Synthesis of Enantioenriched Axially Chiral Olefins via Asymmetric Wittig Reaction

Bernardi et al. have reported the asymmetric Wittig reactions to generate enantioenriched axially chiral olefins. According to their results, a hydrogen-bond donor (-)-4,5-bis[hydroxy(diphenyl)methyl]-2,2-dimethyl-1,3-dioxolane catalyzes the reaction between phosphorus ylides and 4-substituted cyclohexanones, furnishing enantioenriched axially chiral olefins with moderate stereoselectivities. In this reaction, stabilization of the transition state in the asynchronous [2+2] cycloaddition by the coordination of the catalyst is considered to be responsible for the observed stereocontrol.