The mechanism investigation of chiral phosphoric acid-catalyzed Friedel–Crafts reactions – How the chiral phosphoric acid regains the proton

ONIOM method was used to investigate the mechanism of chiral phosphoric acid-catalyzed Friedel–Crafts reactions of pyrrole derivatives and imines. In the reaction of imine with pyrrole, regarding to the step of the regeneration of the chiral phosphoric acid catalyst has not been discussed in details. We are interested in how the chiral phosphoric acid regains the proton in this reaction. Through our results, the catalyst gets back a proton from the CH bond of pyrrole, not from the NH bond of pyrrole. In the real system of imine and N-methylpyrrole reaction, the most stable structure of TS2 is the (R)-product with its Si face, which is formed by N-methylpyrrole with E-s-cis imine with the high ee value 90%.