Alumina Catalyzed Synthesis of Fused Thioxopyrimidine Derivatives under Microwaves

Article abstract of DOI:10.1081/SCC-120025184

An expeditious solventless approach for the synthesis of pyrazolino[3,4-d]/isoxazolino[3,4-d]/pyrano[2,3-d]/iminopyrimidino[4,5-d]/ thioxopyrimidino[4,5-d]/thiazino[5,4-d] pyrimidines from 2-thiobarbituric acid using supported reagents (acidic/basic alumi

Full text of DOI:10.1081/SCC-120025184

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Alumina Catalyzed Synthesis of Fused
Thioxopyrimidine Derivatives Under Microwaves
a
a
a
M. Kidwai , R. Mohan & S. Rastogi
a
Department of Chemistry , University of Delhi , Delhi, India
Published online: 16 Aug 2006.
To cite this article: M. Kidwai , R. Mohan & S. Rastogi (2003) Alumina Catalyzed Synthesis of Fused Thioxopyrimidine
Derivatives Under Microwaves, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 33:21, 3747-3759, DOI: 10.1081/SCC-120025184
To link to this article: http://dx.doi.org/10.1081/SCC-120025184
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Õ
SYNTHETIC COMMUNICATIONS
Vol. 33, No. 21, pp. 3747–3759, 2003
Alumina Catalyzed Synthesis of Fused
Thioxopyrimidine Derivatives Under Microwaves
M. Kidwai,* R. Mohan, and S. Rastogi
Department of Chemistry, University of Delhi,
Delhi, India
ABSTRACT
An expeditious solventless approach for the synthesis of pyrazo-
lino[3,4-d]/isoxazolino[3,4-d]/pyrano[2,3-d]/iminopyrimidino[4,5-d]/
thioxopyrimidino[4,5-d]/thiazino[5,4-d] pyrimidines from 2-thiobar-
bituric acid using supported reagents (acidic/basic alumina) under
microwave irradiation (MWI) is described. The reaction times were
brought down from hours to minutes with yield enhancement. Also
the procedure highlights the versatility of solid supports.
Key Words: Alumina; Catalyst; Solid support; Microwave
irradiation; Thioxopyrimidines; Dry media.
*Correspondence: M. Kidwai, Department of Chemistry, University of Delhi,
Delhi, 110007, India; Fax: (91 11) 27666235; E-mail: mkidwai@mantraonline.com.
3
747
DOI: 10.1081/SCC-120025184
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
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3748
Kidwai, Mohan, and Rastogi
Fused pyrimidine derivatives viz. pyrazolinopyrimidines, isoxazolino-
pyrimidines, pyrimidopyrimidines and pyranopyrimidines generate
[
1–5]
a widespread interest due to diverse biological activities.
pyrimidine derivatives are used as preventive and prophylactic drug in the
These
[
6]
[7]
treatment of male erectile dysfunction, arthritis and Crohn’s disease.
Though various routes for the synthesis of these compounds are
[8–12]
known,
but majority of them involve longer preparation times, low
yield and usage of excess solvent along with external agents. The general
approach, however, for their synthesis involves either cyclization of
[
13,14]
substituted pyrimidines or condensation of specific moieties with it.
In recent years microwave assisted solid supported synthesis
[
15]
[
16–19]
has gained popularity in organic synthesis
selectivity and ease of manipulation. These dry media reactions
due to its reactivity,
[
20]
are
specially appealing as they provide an opportunity to work with open
vessel, avoiding the risk of high pressure development and also providing
a possibility of upscaling the reactions on preparative scale. Aluminas can
[
21]
be selected as acidic or basic catalyst depending on the type of organic
reaction. These mineral oxides are very poor conductors of heat but they
behave as very efficient microwave absorbents resulting in very rapid and
homogeneous heating.
In search of a more efficient and clean methodology for the synthesis
of fused pyrimidine derivatives, we report herein a novel synthesis of
pyrazolino/isoxazolino/pyrimidino/pyrano/thiazino pyrimidines from
thiobarbituric acid in dry media under microwave irradiation.
Synthesis of 5-arylidene thiobarbituric acid 2a–b was modified to give a
better yield and reduced reaction time. A mixture of thiobarbituric acid and
heterocyclic aldehyde 1a–b, adsorbed on neutral alumina, was irradiated
for 2–3 min to yield the product 2 in 90–92% yield (Fig. 1a). The spectra
[
22]
and melting point of the product were in agreement with literature data.
Since compound 2 have requisite features for Michael condensation, it was
condensed with phenylhydrazine, hydroxylamine hydrochloride,
ethylacetoacetate, cyanoguanidine and thiourea (Fig. 1b). The reactions
were carried out both on basic and acidic alumina as solid supports.
The usage of basic alumina gave isoxazolino [3,4-d] pyrimidine 4a–b,
iminopyrimidino [4,5-d] pyrimidine 5a–b, pyrimido [3,4-d] cyclohexenone
6
a–b and thioxopyrimidino [4,5-d] pyrimidine 8a–b on reaction of 2a–b
with hydroxylamine hydrochloride, ethylacetoacetate, cyanoguanidine
and thiourea respectively. This not only eliminated the need for an
external base, but also gave a significant enhancement in yield and
reduction in reaction time (Table 1). The reaction of phenyl hydrazine
with compound 2a–b using basic alumina did not go to completion
whereas the same reaction over acidic alumina under microwave

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Fused Thioxopyrimidine Derivatives
3749
H
N
(
a)
H
N
O
R
S
O
S
Neutral Alumina
MWI
+
RCHO
1a-b
HN
H
HN
1
O
O
2a-b
H
N
N
R
S
N–Ph
HN
H
N
H
N
(
b)
S
HN
NH
PhNHNH2
O
Acidic
Alumina
3
S
Acidic Alumina
MWI
H
N
O
R
S
H
N
S
O
R
N
O
9
a-b
H NCNH2
NH2OH.HCl
S
2
Basic alumina
MWI
HN
HN
H
O
R
H
N
O
2a-b
NH
H2NC–NHCN
S
HN
N
R
S
4a-b
N
Basic
Alumina
H
N
Basic alumina
MWI
NH
NH
CH3COCH2COOEt
S
O
HN
N–CN
8
Acidic
Alumina
Basic
Alumina
O
R
H
N
H
5a-b
O
R
CH3
N
S
O
S
HN
HN
O
COOEt
COOEt
O
R
7a-b
6a-b
R = a =
,
b =
O
N
H
Figure 1.
irradiation gave pyrazolino [3,4-d] pyrimidine 3a–b. Pyrano [2,3-d]
pyrimidine 7a–b and thiazino [5,4-d] pyrimidine 9a–b were obtained in
good yield on condensation of 2a–b with ethylacetoacetate and thiourea
using acidic alumina as solid support (Fig. 1b). The formation of 9a–b
over acidic alumina can be attributed to the fact that in acidic medium
nitrogen gets protonated and hence the attack by sulphur at b-olefinic
carbon becomes more facile while in basic media, the increase in
nucleophilicity of nitrogen leads to the attack at carbonyl carbon through
nitrogen.
The structure of compounds were confirmed by their spectroscopic
and analytical data. In IR spectra the disappearance of band at

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3750
Kidwai, Mohan, and Rastogi
Table 1. Comparison of reaction time and yield.
Conventional solution phase
method A
Microwave solid support
method B
Compd. no.
Time (h)
Yield (%)
Time (min)
Yield (%)
3a
3b
4a
4b
5a
5b
6a
6b
7a
7b
8a
8b
9a
9b
4.0
4.5
3.5
4.0
9.0
10.0
5.5
6.0
5.0
5.5
4.5
4.5
7.0
7.5
65
65
67
66
68
66
69
67
59
54
65
63
52
53
3.0
3.0
2.5
3.0
5.5
6.0
3.5
3.5
3.0
4.0
2.5
3.0
4.0
4.5
89
87
87
83
88
86
85
82
82
80
88
85
84
82
ꢀ
1
1
at 1595 cm
675 cm due to a,b-unsaturated carbonyl and appearance of band
ꢀ1
due to C¼N confirmed the formation of product. In
1
H NMR the signal at ꢀ 5.1 due to allylic proton was missing.
This is the first report on the synthesis of pyrazolino/isoxazolino/
pyrimidino/pyrano/thiazinopyrimidine in dry media using MWI in
absence of any toxic chemical, mineral acid, base or organic solvent,
which makes it a clean, efficient and cheap procedure for the synthesis
of useful heterocyclic compounds. The conventional procedure
[23–27]
reported
for the synthesis of simple pyrazolines, isoxazolines,
pyrans, cyclohexenones, pyrimidines and thiazines from chalcones
was adopted to synthesize fused pyrimidine derivatives from 5-arylidene
thiobarbituric acid 2a–b. A drastic reduction in time was observed in case
of MWI in comparison to conventional methodology (Table 1). Thus,
aluminas (acidic or basic) act not only as catalysts but also as an energy
transfer medium resulting in very rapid and homogeneous heating.
EXPERIMENTAL SECTION
Melting points were determined by Electrothermal melting point
apparatus and are uncorrected. Infrared spectra (in KBr) were recorded

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Fused Thioxopyrimidine Derivatives
3751
1
on 1710 Perkin Elmer FT infrared spectrophotometer. H NMR
spectra were recorded on FT NMR Hitachi R-600 (60 MHz) spectro-
meter. Elemental Analysis were performed on Hareaus CHN-
Rapid Analyzer. For microwave irradiation (MWI) Kenstar microwave
oven, Model No. OM9925E (2450 MHz, 800 W) was used. The purity of
the compounds were checked on silica gel coated Al plates (Merck). The
approximate temperature, as measured by AZ, mini Non-Contact
ꢁ
Infrared Thermometer, Model No. 8868, was 90–120 C (8009 W).
General Procedure for the Synthesis of 5-(2-Furylidene/
3
-indolylidene) Thiobarbituric Acid (2a–b)
To the solution of 2-thiobarbituric acid (0.01 mol) and aldehyde 1a–b
[
28]
in ethanol (15 mL), neutral alumina
(20 g) was added. The reaction
mixture was stirred well and dried in air. It was then placed in an alumina
bath and subjected to MWI for 2–3 min. On completion of reaction, as
followed by TLC, the product was eluted using ethanol (3 ꢂ 15 mL).
The solid obtained on evaporation of solvent was recrystallized from
ethanol.
General Procedure for the Synthesis of 3-Aryl-2-phenyl-6-
thiopyrazolino[3,4-d]pyrimidin-4-(5H,7H)-one(3a–b)
Method A
Phenylhydrazine (0.015 mol) was added to a solution of 2a/2b
0.01 mol) in acetic acid (15 mL) and the reaction mixture was refluxed
(
under constant stirring for 4 h. On completion of reaction, the reaction
mixture was poured over crushed ice. The solid obtained was filtered,
washed with water and recrystallized from ethanol.
Method B
To a solution of 2a/b (0.01 mol), phenylhydrazine (0.015 mol) in
[
28]
ethanol, acidic alumina
(20 g) was added. The reaction mixture was
stirred well, air dried and subjected to MWI intermittently at 30 s
intervals for specified time (Table 1). On completion of reaction, as
monitored by TLC (a small amount of reaction mixture taken in
sample tube and eluted with 0.5 mL ethanol) the product was extracted

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3752
Kidwai, Mohan, and Rastogi
into ethanol (3 ꢂ 15 mL). Removal of solvent under reduced pressure
yielded the product which was recrystallized from ethanol.
3
.1 (d, 1H, CH), 6.2–6.6 (m, 3H, furan), 7.2–7.7 (m, 5H, Ar-H). IR (KBr):
ꢁ
1
a. M.p. 258–259 C. H NMR (60 MHz, DMSO) ꢀ: 3.6 (d, 1H, CH),
4
1
ꢀ
1
585 (C¼N), 1595 (N-C H ) cm . Anal. calcd. for C H N O S:
6
5
15 12
4
2
C, 57.69; H, 3.84; N, 17.94. Found: C, 57.71; H, 3.81; N, 17.95.
3
CH), 4.2 (d, 1H, CH), 7.2–7.8 (m, 10H, Ar-H & indole). IR
ꢁ
1
b. M.p. 262–264 C. H NMR (60 MHz, DMSO) ꢀ: 3.5 (d, 1H,
ꢀ
1
(
KBr): 1580 (C¼N), 1594 (N-C H ) cm
.
Anal. calcd. for
C H N OS: C 63.15; H, 4.15; N, 19.39. Found: C, 63.18; H, 4.17;
6
5
1
9
15
5
N, 19.40.
General Procedure for the Synthesis of 3-Aryl-6-
thioisoxazolino[3,4-d] Pyrimidin-4-(3H,5H)-one (4a–b)
Method A
A mixture of 2a/2b (0.01 mol), hydroxylamine hydrochloride
0.01 mol) and pyridine (25 mL) was refluxed for 3 h. The reaction
(
mixture was cooled, acidified with dil. acetic acid and the solid obtained
was filtered, dried and recrystallized from ethanol.
Method B
To a solution of 2a/b (0.01 mol), hydroxylamine hydrochloride
[
28]
(
0.01 mol) in ethanol, basic alumina
(20 g) was added. The reaction
mixture was stirred well, air dried and subjected to MWI intermittently
at 30 s intervals for specified time (Table 1). On completion of reaction, as
monitored by TLC (a small amount of reaction mixture taken in sample
tube and eluted with 0.5 mL ethanol) the product was extracted into
ethanol (3 ꢂ 15 mL). Removal of solvent under reduced pressure yielded
the product which was recrystallized from ethanol.
ꢁ
1
4
.7 (d, 1H, CH), 6.2–6.5 (m, 3H, furan). IR (KBr): 1230 (C–O–N), 1590
a. M.p. 240–241 C. H NMR (60 MHz, DMSO) ꢀ: 3.4 (d, 1H, CH),
4
(
ꢀ
1
C¼N) cm . Anal. calcd. for C H N O S: C, 48.86; H, 3.16; N, 19.00.
9
7
3
2
Found: C, 48.85; H, 3.13; N, 19.01.
4
.9 (d, 1H, CH), 7.1–7.4 (m, 5H, indole). IR (KBr): 1235 (C–O–N), 1587
ꢁ
1
b. M.p. 265–266 C. H NMR (60 MHz, DMSO) ꢀ: 3.5 (d, 1H, CH),
4
(
ꢀ
1
C¼N) cm . Anal. calcd. for C H N O S: C, 54.54; H, 3.49; N, 19.58.
1
3
10
4
2
Found: C, 54.55; H, 3.47; N, 19.60.

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Fused Thioxopyrimidine Derivatives
3753
General Procedure for the Synthesis of 4-Aryl-3-cyano-2-
imino-7-thiopyrimidino[4,5-d] Pyrimidin-5-(6H,8H)-one (5a–b)
Method A
A mixture of 2a/2b (0.01 mol) and cyanoguanidine, (0.01 mol) in
ethanol (15 mL) was refluxed, while a solution of sodium hydroxide (5 mol)
in water (5 mL) was added portion wise during 2 h. Refluxing was contin-
ued for 10 h and reaction mixture was concentrated under reduced pressure
to give the required product which was recrystallized from ethanol.
Method B
To a solution of 2a/b (0.01 mol), cyanoguanidine (0.01 mol) in
[
28]
ethanol, basic alumina
was added. The reaction mixture was stirred
well, air dried and subjected to MWI intermittently at 30 s intervals for
specified time (Table 1). On completion of reaction, as monitored by TLC
(
0
a small amount of reaction mixture taken in sample tube and eluted with
.5 mL ethanol) the product was extracted into ethanol (3 ꢂ 15 mL).
Removal of solvent under reduced pressure yielded the product which
was recrystallized from ethanol.
ꢁ
1
a. M.p. 210–212 C. H NMR (60 MHz, DMSO) ꢀ: 3.7 (d, 1H, CH),
5
.2 (d, 1H, CH), 6.2–6.6 (m, 3H, furan), 10.3 (br, 1H, N–H). IR (KBr):
4
1
ꢀ
1
650 (exo C¼NH), 1550 (C¼N), 2290 (CꢃN) cm . Anal. calcd. for
C H N O S: C, 45.83; H, 2.77; N, 29.16. Found: C, 45.80; H, 2.78;
1
1
8
6
2
N, 29.18.
b. M.p. 225–226 C. H NMR (60 MHz, DMSO) ꢀ: 3.6 (d, 1H, CH),
.3 (d, 1H, CH), 7.1–7.5 (m, 5H, indole), 10.3 (br, 1H, N–H). IR (KBr):
ꢁ
1
5
4
1
ꢀ
1
645 (exo C¼NH), 1600 (C¼N), 2295 (CꢃN) cm . Anal. calcd. for
C H N OS: C, 53.41; H, 3.26; N, 29.08. Found: C, 53.40; H, 3.24;
1
5
11
7
N, 29.10.
General Procedure for the Synthesis of 5-Aryl-6-ethylcarboxy-
-thiopyrimido[3,4-d]cyclohexen-4,7-(1H,3H)-dione (6a–b)
2
Method A
Compound 2a/2b (0.01 mol) was added to a solution of Na in ethanol
20 mL) followed by ethylacetoacetate (0.01 mol) and more ethanol
20 mL). The reaction mixture was refluxed on a water bath for 6 h and
(
(

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3754
Kidwai, Mohan, and Rastogi
then diluted with water and acidified to give a bright yellow solid which
was recrystallized from ethanol.
Method B
To a solution of 2a/b (0.01 mol), ethylacetoacetate (0.01 mol) in
ethanol, basic alumina
[28]
was added. The reaction mixture was stirred
well, air dried and subjected to MWI intermittently at 30 s intervals for
specified time (Table 1). On completion of reaction, as monitored by TLC
(
0
a small amount of reaction mixture taken in sample tube and eluted with
.5 mL ethanol) the product was extracted into ethanol (3 ꢂ 15 mL).
Removal of solvent under reduced pressure yielded the product which
was recrystallized from ethanol.
ꢁ
a.M.p.286–288 C. H NMR(60 MHz,DMSO)ꢀ:1.2(t,3H,CH ),3.2
3
1
6
(
(
d, 1H, 4-CH), 3.4 (d, 1H, 5-CH), 3.9 (d, 1H, 3-CH), 4.1 (q, 2H, CH ), 5.6
2
s, 1H, 1-CH), 6.1–6.5 (m, 3H, furan). IR (KBr): 1566 (C¼C), 1695 (C¼O
ꢀ
1
in conjugation with C¼C), 1726 (C¼O of ester) cm . Anal. calcd. for C
1
5
H N O S: C, 53.89; H, 4.19; N, 8.38. Found: C, 53.90; H, 4.17; N, 8.35.
1
4
2
5
ꢁ
b.M.p.270–273 C. H NMR(60 MHz,DMSO)ꢀ:1.2(t,3H,CH ),3.2
3
1
6
(d, 1H, 4-CH), 3.5 (d, 1H, 5-CH), 3.9 (d, 1H, 3-CH), 4.2 (q, 2H, CH ), 5.7 (s,
2
1
H, 1-CH), 7.1–7.4 (m, 5H, indole). IR (KBr): 1569 (C¼C), 1697 (C¼O in
ꢀ
19
1
conjugation with C¼C), 1725 (C¼O of ester) cm . Anal. calcd. for C H
N O S: C, 60.31; H, 3.17; N, 11.11. Found: C, 60.32; H, 3.20; N, 11.12.
3 4
1
2
General Procedure for the Synthesis of
-Aryl-6-ethylcarboxy-7-methyl-2-thioxo-5H-
5
pyrano[2,3-d]pyrimidin-4-(1H,3H)-one (7a–b)
Method A
A solution of 0.01 mol. of 2a/2b, 0.01 mol of ethylacetoacetate and
mL of hydrochloric acid in 25 mL ethanol was refluxed on a steam bath
5
for 5 h. The reaction mixture was cooled, poured over crushed ice and the
solid obtained was filtered, dried and recrystallized from acetic acid.
Method B
To a solution of 2a/b (0.01 mol), ethylacetoacetate (0.01 mol) in
ethanol, acidic alumina
[28]
was added. The reaction mixture was stirred

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Fused Thioxopyrimidine Derivatives
3755
well, air dried and subjected to MWI intermittently at 30 s intervals for
specified time (Table 1). On completion of reaction, as monitored by TLC
(
0
a small amount of reaction mixture taken in sample tube and eluted with
.5 mL ethanol) the product was extracted into ethanol (3 ꢂ 15 mL).
Removal of solvent under reduced pressure yielded the product which
was recrystallized from acetic acid.
ꢁ
a. M.p. 256–257 C. H NMR (60 MHz, DMSO) ꢀ: 1.2 (t, 3H, CH ),
3
1
7
1
.9 (s, 3H, CH ), 3.8 (s, 1H, CH), 4.1 (q, 2H, CH ), 6.2–6.6 (m, 3H,
3 2
furan). IR (KBr): 1225 (C–O–C), 1635 (C¼C), 1725 (C¼O of ester)
ꢀ
1
cm . Anal. calcd. for C H N O S: C, 53.89; H, 4.19; N, 8.38.
1
5
14
2
5
Found: C, 53.90; H, 4.21; N, 8.39.
ꢁ
b. M.p. 277–279 C. H NMR (60 MHz, DMSO) ꢀ: 1.3 (t, 3H, CH ),
3
1
7
1
.8 (s, 3H, CH ), 3.7 (s, 1H, CH), 4.1 (q, 2H, CH ), 7.2–7.5 (m, 5H,
3 2
indole). IR (KBr): 1220 (C–O–C), 1634 (C¼C), 1720 (C¼O of
ꢀ1
ester) cm . Anal. calcd. for C H N O S: C, 59.53; H, 4.43; N, 10.96.
1
9
17
3
4
Found: C, 59.55; H, 4.46; N, 10.98.
General Procedure for the Synthesis of 5-Aryl–2,7-
dithiopyrimidino[4,5-d]pyrimidin-4-(1H,3H,6H)-one(8a–b)
Method A
A mixture of 2a/2b (0.01 mol) and thiourea (0.01 mol) in ethanol
10 mL) was added successively to a solution of sodium ethoxide in abso-
(
lute ethanol (10 mL). The reaction mixture was refluxed for 4–5 h. On
concentrating the reaction mixture under reduced pressure the solid
obtained was filtered, washed with water and recrystallized from methanol.
Method B
To a solution of 2a/b (0.01 mol), thiourea (0.01 mol) in ethanol, basic
[
28]
alumina
and subjected to MWI intermittently at 30 s intervals for specified time
Table 1). On completion of reaction, as monitored by TLC (a small
amount of reaction mixture taken in sample tube and eluted with
was added. The reaction mixture was stirred well, air dried
(
0
.5 mL ethanol) the product was extracted into ethanol (3 ꢂ 15 mL).
Removal of solvent under reduced pressure yielded the product which
was recrystallized from methanol.
ꢁ
1
a. M.p. 282–284 C. H NMR (60 MHz, DMSO) ꢀ: 3.2 (d, 1H, CH),
8
.1 (d, 1H, CH), 6.2–6.6 (m, 3H, furan), 9.8 (br, 1H, NH). IR (KBr): 1345
4

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3756
Kidwai, Mohan, and Rastogi
1
(
4
C¼S), 1585 (C¼N), 3100 (N–H) cmꢀ . Anal. calcd. for C H N O S : C,
1
0
8
4
2 2
2.85; H, 2.85; N, 20.00. Found: C, 42.86; H, 2.83; N, 19.98.
8
.2 (d, 1H, CH), 7.1–7.6 (m, 5H, indole), 9.8 (br, 1H, NH). IR (KBr):
ꢁ
1
b. M.p. 250–252 C. H NMR (60 MHz, DMSO) ꢀ: 3.4 (d, 1H, CH),
4
1
ꢀ
1
340 (C¼S), 1580 (C¼N), 3100 (N–H) cm . Anal. calcd. for
C H N OS : C, 51.06; H, 3.34; N, 21.27. Found: C, 51.09; H, 3.37;
5
1
4
11
2
N, 21.29.
General Procedure for the Synthesis
of 5-Aryl-7-iminothiazino[5,4-d]pyrimidin-
4
-one-2-(1H,3H,8H)-thione(9a–b)
Method A
Equimolar quantities of 2a/2b (0.01 mol) and thiourea (0.01 mol)
were dissolved in ethanol (30 mL) and to it dil. sulphuric acid (5 mL)
was added. The action mixture was refluxed for 7 h in an oil-bath. The
reaction mixture was cooled, the solvent removed under reduced pressure
and the solid obtained was washed with water, dried and recrystallized
ꢁ
from benzene petroleum ether (60–80 C).
Method B
To a solution of 2a/2b (0.01 mol), thiourea (0.01 mol) in ethanol,
was added. The reaction mixture was stirred well, air
[28]
acidic alumina
dried and subjected to MWI intermittently at 30 s intervals for specified
time (Table 1). On completion of reaction, as monitored by TLC (a small
amount of reaction mixture taken in sample tube and eluted with 0.5 mL
ethanol) the product was extracted into ethanol (3 ꢂ 15 mL). Removal of
solvent under reduced pressure yielded the product that was recrystallized
ꢁ
from benzene petroleum ether (60–80 C).
ꢁ
1
a. M.p. 233–235 C. H NMR (60 MHz, DMSO) ꢀ: 4.0 (s, 1H, CH),
9
6
.3–6.6 (m, 3H, furan), 10.3 (br, 1H, N-H). IR (KBr): 1620 (C¼C), 1630
ꢀ
1
(exo C¼NH), 3150 (N-H) cm . Anal. calcd. for C H N O S : C, 42.85;
1
0
8
4
2 2
H, 2.85; N, 20.00. Found: C, 42.82; H, 2.81; N, 20.02.
9
ꢁ
1
b. M.p. 290–291 C. H NMR (60 MHz, DMSO) ꢀ: 3.9 (s, 1H, CH),
7
.2–7.6 (m, 5H, indole), 10.2 (br, 1H, N-H). IR (KBr): 1620 (C¼C), 1632
ꢀ
1
(exo C¼NH), 3145 (N-H) cm . Anal. calcd. for C H N OS : C, 51.06;
1
4
11
5
2
H, 3.34; N, 21.27. Found: C, 51.08; H, 3.32; N, 21.24.

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Fused Thioxopyrimidine Derivatives
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2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
3758
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2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
Fused Thioxopyrimidine Derivatives
3759
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used; (b) Aluminium oxide basic, Brockmann
˚
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˚
8A, CAMAG 506-C-1, surface area 155 m /g) was used.
5

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