Asymmetric Mannich Reactions with α-Silylated Trimethylsilyl Enol Ethers and N-Alkoxycarbonyl Imines

Abstract

The Mannich reaction of enantiomerically pure α-dimethylthexylsilylated trimethylsilyl enol ether (Z,S)-2 with titanium complexes of N-alkoxycarbonyl imines afforded αŽ-silylated α,β-disubstituted β-amino ketones (S,R,S)-4a-e in good to excellent yields (70-92%) and diastereomeric excesses (de ≥ 96%). Removal of the directing silyl group gave N-protected and anti-configured β-amino ketones (R,S)-5a-e in excellent yields (90-95%) and stereoselectivities (de, ee ≥ 96%- > 98%).