B/Cu Synergistic Catalysis for the Asymmetric Mannich Reaction between β,γ-Alkynyl-α-ketimino Esters and Ortho-Hydroxy Aryl Ketones.

Herein, we present a B/Cu-catalyzed asymmetric Mannich reaction, utilizing β,γ-alkynyl-α-ketimino esters and ortho-hydroxy aryl ketones. The reaction initiates with the activation of ortho-hydroxy aryl ketones via borinic acid to form a tetracoordinated enol boronate complex, followed by a chiral Cu complex-assisted reaction with an electrophilic ketimino ester. The reaction also works with alkyl-chained ortho-hydroxy aryl ketones, producing Mannich adducts with moderate to good diastereoselectivity. The practical applicability is evidenced by a gram-scale reaction and subsequent elaboration of the Mannich adduct.