2-thiones (l), was added at-5 OC a solution of 5-acetoxy-2-pyrrolidinone"(3, n= 1)(1.5 mol equiv) or 6-acetoxy-2-piperidinone"(3, n= 2)(1.5 mol equiv) in THF. After stirring at-5 to 0 OC for 2 h, the reaction mixture was treated as usual to give the corresponding major product 4a- d in a highly diastereoselective manner [293-297% diastereomer excess (de), Scheme I and Table I]. Pure compounds 4a-d were readily obtained by their chromatographic separation ...
