Organoboranes are among the most widely and frequently used compounds in morden organic synthesis, materials science, drug discovery and other fields. Although much effort has been made in recent years, new strategy for preparation of versatile chiral organoboranes remains rare. 

Recently, Prof. XU Minghua and his co-workers at Shanghai Institute of Materia Medica of Chinese Academy of Sciences succeeded in the development of the first Rh(I)-carbene-mediated asymmetric B-H insertion reaction of α-diazo carbonyl compounds with readily available amine-borane adducts. This Rh(I)-catalyzed process using novel C1-symmetric chiral diene ligands allows practical construction of stereogenic C-B bonds in a highly enantioselective manner under exceptionally mild conditions.

It has been demonstrated that rhodium(I) complexes with diverse chiral ligands are efficient catalysts for various asymmetric reactions, however, the related Rh(I)−carbene chemistry is far less studied. In continuing the interest in rhodium(I)/olefin chemistry, XU's group conceived the possibility of performing the asymmetric metal−carbene insertion into B−H bonds using Rh(I) complex with proper olefin-chelating ligand as catalyst. After careful examinations, they successfully discovered that a variety of α-diazoesters and ketones can be efficiently converted into the corresponding α-boryl products in high yields with excellent enantioselectivities under unprecedented rhodium(I)/diene catalysis at room temperature. 

This finding provided a promising approach to the synthesis of enantiomerically enriched functionalized organoboranes. Notably, the use of easily accessible and inexpensive amine-borane adduct as boron source makes the new method particularly attractive and practical. 

This work has been published in the Journal of the American Chemical Society (JACS) as a cover paper. It has also been selected by the JACS Editorial Office as a feature in JACS Spotlights (Chiral Organoboranes from B-H Insertion by Carbenes, 2015, 137(16), 5239). In addition, the work is highlighted by Synfacts (2015, 11, 502) for its significance in the area.

Figure: The cover paper of JACS (Image by American Chemical Society Publications)