A Convenient Synthesis of Tetrasubstituted Pyrazoles from Nitrile Imines and 2-(Thioxothiazolidin-5-ylidene)acetates

Abstract

Alkyl 2-(3-alkyl-4-oxo-2-thioxothiazolidin-5-ylidene)acetates react with hydrazonoyl chlorides in the presence of triethylamine to ­afford tetrasubstituted pyrazole derivatives. Formally, this transformation is regarded as a 1,3-dipolar cycloaddition of the exocyclic carbon–carbon double bond of the thioxothiazolidine derivatives with nitrile imines generated in situ. This efficient method provides fast access to a range of structurally diverse pyrazoles. The structure of a typical product is confirmed by X-ray crystallography.