CO2-Controlled Reductive Amination Reactions with NaBH4

We report the use of CO2 to curb the reactivity of NaBH4 enabling its use in reductive amination reactions. CO2 readily reacts with NaBH4 to decrease its capacity to reduce aldehydes to alcohols while remaining able to reduce imines and iminium ions for desired alkylation reactions. The formation of NaBH(OCHO)(3) as a reducing reagent was critical to achieve the desired selectivity. A general protocol was established for C-N bond formation reactions and replacing NaBH4 with NaBD4 allowed for reductive amination with concomitant deuteration to be carried out.