α‑Methylation of 2‑Arylacetonitrile by a Trimethylamine-Borane/CO₂ System

A highly selective monomethylation of 2-arylacetonitrile using CO₂ is described. The utilization of trimethylamine-borane facilitates the six-electron reduction of CO₂. This reaction is the first selective six-electron reductive functionalization of CO₂ faciliated by C­(sp³)–H bonds. A variety of 2-arylpropionitrile was obtained in good yields. The reaction could also be applied at the gram scale.