Branched Amine Synthesis via Aziridine or Azetidine Opening with Organotrifluoroborates by Cooperative Bronsted/Lewis Acid Catalysis: An Acid-Dependent Divergent Mechanism

A practical catalytic method to synthesize beta,beta- and gamma,gamma-substituted amines by opening aziridines and azetidines, respectively, using alkenyl, alkynyl, or aryl/heteroaryl trifluoroborate salts is described. This reaction features simple open-flask reaction conditions, the use of transition-metal-free catalysis, complete regioselectivity, and high diastereoselectivity. Preliminary mechanistic studies suggest that carbocation formation is disfavored. Stereoretentive addition is favored with Bronsted acid present, while stereoinversion is favored in its absence, indicating divergent mechanisms.