Low-valent zirconocene-mediated cyclization of γ,δ-unsaturated oximes

γ,δ-Unsaturated O-methyl oximes were cyclized to dihydropyrrole by the treatment of (1-butene)ZrCp23 prepared by Negishi's procedure (reaction with Cp2ZrCl2 and two equivalents of n-BuLi). In this cyclization, the geometry of oximes was affected and syn-oximes were cyclized efficiently. However, it was found that the anti-oxime is not suitable for the cyclization.