Chiral DuPHOS

The numerous chiral phosphine ligands which are available to date [21] can be subclassified into three major categories depending on the location of the chiral center ligands presenting axial chirality (e.g., BINAP 1 and MOP 2), those bearing a chiral carbon-backbone (e.g., DIOP 3, DuPHOS 4), and those bearing the chiral center at the phosphorus atom (e. g., DIPAMP 5, BisP 6), as depicted in Fig. 1. 

Significant advance in the field of asymmetric catalysis was also achieved with the preparation of l,2-bis(phospholano)benzene (DuPHOS 4) and its confor-mationally flexible derivative (l,2-bis(phospholano)ethane, known as BPE) by Burk et al. [59]. Two main distinctive features embodied by these Hgands, as compared to other known chiral diphosphine ligands, are the electron-rich character of the phosphorus atoms on the one hand and the pseudo-chirality at phosphorus atoms, on the other. These properties are responsible for both the high activity of the corresponding metal complex and an enantioselection indepen-... 

An iron complex-catalyzed asymmetric hydrosilylation of ketones was achieved by using chiral phosphoms ligands [68]. Among various ligands, the best enantios-electivities (up to 99% ee) were obtained using a combination of Fe(OAc)2/(5,5)-Me-Duphos in THF. This hydrosilylation works smoothly in other solvents (diethylether, n-hexane, dichloromethane, and toluene), but other iron sources are not effective. Surprisingly, this Fe catalyst (45% ee) was more efficient in the asymmetric hydrosilylation of cyclohexylmethylketone, a substrate that proved to be problematic in hydrosilylations using Ru [69] or Ti [70] catalysts (43 and 23% ee, respectively). 

Recently, the chiral Pt(0) precatalyst Pt[(R, R)-Me-Duphos](trows-stilbene) (11) has been used to prepare enantiomerically enriched chiral phosphines via hydrophosphination of acrylonitrile, t-butyl acrylate and related substrates. This chemistry is summarized in Scheme 5-13. 

The pharmaceutical industry has been giving increased attention to homogeneous asymmetric hydrogenation for the synthesis of chiral molecules due to significant improvements in this technology (1). We recendy synthesized a chiral a-amino acid intermediate using Et-DuPhos-Rh catalyst, obtaining enantiomeric pmities (EP) of... 

Using this technique, Brandts et al. (24-26) have successfully anchored two homogeneous catalysts, that is [(AyR)-(Me-DuPHOS)Rh(COD)]BF4 and the non-chiral [Rh(DiPFc)(COD)BF4],... 

Asymmetric hydrophosphination has been utilized as a route for preparing chiral phosphines. The Pt° complex [(Me-DUPHOS)Pt(t/ tf/ ,s-PhCII ClIPh)] (73) brings about the catalytic P-H addition of bulky secondary phosphines to activated alkenes with modest enantioselectivity. The most promising substrate combinations for further development appear to be bulky alkenes and less bulky phosphines (Scheme 46).195... 

Recently, a series of chiral diphosphines (S. -Me-Duphos, (S. -chiraphos, (R,R)-diop and (+)-Norphos were grafted after an ionic exchange onto Al-MCM-41 134 complexes of the form [Rh(cod)(diphosphine)]+ were tested for the hydrogenation of dimethylitaconate. The supported complex with (S,S)-methyl-Duphos reached an activity for the formation of dimethyl ( -methyl-succinate as high as TON = 4000 with an ee close to 92%. Both (R,R)-diop and (,S S )-chiraphos give lower enantioselectivities (ee = 34% and 47% respectively). With (+)-Norphos, dimethyl-([Pg.457]

Kovacik, I., Wicht, D.K., Grewal, N.S., Glueck, D.S., Incarvito, C.D., Guzei, I.A., and Rheingold, A.L., Pt(Me-Duphos)-catalyzed asymmetric hydrophosphination of activated olefins enantioselective synthesis of chiral phosphines,... 

Chiral Bisphosphane Ligands through Modifications of DuPhos and BPE... 

In the early 1990s, Burk introduced a new series of efficient chiral bisphospholane ligands BPE and DuPhos.55,55a-55c The invention of these ligands has expanded the scope of substrates in Rh-catalyzed enantioselective hydrogenation. For example, with Rh-DuPhos or Rh-BPE as catalysts, extremely high efficiencies have been observed in the asymmetric hydrogenation of a-(acylamino)acrylic acids, enamides, enol acetates, /3-keto esters, unsaturated carboxylic acids, and itaconic acids. 

Hydrogenation of a series of /Z-isomeric mixtures of a-arylenamides with a MOM-protected /3-hydroxyl group catalyzed by a BICP-Rh complex or an Me-DuPhos complex leads to the formation of chiral /3-amino alcohol derivatives with excellent enantioselectivities.70b A 1,4-diphosphane 26 with a rigid 1,4-dioxane backbone is also very effective for this transformation (Equation (28)).76 DIOP -Rh72a and Me-DuPhos-Rh219 catalysts are also effective for this transformation. 

In contrast to the many successful examples for hydrogenation of the parent itaconic acid or its dimethyl ester, only a few ligands have been reported to be efficient for the hydrogenation of / -substituted itaconic acid derivatives. Rh complexes with chiral ligands such as MOD-DIOP,69,69a 69h BPPM,246 Et-DuPhos,247 and TangPhos116 are... 

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