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.