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

A P(NMe)-mediated annulation reaction of -acyldiazenes with isothiocyanates, producing 2-imino-1,3,4-thiadiazoles, is reported. This reaction proceeds well with crude -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 -acyldiazene intermediates. The reaction does not require transition metals and is a simple, scalable operation with broad substrate scope.

Synthesis of Functionalized Imidazolium Salts via Iodine-Mediated Annulations of Enamines.

A novel annulation reaction of two enamine molecules with iodine under basic conditions to form 4-functionalized imidazolium salts has been established. In this reaction, iodine acts as both an iodinating reagent and a Lewis acid catalyst. Features of this synthetic method include facilitative preparation of substrates, no use of transition metals, mild reaction conditions, simplicity of operation, and gram scale synthesis.

Annulation Reactions of In-Situ-Generated N-(Het)aroyldiazenes with Isothiocyanates Leading to 2-Imino-1,3,4-oxadiazolines.

A novel annulation reaction of N-(het)aroyldiazenes and isothiocyanates has been established. This transformation involves a sequential cyclization and desulfurization/intramolecular rearrangement to produce 2-imino-1,3,4-oxadiazolines. The less-stable N-(het)aroyldiazenes can be conveniently generated in situ by I-mediated oxidation of hydrazides, which allows a one-pot synthesis of the products directly from readily accessible hydrazide and isothiocyanate substrates.