New Route of Benzyne Cyclization for Synthesis of 2,3,4,5‐Tetrahydro‐1H‐pyrido[4,3‐b]indole Derivatives Avoiding Highly Toxic Aryl Hydrazines

Abstract

A new route for the regioselective synthesis of 2,3,4,5‐tetrahydro‐1H‐pyrido[4,3‐b]indole derivatives was developed based on cyclization of 3‐chlorophenylimine‐N‐alkyl‐4‐piperidones by “the complex bases” of NaNH2 or KNH2. The procedure was performed under variable reaction conditions in inert proton‐free solvents, such as THF, dioxane, 1,2‐dimethoxyethane, toluene, and xylene, at temperatures varying from 20°C to boiling point of the solvent used. Toxic arylhydrazine intermediates occurring in the classical Fischer indole synthesis are avoided.