Copper Catalyzed Highly Enantioselective B–H Insertion of α-Alkynyl-α-silyl Carbenes for the Synthesis of Chiral Propargylic gem -Silylboranes

Abstract Chiral gem-silylboronates represent a class of pivotal gem-dimetallic reagents in organic chemistry. Despite various synthetic methods emerged recently, the structural diversity of gem-silylboronates remains largely confined to alkyl-, (hetero)aryl-, and alkenyl-substituted variants; notably, alkynyl-substituted counterparts have remained largely underexplored. Herein, we report a Cu(I)/chiral bisoxazoline-catalyzed asymmetric insertion of α-alkynyl silyl carbenes into B–H bonds, affording a series of propargyl chiral gem-silylboronates and thus expanding the repertoire of organo-gem-dimetallics. This protocol features mild reaction conditions, broad functional group tolerance, and diverse downstream transformations, demonstrating significant synthetic utility. Furthermore, mechanistic experiments and theoretical calculations elucidate that the reaction proceeds via a concerted carbene insertion into the B–H bond, which likely serves as the rate-determining step. The enantioselectivity arises mainly from the shielding of the carbene Re face by the aryl groups on the oxazoline indenyl moiety, directing borane attack to the Si face, with additional enhancement from π–π interactions between the pyridine and indene rings. This work provides an efficient approach to chiral propargyl gem-silylboronates, further enriching the structural diversity and synthetic potential of chiral organosilicon–boron chemistry.