2,2-Dihalovinylcyclopropanes as Highly Diastereoselective Three-Atom Addends in Phenylthio Radical Mediated Vinylcyclopentane Synthesis

2,2-Dichloro- or 2,2-dibromovinylcyclopropane was condensed with electron-deficient alkenes in a phenylthio radical catalyzed process to afford 4-substituted and 4,5-disubstituted-l,l-dihalo-3-vinylcyclopentane derivatives in good yield and with good-to-excellent diastereoselectivity for the 3,4-cis isomer. Neither electron-rich nor β-substituted alkenes led to good yields of cyclopentane products. The diastereoselectivity and reactivity profiles of these transformations are satisfactorily rationalized by application of existing transition-state models of radical reactions.