Cyclization reactivities of fluorinated hex-5-enyl radicals

A kinetic study of the effect of fluorine substitution on the rates and regiochemistry of hex-5-enyl radical cyclization is reported. One or more fluorines on or proximate to the double bond of the radical have relatively little electronic effect on either rate or regiochemistry, whereas fluorines substituted at the radical end can have a dramatic impact on both. The relative reactivities of such partially-fluorinated hex-5-enyl radicals can be understood largely in terms of polar effects on the transition state, but radical pyramidalization and, to a lesser extent, addition thermodynamics play a role. The relationship between these fluorine substituent effects and the cyclopolymerizations of fluorinated alpha,omega-dienes are discussed.