Direct, pyrrolidine sulfonamide promoted enantioselective aldol reactions of α,α-dialkyl aldehydes: synthesis of quaternary carbon-containing β-hydroxy carbonyl compounds
摘要:
A procedure has been developed for direct, asymmetric aldol reactions of alpha,alpha-dialkyl aldehydes with aromatic aldehydes, which produces quaternary carbon-containing beta-hydroxy carbonyl compounds. The processes, promoted by the organocatalyst (S) pyrrolidine sulfonamide, take place in high yields with exceptionally high levels of enantioselectivities. (c) 2005 Elsevier Ltd. All rights reserved.
A highly stereoselective direct aldol condensation of ketones to aromatic aldehydes was realized; the trichlorosilyl enolether generated in situ in the presence of tetrachlorosilane is activated by catalytic amounts of an enantiomerically pure biheteroaromatic phosphine oxide to react with aldehydes, coordinated as well as activated by the chiral cationic hypervalent silicon species. This Lewis acid-mediated Lewis base-catalyzed transformation allowed, starting from two carbonyl compounds, to directly synthesize beta-hydroxy ketones generally with high anti stereoselectivity and up to 93% ee for the anti isomer. (C) 2010 Elsevier Ltd. All rights reserved.