Efficient synthesis of trisubstituted [1]benzopyrano[4,3-b]pyrrol-4(1H)-one derivatives from 4-hydroxycoumarin

Various trisubstituted [1]benzopyrano[4,3-b]pyrrol-4(1H)-one derivatives have been synthesized from 4-hydroxycoumarin with a 30–40% yield over six steps. The key step of the synthesis is a base-promoted intramolecular cyclization of enamines 5, followed by dehydration to generate the fused pyrrole ring.