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 trans-position (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, and scalability. In this Communication, we report a nickel-catalyzed plat-form for the stereodivergent E- or Z-selective synthesis of internal alkenes at room temperature. Under the developed protocols, conjugated and non-conjugated products that contain sensitive functional groups can be obtained in high yield and isomeric purity using commercially available catalysts and reagents. Notable mechanistic discoveries include the substoichiometric addition of an aryl iodide to enhance reactivity and selectivity for the synthesis of Z-isomers and the unusual finding of a phosphonium salt to enhance E-selectivity that we hope will inspire new perspectives on how these reagents interact with nickel centers.

A Hydride Migration Mechanism for the Mo‐Catalyzed Z‐2‐Selective Isomerization of Terminal Alkenes

“…A few Z-selective approaches overcome the thermodynamic preference for E and offer facile access to Z alkenes of synthetic value, including thermal [15,[22][23][24][25][26][27][28] and photocatalytic E-to-Z methods. [29][30][31] The one-bond transposition, or isomerization, of 1-alkenes to Z-2-alkenes [2,4,9,[32][33][34][35][36] is a promising approach (Scheme 1). [37] However, while one-bond alkene transposition of 1-alkenes is energetically downhill, targeting specific isomers remains a challenge.…”

Electroreductive Synthesis of Nickel(0) Complexes**

“…Lastly, the Z-selective olefin transposition of terminal olefins was undertaken (Scheme 5E). [36] Using the in situ reduction protocol, an alkenyl chloride, allyl arene, and homoallyl arene underwent the Z-selective alkene transposition in moderate yields and selectivities (15)(16)(17). All the selected examples were unsuccessful without electrolysis.…”

Electroreductive Synthesis of Nickel(0) Complexes

“…With slight modifications from previously described conditions, a catalytic amount of Ni(acac)2 was electrochemically reduced in the presence of terminal olefin, ligand, and additive (Scheme 4B). [25] Using the in-situ reduction protocol, an alkyl chloride, allyl arene, and homoallyl arene underwent the Zselective alkene transposition in moderate yields and selectivities (1Z, 2Z, 3Z).…”