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A metal-free method for the construction of 2-substituted quinolines and benzofquinolines from aromatic amines, aldehydes, and tertiary amines has been demonstrated. Cheap and readily available tertiary amines acted as the vinyl source. A new pyridine ring was selectively formed via 4 + 2 condensation that was promoted by ammonium salt under neutral conditions and an oxygen atmosphere. This strategy provided a new route for the preparation of various quinoline derivatives with different substituents at the pyridine ring, which provides the possibility of further modification.
Ma et al. (Mon,) studied this question.