Paal Knorr reaction for novel pyrrolo[2,3-d]pyrimidines

Article abstract of DOI:10.1002/jhet.5570430514

An expeditious and convenient solid supported synthesis of 1,3,7-triaryl-6-phenyl-2-thioxo-1,2,3,7-tetrahydropyrrolo[2,3-d]pyrimidin-4-one derivatives from readily accessible N,N-disubstituted thiobarbituric acids under microwaves utilising Paal Knorr rea

Full text of DOI:10.1002/jhet.5570430514

Sep-Oct 2006
1231
Paal Knorr Reaction for Novel Pyrrolo[2,3-d]pyrimidines
Mazaahir Kidwai*, Kavita Singhal and Shweta Rastogi
Green Research Laboratory, Department of Chemistry,
University of Delhi, Delhi-110007, India
E-mail: kidwai.chemistry@gmail.com; TeleFax: (91 11) 27666235
Received November 15, 2005
O
O
R
R
Ph
N
N
+ Br CH2-CO-Ph
ꢀ
O
μ
O
O
N
R
S
N
R
S
ꢀ
μ
O
R
N
Ph
N
N
R
S
R'
An expeditious and convenient solid supported synthesis of 1,3,7-triaryl-6-phenyl-2-thioxo-1,2,3,7-tetra-
hydropyrrolo[2,3-d]pyrimidin-4-one derivatives from readily accessible N,N-disubstituted thiobarbituric
acids under microwaves utilising Paal Knorr reaction is described.
J. Heterocyclic Chem., 43, 1231 (2006).
Pyrimidine and its derivatives have been studied for
pyrrole rings and has not been explored much for fused
systems. Thus, 1,4-diketones are synthesized using N,N-
disubstituted thiobarbituric acid and finally condensed
with amines used as nitrogen source to furnish novel
pyrrolo[2,3-d]pyrimidines utilizing the Paal Knorr
mechanistic approach.
No general method for the synthesis of titled
compounds using Paal Knorr mechanism starting from
N,N-disubstituted thiobarbituric acids and ꢀ-halo ketones
has ever been reported. With a view to develop an
environmentally benign green synthesis, biopotential of
pyrrolopyrimidines and extending the applicability of Paal
Knorr reaction, it was thought worthwhile to study the
synthetic aspects of pyrrolo[2,3-d]pyrimidines with
microwaves (MWs) under dry media. Conventional
studies were also attempted to compare the reaction
conditions and versatility of the supports.
over a century due to its wide pharmaceutical applications
as antimicrobial [1a], antitumor [1b], antihypertensive
[1c] and anti-inflammatory [1d] agents. Also pyrroles
constitute the core unit of many natural products
including alkaloids, porphyrins and bile pigments [2]. The
fusion of pyrrole with pyrimidines further constitutes a
structural unit of nucleobases, which is of current interest
to both chemists and biologists because of the enhanced
biopotential. Pyrrolo[2,3-d]pyrimidines reveal significant
biological profiles as broad-spectrum antitumors [3],
antivirals, antibacterials [4], immunosuppressive agent
and also has been useful in the treatment of Crohn’s
disease, Alzheimer’s disease and leukemia [5]. They also
possess
significant
inhibitory
activity
against
dihydrofolate reductase (DHFR) [6] and thymidylate
synthase enzymes [7].
Due to strict environmental legislation, there is an
increasing awareness for the toxic effects of chemicals on
the environment. In this endeavor, solid supported
reactions [8,9] with microwaves [10] are widely explored
for selective organic functional group transformations.
These solid supports, which are usually of mineral origin,
act as both catalyst [11] as well as an energy transfer
media. Such dry media reactions are especially appealing
as they provide an opportunity to work with open vessels
avoiding the risk of high-pressure development with the
possibility of up-scaling the reactions to industrial scale
[12].
Few strategies for the synthesis [14-15] of pyrrolo[2,3-
d]pyrimidine backbone have been reported starting from
uracil [16] or dimethyl acetal of uracils [17]. This
employs harsh reaction conditions, use of toxicological
chemicals and tedious work up procedure with unsatis-
factory yields. Moreover, these multistep reactions
include the limitations towards the structural diversity.
For this reason, a great deal of effort has been devoted to
the development of a facile and efficient method for the
synthesis of pyrrolo[2,3-d] pyrimidines.
Our environmentally friendly approach involved the
reaction of N,N-disubstituted thiobarbituric acids (1a-d)
with phenacyl bromide (2), an ꢀ-halo ketone (step 1) over
basic alumina [18] or anhydrous potassium carbonate
Paal Knorr reaction [13], a well known pathway,
generalized mostly for the synthesis of highly substituted

1232
M. Kidwai, K. Singhal and S. Rastogi
Vol 43
(K2CO3) as solid support under MW irradiation (Method A)
resulting in 1,4-diketone (intermediate) (3a-d) which
further cyclised with numerous aromatic/heteroaromatic
amines (4a-c) over acidic alumina [19] / montmorillonite
K-10 clay [20] furnishing 1,3,7-tetraryl-6-phenyl-2-thioxo-
1,2,3,7-tetrahydropyrrolo[2,3-d]pyrimidin-4-one (5a-l) as
the required product in step 2. The property of thiobar-
bituric acid (TBA) and barbituric acid (BA) to act as cyclic
active methylene moiety was utilized to synthesize a series
of intermediates. Initially, to synthesize novel pyrrolo[2,3-
d]pyrimidines, alkylation of thiobarbituric acid (TBA) and
barbituric acid (BA) with phenacyl bromide was attempted.
This resulted in the formation of aromatized pyrimidine
ring in which the two hydroxy groups were placed at 4 and
6 positions. This configuration is generated in situ as the
carbonyl groups of TBA and BA at 4 and 6 positions
undergo tautomerisation. Thus thiobarbituric acid and
barbituric acid upon reaction with phenacyl bromide gave
4,6-dihydroxy ketone instead of the respective 1,4-
dicarbonyl (triketone) as an intermediate, which in turn
failed to react in step 2 with amines. In another attempt, in
place of TBA and BA, N,N-disubstituted thiobarbituric
acids (1a-d) were used with a view to utilize its active
methylene group as in this case, there are no chances of
tautomerisation. N,N-Disubstituted thiobarbituric acids
upon reaction with ꢀ-halo ketones resulted in 1,4-diketone
as intermediates (3a-d) (Table 1). Furthermore, some
specific intermediates were selected according to the
reaction condition, which were reacted smoothly with some
of the aromatic/heteroaromatic amines (4a-c) via Paal
Knorr reaction to afford pyrrolo[2,3-d]pyrimidines (5a-l) in
just a few minutes with higher yield. However, it was
observed that the reactivity of different amines varied in the
reaction conditions employed. In the case, where amines
with electron withdrawing groups were used, the reaction
did not proceed, giving negative results.
Scheme
O
O
R
Basic Alumina/
Anhyd. K2CO3
R
Ph
N
+ Br CH2-CO-Ph
N
ꢀ
μ
O
O
N
R
S
O
N
R
S
STEP 1
1(a-d)
2
3 (a-d)
Acidic Alumina/
Montmorillonite
K-10 Clay
ꢀ
μ
R' NH2 4 (a-c)
STEP 2
O
R
N
R = Phenyl, furyl, m-tolyl, p-chlorophenyl
R' = Phenyl, furyl, m-tolyl
Ph
N
N
R
S
R'
5 (a-l)
For comparative studies, the conventional reaction
conditions were also developed (Method B), in which
piperidine and glacial acetic acid were used in step 1 and
step 2 respectively. In step 2 (Table 2), the reaction
catalyzed by montmorillonite K-10 clay was found to give
the required products (5a-l) more beneficially in reduced
time with satisfactory yields. This was attributed to the
ditopic nature [21] of montmorillonite K-10 clay. Finally,
Table 1
Comparison of Reaction Time and Yield for the Synthesis of 1,4-Dicarbonyl
Compounds (3a-d) in Step 1
Compd.
No.
R
METHOD A
METHOD B
Recrystallisation
Solvent
Time (min)/Yield(%)
Time(hrs)/Yield (%)
Basic Alumina
6/80
Anhydrous Potasium
carbonate
(v/v)
CHCl3/Et2O
2 : 8
4.5/78
7.5/67
3a
O
4.5/78
5/80
3.5/82
4/85
5/72
6/75
CHCl3/Et2O
1 : 9
3b
3c
3d
CHCl3/Et2O
1 : 9
CH3
6/76
6/80
7.5/65
CHCl3/Et2O
2 : 8
Cl

Sep-Oct 2006
Paal Knorr Reaction for Novel Pyrrolo[2,3-d]pyrimidines
1233
Table 2
Comparison of Reaction Time and Yield for the Synthesis of (5a-l) in Step 2
S. No.
R
Rꢀ
METHOD A
Time (min) / Yield (%)
METHOD B
Time (hrs) /
Yield (%)
Acidic Alumina
Montmorillonite
K-10 Clay
5a
5b
5c
8/74
6.5/80
10.5/63
1s4.5/60
12/68
O
7.5/80
7/76
7/80
7/78
CH3
O
5d
5e
7/74
5/76
5/82
7/68
O
O
6.5/80
10/65
O
CH3
5f
5.5/76
10/80
4/77
7/85
10/70
12/64
CH3
5g
O
CH3
5h
5i
7.5/65
5/78
6.5/74
5/84
13.5/58
12/70
CH3
CH3
Cl
O
Cl
5j
7/80
6.5/78
13/65
Cl
CH3
5k
5l
5.5/76
8/74
3.5/88
7/80
10/70
11.5/62
anhydrous potassium carbonate and montmorillonite K-10
clay were found to be the best catalytic support for step 1
and step 2 respectively. The observed optimal yield for
this sequential process indicated that Paal Knorr reaction
is about 80% efficient on average under MWs. In
addition, the condensation steps in which anhydrous
conditions are desirable can be achieved with the use of
these solid supports.
spectral absorption bands at 1715-1725 cm-1 and 1680-1700
cm-1 suggested the presence of carbonyl group in N,N-
disubstituted thiobarbituric acids (1a-d) and intermediates
(3a-d) respectively. Further, in the case of pyrrolo[2,3-
d]pyrimidines, absorption band was observed at 1640-1660
cm-1. This shift of about 40-50 cm-1 in the carbonyl band
towards the lower frequency region was attributed to the
presence of ꢀ,ꢁ-unsaturated carbonyl group, which
confirmed the structure of the final products (5a-l). In the 1H
NMR spectrum of intermediates (3a-d), a triplet for one
proton and a doublet for two protons were observed at ꢂ 3.9
The structures of the intermediates (3a-d) and the final
product pyrrolo[2,3-d]pyrimidines (5a-l) were established
on the basis of elemental analysis and spectral data. IR

1234
M. Kidwai, K. Singhal and S. Rastogi
Vol 43
Method B (Conventional Procedure).
and ꢀ 3.65 respectively along with other usual signals. The
disappearance of these peaks with the appearance of a new
singlet at ꢀ 6.4-6.6 value further supported the Paal Knorr
reaction mechanism, which involved the heterocyclisation
of 1,4-dicarbonyl compounds to the pyrrole ring.
In conclusion, Paal Knorr reaction was explored using
different inorganic solid supports under MW irradiation
for the synthesis of pyrimidine fused N-substituted
pyrroles and to make this important moiety available for
biological screening in the search for better medicinal
agents. The proposed methodology thus, offered the
advantages of being simple and practically convenient and
environmentally benign, cost effective protocol with
excellent yield of the products in lesser reaction time.
Synthesis of intermediates (3a-d) Step 1.
N,N-Disubstituted thiobarbituric acids (1a-d) (0.012 mol),
phenacyl bromide (2) (0.01 mol) and piperidine (few drops) in
chloroform (20 ml) were refluxed on a steam bath. The heating
was continued for appropriate time of approximately 5-7.5 hrs
and the reaction was monitored by TLC. Upon completion of the
reaction, the solvent was evaporated. The crude mass isolated by
suction is then dried and recrystalized from appropriate solvent.
Synthesis of pyrrolo[2,3-d]pyrimidines (5a-l) Step 2.
An equimolar mixture of intermediate (3a-d) (0.01 mol) and
aromatic/heteroaromatic amines (4a-c) (0.01 mol) in glacial acetic
acid (15 ml) was stirred at refluxing temperature for 7-15 hrs. Upon
completion of the reaction, the reaction mixture was cooled,
concentrated and left at room temperature. Ice-cold water and
aqueous ammonia solution was added to neutralize the reaction
mixture and the solid that separated was collected by filtration,
dried and recrystallised to get pyrrolo[2,3-d]pyrimidines (5a-l).
EXPERIMENTAL
Melting points were taken on a Thomas Hoover melting point
apparatus and are uncorrected. IR (in Nujol) spectra were
recorded on a model Perkin-Elmer FTIR-1710 spectrophoto-
meter, 1H NMR spectra were recorded on a Bruker Avance
Spectrospin 300 (300 MHz) using TMS as internal standard.
Elemental analysis was performed on a Heraeus CHN Rapid
Analyser. The purity of compounds was checked on silica gel
coated aluminium plates (Merck). A Kenstar microwave oven,
Model No. OM9925E at (2450 MHz, 800W) was used for MWI.
Temperature of the reaction was measured through AZ, Mini
Gun Type, Non-Contact IR Thermometer, Model No. 8868.
1,3,6,7-Tetraphenyl-2-thioxo-1,2,3,7-tetrahydropyrrolo[2,3-d]-
pyrimidin-4-one (5a).
This compound has the following spectral properties: mp 206-
210°; ir: 1664.35 (C=C-C=O), 1605.02 (C=C arom), 1300.65
(C=S) cm-1; 1H nmr: (300 MHz, deuteriochloroform): ꢀ 6.41
(1H, s, C5-H), 7.18-7.59 (20 H, m, arom)
Anal. Calcd. for C30H21N3OS: C, 76.43; H, 4.45; N, 8.91.
Found: C, 76.49; H, 4.37; N, 8.98.
7-(Furan-2-yl)-1,3,6-triphenyl-2-thioxo-1,2,3,7-tetrahydropyrrolo-
[2,3-d]pyrimidin-4-one (5b).
General procedure for the synthesis of Pyrrolo[2,3-d]pyrim-
idines (5a-l).
This compound has the following spectral properties: mp 198-
200°; ir: 1638.34 (C=C-C=O), 1596.38 (C=C arom), 1263.81
(C=S) cm-1; 1H nmr (300 MHz, deuteriochloroform): ꢀ 6.35 (1H,
s, C5-H), 7.26-7.59 (18 H, m, arom).
Anal. Calcd. for C28H19N3OS: C, 75.50; H, 4.26; N, 9.43.
Found: C, 75.61; H, 4.35; N, 9.49.
Method A (Microwave Assisted Solid Supported Synthesis).
Synthesis of 1,4-Dicarbonyl Compound (Intermediate) (3a-d)
Step 1.
To the solution of N,N-disubstituted thiobarbituric acids (1a-
d) (0.012 mol) and phenacyl bromide (2) (0.01 mol) in
chloroform, anhydrous K2CO3/basic alumina (20 g) was added.
The reaction mixture was air-dried. This was then placed in an
alumina bath [22] and subjected to MWI for the time interval of
30 sec. Upon completion of reaction as monitored by TLC, the
reaction mixture was cooled and products (3a-d) were extracted
using (3x10 ml) of ethanol and recrystalized using appropriate
solvents to afford intermediate (3a-d) in high yield.
7-(m-Tolyl)-1,3,6-triphenyl-2-thioxo-1,2,3,7-tetrahydropyrrolo-
[2,3-d]pyrimidin-4-one (5c).
This compound has the following spectral properties: mp 260-
264°, ir: 1649.72 (C=C-C=O), 1590.02 (C=C arom), 1281.63
1
(C=S) cm-1; H nmr (300 MHz, deuteriochloroform): ꢀ 2.35 (3H, s,
CH3), 6.38 (1H, s, C5-H), 7.21-7.58 (19 H, m, arom).
Anal. Calcd. for C31H23N3OS: C, 76.70; H, 4.74; N, 8.65.
Found: C, 76.66; H, 4.82; N, 8.56.
Reaction of 5-(2-Oxo-2-phenylethyl)-1,3-diaryl/heteroaryl-2-thioxo-
1,3-dihydropyrimidin-4,6-dione (intermediate) (3a-d) with
Aromatic/Heteroaromatic Amines (4a-c) Step 2.
1,3-Di(furan-2-yl)-6,7-diphenyl-2-thioxo-1,2,3,7-tetrahydropyrrolo-
[2,3-d]pyrimidin-4-one (5d).
This compound has the following spectral properties: mp 222-
225°; ir: 1652.81 (C=C-C=O), 1596.19 (C=C arom), 1267.01
(C=S) cm-1; 1H nmr (300 MHz, deuteriochloroform): ꢀ 6.49 (1H,
s, C5-H), 7.30-7.59 (16 H, m, arom).
Anal. Calcd. for C26H17N3O3S: C, 69.17; H, 3.76; N, 9.31.
Found: C, 69.24; H, 3.88; N, 9.44.
Acidic alumina/montmorillonite K-10 clay was added to the
equimolar solution of intermediate (3a-d) (0.01 mol) in CHCl3
and amines (4a-c) (0.01 mol) at room temperature. The reaction
mixture was thoroughly mixed and dried in air. It was then
placed in an alumina bath and subjected to MWI. Temperature
of the reaction mixture was 130-140 °C. At every interval of 30
sec, the reaction was monitored by TLC, after completion, the
product pyrrolo[2,3-d]pyrimidines (5a-l) were extracted using (3
x 10 ml) of chloroform, which was further purified by column
chromatography [column of SiO2; preadsorption of the crude
product at SiO2; elution with benzene/ethyl acetate = 90:10 v/v].
1,3,7-Tri(furan-2-yl)-6-phenyl-2-thioxo-1,2,3,7-tetrahydro-
pyrrolo[2,3-d]pyrimidin-4-one (5e).
This compound has the following spectral properties: mp 246-
248°, IR: ꢁ (cm-1) 1654.68 (C=C-C=O), 1608.77 (C=C arom),

Sep-Oct 2006
Paal Knorr Reaction for Novel Pyrrolo[2,3-d]pyrimidines
1235
1
1298.90 (C=S) cm-1; H nmr (300 MHz, deuteriochloroform): ꢀ
1,3-Bis(4-chlorophenyl)-6-phenyl-7-(m-tolyl)-2-thioxo-1,2,3,7-
tetrahydropyrrolo[2,3-d]pyrimidin-4-one (5l).
6.46 (1H, s, C5-H), 7.32-7.54 (14 H, m, arom).
Anal. Calcd. for C24H15N3O4S: C, 65.30; H, 3.40; N 9.52.
Found: C, 65.19; H, 3.32; N, 9.64.
This compound has the following spectral properties: mp 260-
262°; ir: 1647.24 (C=C-C=O), 1583.02 (C=C arom), 1274.43
(C=S) cm-1; 1H nmr (300 MHz, deuteriochloroform): ꢀ 2.35 (3H,
s, CH3), 6.47 (1H, s, C5-H), 7.34-7.69 (17 H, m, arom),.
Anal. Calcd. for C31H21N3OSCl2: C, 67.14; H, 3.79; N, 7.58.
Found: C, 67.21; H, 3.83; N, 7.64.
1,3-Di(furan-2-yl)-6-phenyl-7-(m-tolyl)-2-thioxo-1,2,3,7-tetra-
hydropyrrolo[2,3-d]pyrimidin-4-one (5f).
This compound has the following spectral properties: mp
200-202°, IR: ꢀ (cm-1) 1651.09 (C=C-C=O), 1611.83 (C=C
arom), 1274.31 (C=S) cm-1; 1H nmr (300 MHz, deuterio-
chloroform): ꢀ 2.38 (3H, s, CH3), 6.46 (1H, s, C5-H), 7.28-
7.59 (15 H, m, arom).
Acknowledgement.
One of the authors Kavita Singhal acknowledges the financial
assistance by the Council of Scientific and Industrial Research
(CSIR), New Delhi.
Anal. Calcd. for C27H19N3O3S: C, 69.67; H, 4.08; N, 9.03.
Found: C, 69.74; H, 4.20; N, 9.11.
1,3-Di(m-tolyl)-6,7-diphenyl-2-thioxo-1,2,3,7-tetrahydropyrrolo-
[2,3-d]pyrimidin-4-one (5g).
REFERENCES AND NOTES
This compound has the following spectral properties: mp 216-
218°; ir: 1664.21 (C=C-C=O), 1600.61 (C=C arom), 1280.05
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M. Kidwai and R. Venkataramanan, Bull. Chem. Soc. Jpn., 76, 203
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R. Richardson, J. Pharmacol. Exp. Therm., 101, 368 (1951); [d] G.E.
Hardtmann and F.G. Kathawala, U.S. Patent 4,053,600, 1977; Chem.
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1
(C=S) cm-1; H nmr (300 MHz, deuteriochloroform): ꢀ 2.41(6H, s,
CH3), 6.41 (1H, s, C5-H), 7.20-7.64 (18 H, m, arom).
Anal. Calcd. for C30H25N3OS: C, 75.78; H, 5.26; N, 8.84.
Found: C, 75.87; H, 5.33; N, 8.75.
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Duyne and J. Clardy, J. Am. Chem. Soc., 107, 5492 (1985); [b] A. Rudi,
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1,3-Di(m-tolyl)-7-(furan-2-yl)-6-phenyl-2-thioxo-1,2,3,7-tetra-
hydropyrrolo[2,3-d]pyrimidin-4-one (5h).
This compound has the following spectral properties: mp 192-
194°; ir: 1650.84 (C=C-C=O), 1599.27 (C=C arom), 1268.65
(C=S) cm-1; 1H nmr (300 MHz, deuteriochloroform) ꢀ: 2.48 (6H,
s, CH3), 6.52 (1H, s, C5-H), 7.26-7.64 (16 H, m, arom).
Anal. Calcd. for C28H23N3O2S: C, 72.25; H, 4.94; N, 9.03.
Found: C, 72.28; H, 4.99; N, 9.11.
[6a] E. C. Taylor, D. Kuhnt, C. Shih, S. M. Rinzel, G. B. Grindey,
J. Barredo, M. Jannatipour and R. Moran, J. Med. Chem., 35, 4450
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49976f (2000).
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Biomed. & Chem. Lett., 15 (19), 4295 (2005); [b] B. S. Chhikara, V.
Tandon and A. K. Mishra, Hetero. Commun., 10, 441 (2004).
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419 (2005).
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up of some typical organic reactions under focused microwaves, presented at
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Republic, September 6-11, 1998.
1,3,7-Tri(m-tolyl)-6-phenyl-2-thioxo-1,2,3,7-tetrahydropyrrolo-
[2,3-d]pyrimidin-4-one (5i).
This compound has the following spectral properties: mp 212-
215°; ir: 1649.27 (C=C-C=O), 1608.84 (C=C arom), 1271.05
(C=S) cm-1; 1H nmr (300 MHz, deuteriochloroform): ꢀ 2.35 (9H,
s, CH3), 6.39 (1H, s, C5-H), 7.28-7.59 (17 H, m, arom)
Anal. Calcd. for C31H27N3OS: C, 76.07; H, 5.52; N, 8.58.
Found: C, 76.16; H, 5.61; N, 8.64.
1,3-Bis(4-chlorophenyl)-6,7-diphenyl-2-thioxo-1,2,3,7-tetrahydro-
pyrrolo[2,3-d]pyrimidin-4-one (5j).
This compound has the following spectral properties: mp 188-
190°; ir: 1664.91 (C=C-C=O), 1605.62 (C=C arom), 1268.05
(C=S) cm-1; 1H nmr (300 MHz, deuteriochloroform): ꢀ 6.46 (1H,
s, C5-H), 7.31-7.65 (18 H, m, arom).
Anal. Calcd. for C30H19N3OSCl2: C, 66.66; H, 3.51; N, 7.77.
Found: C, 66.70; H, 3.44; N, 7.67.
[13] M. P. Sammes, P. N. Maini and A. R. Katritzky, J. Chem.
Soc. Chem. Commun., 354 (1984).
[14] E. C. Taylor and B. Liu, Tetrahedron Lett., 40, 4027 (1999).
[15] H. Ogura, M. Sakaguchi and K. Takeda, Chem. Pharma.
Bull., 20(2), 404 (1972).
1,3-Bis(4-chlorophenyl)-7-(furan-2-yl)-6-phenyl-2-thioxo-1,2,3,7-
tetrahydro-pyrrolo[2,3-d]pyrimidin-4-one (5k).
[16] E. D. Edstrom and Y. Wei, J. Org. Chem., 60, 5069 (1995).
[17] X. Chen, S. M. Siddiqi and S. W. Schneller, Tetrahedron
Lett., 33, 2249 (1992).
[18] Aluminium Oxide Basic, Brockmann I (Aldrich Chem. Co.,
Cat. No. 19, 944-3), ~150 mesh, 58 Å, surface area 155 m2/gm.
[19] Aluminium Oxide Acidic, Brokmann I (~ 150 mesh, 58 Å,
CAMAG 506-C-1, surface area 155 m2/gm).
This compound has the following spectral properties: mp
236-238°; ir: 1652.68 (C=C-C=O), 1599.36 (C=C arom),
1
1290.19 (C=S) cm-1; H nmr (300 MHz, deuteriochloroform): ꢀ
6.41 (1H, s, C5-H), 7.29-7.60 (16 H, m, arom).
Anal. Calcd. for C28H17N3O2SCl2: C, 63.39; H, 3.20; N, 7.92.
Found: C, 63.41; H, 3.28; N, 7.87.

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M. Kidwai, K. Singhal and S. Rastogi
Vol 43
[20] Montmorillonite K10: K Catalyst, 69866 Fluka, surface; 200
64, 1033 (1999).
[22] G. Bram, A. Loupy and M. Majdoub, Tetrahedron 46, 5167
(1990).
± 20 m2/gm.
[21] F. Bigi, L. Chesini, R. Maggi and G. Sartori, J. Org. Chem.,