Formation of cyclopropane rings via Zr—X (X = Cl, Br) γ-elimination

Abstract

(η-C 5H 5) 2Zr(Cl)H (I) reacts with 4-chlorocyclohexene and 4-bromocyclohexene to give moderate yields of bicyclo[3.1.0]hexane. Reaction of I with 4-chloropent-1-ene gives low yields of cis- and trans-1,2-dimethylcyclopropanes, 42% trans-pent-2-ene, and no cis-pent-2-ene. Reaction of I with 2-methyl-3-chloropropene gives 31% methylcyclopropane. Formation of these rings is believed to proceed by ZrX (X = Cl, Br) γ-elimination. Side reactions include (1) ZrX β-elimination to yield halogen-free olefins and (2) formation of halogen-free olefins by direct reduction of CX by ZrH.