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

Abstract

Compared with an enormous amount of reactions of the B-H bond of the Lewis base BH3 adducts, the reactions of the B-H bond of the multinuclear boranes have been less studied, probably relative to the distinct nature of the B−H bond in the BH3 moiety and in the 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 diazos. 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-Diazos to form both bottom B(2,3)-disubstituted triborane products. Moreover, this synthesis method is also applicable to ¹⁰B-labeled Lewis base-¹⁰B3H7 adduct to synthesize ‘targeted drugs’ suitable for boron neutron capture therapy (BNCT).