1,3-Dipolar cycloaddition reactions of nitrilium betaines with aryl thiocyanates and selenocyanates

Abstract

The carbon–nitrogen triple bond of aryl thiocyanates acts as a dipolarophile in 1,3-dipolar cycloadditions. Reaction with nitrile oxides, nitrile sulphides, and benzonitrile N-phenylimide yields, respectively, 5-arylthio-1,2,4-oxadiazoles, -thiadiazoles and -triazoles. Aryl selenocyanates behave similarly forming 5-arylseleno-1,2,4-oxadiazoles and -thiadiazoles from nitrile oxides and sulphides. Divergent pathways are followed, by the reactions of secondary amines such as piperidine with 5-arylthio-1,2,4-oxadiazoles and -thiadiazoles, the former yielding 5-piperidyl-1,2,4-oxadiazoles and the latter dihydro-1,2,4-thiadiazole-5-thiones.