An Alkyne Hydrosilylation-Oxidation Strategy for the Selective Installation of Oxygen Functionality

Alkynes bearing propargylic, homopropargylic, and bishomopropargylic hydroxyl groups are shown to serve as precursors for ketone or alpha-hydroxy ketone functionality. The approach hinges on the intermediacy of vinylsilanes created through regioselective hydrosilylation catalyzed by the complex [Cp*Ru(MeCN)3]PF6. Several oxidative pathways of linear and cyclic vinylsilanes are studied, and the possibility of diastereoselective epoxidation of cyclic vinylsilanes is demonstrated. The sequences constitute the equivalent of stereoselective aldol, homo-aldol, and bishomo-aldol type processes. The method is applied to a short synthesis of the piperidine alkaloid, spectaline.