The Baeyer-Villiger oxidation of cyclohexanone (2a) and of acetophenone (2b) by bis (trimethylsily1) peroxomonosulfate (1) has been reinvestigated using 180-labeling techniques. Starting with doubly labeled Me3Si180180S03SiMe3, mass spectrometric analyses allowed determination of the amount of label appearing in the carbonyl and the OR moiety of the ester (or of the lactone). It has been observed that 2a also promotes the ...