Chiral Cobalt(II) Complex Catalyzed Asymmetric [2,3]-Sigmatropic Rearrangement of Allylic Selenides with alpha-Diazo Pyrazoleamides

Organoselenium compounds, due to their high structural diversity, special function, and biological activities, have drawn attention in synthetic chemistry. Herein, a novel example of chiral N,N'-dioxide/ cobalt(II) complex catalyzed asymmetric [2,3]-sigmatropic rearrangement of allylic selenides with a-diazo pyrazoleamides is disclosed, which represents a highly efficient approach to optically active selenides bearing a quaternary C-Se stereocenter. Most of the reactions proceed with 0.5-2 mol % catalyst loading in an inert-free gas atmosphere, and a wealth of chiral selenides are obtained in up to 99% yield and 97% enantiomeric excess (ee). The control experiments demonstrate the high reactivity of allylic selenides, as well as the conspicuous superiority of chiral N,N'-dioxide ligand and a-diazo pyrazoleamide in [2,3]-sigmatropic rearrangement. The mechanism studies reveal that the key to asymmetric rearrangement of allylic selenium ylides is the transfer of chirality from the stable chiral selenium to the carbon of the product. A feasible catalytic cycle is proposed as well.