Substituent-controlled domino-Knoevenagel-hetero Diels–Alder reaction—a one-pot synthesis of polycyclic heterocycles

The reaction of 2-(N-alkenyl-N-aryl)amino-4-oxo-4H-1-benzopyran-3-carbaldehyde with dimedone/Meldrum’s acid/4-hydroxycoumarin by heating in ethanol in the presence of pyridine produces polycyclic heterocycles bearing pyridine and pyran rings in a one-pot reaction. The effect of substituents on N-atom of the amino function controls the mode of reaction. Terminal alkenes prefer intramolecular Michael type reaction, but non-terminal alkenes favour Diels–Alder reaction, whereas, under similar condition, 2-(N-alkyl-N-allyl)amino-4-oxo-4H-1-benzopyran-3-carbaldehyde undergoes domino-Knoevenagel-hetero Diels–Alder reaction.