PTSA‐Catalyzed [3+2] Cycloaddition of in Situ Generated 3‐Ylidene Oxindoles with Coumarin‐Based N‐Phenyl Enamine Derivatives.

Brønsted acid mediated [3+2] cycloaddition of coumarin‐based enamines with 3‐ylidene oxindoles generated in situ from 3‐hydroxy‐3‐aroylmethyl oxindoles enabled the synthesis of polyheterocyclic compounds with a pyrrolocoumarin core structure in a highly regioselective manner. The synthetic procedure is highly efficient and metal‐free, and no chromatographic purification of the products is required. The chromenopyrrole derivatives bearing an oxindole moiety formed as rapidly interconverting rotamers. [ABSTRACT FROM AUTHOR]