Stereodivergent, Kinetically Controlled Isomerization of Terminal Alkenes via Nickel Catalysis.

ABSTRACT

Because internal alkenes are more challenging synthetic targets than terminal alkenes, metal-catalyzed olefin mono-transposition (i.e., positional isomerization) approaches have emerged to afford valuable E- or Z- internal alkenes from their complementary terminal alkene feedstocks. However, the applicability of these methods has been hampered by lack of generality, commercial availability of precatalysts, and scalability. Here, we report a nickel-catalyzed platform for the stereodivergent E/Z-selective synthesis of internal alkenes at room temperature. Commercial reagents enable this one-carbon transposition of terminal alkenes to valuable E- or Z-internal alkenes via a Ni-H-mediated insertion/elimination mechanism. Though the mechanistic regime is the same in both systems, the underlying pathways that lead to each of the active catalysts are distinct, with the Z-selective catalyst forming from comproportionation of an oxidative addition complex followed by oxidative addition with substrate and the E-selective catalyst forming from protonation of the metal by the trialkylphosphonium salt additive. In each case, ligand sterics and denticity control stereochemistry and prevent over-isomerization.