Addition of borane-protected secondary phosphines to imines. A route to protected mono-N-substituted-α-aminophosphines

Addition of a secondary phosphine–borane adduct to imines was examined in order to improve the synthesis of mono-N-substituted-α-aminophosphines. The reaction demonstrates, for the first time, successful addition of a phosphine–borane to a multiple carbon–nitrogen bond. The process tolerates a range of substituents on the imine and results in an efficient formation of a borane-protected α-aminophosphine. Borane protects the aminophosphine and improves the reliability of the Mannich-like phosphine addition to imines.