Enantioselective 1,4-addition of diarylphosphine oxides to α,β-unsaturated ketones catalyzed by oxazaborolidines

Classical proline-derived oxazaborolidines as powerful and versatile organocatalysts (CBS, Corey-Bakshi-Shibata) have significant applications in asymmetric catalysis, especially in enantioselective reduction of prochiral ketones and various asymmetric cycloaddition reactions. Despite having been well-studied, their new applications are still very attractive and challenging. Hence, in this research, we disclose a new strategy for the asymmetric carbon-phosphorus bond forming reaction by using CBS catalysts via non-covalent interactions. Notably, various alpha,beta-unsaturated ketones as substrates showed remarkable tolerance to various diarylphosphine oxides. A new application of oxazaborolidines in enantioselective phospha-Michael addition to alpha,beta-unsaturated ketones under mild reaction conditions was developed and the possible mechanism is described.