The asymmetric oxidation of 2-substituted dithianes, dithiolanes and oxathiolanes catalyzed by cyclohexanone monooxygenase (CMO) has been examined. The introduction of substituents at the C-2 causes a decrease of the ee with the exception of 2-benzoyl-1, 3- dithiane monosulfoxide (90% ee). With 2-monosubstituted dithioacetals CMO yields preferentially or exclusively the trans diastereoisomer. The binding of the 1, 3- ...