Synthesis of Chiral γ,γ-Disubstituted γ-Butenolides via Direct Vinylogous Aldol Reaction of Substituted Furanone Derivatives with Aldehydes.

An organocatalyzed method for synthesizing chiral γ,γ-disubstituted γ-butenolides via direct vinylogous aldol reactions of γ-substituted β,γ-butenolides with aldehydes is reported. This reaction is catalyzed by a squaramide-sulfonamide organocatalyst to afford a range of anti-aldol adducts possessing vicinal quaternary and tertiary stereocenters with high to excellent enantioselectivities (reaching 95% ee). This is the first report of a successful stereoselective direct vinylogous aldol reaction of aldehydes with γ-substituted β,γ-butenolides.