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-BH 2 R. The reaction is catalyzed by the rhodium(I) complex with the chiral diene ligand t Bu 2 -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.