Three-component coupling using arynes and DMF: straightforward access to coumarins via ortho-quinone methides

ortho-Quinone methides, arising from a formal [2 + 2] cycloaddition between arynes and DMF, were found to facilely undergo a [4 + 2] cycloaddition with ester enolates or ketenimine anions to produce diverse coumarins in a straightforward manner.