Synthesis of Oxasilolanes by TBAT-Catalyzed Hydroxyl-Directed Hydrosilylation

The reaction of allylic and homoallylic styrenyl alcohols with diphenylsilane and catalytic tetrabutylammonium difluorotriphenylsilicate (TBAT) produces 5- and 6-membered ring oxasilolanes, respectively. Differing substitution at the carbinol position, phenyl ring, and carbon-carbon double bond were all found to have significant impacts on both yield and diastereoselectivity. A mechanism is proposed involving fluoride-promoted intramolecular hydrosilylation and formation of an intermediate benzylic anion, followed by cyclization and oxasilolane formation. This mechanism is supported by double bond stereospecificity experiments along with the scope and stereochemical outcome of the reaction.