Abstract: A number of different piperidoindole systems have been subjected to oxidation with selenium dioxide. The bonding between the indole and piperidine unit has been varied to provide different systems, the oxidation of which has led to formation of either 2-acyl-or 3- acylindoles or fully aromatic P-carbolines, depending on the substrate chosen. The pattern of reactivity observed was in complete agreement with the ene mechanism proposed for ...