A new photochemical synthesis of dihydropyrazoles. Novel mode of photocyclization of some 1-iuminobut-3-enes derivatives

Abstract

While some hydrazine derivatives 3 of 2,2-dimethyl-4,4-diphenylbut but-3-enal undergo both the aza-di-π-methane (ADPM) rearrangement and a novel cyclization to afford dihydropyrazole derivatives 5 in varying yields, the tosylhydrazone derivative of 3,3-dimethyl-5,5-diphenylpent-4-en-d-one 7 gives exclusively an excellent yield of the corresponding dihydropyrazole 8, in a reaction that is proposed to involve an electron transfer process.