DuPhos

DuPhos is a class of asymmetric ligands for asymmetric synthesis. The name DuPhos is derived from the chemical company that developed this type of ligand (DuP, DuPont) and the compound class of phospholanes (Phos) it belongs to. This diphosphine ligand type was introduced in 1991 by M.J. Burk and first demonstrated in asymmetric hydrogenation of certain enamide esters to amino acid precursors:

Other phosphine asymmetric ligands were known at the time (DIPAMP, BINOL, CHIRAPHOS) but the new ligand was found to be more effective.

The ligand consists of two 2,5-alkyl-substituted phospholane rings (the phosphorus analog of THF) connected via a 1,2-phenyl bridge. The alkyl group can be methyl, ethyl, propyl or isopropyl. In the closely related bis(dimethylphospholano)ethane or BPE ligand the o-phenylene bridge is replaced by an 1,2-ethylene bridge. Both compounds can be obtained from the corresponding chiral diol through conversion to the cyclic sulfate and reaction with lithiated phenylbisphosphine. In DuPhos the phosphorus atoms are electron-rich making the resulting metal complexes reactive. The phosphorus atoms also introduce a kind of pseudo-chirality making enantioselection independent of the overall chemical conformation

Another early application is the synthesis of unnatural chiral amino acids in a formal reductive amination for example starting from benzophenone and the hydrazone of benzoyl chloride:

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