<i>gem</i>-Difluorination of Aminoalkynes via Highly Reactive Dicationic Species in Superacid HF−SbF<sub>5</sub>: Application to the Efficient Synthesis of Difluorinated Cinchona Alkaloid Derivatives
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.