A NEW PHOTOCHEMICAL-SYNTHESIS OF DIHYDROPYRAZOLES - NOVEL MODE OF PHOTOCYCLIZATION OF SOME 1-IMINOBUT-3-ENES DERIVATIVES

While some hydrazine derivatives 3 of 2,2-dimethyl-4,4-diphenylbut-3-e nal undergo both the aza-di-pi-methane (ADPM) rearrangement and a nove l cyclization to afford dihydropyrazole derivatives 5 in varying yield s, the tosylhydrazone derivative of 3,3-dimethyl-5,5-diphenylpent-4-en -2-one 7 gives exclusively an excellent yield of the corresponding dih ydropyrazole 8, in a reaction that is proposed to involve an electron transfer process.