DYE-SENSITIZED PHOTOOXYGENATIONS OF 1,3-ISOQUINOLINEDIONES

Singlet oxygen reactions of 1,3-isoquinolinediones 1a-1e could be sens itized by the anionic sensitizer Rose Bengal (RE) in methanol or by te traphenylporphin (TPP) in the presence of pyridine as a base and a cos olvent in benzene. The products are the corresponding 1,3,4-isoquinoli netriones 2a-2e and methyl 1-hydroxy-3-oxoisoindole-1-carboxylates 3b- 3e in methanol and the triketones 2a-2e and the 3-hydroxy-3-alkyl (ary l)aminocarbonylbenzoisofuran-1-ones 4b-4e in benzene-pyridine. TPP sen sitized photooxygenations of the 4-alkylated 1,3-isoquinolinediones 5a -5c yielded the 4-alkyl-4-hydroxy-1,3-isoquinolinediones 6a-6c, the 4- alkyl-4-hydroperoxy-1,3-isoquinolinediones 7a-7c and the 3-alkyl-3-hyd roxybenzoisofuran-1-ones 8a-8b. Reaction mechanisms have been proposed . (C) 1998 Elsevier Science Ltd. All rights reserved.