A four-step route from aldehydes to C-2-elongated enantiomerically pure alpha,beta-unsaturated gamma-hydroxy esters

Asymmetric dihydroxylation of beta,gamma -unsaturated esters 4 provided bet a -hydroxy-gamma -lactones 3 or ent-3. Methanolysis acetonide formation and LDA-mediated fragmentation of the resulting esters 5/ent-5 furnished the g amma -chiral acrylates 6/ent-6 containing disubstituted C = C bonds (93-99% ee). Also, beta -hydroxy-gamma -lactones ent-3a and 3b were alpha -butylat ed and alpha -brominated, respectively, prior to methanolysis, acetonide fo rmation, and fragmentation which led to the gamma -chiral acrylates 9 and 1 2 with trisubstituted C = C bonds (94 and 95% ee, respectively).