Divergent Geminal Alkynylation-Allylation and Acylation-Allylation of Carbenes: Evolution and Roles of Two Transition-Metal Catalysts.

Cooperative bimetallic catalysis to access novel reactivities is a powerful strategy for reaction development in transition-metal-catalyzed chemistry. Particularly, elucidation of the evolution of two transition-metal catalysts and understanding their roles in dual catalysis are among the most fundamental goals for bimetallic catalysis. Herein, a novel three-component reaction of a terminal alkyne, a diazo ester, and an allylic carbonate was successfully developed via cooperative Cu/Rh catalysis with Xantphos as the ligand, providing a highly efficient strategy to access 1,5-enynes with an all-carbon quaternary center that can be used as immediate synthetic precursors for complex cyclic molecules. Notably, a Meyer-Schuster rearrangement was involved in the reactions using propargylic alcohols, resulting in an unprecedented acylation-allylation of carbenes. Mechanistic studies suggested that in the course of the reaction Cu(I) species might aggregate to some types of Cu clusters and nanoparticles (NPs), while the Rh(II) precursor can dissociate to mono-Rh species, wherein Cu NPs are proposed to be responsible for the alkynylation of carbenes and work in cooperation with Xantphos-coordinated dirhodium(II) or Rh(I)-catalyzed allylic alkylation.