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

The reaction of tartrate-derived silylketene acetals and benzaldehyde has b een investigated and the yields and diastereoselectivities have been found to be dependent upon the nature of the tartrate ester. Utilising the di-ter t-butyl tartrate derivatives, high yields were achieved using a variety of aldehyde substrates. The reactions all proceeded with excellent levels of s tereoselectivity (greater than or equal to 82:18); the sense of induction b eing dependent upon the choice of Lewis acid. BF3. OEt2 and TiCl3((OPr)-Pr- i) furnished complementary products in several cases and a model has been p roposed to account for this observation.