The selective formation of optically active 2-acyl-2-alkyl-1,3-dithiolane 1,1-dioxides from the corresponding 2-acyl-2-alkyl-1,3-dithiolane 1-oxides, by reaction with OsO4 and NMO in acetone, is reported. These compounds underwent stereoselective reactions at the carbonyl group of the acyl group with organometallic reagents. These reactions were completely regioselective, and no attack at either of