Substituted 1,3-dihydro-
2H-isoindoles (
2, isoindolines) were prepared and subjected to palladium-catalyzedformate reduction. Alkyl isoindolines were reduced to 4,5,6,7-tetrahydro-
2H-isoindoles (
1). Only partialreduction was observed for 5-methoxyisoindoline, and 4-methoxy-, 5-carbomethoxy-, amino-, andamidoisoindolines were inert to the reaction. Halogen-substituted isoindolines were dehalogenated andreduced to 4,5,6,7-tetrahydro-
2H-isoindoles. Isoindole
24 was also reduced to a mixture of an isoindolineand a 4,5,6,7-tetrahydro-
2H-isoindole. In contrast, 2,3-dihydro-1
H-indoles
21 underwent dehydrogenationto give thermodynamically stable indoles. Theoretical calculations show the significant difference inaromaticity between isoindoles and indoles, corresponding to the observed differences in reactivities.Tetrahydro-2
H-isoindoles
1 were oxidized to 4,5,6,7-tetrahydroisoindole-1,3-diones in the presence ofNBS and air.
