Chiral Silyl Ketene Acetals from Thioesters: Reaction with Acetals and Peroxyacetals to form 3-Alkoxy- and 3-Peroxyalkanoates

The Lewis acid-mediated reaction of chiral O- and S-silyl ketene acetals (SKAs) with peroxyacetals and acetals was investigated as an approach to the asymmetric synthesis of 3-peroxy- and 3-alkoxyalkanoates. SKAs derived from chiral O-acetates fail to react with peroxyacetals and provide little diastereoselection in reactions of nonperoxidic acetals. Reaction of thioacetate SKAs with peroxyacetals furnishes 3-peroxyalkanoate thioesters in good yield but with poor diastereoselection. In the case of silyl ketene acetals based upon a camphorsulfonamide chiral auxiliary the diastereomeric peroxyalkanoates are easily separated.