Monotrifluoroacetoxyborane-amines: chemoselective reagents for challenging reductive aminations.

Borane-amines undergo exclusive monoacetoxylation to trifluoroacetoxyborane-amines (TFAB-amines), which serve as chemoselective reagents for direct reductive amination of aldehydes and ketones. TFAB-NEt3 has been established as mild and highly selective compared to widely-used NaBH3CN and Na(AcO)3BH, even at higher temperatures with challenging substrates. A mechanism involving polyaminoborane formed via dehydroacetoxylation of TFAB-NH3 has been described.