J. CHEM. RESEARCH (S), 1998 615
In conclusion, the results described herein demonstrate
the novelty of zeolite catalysts which exercises unique
selectivity in the lactonisation of hippuric acid to 4,5-
dihydrooxazol-5-ones. The present method also oers
signi®cant improvements over the existing procedures and
constitutes a useful and important addition to the present
methodologies.
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Experimental
Melting points were recorded in open capillary tubes on
Buchi apparatus and are uncorrected. All chemicals were puri®ed
by distillation or crystallisation prior to use.
a
General procedure for the preparation of 4-arylidene-4,5-dihydro-
5-ones using zeolite-HY under microwave irradiationÐIn a typical
procedure, about 1 g of zeolite-HY was impregnated with the
melted hippuric acid (1.8 g, 10 mmol) in a commercial microwave
oven (operating at 2450 MHz) for 6 min and then benzene (20 ml)
was added to extract the lactone. The catalyst was separated by
®ltration and the benzene was evaporated to dryness. To the
residue, benzaldehyde (1.06 ml, 10 mmol) was added and then dry
triethylamine (4.03 ml, 30 mmol) in dichloromethane (10 ml) drop-
wise. The resulting mixture was stirred at room temperature for 6 h,
washed with water (2 Â50 ml) and the organic solvent was dried
over anhydrous sodium sulfate. Evaporation of the solvent and
recrystallisation of the residue from ethanol yielded the 2-phenyl-
4-phenylmethylene-4,5-dihydrooxazol-5-one 4a in 80% yield.
Similarly other acylamino acids and aldehydes were reacted and the
corresponding 4,5-dihydrooxazol-5-ones were obtained in 75±85%
yields. All the products obtained were characterised by IR and
1H NMR spectroscopy and ®nally by comparison with authentic
samples.
Received, 16th April 1998; Accepted, 2nd June 1998
Paper E/8/02863J