Hydrogenation of functionalized olefins

Chirally modified Pd is the best catalyst for the enantioselective hydrogenation of olefins, ee 50 % has been achieved in two types of reaction in both the reactant has an interacting functional group in the a-position. 

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In general, applications of AMPP have concentrated on the asymmetric hydrogenation of functionalized olefins, especially dehydroamino acids. Among... 

The development of chiral hydrogenation catalysts for unfunctionalized alkenes also allows enantioselective hydrogenation of functionalized olefins where the functionality in the molecule is remote from the double bond. A series of oxazoline-, imidazoline- and pyridine-derived catalysts have been screened for the hydrogenation of unsaturated derivatives of vitamin E (Scheme 30.3). Hy-... 

In 1971, Kagan published his ground-breaking research in the field.141 He demonstrated that high enantioselectivities could be obtained in the Rh-catalyzed hydrogenation of functionalized olefins, such as the dehydroamino acid derivatives 3 and 4, using a novel diphosphine ligand which he called DIOP 2 (Scheme 2). 

Scheme 3. The mechanism of Rh-catalyzed hydrogenation of functionalized olefins in the presence of a bidentate P,P-ligand (S = solvent, P = phosphine unit, R = alkyl).

Hydrogenation of Functionalized Olefins with Ruthenium Catalysts... 

The BINAP-Rh catalyzed hydrogenation of functionalized olefins has a mechanistic drawback as described in Section 1.2.1. This problem was solved by the exploitation of BINAP-Ru(ll) complexes.Ru(OCOCH3)2(binap) catalyzes highly enantioselective hydrogenation of a variety of olefinic substrates such as enamides, a, (3- and (3,y-unsaturated carboxylic acids, and allylic and homoallylic alcohols (Figure 1.9). " " Chiral citronellol is produced in 300 ton quantity in year by this reaction. ... 

Figure 1.9 Asymmetric hydrogenation of functionalized olefins catalyzed by BINAP-Ru...

Although Ru(OCOCH3)2(binap) exhibits excellent catalytic performance on asymmetric hydrogenation of functionalized olefins, it is feebly active for reaction of ketones. This failure is due to the property of the anionic ligands. Simple replacement of the carboxylate ligand by halides achieves high catalytic activity for reaction of functionalized ketones. 

To summarize, chiral heterogeneous catalysts were prepared from rhodium-diphosphine complexes and aluminum-containing mesoporous materials. The bonding occurred via an ionic interaction of the cationic complex with the host. These catalysts were suitable for asymmetric hydrogenation of functionalized olefins. The catalysts can be recycled easily by filtration or centrifugation with no significant loss of activity or enantioselectivity. 

Bppfoh (9) and bppfa (8) derivatives have been successfully applied for the Rh-catalyzed hydrogenation of functionalized olefins and ketones (Table 15.1). The nature of auxiliary group has a significant effect on the enantioselectivity and often also on activity and is used to tailor the ligand for a particular substrate. These effects could be the result of electrostatic interactions between substrate and catalyst. Rh-bppfa complexes were among the first catalysts able to hydrogenate tetrasubstituted C = C bonds, albeit with rather low activity. 

Hydrogenation of Functionalized Olefins Bearing Chiral Residues... 

Among the vast number of chiral homogeneous catalysts, rhodium(I) and ruthenium(II) diphosphane complexes revealed to be the most efficient ones in asymmetric hydrogenation of functionalized olefins of practical importance. In certain cases described below (including also the BINAP-containing systems), enzyme-like enantioselectivities matching the requirements of natural product synthesis were reported. 

Ir(I)-oxazolinyl-phosphane complexes are also effective catalysts for hydrosilylation of imines (246). Chiral poisoning of iridium complexes containing racemic DIOP with PRONOP provides an enantioselective catalyst (247). Iridium complexes containing phosphinooxazoline or dithioether ligands (like DIOSPr or DIOSPh) catalyze the enantioselective hydrogenation of functionalized olefins (248). 

Borner, A., The effect of internal hydroxy groups in chiral diphosphine rhodium(I) catalysts on the asym metric hydrogenation of functionalized olefins, Eur. J. Inorg. Chem., 2001, 327. 

RHODIUM-CATALYZED STEREOSELECTIVE HYDROGENATION OF FUNCTIONALIZED OLEFINS... 

Fu Y, Guo XX, Zhu SF, Hu AG, Xie JH, Zhou QL. Rhodium-catalyzed asymmetric hydrogenation of functionalized olefins using monodentate spiro phosphoramidite ligands. J. Org. Chem. 2004 69(14) 4648 655. 

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