Microwave and ultrasound-assisted synthesis of thiosemicarbazones and their corresponding (4,5-substituted-thiazol-2-yl)hydrazines

Abstract

Hantzsch cyclization of thiosemicarbazone intermediates is a very popular approach to the synthesis of substituted thiazoles. We developed a convenient microwave and ultrasound-assisted method both for the synthesis of 1-(alkyliden/cycloalkyliden/aryliden)thiosemicarbazone intermediates and their cyclization into (4,5-substituted-thiazol-2-yl)hydrazines. The search for optimal reaction conditions included the use of different catalysts (Lewis acids and resins) and solvents at discrete temperatures, pressures, and irradiation powers. Comparing yields, reaction times, and efforts proved that microwave and ultrasound-assisted techniques outmatch conventional heating and have a remarkable influence on the synthesis.