Diastereoselective Magnesium Halide-Catalyzed anti -Aldol Reactions of Chiral N -Acyloxazolidinones

A chiral auxilliary-based direct aldol reaction is reported. The reactions are catalytic in magnesium salts and are facilitated by silylation with chlorotrimethylsilane. The adducts isolated are in high diastereoselectivity (up to 32:1 dr) and favor the anti-aldol diastereomer B. Reactions are operationally simple and can be run under ambient atmosphere without rigorous exclusion of water. Many of the adducts are highly crystalline and a single diastereomer can be isolated without chromatography.