A copper-catalyzed B–H bond insertion reaction of triboranes (L·B3H7) with diazo compounds

Abstract

Compared with the enormous amount of reactions of the B–H bond of Lewis base BH₃ adducts, the reactions of the B–H bond of multinuclear boranes have been less studied, probably related to the distinct nature of the B–H bond in the BH₃ moiety and multinuclear boranes. Herein, we report a protocol for the highly regioselective functionalization of triborane, the oldest multinuclear borane, via copper-catalyzed B–H bond insertion reactions with diazo compounds. A variety of beneficial organoboron compounds are synthesized with generally high yields, broad substrate versatility, and robust functional group compatibility under gentle reaction conditions. Notably, the B–H bond in the reactions is highly selective, located at the bottom B(2) position of the triboranes, leading to the formation of compounds with boron-stereogenic centers. The B(2)-substituted triborane product can continue to react with α-diazo compounds to form both bottom B(2,3)-disubstituted triborane products. Moreover, this synthesis method is also applicable to ¹⁰B-labeled Lewis base-¹⁰B₃H₇ adducts to synthesize ‘targeted drugs’ suitable for boron neutron capture therapy (BNCT).