tert-amino effect at a coumarin and a 2-quinolone system: Synthesis of 1,2 fused 5H-chromeno [4,3-b] pyridin-5-ones and a 6H-benzo[h][1,6]naphthyridin-5-one

摘要

Some novel 1,2-fused 5H-chromeno[4,3-b]pyridin-5-ones (5a,b) and a 6H-benzo[h][1,6]naphthyridin-5-one (5c) have been synthesized starting from the 4-chlorocoumarin-3-carbaldehyde (1a) or its N-methyl-2-quinolone analogue (1b) via subsequent Knoevenagel condensation and ring closure reaction known as the 'tert-amino effect'. These are rare examples of the tert-amino effect occurring at 2-pyrone and 2-pyridone ring. An unusual intramolecular redox reaction of the iminium ion 6, reported earlier, most probably follows analogous mechanism as the tert-amino effect reactions leading to 5.