Beta-Keto Sulfoxide reduction-intramolecular delivery

The transition state is a six-membered chair with the toluyl group equatorial. This is the least hindered of the 4 possible transition states.

The stereochemistry of the reaction is controlled by the sulfoxide. In the absence of the ZnCl₂, the hydride transfer occurs intramolecularly yielding the R,S enantiomer.

Summary page : Without ZnCl₂ : With ZnCl₂

A. Solladié-Cavallo, J. Suffert, A. Adib and G. Solladié, Tetrahedron Lett., 1990, 31, 6649–6652.