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 exclusi
vely 3,4-dihydro products (2) with a yield of 28-94 %. Only in few cas
es (1c, 1i, 1m) the reaction was non-selective and a significant amoun
t of the fully aromatized products (3) (30-40 % of the reaction mixtur
e) was observed. The influence of both the substituent nature and the
substitution modes on the observed yield and selectivity of the reacti
on was discussed.