Synthesis of 2-Imino-1,3,4-thiadiazoles from Hydrazides and Isothiocyanates via Sequential Oxidation and P(NMe2)3-Mediated Annulation Reactions.

A P(NMe2)3-mediated annulation reaction of N-acyldiazenes with isothiocyanates, producing 2-imino-1,3,4-thiadiazoles, is reported. This reaction proceeds well with crude N-acyldiazenes derived from the oxidation of hydrazides by iodine and permits the sequential synthesis of products directly from hydrazides without purification of the less stable N-acyldiazene intermediates. The reaction does not require transition metals and is a simple, scalable operation with broad substrate scope.