FISCHERS INDOLE RING CLOSURE WITH 1,3-DISUBSTITUTED 4-PIPERIDONES .7. SYNTHETIC INDOLE COMPOUNDS

Treatment of the arylhydrazones of 1, 3‐disubstituted 4‐piperidones with ethanolic hydrogen chloride (FISCHER reaction conditions) affords 1, 2, 3, 4‐tetrahydropyrimido [3, 4‐a]‐indoles in good yields. During catalytic hydrogenation in the presence of protons these tetrahydropyrimido‐indoles are split into 2‐(2‐methylamino‐ethyl)‐indoles. The formation of these tricyclic products can be explained by rearrangement immediately following the normal FISCHER reaction. If the substituent at the piperidine nitrogen is an acyl group, normal or rearranged products are formed, depending on the nature of the 3‐substituent. Copyright © 1969 Verlag GmbH & Co. KGaA, Weinheim