Cobalt-catalyzed asymmetric phospha-Michael reaction of diarylphosphine oxides for the synthesis of chiral organophosphorus compounds

Abstract

The asymmetric Michael addition of phosphorus nucleophiles to electron-deficient alkenes is one of the most direct and atom-economical methods to provide chiral organophosphorus compounds with high efficiency in recent years. Herein, we report a cobalt-catalyzed imidazolyl-directed asymmetric phospha-Michael-type reaction of diarylphosphine oxides with electron-deficient alkenes for synthesizing chiral organophosphorus compounds in moderate to good yields and good to excellent enantioselectivities (25 examples, up to 99% yield, and 99% ee). This protocol features broad substrate scope, good functional group tolerance, and mild conditions as well as avoids the release of massive metal wastes and the use of noble transition metal catalysts. The excellent enantioselectivity of the phospha-Michael reaction can be due to the adoption of a novel chiral N4-ligand. Furthermore, the DFT calculation indicates that the bulky 2,4,6-(i-Pr)₃C₆H₂ group of the ligand induces large steric hindrance which blocks the nucleophilic attack from the Si-face.