title: Lewis base catalyzed, enantioselective aldol addition of methyl trichlorosilyl ketene acetal to ketones.
abstract: 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.SiCl(4))) has been obtained. Extensive computational analysis provides a stereochemical rationale for the observed trends in enantioselectivities.
authors.affiliation: Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, IL 61801, USA. denmark@scs.uiuc.edu
authors.forename: Scott E
authors.initials: SE
authors.lastname: Denmark
authors.forename: Yu
authors.initials: Y
authors.lastname: Fan
authors.forename: Martin D
authors.initials: MD
authors.lastname: Eastgate