4-Chlorophenylsulfinylacetates of defined stereochemistry at sulfur were prepared from monochiral alcohols: compound 2 from (+)-menthol; 3 and 4 from (-)-8-phenylmenthol; 5 and 6 from (+)-trans-2-phenylcyclohexanol; and, 7 and 9 from (-)-10-dicyclohexylsulfamoyl-D-isoborneol. Reagents for which the sulfoxide asymmetry is matched with the inducing effect of the auxiliary give good diastereoselection in SPAC reactions affording gamma-hydroxy-alpha,beta-unsaturated alcohols of high optical purity. Asymmetry at the sulfoxide has a greater effect than the auxiliaries on the stereochemical outcome of these reactions.