DuPhos

Description

The ligand consists of two 2,5-alkyl-substituted phospholane rings connected by 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 a 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:

:[[File:ReductiveAminationDuPhosBurk1994.svg|580px|Reductive Amination DuPhos Burk 1994]]

In the original scope the metal catalyst was rhodium but catalysis by ruthenium was introduced in 1995 with the hydrogenation of the ketone group in β-keto esters:

:[[File:HydrogenationketoesterDuPhosGenet1994.svg|415px|Hydrogenation ketoester DuPhos Genet 1994]]

Applications

An application of an asymmetric synthesis with a DuPhos ligand is the hydrogenation of dehydrowarfarin to warfarin:

:[[File:WarfarinSynthDuPhos.svg|536px|Warfarin synthesis]]

Duphos is also applied in the synthesis of tryptophan derivatives.

In polymerization catalysis

DuPhos ligands are used in metal catalyzed alpha-olefin/carbon monoxide copolymerization to form chiral isotactic polyketones. The first publication in this field dates back to 1994 with catalyst system Pd(Me-DuPhos(MeCN)2)2

BozPhos ligand

Mono oxidation of (R,R)-Me-Duphos using borane dimethylsulfide as protective group and hydrogen peroxide as oxidizing agent gives bozPhos This ligand is useful in copper-catalyzed asymmetric addition of diorganozinc reagents to N-diphenylphosphinoylimines.

References

References

1. Mark J. Burk. (1991). "C₂-symmetric bis(phospholanes) and their use in highly enantioselective hydrogenation reactions". [[J. Am. Chem. Soc.]].
2. Mark J. Burk. (1993). "Preparation and use of C₂-symmetric bis(phospholanes): production of .alpha.-amino acid derivatives via highly enantioselective hydrogenation reactions". Journal of the American Chemical Society.
3. ''New electron-rich chiral phosphines for asymmetric catalysis'' Mark J. Burk, John E. Feaster, Richard L. Harlow [[Organometallics]], '''1990''', 9 (10), pp 2653–2655 {{doi. 10.1021/om00160a010
4. New chiral phospholanes; Synthesis, characterization, and use in asymmetric hydrogenation reactions Tetrahedron: Asymmetry, Volume 2, Issue 7, '''1991''', Pages 569-592 Mark J. Burk, John E. Feaster, Richard L. Harlow {{doi. 10.1016/S0957-4166(00)86109-1
5. ''Recent Developments in Catalytic Asymmetric Hydrogenation Employing P-Chirogenic Diphosphine Ligands'' Karen V. L. Crépy, Tsuneo Imamoto Advanced Synthesis & Catalysis Volume 345 Issue 1-2, Pages 79 - 101 '''2003''' {{doi. 10.1002/adsc.200390031
6. ''Enantioselective hydrogenation of the C:N group: a catalytic asymmetric reductive amination procedure'' Mark J. Burk, John E. Feaster [[J. Am. Chem. Soc.]], '''1992''', 114 (15), pp 6266–6267 {{doi. 10.1021/ja00041a067
7. 10.1016/S0040-4020(01)89375-3
8. ''Practical asymmetric hydrogenation of β-keto esters at atmospheric pressure using chiral Ru (II) catalysts'' J. P. Genêt, V. Ratovelomanana-Vidal, M. C. Caño de Andrade, X. Pfister, P. Guerreiro and J. Y. Lenoir [[Tetrahedron Letters]] Volume 36, Issue 27, 3 July '''1995''', Pages 4801-4804 {{doi. 10.1016/0040-4039(95)00873-B
9. ''The first practical asymmetric synthesis of R and S-Warfarin'' Andrea Robinson and Hui-Yin Li John Feaster [[Tetrahedron Letters]] Volume 37, Issue 46, 11 November '''1996''', Pages 8321-8324 {{doi. 10.1016/0040-4039(96)01796-0
10. ''A highly enantioselective asymmetric hydrogenation route to β-(2R,3S)-methyltryptophan'' R. Scott Hoerrner, David Askin, R.P. Volante and Paul J. Reider [[Tetrahedron Letters]] Volume 39, Issue 21, 21 May '''1998''', Pages 3455-3458 {{doi. 10.1016/S0040-4039(98)00604-2
11. ''Palladium(II)-Catalyzed Isospecific Alternating Copolymerization of Aliphatic .alpha.-Olefins with Carbon Monoxide and Isospecific Alternating Isomerization Cooligomerization of a 1,2-Disubstituted Olefin with Carbon Monoxide. Synthesis of Novel, Optically Active, Isotactic 1,4- and 1,5-Polyketones'' Zhaozhong Jiang, Ayusman Sen [[J. Am. Chem. Soc.]], '''1995''', 117 (16), pp 4455–4467 {{doi. 10.1021/ja00121a003
12. Alexandre Côté. (2006). "Preparation of enantiomerically pure (''R'',''R'')-BozPhos".
13. Jean-Nicolas Desrosiers. (2006). "Preparation of enantiomerically enriched (1''S'')-1-Phenylpropan-1-amine hydrochloride by a catalytic addition of diorganozinc reagents to imines".