The role of SET in the deprotection of (thio)ketals under photosensitization by π-acceptors

Efficient deprotection of 2-methyl-2-tert-butyl-1,3-dithiolane and the corresponding oxathiolane to give the ketone is obtained by photosensitization by a catalytic amt. of arom. nitriles (benzenetetracarbonitrile, TCB, and anthracenedicarbonitrile, the latter only in the presence of biphenyl) or of heterocyclic salts (triphenylpyrylium tetrafluoroborate, and methylacridinium perchlorate) in O-satd. solns. The reaction involves SET to the excited π-acceptor and interception of the substrate radical cation either by O (in the case of the heterocyclics) or by the superoxide anion