Synthesis of chiral boranes via asymmetric insertion of carbenes into B–H bonds catalyzed by the rhodium(I) diene complex.

Molecules with chiral boron atoms have been scarcely studied due to limited synthetic access. Herein, we report a new method for their synthesis via asymmetric insertion of arydiazoacetates into the B–H bonds of prochiral carbene–boranes NHC–BH2R. The reaction is catalyzed by the rhodium(I) complex with the chiral diene ligand tBu2-TFB, which can be conveniently prepared by diastereoselective coordination of the racemic diene with (S-Salox)Rh(CO)2. The target boranes were typically obtained in 75–90% yields with 90–95% ee. [ABSTRACT FROM AUTHOR]