Synthesis of [1,2-a]-fused tricyclic dihydroquinolines by palladium-catalyzed intramolecular C-N cross-coupling of polarized heterocyclic enamines

A simple methodology for [1,2-a]-fused tricyclic dihydroquinolines is established. The key step of the methodology is an intramolecular Buchwald-Hartwig amination reaction of suitable halogenated (both bromo and chloro) cyclic enaminoketones, enaminoesters and enaminonitriles with various ring size (from five- to seven-membered). Optimal reaction conditions (palladium source, base, ligand) depend on the ring size of the starting enamine, giving 65-98% yield of the tricyclic product. A treatment of the products with perchloric acid gives respective quinolinium perchlorates.