,17.40.
found C, 47.80; H, 1.80; N, 20.25.

550
Communication to the Editor
Vol. 40
3-Bromo-4-oxo-2-phenylpyrazolo[3',4':4,5]pyrimido[2,1-b]-
benzothiazole (5h).
3-Hydrazino-4-oxo-(2H)-pyrazolo[3',4':4,5]pyrimido[2,1-b]
benzothiazole (5m).
This compound (0.145 g, 0.36 mmole) was prepared from 3b
(0.333 g, 1 mmole) in 36% yield in a manner similar to that
described for 5g, mp 285-287 °C; ir (potassium bromide): ν
Compound 3a (0.257 g, 1 mmole) of 3a was dissolved in 2
ml of conc. sulphuric acid and 2 ml of water. The mixture was
cooled to 0-5 °C, diazotized by adding 0.069 g (1 mmole) of
sodium nitrite in 1 ml of water; stirring was continued for
5 minutes. To the above mixture with stirring was added an
ice-cold solution of 0.504 g of hydrated sodium sulphite and
1 g of sodium hydroxide in 10 ml of water. The solution was
allowed to stand for 10 minutes, acidified with 5 ml of conc.
hydrochloric acid and the mixture was heated on water bath
for 5 minutes then allowed to stand for overnight. The
separated salt was taken up in water and the free base was
obtained by adding a saturated solution of sodium acetate. The
solid that appeared was collected by filtration, washed with
water and recrystallized from ethanol to give 0.11 g
1
max cm- 1705(C=O); 550(C-Br); ms: m/z 398(M+2, 59%),
+
1
396(M , 61%); H-nmr (deuteriochloroform): δ 7.1-8.0 (m, 9H,
aromatic-H).
Anal. Calcd. for C H N OSCl:C, 51.51; H, 2.27; N, 14.14.
17
9 4
Found C, 51.50; H, 2.25; N, 14.10.
3-Bromo-4-oxo-2(2'-benzothiazolyl)pyrazolo[3',4':4,5]pyrim-
ido[2,1-b]benzothiazole (5i).
This compound (0.18 g, 0.39 mmole) was prepared from 3c
(0.39 g, 1 mmole) in 39% yield in a manner similar to that
described for 5g, mp 290-292 °C; ir (potassium bromide): ν
-1
max cm 1690(C=O), 570(C-Br); ms: m/z 455(M+2, 62%),
(0.4 mmole, 40%) of crystalline solid of 5m, mp 260 °C; ir
+
1
1
453(M , 64%). H-nmr (deuteriochloroform): δ 7.3-7.9 (m, 8H,
(potassium bromide): ν max cm- 3320, 3200(NH ),
2
+
1
3130(NH), 1705(C=O); ms: m/z 272(M , 80%); H-nmr
(deuteriochloroform): δ 4.9 (s, 1H, NH exchangeable with
D O), 5.8(broad s, 2H, NH exchangeable with D O), 10.7
aromatic-H).
Anal. Calcd. for C H N OS Br: C,47.68; H, 1.77; N, 15.45.
18
8
5
2
Found C, 47.65; H, 1.75; N, 15.40.
2
2
2
(s, 1H, NH exchangeable with D O), 7.1-7.7 (m, 4H,
aromatic-H).
2
3-Iodo-4-oxo-(2H)-pyrazolo[3',4':4,5]pyrimido[2,1-b]benzothia-
zole (5j).
Anal. Calcd. for C H N OS: C, 48.52; H, 2.94; N, 30.88.
11
8 6
Compound 3a (0.257 g, 1 mmoles) was dissolved in 2 ml of
conc. sulphuric acid and 2 ml of water. The mixture was cooled to
0-5 °C, diazotized by adding 0.069 g (1 mmole) of sodium nitrite
in 1ml of water. While diazotization was in progress, the calcu-
lated amount of potassium iodide in 1 ml of water was added with
stirring. The mixture was stirred for 15 minutes followed by heat-
ing on water bath for 30 minutes. The solid that appeared was
collected by filtration and recrystallized from ethanol to give
0.105 g (0.28 mmoles, 28%) of crystalline solid of 5j, mp 220-
Found C, 48.35; H, 2.92; N,30.82.
Synthesis of 5m from 5j Using Hydrazine Hydrate.
A mixture of 0.138 g (0.5 mmoles) of 5j, 0.2 ml of hydrazine
hydrate (80%) and 2 ml of methanol was refluxed for 2 hours.
The separated solid was collected by filtration and recrystal-
lized from ethanol to give 0.03 g (22%) of 5m, mp 255-260 °C
3-Hydrazino-4-oxo-2-phenylpyrazolo[3',4':4,5]pyrimido[2,1-b]-
benzothiazole (5n).
1
225 °C; ir (potassium bromide): ν max cm- 3169(NH),
This compound (0.12 g, 0.35 mmole) was prepared from 3b
(0.333 g, 1 mmole) in 35% yield in a manner similar to that
+
1
1684(C=O); 570(C-I) ms: m/z 368(M , 80%); H-nmr (deuterio-
chloroform): δ 10.7(s, 1H, NH, exchangeable with D O), 7.2-7.8
2
described for 5m, mp 274-276 °C; ir (potassium bromide): ν max
(m, 4H, aromatic-H).
1
cm- 3300, 3270(NH ), 3190(NH), 1690(C=O); ms: m/z
2
Anal. Calcd. for C H N OSI: C, 35.86; H, 1.35; N, 15.21.
11
5 4
+
1
348(M , 75%); H-nmr (deuteriochloroform): δ 5.0 (s, 1H, NH
Found C, 35.80; H, 1.34; N, 15.20.
,
exchangeable with D O), 5.7(broad s, 2H, NH , exchangeable
2
2
3-Iodo-4-oxo-2-phenylpyrazolo[3',4':4,5]pyrimido [2,1-b]
benzothiazole (5k).
with D O), 7.2-8.0 (m, 9H, aromatic-H).
2
Anal. Calcd. for C H N OS: C, 58.62; H, 3.49; N, 24.13.
17 12
6
Found C, 58.60; H, 3.45; N, 24.10.
This compound (0.12 g, 0.34 mmole) was prepared from 3b
(0.333 g, 1 mmole) in 34% yield in a manner similar to that
described for 5j, mp 235-240 °C; ir (potassium bromide): ν max
cm- 1710(C=O); 540(C-I); ms: m/z 444(M , 70%); H-nmr
(deuteriochloroform): δ 7.1-7.9 (m, 9H, aromatic-H).
Synthesis of 5n from 5k Using Hydrazine Hydrate.
1
+
1
A mixture of 0.22 g (0.5 mmoles) of 5k, 0.2 ml of hydrazine
hydrate (80%) and 2 ml of methanol was refluxed for 2 hours, the
separated solid was collected by filtration and recrystallized from
ethanol to give 0.035 g (20%) of 5n, mp 272-274 °C
Anal. Calcd. for C H N OSI: C, 45.94; H, 2.02; N, 12.61.
17
9 4
Found C, 45.92; H, 2.01; N, 12.57.
3-Hydrazino-4-oxo-2(2'-benzothiazolyl)pyrazolo[3',4':4,5]-
pyrimido[2,1-b]benzothiazole (5o).
3-Iodo-4-oxo-2(2'-benzothiazolyl)pyrazolo[3',4':4,5]pyrimido-
[2,1-b]benzothiazole (5l).
This compound (0.155 g, 0.38 mmole) was prepared from 3c
(0.39 g, 1 mmole) in 38% yield in a manner similar to that
described for 5m, mp 290-295 °C; ir (potassium bromide): ν max
This compound (0.185 g, 0.36 mmole) was prepared from 3c
(0.39 g, 1 mmole) in 36% yield in a manner similar to that
described for 5j, mp 240-242 °C; ir (potassium bromide): ν max
cm 1695(C=O), 570(C-I); ms: m/z 501 (M , 74%); H-nmr
(deuteriochloroform) : δ 7.3-7.8 (m, 8H, aromatic-H).
1
-1
+
1
cm- 3350, 3240(NH , 3180(NH), 1730(C=O); ms: m/z
2)
+
1
405(M , 70%); H-nmr (deuteriochloroform): δ 4.7 (s, 1H, NH
,
Anal. Calcd. for C H N OS Br: C,43.11; H,1.59; N, 13.97.
exchangeable with D O), 5.7 (broad s, 2H, NH , exchangeable
18
8
5
2
2
2
Found C, 43.08; H, 1.55; N, 13.95.
with D O), 7.3-8.1 (m, 8H, aromatic-H).
2

May-Jun 2003
Communication to the Editor
551
REFERENCES AND NOTES
Anal. Calcd. for C H N OS Br: C,53.33; H, 2.71; N, 24.19.
18
8
5
2
Found C, 53.30; H, 2.70; N, 24.17.
[1] J. Garin, C. Guillen, E. Melendez, F. L. Merchan,
J. Orduna and T. Tejero, Heterocycles, 26, 2371 (1987).
[2] J. Garin, C. Guillen, E. Melendez, F. L. Merchan,
J. Orduna and T. Tejero, Bull. Soc. Chim. Belg., 96, 797 (1987).
[3] F. Russo, S. Guccione, G. Romeo, L.Monsu Scolaro,
A.Caruso ,V.Cutuli, Boll. Chim. Farm., 130, 89 (1991); Chem.
Abstr., 116, 6506 (1992).
Synthesis of 5o from 5l Using Hydrazine Hydrate.
A mixture of 0.25 g (0.5 mmoles) of 5l, 0.2 ml of hydrazine
hydrate (80%) and 2 ml of methanol was refluxed for 4 hours, the
separated solid was collected by filtration and recrystallized from
ethanol to give 0.05 g (25%) of 5o, mp 290-292 °C
Acknowledgment.
[4] K. G. Baheti, S. B. Kapratwar and S. V. Kuberkar, Synth.
Commun.,32, 2237 (2002).
[5] Leon Katz, J. Am. Chem. Soc., 73, 4007 (1951); Chem.
Abstr., 46, 3044 (1951).
Authors are grateful to Dr. B. S. Dhengle, Principal, Yeshwant
College, Nanded (India) for providing laboratory facilities and
Director, Indian Institute of Chemical Technology, Hyderabad
(India) for providing spectra.