부산대학교 도서관

2,4,6-Trimethylphenyl (mesityl) cyclohexanecarboxylate 1cand related mesityl esters 1a,band d-fwere photodecarboxylated upon irradiation at 254 nm in neutral solvents to give alkylmesitylenes 15in good yields. In contrast, in the presence of a catalytic amount of acid and a sufficient amount of alcohol, the same compounds underwent facile phototransesterification to afford the corresponding ester 9and phenol 10in almost quantitative yields. Photolyses of less-substituted aryl alkanoates such as 2,6-dimethylphenyl (xylenyl), phenyl, 4-methoxyphenyl (4-anisyl) and 4-methoxynaphthyl alkanoates 2–4and 8were also investigated to elucidate the reaction mechanism of acid-catalyzed phototransesterification. Irradiation of these esters afforded the corresponding photo-Fries rearrangement products 20–23both in neutral and acidic acetonitrile with significant acceleration of the processes in the presence of acid. It was elucidated that the photolysis of the esters affords the geminate radical pair 28, which in turn recombines to cyclohexadienone intermediates 29and 30. Added acid accelerates not only the nucleophilic attack of alcohol to 29and 30but also other processes. Prolonged irradiation of the esters in neutral solution led to skeletal rearrangements of the initial product, affording isomeric alkylbenzenes. The phototransposition of cyclohexylmesitylene 15cviabenzvalene intermediates was, on the contrary, retarded under acidic conditions. These acid-controlled competitive photoreactions are representative examples, in which a catalytic amount of acid can alter the fate of reactive intermediates on both ground-state and excited-state surfaces.