Photochemisches Verhalten von N‐Acyl‐11‐methyl‐hexahydrocarbazolen

The irradiation of N‐acylated 11‐methyl‐1,2,3,4,10,11‐hexahydrocarbazoles (compounds 6–10) and of the 8‐methoxy derivatives 11–13 in hexane solution, with 254 nm light, in the presence of air, leads to 11‐methyl‐2,3,4,11‐tetrahydro‐1 H‐carbazole (2) (table 1) and its 8‐methoxy derivative 21, respectively (scheme 2). Furthermore the 8‐acylated products. 14, 15, 16, 18, are formed in minor amounts by a “photoanilide” rearrangement. Irradiation of the N‐acetyl‐8‐methoxy‐indoline 12 gives in addition (by elimination of the 8‐methoxy group) the 8‐acetyl‐indoline 14 and, by coupling, the dimeric compound 23 (schemes 2 and 4). Irradiation of the N‐formyl‐indoline 6 yields, besides the indolenine 2 the indoline 1 (table 1). The mechanism of the anaerobic part of these photoreactions were investigated by CIDNP experiments. It is possible to convert directly indoline 1 to the indolenine 2, in 33% yield, by irradiation at 60° in the presence of oxygen.