Diastereoselective Additions of Nucleophiles to α-Acetoxy Ethers Using the α-(Trimethylsilyl)benzyl Auxiliary

We report the diastereoselective addition of a variety of nucleophiles to α-(trimethylsilyl)benzyl-substituted oxocarbenium ions. The oxocarbenium ions are generated from α-acetoxy ethers, which are easily prepared via reductive acetylation of esters. The α-(trimethylsilyl)benzyl auxiliary produces good to excellent facial selectivity with a variety of nucleophiles, including silyl enol ethers, silyl ketene acetals, allylsilanes, and crotylsilanes. The utility of this auxiliary is further demonstrated in a complex ketone aldol coupling reaction.