Convenient one‐pot syntheses of pyrazoles from imines, a vilsmeier type reagent and hydrazine

Abstract

Abstract A simple one‐pot procedure for the regioselective synthesis of pyrazoles from readily available starting materials is described. Vilsmeier type reagent 1 reacts with imines 10 ( via the corresponding tautomeric secondary enamines) in tetrahydrofuran to give enaminoimine hydrochlorides 11 . Nonsymmetrical imines generally react preferentially with 1 at the sterically less hindered α‐position. The enaminoimine hydrochlorides 11 are transformed in situ to the corresponding pyrazoles 12 in moderate to high yields by the addition of hydrazine.