Combinatorial Synthesis of Fused Tetracyclic Heterocycles Containing [1,6]Naphthyridine Derivatives under Catalyst Free Conditions

A three-component reaction between an aromatic aldehyde, an amine, and tert-butyl 2,4-dioxopiperidine-1-carboxylate in EtOH at refluxing temperature gave fused tetracyclic heterocycles in high yields. The amines include 1H-indazol-5-amine, 1H-indazol-6-amine, 1H-indol-5-amine, and 1H-benzo­[d]­imidazol-5-amine, giving 11-aryl-3H-indazolo­[5,4-b]­[1,6] naphthyridine, 11-aryl-1H-indazolo­[6,7-b]­[1,6]­naphthyridine, 11-aryl-3H-indolo­[5,4-b]­[1,6]­naph-thyridine, and 11-aryl-3H-imidazo­[4′,5′:3,4]­benzo­[1,2-b]­[1,6]­naphthyridine derivatives, respectively.