Benzoin in heterocyclic synthesis: Synthesis and reactions of 2,3-Diphenyl-4-cyanopyrrole-5-thione

Abstract

2,3-Diphenyl-4-cyano-pyrrole-5-thione (4) was prepared either by the reaction of benzoin (1) and cyanothioacetamide (3) followed by cyclization using AcOH/sodium acetate or by refluxing a mixture of benzoin (1) and cyanothioacetamide in pyridine to afford directly4. Several new pyrrole and pyrazole derivatives were synthesised using4 as synthon. The structure of the newly synthesised derivatives were based on celemental and spectral data studies. Methylation of the SH group in4 afforded5. Reaction of4 with ethyl bromo acetate afforded (6). Treatment of (5) and (6) with hydrazine hydrate afforded the same pyrazole derivative (10) through the intermediate (9). Treatment of6 with aniline and phenylhydrazine afforded the pyrrole derivatives8a,b respectively. Treatment of6 while dil HCl gave 2,3-diphenyl-4-cyano-pyrrole-5-one (7). Treatment of6 with NH₃/EtOH afforded the amidic derivatives (11) with treatment of6 with NH₃/heat then acidification it gave the carboxylic derivatives (12).