Ru -catalysed asymmetric hydrogenation

The seven-membered ring containing chiral bisphosphine 121 (n = 1) was made as part of a series of bisphosphines (n = 1-6) to study the influence of ligand dihedral angles on the enantioselectivity of Ru-catalysed asymmetric hydrogenation of p-ketoesters . 

Copolymer of PEG, (R)-5,5 -diamino-BINAP, and terephthaloyl chloride =0.05 H20 ,Me0H =, ethylene glycol", Et0Ac/H20" Ru-catalysed asymmetric hydrogenation of a,p unsaturated carhoxyhc acids (-t) Precipitation (ether) [145]... 

Ru-catalysed asymmetric hydrogenation of unsaturated carboxylic acids... 

Scheme 14.2 Application of Ru-catalysed asymmetric hydrogenation to (i )-citronellol. ...

The broad range of alkenes undergoing asymmetric hydrogenation using ruthenium-based systems as catalysts has attracted the attention of chemists engaged in the synthesis of chiral biologically active natural products (Scheme 13)[60] and other pharmaceuticals (Scheme 14)[61]. a, (3-Unsaturated phosphoric acids and esters have also proved to be suitable substrates for Ru(II)-catalysed asymmetric hydrogenation [62]. 

Ferrocene-based aminophosphines are shown to be effective ligands in the Ru(II)- catalysed asymmetric hydrogenation of ketones. The enantioselectivity is mainly determined by the C-centred chirality of the ligands, but the planar chirality is also important, and (Rc,SFc)- or (Sc,Rfc)- is the matched combination of chiralities.334 Dimethyl oxalate is selectively hydrogenated to methyl glycolate with Ru(acac)3,... 

Asymmetric hydrogen transfer from 2-propanol to aromatic ketones such as acetophenone (99) has been achieved by using the same chiral Ru complex in 2-propanol containing KOH at room temperature, and (S)-1 -phenylethanol (100) with 98% ee was obtained [68,69]. Similarly, efficient Ru-catalysed transfer hydrogenation of aromatic ketones using the cyclic amino alcohol [(I. S, 3R,4i )-2-azanorbomylmetha-nol] (110) [70] and bis(oxazolinylmethyl) amine (111) [71] was reported. 

The complex Ru( -methallyl)2(cod)-PhTRAP [using (R,R)-(5, 5)-PhTRAP (220) and (5,S)-(R,R)-PhTRAP (221)] catalysed asymmetric hydrogenation of the substituted imidazoles and oxazoles into the corresponding chiral imidazolines and oxazolines, respectively. The optically active products (up to 99% ee) could be converted to chiral... 

A class of simple, modular, and highly efficient a-amino acid amides ligands for Ru-and Rh-catalysed asymmetric transfer hydrogenation of aromatic ketones in propan-2-ol has been developed. A remarkable feature with these ligands is the switch of product enantioselectivity observed when the amide functionality is replaced by the corresponding thioamide. The results obtained have significant mechanistic implications... 

Ketones are reduced by asymmetric hydrogen transfer from either HCO2H or 2-propanol as hydrogen sources, catalysed by chiral Ru complexes [66]. HCO2H is used... 

Mainly the hydrogenations are mediated through a platinum-group-metal-catalysed reaction with chiral ligands bound to the metal. Koten and coworkers210 proposed the use of Ru- and Rh-containing catalysts immobilised on silica in asymmetric hydrogenation. As a chiral compound, they used BINAP (2,2 -bis(diphenylphosphino)-1,1 -binaphthyl) (Scheme 4). 

Ohta, T., Miyake, T. and Takaya, H. (1992) An efficient synthesis of optically active methyloxetan-2-one asymmetric hydrogenation of diketene catalysed by BINAP-Ru complexes, J. Chem. Soc., Chem. Comm. 1725-1726. 

Complexes (240) and (241) were used to catalyse transfer hydrogenation and asymmetric transfer hydrogenation of various aromatic ketones. The transfer hydrogenation reaction gave corresponding alcohols in quantitative yield, which is attributed to the establishment of an unsymmetrical environment around the Ru(II) by two different... 

The scope of the ruthenium-catalysed asymmetric transfer hydrogenation methodology was very recently extended to a-alkyl-substituted )S-ketoamides by Limanto et Indeed, the first enantio- and diastereoselective synthesis of various syn a-alkyl-substituted jS-hydroxyamides via highly efficient Ru-cata-lysed hydrogenation through DKR of the corresponding ) -ketoamides has been successfully demonstrated. As shown in Scheme 2.31, excellent diastereo-and enantioselectivities of up to 98% de and > 99% ee, respectively, were observed when the process was performed in CH2CI2 or toluene as the solvent. 

The asymmetric hydrogenation of several / -amino ketones in toluene-water mixture is catalysed by the chiral complex RuPHOX-Ru (43), stable in air and moisture, in the presence of KOH to corresponding y-amino alcohols with up to 99.9% ee. The key intermediates of fluoxetine, tomoxetine, and nisoxetine were obtained in quantitative yield and in up to 99.9% ee ... 

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