Asymmetric hydrogenation in the presence of bicyclic chiral phosphines

Both enantiomers of trans-2,3-diphenylphosphinomethyl-norbornene-(5), prepared by two independent synthetic routes, were used as ligands in the asymmetric hydrogenation of -acetamidocinnamic acid in the presence of rhodium(I). Small variations in the ligand structure have a remarkable influence on the activity of the catalytic system.

---

-2,3----(5), , - (I). .

     

Novel chiral water soluble phosphines II. Applications in catalytic asymmetric hydrogenation

The results of the homogeneous asymmetric hydrogenation of several dehydroamino acids by rhodium-diene complexes of the chiral ligands; 2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(-bis(-p-N,N-dimethylaminophenyl)phosphino)butane, 2a; 2,4-bis(-bis(-p-N,N-dimethylaminophenyl)phosphino)pentane, 3a; and 2,3-bis(-bis(-p-N,N-dimethylaminophenyl)phosphino) butane, 4a; and their N-protonated and N-Me quaternized analogues are reported. The ligands comprise a versatile set which can be used both in organic and aqueous solvents. A detailed investigation of solvent and substituent effects is provided. The presence of p-NMe₂ groups enhances the rate of reaction in all cases. For the DIOP derivative, 2a, the presence of the dimethylamino group causes a reversal in the observed dominant product antipode. This is attributed predominantly to a change in preferred ligand conformation rather than to a kinetic difference between the two diastereomers of a single ligand conformation.     

Asymmetric hydrogenation of chiral pyruvamides

Asymmetric catalytic hydrogenations of three kinds of chiral pyruvamides were carried out using palladium on charcoal as a catalyst to give lactamides with diastereomeric ratios ranging from 76:24 to 98:2.     

Asymmetric hydrogenation on chiral cobalt complexes

Conclusions We were the first to effect the enantioselective hydrogenation of a mixture of isomeric 2-phenylbutenes on chiral cobalt catalytic systems of the Ziegler-Natta type in an optical yield of 25%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2621–2622, November, 1981.     

Enantioselective rhodium-catalyzed hydrogenation of enol carbamates in the presence of monodentate phosphines

The rhodium-catalyzed asymmetric hydrogenation of different acyclic and cyclic enol carbamates to give optically active carbamates has been examined in the presence of chiral monodentate ligands based on a 4,5-dihydro-3H-dinaphthophosphepine motif 4. The enantioselectivity is largely dependent upon the reaction conditions, the nature of substituents on the phosphorus ligand and structure of the enol carbamate. By applying the optimized reaction conditions, enantioselectivities of up to 96% ee have been achieved.     

Asymmetric hydrogenation using chiral phosphinite rhodium complexes

The Cu(I) complex of (1R,3R)-bis(diphenylphosphinoxy)-1,3-diphenylpropane (BDPODP) has been prepared and used for the transfer of the ligand to Rh(I). The Rh(I) complexes of this new phosphinite obtained by this method act as efficient asymmetric homogeneous hydrogenation catalysts for (Z)-α-(acylamino)-cinnamic acids.     

Asymmetric hydrogenation by chiral aminophosphine-phosphinite rhodium compexes

The ligands (S)-$\text{N}$-(diphenylphosphino)-2-diphenylphosphinoxymethylpyrrolidine, (S)-prolophos, and (S)-1-diphenylphosphinoxy-2-$\text{N}$-diphenylphosphinoaminobutane, (S)-butaphos, have been prepared. The Rh(I) complexes of these phosphines act as efficient homogenous hydrogenation catalysts at ambient temperature and pressure for A-N-acetaminoacrylic acid and itaconic acid.     

Asymmetric hydrogenation of chiral vinyloxazaborolidines under ambient conditions

Novel homochiral vinyloxazaborolidines have been synthesized and subsequently hydrogenated using palladium on carbon under ambient conditions to produce, after oxidation of the boronate group, enantiomerically enriched secondary alcohols (up to 20% ee). Herein, the first example of asymmetric hydrogenation utilizing oxazaborolidines as chiral auxiliaries is reported.     

Asymmetric transfer hydrogenation: chiral ligands and applications

Hydrogen transfer reduction processes are attracting increasing interest from synthetic chemists in view of their operational simplicity and high selectivity. In this tutorial review the most significant advances recently achieved in the stereoselective reduction of unsaturated organic compounds catalyzed by homogeneous transition metal complexes are critically reviewed. A sharp growth of the synthetic applications of this technique in the synthesis of fine chemicals is predictable as the use of transition metal catalyzed reactions will become more familiar to synthetic chemists.     

Asymmetric hydrogenation for the synthesis of 2-substituted chiral morpholines

Asymmetric hydrogenation of unsaturated morpholines has been developed by using a bisphosphine-rhodium catalyst bearing a large bite angle. With this approach, a variety of 2-substituted chiral morpholines could be obtained in quantitative yields and with excellent enantioselectivities (up to 99% ee). The hydrogenated products could be transformed into key intermediates for bioactive compounds.

2-Substituted chiral morpholines were synthesized via a newly developed asymmetric hydrogenation of dehydromorpholines catalyzed by a bisphosphine–rhodium complex bearing a large bite angle.     

Asymmetric hydrogenation of ketones with polymer-supported chiral 1,2-diphenylethylenediamine

[reaction: see text] A poly(ethylene glycol)-supported chiral diamine (PEG-2), in which the polymer is attached to the phenyl rings, has been synthesized and shown to be highly effective in asymmetric hydrogenation of unfunctionalized aromatic ketones with the possibility of reuse. PEG-2 can also serve as a chiral scaffold on which various immobilized chiral catalysts could be easily built.     

Asymmetric hydrogenation using readily prepared chiral sugar diphosphiniterhodium complexes

Asymmetric hydrogenation of N-acetamidoacrylic acid derivatives has been achieved using a rhodium complex in the presence of a series of readily made chiral diphosphinites, small changes in the stereochemistry of which lead to significant difference in the optical yield of reduced product.     

Asymmetric transfer hydrogenation of ketones with a polymer-supported chiral diamine

A new supported chiral diamine has been developed and shown to be highly effective in ruthenium-catalysed asymmetric transfer hydrogenation of simple aromatic ketones.     

Asymmetric transfer hydrogenation of ketones catalyzed by chiral phosphineiridium complexes

The complexes formed in situ from Ir(COD)acac and chiral menthylphenylphosphines proved to be active catalysts in the hydrogen transfer reaction from isopropanol to prochiral ketones. When acetophenone was used, optical yields of up to 42% were achieved, the configuration of the carbinols being dependent on the bulkiness of the phosphine employed. Concerning the reaction rate, the activation process and the P/Ir ratio, the two menthyl-substituted phenylphosphines display different behaviour.     

Asymmetric hydrogenation of enamides with catalysts containing chiral thiourea ligands

The asymmetric reduction of enamides with molecular hydrogen and catalytic amounts of rhodium, iridium or ruthenium complexes containing chiral N,S-ligands is reported. Various enantiomerically pure mono- and dithioureas were examined. The C₂-symmetry of the dithiourea ligands seems essential to the enantioselectivity achieved. Ee values of up to 70% were observed.