[Indole cleavage with mebhydroline by sodium periodate--part 2. Mechanism of the dilactam formation].

The gamma-carbolines 1a-d reacted with periodate by loss of one carbon--without available precursors to the eight-membered dilactams 3a-c and the amino acid 9d. As possible intermediates of an indole cleavage alpha-aminoketones as models were examined. While the oxidation of chain-formed 13 afforded only a small amount of C-lost amide 23, the cyclic species 24 and 32 gave rise to considerably higher yields of the corresponding lactams 29 and 36. From the benzazepinone 32 with Hg(II)-EDTA the intermediate product 43, containing all genuine C-atoms, was formed, which could quantitatively cleaved by periodate to the lactam 36 and formic acid. This mechanism can be transferred to the reactions of the gamma-carbolines 1a-d.