Mechanism and origins of ligand-controlled regioselectivity of copper-catalyzed borocarbonylation of imines with B2pin2 and alkyl iodides: a computational study

Density functional theory calculations have been performed to investigate the copper-catalyzed borocarbonylation of imines with B(2)pin(2) and alkyl iodides. The computations reveal that the reaction is initiated by the selective migratory insertion of the C-N double bond into the Cu-B bond to forge the key alpha-boryl amido-copper complex, which could undergo the 1,2-rearrangment via a stepwise dearomatization-rearomatization pathway to give alpha-amino alkyl-copper species. From these intermediates, the following C-I bond cleavage of alkyl iodide through halogen-atom abstraction, radical association, and reductive elimination would lead to alpha-boryl amide and alpha-amino ketone products. The regioselectivity of the overall reaction is determined by the competition between the 1,2-rearrangement and C-I bond cleavage from the alpha-boryl amido-copper complex. The experimentally observed ligand-controlled regioselectivity is reproduced very well by the computations, which is rationalized on the basis of CuMIDLINE HORIZONTAL ELLIPSISO interaction and Cu-N bond strength.

Automated summary

Density functional theory calculations were used to investigate the mechanism of copper-catalyzed borocarbonylation of imines with B(2)pin(2) and alkyl iodides. The calculations showed that the reaction starts with the selective migratory insertion of the C-N double bond into the Cu-B bond to form the key alpha-boryl amido-copper complex, which can undergo a stepwise rearrangement to give alpha-amino alkyl-copper species. The C-I bond cleavage of alkyl iodide through halogen-atom abstraction, radical association, and reductive elimination leads to the formation of alpha-boryl amide and alpha-amino ketone products. The regioselectivity of the reaction is determined by the competition between the 1,2-rearrangement and C-I bond cleavage from the alpha-boryl amido-copper complex, which is in good agreement with experimental observations.