gem-Difluorination of Aminoalkynes via Highly Reactive Dicationic Species in Superacid HF−SbF5:  Application to the Efficient Synthesis of Difluorinated Cinchona Alkaloid Derivatives

A variety of alkynylated amines, amides, and imides are reacted in the superacid system HF−SbF5 to give regioselectively new β-gem-difluoroamines. The reaction, which is not observed in pure HF, is consistent with the formation of a dicationic intermediate (i.e., both vinylic and adjacent protonated N-ammonium cations). Application to the regioselective and efficient synthesis of difluorinated cinchona alkaloid derivatives is described.