MILD OXIDATION OF 1,2,3,4-TETRAHYDRO-BETA-CARBOLINES

Oxidation of 1-(aryl or heteroaryl)1,2,3,4-tetrahydro-beta-carbolines (1a-r) with KMnO4 in dry THF afforded in the most cases almost exclusively 3,4-dihydro products (2) with a yield of 28-94 %. Only in few cases (1c, 1i, 1m) the reaction was non-selective and a significant amount of the fully aromatized products (3) (30-40 % of the reaction mixture) was observed. The influence of both the substituent nature and the substitution modes on the observed yield and selectivity of the reaction was discussed.