β-Boron or β-Silicon Effect Enables a Regioselective Ni-Catalyzed Hydrocyanation of Internal Alkynes

Abstract

Transition-metal-catalyzed hydrocyanation of alkynes offers a straightforward and atom-economic method to access alkenyl nitriles. However, achieving regio-control remains challenging, especially for unsymmetric di-alkyl substituted inter-nal alkynes. In this study, we investigate the use of propargylic B(MIDA)s or silanes as substrates in an earth-abundant nickel-catalyzed hydrocyanation reaction. The reaction employs AIBN (2,2'-azobis(2-methylpropionitrile)) as a low-toxicity H-CN source and 1,4-dioxane or ethyl acetate as reaction solvent. The presence of β-boron or β-silicon groups induces a strong directing effect, favoring cyano group installation at the carbon adjacent to the boryl or silyl substituent. Mechanistic investigations reveal that this regioselectivity arises from the increased nucleophilicity of the γ-carbon and the protic nature of the hydrogen in the Ni–H complex. Addi-tionally, a notable hyperconjugative σ(C–B)→σ*(C–Ni) interaction provides a thermodynamic driving force that further enhances regioselectivity. The resulting regio- and stereodefined products serve as versatile intermediates for the synthesis of a wide range of valuable molecules.