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

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Various trisubstituted [1]benzopyrano[4,3- b]pyrrol-4(1 H)-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.