Cyclization of 3-allylhex-5-enyl radical: mechanism, and implications concerning the structures of cyclopolymers

Abstract

Radical-initiated reduction of 3-allylhex-5-enyl bromide (15) with tributylstannane affords 4-ethylhepta-1,6-diene (17), cis- and trans-1-allyl-3-methylcyclopentane (23) and (19), bicyclo[4.2.1]nonane (33), exo-3-methyl-bicyclo[3.2.1]octane (35), and other hydrocarbons. The formation of bicyclic systems from the 3-allylhex-5-enyl radical (16) involves two discrete steps, the kinetic parameters of which have been determined. The results suggest that homoconjugative interaction between the double bonds in the dienyl radical (16) affects the rate and stereoselectivity but not the regioselectivity of the first cyclization step. The failure of the reaction to afford bicyclo[3.3.1]nonane indicates that structures previously assigned to the cyclopolymers derived from triallyl monomers may be incorrect.