Synthesis of 1-substituted-2,3,4,9-tetrahydro-(2-oxopropyl)-1H-pyrido [3,4-b] indoles and their base-catalyzed rearrangements to N- [2-[2-(1-alkyl-3-oxobutenyl)-1H-indol-3-yl] ethyl]acetamides

The condensation of 1H-indole-3-ethanamides, 1 , with 2,4-pentanediones, 2 , gave enamines 3 . Acid catalyzed ring closure of 3 gave 1-(1-substituted-2,3,4,9-tetrahydro- (2-oxopropyl) -1H-pyrido 3,4-b] indoles 4 . Subsequent N-acetylation yielded 5 which sequentially produced 2,3-disubstituted indoles 6 and 7 resulting from C? N bond cleavage after treatment with sodium alkoxide in ethanol. Controlled catalytic hydrogenation of the latter gave saturated derivatives 8 and 9 .