Asymmetric Hydrogenation Of Enamides Research Articles

Modified Cellulose with BINAP-Supported Rh as an Efficient Heterogeneous Catalyst for Asymmetric Hydrogenation

Asymmetric catalysis is the preferred method for the synthesis of pure chiral molecules in the fine chemical industry. Cellulose has long been sought as a support in enantioselective catalysis. Dialdehyde cellulose (DAC) is produced by the selective oxidation of cellulose and is used to bind 5,5′-diamino Binap by forming a Schiff base. Here, we report the synthesis of modified cellulose-supported Rh as a novel biomass-supported catalyst and the characterization of its morphology, composition, and thermal stability. DAC-BINAP-Rh was a very effective catalyst in the asymmetric hydrogenation of enamides and could be easily recycled. This work provides a novel supported catalyst that broadens the applications of cellulose in asymmetric catalysis.

Recent Developments in Transition-Metal-Catalyzed Asymmetric Hydrogenation of Enamides

AbstractThe catalytic asymmetric hydrogenation of prochiral olefins is one of the most widely studied and utilized transformations in asymmetric synthesis. This straightforward, atom economical, inherently direct and sustainable strategy induces chirality in a broad range of substrates and is widely relevant for both industrial applications and academic research. In addition, the asymmetric hydrogenation of enamides has been widely used for the synthesis of chiral amines and their derivatives. In this review, we summarize the recent work in this field, focusing on the development of new catalytic systems and on the extension of these asymmetric reductions to new classes of enamides.1 Introduction2 Asymmetric Hydrogenation of Trisubstituted Enamides2.1 Ruthenium Catalysts2.2 Rhodium Catalysts2.3 Iridium Catalysts2.4 Nickel Catalysts2.5 Cobalt Catalysts3 Asymmetric Hydrogenation of Tetrasubstituted Enamides3.1 Ruthenium Catalysts3.2 Rhodium Catalysts3.3 Nickel Catalysts4 Asymmetric Hydrogenation of Terminal Enamides4.1 Rhodium Catalysts4.2 Cobalt Catalysts5 Rhodium-Catalyzed Asymmetric Hydrogenation of Miscellaneous Enamides6 Conclusions

Rhodium-Catalyzed Asymmetric Hydrogenation of Enamides

Rhodium-Catalyzed Asymmetric Hydrogenation of Enamides

ChemInform Abstract: Enamide Derivatives: Versatile Building Blocks for Total Synthesis

AbstractReview: [100 refs.

ChemInform Abstract: Highly Enantioselective Hydrogenation of o‐Alkoxy Tetrasubstituted Enamides Catalyzed by a Rh/(R,S)‐JosiPhos Catalyst.

AbstractAn efficient enantioselective synthesis of β‐amino alcohols is achieved by rhodium‐catalyzed asymmetric hydrogenation of enamides.

Enamide Derivatives: Versatile Building Blocks for Total Synthesis

Enamides and enecarbamates are versatile building blocks in organic synthesis. This review describes the development of enamide chemistry and the utility of the resulting products in the synthesis of a variety of important, biologically active molecules. 1 Introduction 2 Asymmetric Hydrogenation of Enamides 3 Monofunctionalization of Enamide Derivatives 3.1 Palladium-Catalyzed α-Functionalization of Enamide Derivatives 3.2 Ruthenium-Catalyzed β-Functionalization of Enamide Derivatives 4 Ionic Vicinal Difunctionalization of Enamide Derivatives 4.1 Tandem Difunctionalization of Enamide Derivatives 4.2 Cycloadditions 4.2.1 [4+2] Cycloadditions 4.2.2 [2+2] Cycloadditions 4.2.3 Cyclopropanation of Enamides 4.3 Other Pericyclic Reactions 4.3.1 Electrocyclization Reactions 4.3.2 Overman Rearrangement 4.4 Platinum-Catalyzed Vicinal Difunctionalization of Enamide Derivatives 5 Radical Vicinal Difunctionalization of Enamide Derivatives 6 Oxidative Vicinal Difunctionalization of Enamide Derivatives 7 N-Arylation of Enecarbamates 8 Conclusion 9 Ligand Glossary

Challenging the Major/Minor Concept in Rh-Catalyzed Asymmetric Hydrogenation

Herein, we provide evidence showing that the long-held major–minor concept for catalytic asymmetric reactions needs to be readdressed. The asymmetric hydrogenation of enamide 1 catalyzed by the chiral Rh(I) complex of (R,R)-BenzP* quantitatively yields the corresponding hydrogenated R-product 2 with 89.6% ee. The most abundant catalyst–substrate species in the reaction pool was found to be [Rh((R,R)-BenzP*)(Ph(MeCONH)C═CH2)]+SbF6– (5). This species is also the most reactive to hydrogen among the various Rh complexes. Low-temperature hydrogenation experiments showed direct transformation of 5 to 2 with over 98% ee (R). However, the oxidative addition of H2 to 5 would yield the S-product. Computation has now revealed a low-energy R-enantioselective route, whereby H2 addition to 5 is followed by π-bond dissociation, isomerization of nonchelating Rh species, and recoordination of the double bond before C–H bond formation occurs.

ChemInform Abstract: Readily Available and Recoverable Chiral Ionic Phosphite Ligands for the Highly Enantioselective Hydrogenation of Functionalized Olefins.

AbstractA new ligand bearing carbohydrate groups is successfully applied in the asymmetric hydrogenation of enamides (I), α‐dehydroamino acid esters (III), and dimethyl itaconate (V).

Readily available and recoverable chiral ionic phosphite ligands for the highly enantioselective hydrogenation of functionalized olefins

A series of novel ionic phosphite ligands bearing carbohydrate groups were conveniently synthesized and successfully applied in the asymmetric hydrogenation of enamides, α-dehydroamino acid esters, and dimethyl itaconate. High efficiency and excellent reusability were obtained in an ionic liquid–toluene biphasic system.

ChemInform Abstract: Readily Available Chiral Phosphine—Aminophosphine Ligands Derived from 1‐Phenylethylamine for Rh‐Catalyzed Enantioselective Hydrogenations.

AbstractAmong the novel phosphineaminophosphine derivatives prepared, effective ligands are identified for the Rh‐catalyzed asymmetric hydrogenation of enamides (II), Z‐β‐dehydroamino acid esters (VI), and itaconate (IX).

Asymmetric hydrogenation with the use of chiral carborane amidophosphite derivatives in supercritical carbon dioxide and CH2Cl2

New chiral carborane-containing amidophosphites containing the BINOL fragment (BINOL stands for 2,2′-dihydroxy-1,1′-binaphthyl) have been synthesized. The study of efficiency of these compounds as ligands in the Rh-catalyzed asymmetric hydrogenation of enamides in supercritical carbon dioxide (scCO2) and CH2Cl2 showed that enantioselectivity of the process is considerably higher in scCO2.

Asymmetric Hydrogenation of Enamides, α-Enol and α-Enamido Ester Phosphonates Catalyzed by IndolPhos-Rh Complexes

The scope of the IndolPhos-Rh-catalyzed asymmetric hydrogenation of enamides, alpha-enol and alpha-enamido ester phosphonates, has been investigated. In addition, Taddol-based IndolPhos ligands are introduced. High activities and good to excellent enantioselectivities up to 99% ee are obtained for a broad range of structurally diverse substrates, giving important chiral products such as alpha, beta(2), and beta(3) amino acid derivatives, arylamines, and amino and hydroxy phosphonates.

Iridium‐Catalysed Asymmetric Hydrogenation of Enamides in the Presence of 3,3′‐Substituted H8‐Phosphoramidites

Abstractmagnified imageIn situ generated iridium complexes containing bulky 3,3′‐substituted H8‐phosphoramidites as ligands catalyse the asymmetric hydrogenation of non‐functionalised enamides in high yield and good to excellent selectivity.

Asymmetric Hydrogenation of Enamides

An asymmetric Hantzsch ester mediated transfer hydrogenation of aromatic enamides catalyzed by a combination of chiral phosphoric acid 1 and acetic acid is reported. Mechanistic assumptions involve the acid-dependent generation of iminium ions 2 and 3, wherein the phosphoric acid activated intermediate 2 exclusively undergoes further reaction. The role of the achiral acid apparently lies in the perpetuation of a sufficient quantity of the iminium species, as well as in the neutralization of the basic pyridine byproduct.

Supramolecular chiral dendritic monophosphites assembled by hydrogen bonding and their use in the Rh-catalyzed asymmetric hydrogenation

A new type of supramolecular chiral dendritic monophosphite ligands has been prepared via a hydrogen-bonding assembly. The Rh complexes of these supramolecular ligands have been successfully applied in the asymmetric hydrogenation of enamides and dehydroamino acid derivatives with good enantioselectivities, which are comparable to those obtained from the free monophosphite ligands. The supramolecular catalyst could be easily recycled via solvent precipitation.

Unnatural α‐Amino Acids via Asymmetric Hydrogenation of Enamides

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Allosteric effects in asymmetric hydrogenation catalysis? Asymmetric induction as a function of the substrate and the backbone flexibility of C1-symmetric diphosphines in rhodium-catalysed hydrogenations

The new unsymmetrical, optically active ligands 1,2-C(2)H(4)(PPh(2))(2'R,5'R-2',5'-dimethylphospholanyl) (L(a)) and 1,3-C(3)H(6)(PPh(2))(2'R,5'R-2',5'-dimethylphospholanyl) (L(b)) form complexes of the type [Rh(L)(cyclooctadiene)][BF(4)] where L = L(a) (1a) or L(b) (1b), [PtCl(2)(L)] where L = L(a) (2a) or L(b) (2b) and [PdCl(2)(L)] where L = L(a) (3a) or Lb (3b). The crystal structures of 2a and 2b show the chelate ligand backbones adopt delta-twist and flattened chair conformations respectively. Asymmetric hydrogenation of enamides and dehydroaminoesters using 1a and 1b as catalysts show that the ethylene-backboned diphosphine L(a) gives a more efficient catalyst in terms of asymmetric induction than the propylene-backboned analogue L(b). The greatest enantioselectivities were obtained with 1a and enamide substrates with ees up to 91%. Substrate-induced conformational changes in the Rh-diphosphine chelates are proposed to explain some of the ees observed in the hydrogenation of enamides.

Asymmetric hydrogenation of enamides with a new chiral phosphine–phosphinite ligand

A new mixed chiral phosphine–phosphinite 4 obtained from enantiomerically pure ( S)-(+)-3-boronatodiphenyl-phosphanyl butanoic acid 1 was synthesized in four steps. This new chiral ligand was used in the asymmetric hydrogenation of dehydroamino acids with enantioselectivities being obtained of up to 90.8%.

Asymmetric Hydrogenation of Enamides in Aqueous Media with a New Water‐Soluble Chiral Rhodium‐α,α‐trehalose‐Derived Phosphine—Phosphinite Catalyst.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Asymmetric hydrogenation of enamides in aqueous media with a new water-soluble chiral rhodium-α,α-trehalose-derived phosphine–phosphinite catalyst

A new chiral rhodium catalyst with α,α-trehalose-derived phosphine–phosphinite (α,α-TREHAPPN) ligand, [(TREHAPPN)Rh(cod)]BF 4 8 has been prepared. This catalyst is soluble in water and is an effective chiral catalyst for asymmetric hydrogenation of N-acyldehydroamino acids in aqueous media to give enantiomerically enriched α-amino acid derivatives with R configuration. The simple decantation allows retrieval of the catalyst from the reaction mixture, the recovered catalyst being re-used without marked loss of enantioselectivity.