D. Armesto et al., A NEW PHOTOCHEMICAL-SYNTHESIS OF DIHYDROPYRAZOLES - NOVEL MODE OF PHOTOCYCLIZATION OF SOME 1-IMINOBUT-3-ENES DERIVATIVES, Journal of the Chemical Society, Chemical Communications, (9), 1993, pp. 721-722
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.