Hydrogen Bond Enhanced Enantioselectivity in the Nickel-Catalyzed Transfer Hydrogenation of α-Substituted Acrylic Acid with Formic Acid
Yaxin Sun, Chao Wang, Peng Yang, Jieyu Yue, Chang Xu, Jianrong Steve Zhou, Bo Tang
Abstract
A chiral nickel complex that catalyzed asymmetric transfer hydrogenation of α-substituted acrylic acids under mild conditions and avoided the use of high-pressure hydrogen gas was developed. The products included chiral β-amino acids and α-methyl carboxylic acids such as three nonsteroidal anti-inflammatory profens. Deuterium-labeling experiments and DFT studies pointed to an unconventional protonation of a metalacyclopropane complex formed by α-phenylacrylic acid which was hydrogen bonded with formic acid. An alternative conventional pathway of nickel hydride insertion cannot explain selective deuteration at β-position of α-phenylacrylic acid when HCO 2 D was used.