Polyphosphoric Acid Catalyzed Indolization of 4-Piperidone Phenylhydrazones

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A convenient synthesis of 1,3-diphenyl 1,2,3,4-tetrahydro-γ-carboline in quite encouraging yield through the Fischer-type indolization of phenylhydrazones (either preformed or formed in situ) of 2.6-diphenyl-4-piperidone in the presence of polyphosphoric acid is described. This involves a new synthetic strategy of 4-substituted 1.3-diphenyl-1,2,3,4-tetrahydro--γ-carbolines 3a-d. These compounds have been characterised through their IR and 1H NMR spectral analysis.

Phenylhydrazones; Diphenyl; Tetrahydro Carbolines