The asymmetricdirect vinylogous aldolreaction of unactivated γ-butenolide with aldehydes has been developed, giving the corresponding 5-(1′-hydroxy)butenolide derivatives in high yields (up to 93%) and enantioselectivities (up to 83% ee) under mild conditions.
Asymmetric direct vinylogous aldolreactions of furan-2(5H)-one with aldehydes in the presence of a catalytic amount of novel squaramide–sulfonamide organocatalyst resulted in the corresponding addition products with high to excellent enantioselectivities. This is the first successful report illustrating an example of highly stereoselective reactions using a squaramide–sulfonamide organocatalyst.
Reactions of 2-(trimethylsilyloxy)furan 1 and aldehydes catalyzed by a chiral cationic Cr(salen) complex proceeded with remarkably improved enantioselectivity, when a secondary alcohol was added. The role of the alcohol is acceleration of the conversion of an intermediary 1-aldehyde adduct into the final product.