Synthesis of methyl substituted [5,6]- and [7,8]-fused pyridocoumarins via the iodine-catalyzed reaction of aminocoumarins with n-butyl vinyl ether

The three-component reactions of aminocoumarins with n-butyl vinyl ether using a catalytic amount of I2 resulted in 2-methyl substituted fused pyridocoumarin derivatives. 2-Methyl substituted [5,6]- or [7,8]-fused pyridocoumarins are prepared from the Povarov-type, three-component reactions of 6- or 7-aminocoumarins with n-butyl vinyl ether, catalyzed by iodine in refluxing acetonitrile, through the aza-Diels–Alder reaction of the initially formed N-iminoaminocoumarins with a second equivalent of the vinyl ether.