Chiral monodentate phosphorus

For a perspective on the use of chiral monodentate phosphorus ligands in enantioselective olefin hydrogenations see ... 

Breakthroughs that took place around the year 2000 have shown, in contrast to the common view, that indeed chiral monodentate phosphorus ligands can also lead to high enantioselectivities in a number of asymmetric hydrogenations. In the years following, monophosphines, monophos-phonites, monophosphoramidites, and monophosphites have been successfully used in the enantioselective hydrogenation of a-dehydroamino acids and itaconic acid derivatives [25],... 

Recent review about monodentate ligands, see (a) Jerphagnon, T., Renaud, J.-L. and Brrmeau, C. (2004) Chiral monodentate phosphorus ligands for rhodium-catalyzed asymmetric hydrogenation. Tetrahedron Asymmetry, 15, 2101-2111, and references cited therein, (b) de Vries, J.G. (2005)... 

For a historical review on the use of chiral monodentate phosphorus ligands in enantioselectieve olefin hydrogenations, see Komarov, I. V., Borner, A. Angew. Chem., Int. Ed 2001, 40, 1197. 

Asymmetric hydrogenation ofenamides with mixed chiral monodentate phosphorus... 

In the Rh catalyzed asymmetric hydrogenation of enamides, why can the mixed two different chiral monodentate phosphorus hgands improve the enantioselectivity of reaction in some cases ... 

Chiral Monodentate Phosphorus Ligands (Monophosphanes and Phospho-ramidites). The initial attempts to convert Wilkinson s catalyst into a chiral system involved incorporating chiral unidentate phosphanes (Fig. 2). Historically, (S)-PMePh(nPr) (MPNPP) (5) and (S)-PMePh(iPr) (MPIPP) (6) (Horner phosphanes) were the first chiral phosphorus ligands used in enantioselec-tive catalysis. In 1968, the two independent work of Horner and Knowles and... 

Up to now, all studies point to the fact that chiral monodentate phosphorus Ugands do not fulfill the expectations for highly efficient AHF [10]. The most... 

Jerphagnon T, Renaud J-L, Bmneau C. Chiral monodentate phosphorus ligands for rhodium-catalyzed asymmetric hydrogenation. Tetrahedron Asymm. 2004 15(14) 2101-2111. 

It thus came as a surprise that in the year 2000, three groups independently reported the use of three new classes of monodentate ligands (Scheme 28.2) [12], The ligands induced remarkably high enantioselectivities, comparable to those obtained using the best bidentate phosphines, in the rhodium-catalyzed enantioselective alkene hydrogenation. All three being based on a BINOL backbone, and devoid of chirality on phosphorus, these monophosphonites [13], monophosphites [14] and monophosphoramidites [15] are very easy to prepare and are equipped with a variable alkyl, alkoxy, or amine functionality, respectively. 

Knowles next reported optical yields of up to 90% in the hydrogenation of further a-acetamidocinnamic acid derivatives, still using monodentate phosphines chiral at phosphorus. Again the catalysts were prepared in situ from the ligand and [RhCl(l,5-hexadiene)2] or a related complex. The best optical yield of 90% was obtained using cyclohexyl(o-anisyl)methylphosphine (CAMP).224... 

After being neglected for about 30 years, monodentate phosphorus ligands [47] have recenhy begun to athact increasing amounts of attention. Chiral monoden-... 

Monodentate phosphites are another type of prominent monodentate phosphorus ligands applied in asymmetric hydrogenation of enamides for the synthesis of chiral amines. Chiral monodentate phosphites can be easily prepared from a chiral diol and an alcohol. Generally, the chiral diol was first reacted with a phosphorus trichloride to form a phosphorochloridite, followed by the reaction with an appropriate alcohol to yield a chiral monodentate phosphite [35[. The reaction of an alcohol with phos phorus trichoride to yield a phosphorodichloridite, which was then treated with a chiral diol, is also a good procedure for the synthesis of chiral monodentate phosphites [36]. 

The diversity requirement of chiral amines in the synthesis of natural products and chiral drugs is everlasting and the most studies about the catalytic asymmetric hydrogenation of enamines have dealt with simple substrates to date. Hence, it is necessary to explore highly efficient enantioselective protocol to provide more complex and also industrially useful chiral amines. We are confident that the easily accessible and changeable monodentate phosphorus hgands will find a wide appli cation in this field. 

Xie J-H, Zhou Q-L. Chiral diphosphine and monodentate phosphorus ligands on a spiro scaffold for transition-metal-catalyzed asymmetric reactions. Acc. Chem. Res. 2008 41(5) 581-593. 

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