Approach for 2-(arylthio)imidazoles and imidazo[2,1-b]thiazoles from imidazo[2,1-b][1,3,4]thiadiazoles by ring-opening and -reconstruction

Abstract

A highly efficient one-pot synthesis of imidazo[2,1-b]thiazole derivatives has been developed and proceeds via a ring-opening and ring-closing reconstruction of imidazo[2,1-b][1,3,4]thiadiazoles with phenylacetylene in the presence of potassium tert-butoxide (t-BuOK) under very mild reaction conditions. A proposed mechanism is calculated computationally using a DFT method at the B3LYP/6-31+G(d,p) level. The imidazo[2,1-b][1,3,4]thiadiazoles are also successfully converted to a series of 2-(arylthio)-1H-imidazoles using aryl halide as a reactant and copper(II) acetylacetonate (Cu(acac)₂) as a catalyst under microwave irradiation conditions. The key features of these reactions are the use of readily available reagents, simple operation, the convenient utilization of new heterocyclic synthons, and a great variety of substrates with functional group compatibility.