<i>tert</i>‐Amino effect at a coumarin and a 2‐quinolone system: Synthesis of 1,2 fused 5<i>H</i>‐chromeno[4,3‐<i>b</i>]pyridin‐5‐ones and a 6<i>H</i>‐benzo[<i>h</i>][1,6]naphthyridin‐5‐one

Abstract

Abstract magnified image Some novel 1,2‐fused 5 H ‐chromeno[4,3‐ b ]pyridin‐5‐ones ( 5a,b ) and a 6 H ‐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 .