Phosphine-dependent stereoselectivity in the mitsunobu cyclodehydration of 1,2-diols: stereodivergent approach to triaryl-substituted epoxides.

Triaryl-1,2-ethanediols, readily available from natural mandelic acid, can be stereospecifically converted into their corresponding chiral nonracemic epoxides by means of a Mitsunobu cyclodehydration reaction. Upon selection of the phosphine component in the reaction, the two enantiomers of the final epoxides are accessible in high enantiomeric excess. In view of this surprising phosphine-dependent stereoselectivity, here we examine the influence of the steric and electronic nature of both the phosphine and the substrate. [reaction: see text].