Rose bengal sensitized singlet oxygenation of 1-methyl-2- phenylindole (1) in methanol yielded 1-methyl-2-methoxy-2-phenyl-1, 2- dihydro-3H-indol-3-one (4) and 1-methyl-2-hydroxy-2-phenyl-1, 2- dihydro-3H-indol-3-one (6), the latter underwent benzilic acid-type rearrangement in alkline medium to give 1-methyl-3-hydroxy-3- phenyloxindole (14). The solvolysis of 6 and the influence of added base on photooxygenation reaction were studied and the formation pathways of photooxygenation products were also discussed. A possible mechanism involving interception of the initially generated zwitterionic intermediate 2 by methanol, followed by dehydration leading to 4, as well as the O-O homolysis of 1, 2-dioxetane 7, followed by hydrogen abstraction to give 6 was proposed.

Key words: SENSITIZATION