DIC-borane-catalyzed selective methylation of primary amines with CO2 using boranes as reducing agents

The selective reductive N-methylation and N,N-dimethylation of primary amines using CO2 are some of the most significant challenges faced by organic chemists. Herein, we report the highly selective N,N '-diisopropylcarbodiimide-catalyzed methylation of primary amines using 1 atm CO2 under metal-free conditions. Borane-piperazine and borane-trimethylamine complexes were used as reducing agents for the N-methylation and N,N-dimethylation of various aromatic primary amines, respectively, in the presence of CO2. Mechanistic studies suggest that the selectivity of methylation is controlled by the steric effects of amines and boranes.