Nitrile sulfides. Part 13.1 Synthesis of 5-acyl-1,2,4-thiadiazoles by cycloaddition of nitrile sulfides to acyl cyanides

Abstract

The periselectivity of the nitrile sulfide cycloaddition to acyl cyanides has been examined. Benzonitrile sulfide, generated by thermal decarboxylation of 5-phenyl-1,3,4-oxathiazol-2-one, reacted exclusively at the cyano group of benzoyl cyanide to afford 5-benzoyl-3-phenyl-1,2,4-thiadiazole. Similar perispecificity was observed with p-toluonitrile sulfide and acetonitrile sulfide, and for cycloaddition of benzonitrile sulfide to 2-furoyl cyanide, acetyl cyanide and 2-oxooctanonitrile. The reactivity of benzoyl cyanide as a dipolarophile was shown to be similar to that of ethyl cyanoformate in a competition experiment which afforded a 51:49 mixture of 5-benzoyl-and 5-ethoxycarbonyl-3-phenyl-1,2,4-thiadiazoles.