Phosphine-Mediated MBH-Type/Umpolung Addition Domino Sequence: Divergent Construction of Coumarins.

We herein report a phosphine-mediated domino process of MBH-type reaction/umpolung γ-addition through the rational integration of the privileged reactivities of alkynoate. Simply by manipulating the nucleophilic reagent, the developed protocol offers a facile, diversity-oriented construction of a wide range of three-substituted coumarins.