Photosensitized oxygenation of some benzyl sulfides. The role of persulfoxide

Benzyl ethyl sulfide (6a) is photo-oxidized to benzaldehyde in benzene, whe reas diethyl sulfide is known to give inefficiently the sulfoxide under the se conditions. Oxidative C-S cleavage is the main process also with benzhyd ryl ethyl sulfide (6c), but not with alpha-methylbenzyl ethyl sulfide (6b), which mainly gives the sulfoxide. The carbonyl derivatives reasonably aris e from S-hydroperoxy ylides (3). Consistently with this finding, calculatio ns at the PM3 level suggest that the first intermediate, the persulfoxide ( 1), undergoes intramolecular hydrogen transfer when an activated a-hydrogen is available and gives 3. This is the case for the above benzyl sulfides ( Delta H-not equal for the process decreases with decreasing C-H BDE). Howev er, only some of the persulfoxide conformations are correctly oriented for this rearrangement, and this may slow this process and make other reactions compete, as happens with 6b. Copyright (C) 1999 John Wiley & Sons, Ltd.