Phosphine-Catalyzed Reductions of Alkyl Silyl Peroxides by Titanium Hydride Reducing Agents: Development of the Method and Mechanistic Investigations

A method that allows for the reduction of protected hydroperoxides by employing catalytic amounts of phosphine is presented. The combination of a titanium(IV) alkoxide and a siloxane allowed for the chemoselective reduction of phosphine oxides in the presence of alkyl silyl peroxides. Subsequent reduction of the peroxide moiety by phosphine provided the corresponding silylated alcohols in useful yields. Mechanistic experiments, including crossover experiments, support a mechanism in which the peroxide group was reduced and the silyl group was transferred in a concerted step. Labeling studies with O-17-labeled peroxides demonstrate that the oxygen atom adjacent to the silicon atom is removed from the silyl peroxide.