Synthesis of Cinchonine Quaternary Ammonium Salts and the Catalysis of Asymmetric Alkylation

Eleven catalysts bearing a free hydroxyl group were prepared by direct N-alkylation with corresponding substituted benzyl bromides under a reflux condition in good yields(57%-88%). Other 4 catalysts with the chiral secondary alcohol protected by ally!, benzyl, propynyl and benzoyl were synthesized via two steps. The ether group at the phase-transfer catalysts could be approached before or after the N-benzylation reaction. In contrast, the hydroxyl group was changed to benzoic acid ester when the quaternary ammonium salt had been prepared. Fifteen phase-transfer catalysts were gotten, and 5 catalysts of them had never been reported. Then, various catalysts were screened for alkylating reactivity of glycine imine ester. Cinchonine derived catalysts Cn-9 proved to be highly reactive in 93% yield with 91% e. e. value.