Nickel‐Catalyzed Asymmetric Three‐Component Reaction of Unactivated Alkyl Halides, 1,3‐Enynes and Aldehydes

Abstract The π‐propargylnickel(II) complexes, or their resonances, the η 1 ‐allenylnickel(II) ones, are typically generated from propargylic derivatives under Ni 0 catalysis, and act as versatile electrophilic partners in diverse transformations. Here, we demonstrate that η 1 ‐propargylnickel(II) species can alternatively be generated from unactivated alkyl halides and 1,3‐enynes via a Ni 0 ‐mediated radical alkylation of the alkene. Subsequent isomerization to η 1 ‐allenylnickel(II), followed by reduction, affords η 1 ‐allenylnickel(I) intermediates, which serve as reliable nucleophilic species for the stereoselective addition to aldehydes in the presence of benzoic acid. This protocol features broad substrate scope and good functional group tolerance, and nickel plays multiple roles in accomplishing a complicated Ni 0 /Ni I /Ni II /Ni I /Ni 0 catalytic cycle. A wide range of chiral homopropargylic alcohols, even the ones having a medium‐sized ring, are modularly furnished in fair to good yields with moderate to excellent diastereo‐ and enantioselectivity. A series of control experiments and density functional theory (DFT) calculations are conducted to illuminate the catalytic pathways and the origin of regio‐ and stereoselectivity.