Regiospecific Synthesis of 3,4-Dihydrocoumarins via Substrate-Controlled [1,3]- or [3,3]-Sigmatropic Rearrangement

A regiospecific synthesis of 3,4-dihydrocoumarin derivatives has been achieved involving tandem rearrangement-cyclization of (E)-2-(aryloxymethyl) alk-2-enoates catalyzed by a Pd/Cu bimetallic system. Unexpected substrate-controlled [1,3]- or [3,3]-sigmatropic rearrangement was observed in the transformations.