Rh-catalyzed Asymmetric Addition Of Arylboric Acids To β,γ-unsaturated Keto Esters

Chiral γ,γ-diaryl substituted carbonyl compounds and α-hydroxyesters with quaternary carbon chiral centers are widely found in natural products and bioactive molecules,so the development of efficient methods to synthesize these compounds has aroused extensive attention.Rhodium-catalyzed asymmetric addition of arylboric acids to electron-deficient olefins,ketones and imines is one of the most effective way to build C-C bonds.There will be competitive reactions for rhodium-catalyzed asymmetric addition of arylboric acid to β,γ-unsaturated α-keto easters because they might be subjected to 1,2-addition and 1,4-addition simultaneously,which can be used to construct chiral γ,γ-diaryl substituted carbonyl compounds and α-hydroxy esters with quaternary carbon chiral centers in one step.The most important and difficult thing is to control the reaction sites of β,γ-unsaturated α-keto esters.In order to solve this problem,through screening several types of chiral olefin ligands and optimizing the substrates,the 1,2-/1,4-site selective and enantioselective addition of arylboric acids to β,γ-unsaturated keto esters has been successfully realized,which includes the following sections: Under the catalysis of rhodium/chiral diene ligands,1,4-adducts have been obtained with brode substrate scopes and excellent site-selectivity and enantioselectivity(up to 99% ee).Under the catalysis of rhodium/chiral sulfur-based olefin ligands,α-hydroxyesters with quaternary carbon chiral centers have been obtained in almost quantitative yield and excellent enantioselectivity,and achieved the 1,2-addition of arylboric acids to β,γ-unsaturated keto esters.