Asymmetric Tandem Wittig Rearrangement/Aldol Reactions

A new method for the asymmetric synthesis of a-alkyl-a,B-dihydroxy esters that involves tandem Wittig rearrangement/aldol reactions of O-benzyl- or O-allylglycolate esters derived from 2-phenylcyclohexanol is described. This sequence constructs two C-C bonds and two stereocenters, one of which is quaternary, to afford syn diol products with excellent stereocontrol. Cleavage of the chiral auxiliary affords enantiomerically enriched products with up to 95% ee. The application of this method to the preparation of a key intermediate in the synthesis of the antifungal agent alternaric acid is also described.