Crab-shape C2-symmetric chiral Tpy-bisulidine ligands: design, synthesis and application in diversity-oriented asymmetric catalysis

Abstract

Terpyridine-type ligands are renowned for their rich coordination with various metal ions. However, their high cost and tedious preparation methods limit their further application in asymmetric catalysis. Herein, we report the preparation of diverse crab-shape C₂-symmetric chiral terpyridine-tethered bisulidine ligands (abbreviated as Tpy-bisulidines), readily derived from optically pure sulfonylated 1,2-diphenylethylenediamine, in an operationally simple one-step process with yields of up to 57%. They were proven to be a class of efficient chiral ligands for Ni(II)-catalyzed asymmetric inverse-electron-demand Hetero-Diels–Alder (HDA) reactions between β,γ-unsaturated α-ketoesters and electron-rich alkenes, such as 2,3-dihydrofuran and enecarbamates, affording the products with excellent enantioselectivities. In addition to the HDA reaction, the in situ-generated chiral Tpy-bisulidines/Ni(OTf)₂ complex was also applied in the asymmetric Michael addition, Friedel–Crafts alkylation and Mukaiyama–Michael reactions, achieving high stereoselectivities. These findings demonstrate the promising potential of the Tpy-bisulidine ligand as a privileged ligand for diversity-oriented asymmetric catalysis.