The allylic rearrangement of hydroperoxides: the allylperoxyl radical

Abstract

The free-radical rearrangement of pinocarveyl hydroperoxide (1) or myrtenyl hydroperoxide (2) in hexane produces an equilibrium mixture of both hydroperoxides. The absence of carbon skeletal rearrangement suggests that the intermediate radical involved in hydroperoxide isomerization has its unpaired electron localized elsewhere than the α-carbon atom. The failure of oxygen to react with pino-carveyl, myrtenyl, and acyclic hydroperoxides (8) and (9) during the allylic rearrangement supports this suggestion. The kinetics of the rearrangements of 1-isopropyl-2-methylallyl hydroperoxide (8) is compatible with a mechanism in which the intermediate is a common allylperoxyl radical produced directly from either allylic isomer.