ChiralQuest Phosphine Ligands

ChemFiles Volume 5 Article 10

The field of asymmetric catalysis has been primarily represented by methodologies that have focused on incorporating hydrogen in a stereoselective manner into achiral molecules, especially in industrial applications. It is well known that hydrogen is the most common constituent in the immense realm of stereogenicity. Catalytic asymmetric hydrogenations are among the most widely used industrial catalytic processes due to their high turnover rates, efficiency, atom economy, and inexpensive material costs. Transition metal complexes associated with chiral phosphorus ligands are the preeminent choice of catalysts for asymmetric hydrogenation as a result of the tremendous efforts of researchers worldwide. The requirement of an electron-rich chiral phosphine ligand is at the core of this transformation.

Professor Xumu Zhang at Penn State has made remarkable advances by creating a toolbox of chiral phosphines that can be used on a variety of substrates, some of which have been historically resistant to facile hydrogenation.1 Furthermore, an additional benefit in some reductions is reduced catalyst loading due to increased turnover numbers (TON). Sigma-Aldrich is pleased to announce an agreement with ChiralQuest to distribute research quantities of a series of Zhang’s chiral phosphines and metal–ligand complexes for catalytic asymmetric hydrogenations (Schemes 21–25).

C3-TunePhos, a member of the atropisomeric aryl bisphosphine ligand family with tunable dihedral angles, provides comparable or superior enantioselectivities and catalytic abilities to BINAP in Ru-catalyzed asymmetric hydrogenation of b-ketoesters, cyclic b-(acylamino) acrylates, and a-phthalimide ketones (Scheme 21).

A highly electron-donating, low molecular weight, and rigid P-chiral bisphospholane ligand, TangPhos proves highly efficient in the rhodium-catalyzed hydrogenation of a variety of functionalized olefins such as a-dehydroamino acids, a-arylenamides, b-(acylamino)- acrylates, itaconic acids, and enol acetates (Schemes 22–23).

Binapine, a highly electron-donating rigid ligand, demonstrates excellent enantioselectivity and reactivity, with TON up to 10,000 for the asymmetric hydrogenation of Z-b-aryl(b-acylamino) acrylates (Scheme 24).

(R)-Binaphane shows excellent enantioselectivity (up to >99% ee) for hydrogenation of E/Z-isomeric mixtures of b-substituted arylenamides (Scheme 25).

Scheme 21

Scheme 22

Scheme 23

Scheme 24

Scheme 25

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Materials

     

References

  1. (a) Zhang, Z. et al. J. Org. Chem. 2000, 65, 6223. (b) Tang, W. et al. J. Am. Chem. Soc. 2003, 125, 9570. (c) Lei, A. et al. J. Am. Chem. Soc. 2004, 41, 1612. (d) Tang W. et al. Angew. Chem., Int. Ed. Engl. 2002, 41, 1612. (e) Tang, W. et al. Org. Lett. 2002, 4, 4159. (f) Tang, W. et al. Angew. Chem., Int. Ed. Engl. 2003, 42, 3509. (g) Xiao, D. et al. Org. Lett. 1999, 1, 1679.

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