A Chiral Bis(arsine) Ligand: Synthesis and Applications in Palladium-Catalyzed Asymmetric Allylic Alkylations

The new chiral bis(arsine) ligand N,N'-bis[2'(diphenylarsino)benzoyl]-(1R,2R)-cyclohexanediamine (BiAsBA, 3), based on the backbone of the Trost modular ligand (TML), was synthesized in three steps. A useful approach to introduce the -AsPh2 group on arsine ligands by Pd-catalyzed arsination was used. The molecular structure and configuration of the BiAsBA ligand was determined by single-crystal X-ray crystallography. In the asymmetric allylic alkylation of 1,3-diphenyl-2-propenyl acetate with dimethyl malonate very high to complete conversion and modest enantioselectivity were achieved. Despite the low enantioselectivity obtained, the bis(arsine) ligand BiAsBA showed significant potential, since it provided a higher ee value than the phosphorus-containing homologous "Trost standard ligand" (TSL) with the same substrate.