The catalytic enantioselective addition of an acetate enolate equivalent to ketones is described. Methyl trichlorosilyl ketene acetal reacts with a wide range of ketones in the presence of pyridine N-oxide to afford the aldol addition products in excellent yields. Chiral 2,2′-pyridyl bis-N-oxides bearing various substituents at the 3,3′- and 6,6′-positions also provide excellent yields of the aldol products with variable enantioselectivities ranging from 94/6 er for aromatic ketones to nearly racemic for aliphatic ketones. An X-ray crystal structure of the complex between a catalyst and silicon tetrachloride (((P)-(R,R)-19-SiCl4)) has been obtained. Extensive computational analysis provides a stereochemical rationale for the observed trends in enantioselectivities.
ASJC Scopus subject areas
- Organic Chemistry