The effects of different ester and ketal protecting groups on the reactivity and selectivity of tartrate-derived silylketene acetals

Abstract

The reaction of tartrate-derived silylketene acetals and benzaldehyde has been investigated and the yields and diastereoselectivities have been found to be dependent upon the nature of the tartrate ester. Utilising the di-tert-butyl tartrate derivatives, high yields were achieved using a variety of aldehyde substrates. The reactions all proceeded with excellent levels of stereoselectivity ( 82∶18); the sense of induction being dependent upon the choice of Lewis acid. BF₃·OEt₂ and TiCl₃(OⁱPr) furnished complementary products in several cases and a model has been proposed to account for this observation.