Novel Cinchona alkaloid derived ammonium salts as catalysts for the asymmetric synthesis of β-hydroxy α-amino acids via aldol reactions

Using the cinchonidine-derived phase-transfer catalyst developed by Park and Jew as a lead structure, we have prepared novel chiral ammonium salts and investigated their efficacy for the preparation of β-hydroxy α-amino acids via asymmetric aldol reactions. The modifications were performed at C3 of the cinchonidine nucleus and include dimers as well as catalysts possessing electron-deficient alkyne and alkene moieties. Some of the new catalysts yielded improvements relative to the Park–Jew catalyst in the aldol reaction.