Synthesis Chooses Article by Chemistry Prof. William Wulff's Group as Cover Highlight
A recent paper by Chemistry Prof. William Wulff and colleagues has been chosen as
Cover Article by the journal Synthesis.
In the article, Prof. Wulff’s group reports for the first time the structure of a VANOL-BOROX catalyst-substrate complex as determined by x-ray diffraction. This confirms the formation of a six-membered boroxine ring with three borons and three oxygens when the VANOL ligand is treated with a boron source, water and phenol, and then an imine, as previously characterized by NMR methods. In addition, they confirmed one of the borons is bonded to a fourth oxygen and thus the overall catalyst has a negative charge that is balanced by an iminium ion.
The BOROX catalyst is effective in promoting several different reactions of imines, and in this paper (see cover) this is illustrated with the formation of aziridines from imines and diazoacetates. The importance of the determination of this structure is that it both confirms the presence of the boroxine ring and also reveals several interactions between the catalyst and the bound imine substrate. There is a bifurcated hydrogen bond between the hydrogen of the protonated imine and two of the oxygens of the catalyst. In addition, there are CH-πinteractions between the catalyst and the substrate. Understanding these structures will be very important for determining how the imine and diazoacetate get together to form aziridines.
Most of the reactions in this paper were run by Prof. Wulff’s graduate student, Yong Guan. The crystals were grown by Dr. Zhenjie Lu, and the structure was solved by Dr. Richard Staples in the Chemistry Department’s X-ray Diffraction Facility.
“Catalytic Asymmetric Aziridination of Benzhydryl Imines and Diazoacetate Esters with BOROX Catalysts from 3,3′-Disubstituted VANOL Ligands”, Yong Guan, Zhenjie Lu, XiaopengYin, Aliakbar Mohammadlou, Richard J. Staples and William D. Wulff, Synthesis,2020, 52, 2073-2091.
