TiO2-sensitised photo-oxidation mechanism of indane and some of its hetero-analogues in deaerated CH3CN

A mechanistic study, principally based on product analysis, relative to the TiO2-photosensitized oxidation of indane and some of its hetero-analogues, in deaerated CH3CN and in the presence of Ag2SO4, was performed. In particular: (i) I-acetamidoindan (principal product), indene, I-indanol and I-indanone were obtained from indan; (ii) 5-methoxyindan gave 6-methoxyindene (principal product) and 5-methoxy-l-indanone; (iii) 2,3-dihydrobenzofuran, 2,3-dihydroindole and 2,3-dihydrobenzothiophene produced benzofuran, indole and benzothiophen (the last one accompanied by minor amounts of 2,3-dihydrobenzothiophene- I-oxide), respectively. Considering the previous studies on photo-oxidation of analogous substrates as benzylic derivatives (arenes, alcohols and ethers) and from reaction product profiles, an electron-transfer mechanism (from the substrate to the photogenerated hole) is suggested, where the radical cation intermediate should deprotonate to a benzylic radical. The carbocation obtained from the oxidation of this radical should competitively evolve to alkene, alcohol and acetamide. H-2 O-18 labelling photo-oxidation experiments suggest that the ketone, when present, should derive from the substrate, through the alcohol as intermediate. Copyright (c) 2006 John Wiley & Sons, Ltd.