Reductive Amination with 2-picoline-borane Complex

One-pot reductive amination of aldehydes and ketones is an important transformation in organic chemistry, and several common reducing agents are available for the direct conversion of carbonyl products into amines. However, many of these reagents have limitations (i.e., require significant excess of amine, necessitate the use of organic solvents, or cannot be used in large-scale applications) that restrict their use.

It has been recently reported¹ that 2-picoline-borane (pic-BH₃) is an excellent alternative reagent for reductive aminations. Pic-BH₃ is a stable solid that can be stored for long periods without detectable decomposition. Furthermore, this reagent is effective at direct reductive aminations in methanol, water, or even solvent-free conditions (Scheme 1).

Reactions in water proceed in good yields for poorly water-soluble amines, but not for highly water-soluble amines. Reductive aminations also proceed in good yields for selected secondary amines.