Diastereoselective aldol condensation of acylsilane silyl enol ethers with acetals

Treatment of E- or Z-acylsilane silyl enol ethers derived from acylsilanes having an enolizable methylene proton with a mixture of aromatic aldehyde dimethyl acetals and TiCl4 in dichloromethane gives the corresponding 2,3-anti-3-methoxyacylsilanes in high d.e., independent of the geometry of double bond in acylsilane silyl enol ethers. On the other hand, E-acylsilane silyl enol ethers react with acetals of aliphatic aldehydes to afford the corresponding aldol adducts with syn-selectivity, while the reaction of Z-isomers provides the products with anti-selectivity.