Relay Catalysis by Achiral Borane and Chiral Phosphoric Acid in the Metal-Free Asymmetric Hydrogenation of Chromones
Jingjing Chen, Bochao Gao, Xiangqing Feng, Wei Meng, Haifeng Du
Abstract
A strategy of relay catalysis by achiral borane and chiral phosphoric acid was successfully developed for the asymmetric hydrogenation of chromones, giving the desired products in high yields with up to 95% ee. Achiral borane and chiral phosphoric acid are highly compatible in this reaction. The achiral borane acts as a Lewis acid for the first-step hydrogenation, and the chiral phosphoric acid acts as an effective chiral proton shuttle to control the enantioselectivity.
Topics & Concepts
BoraneChemistryPhosphoric acidCatalysisLewis acids and basesOrganic chemistryAsymmetric hydrogenationCombinatorial chemistryEnantioselective synthesisOrganoboron and organosilicon chemistryAsymmetric Hydrogenation and CatalysisChemical Synthesis and Analysis