Preparation of dithiadiazafulvalene precursors: 2-piperidino-2,3-dihydro-1,3-thiazoles or 2-unsubstituted 2,3-dihydro-1,3-thiazoles from the reduction of the corresponding 2-piperidino mesoionic thiazoles

Abstract

Depending on the experimental conditions, either the 2-piperidino-3-aryl-4-alkylthio-5-aryl- or -alkyl-2,3-dihydro-1,3-thiazoles 8 or the 2-unsubstituted 3-aryl-4-alkylthio-5-aryl- or -alkyl-2,3-dihydro-1,3-thiazoles 10 have been prepared starting from mesoionic 5-alkyl- or 5-aryl-2-piperidino-1,3-thiazole-4-thiolates 6. After alkylation of the mesoionic compound, the best conditions to isolate these two dihydrothiazoles were established from a mechanistic study of the reduction. Compound 8 is known to give dithiadiazafulvalenes through its thiazolium tetrafluoroborate salts. We show here that such salts can also be obtained from 10.