Chiral Ligands For Asymmetric Catalysis Research Articles

The pentafluorophenyl group as a module for the direct modification of chiral diamines for asymmetric catalysis

A pentafluorophenyl group embedded in a chiral diamine allows the direct modification of an aryl group. The diamine is readily converted into para-disubstituted diamines. Although the electronic effect of the modified diamine somewhat lowers the catalytic activity of BINAP–Ru–diamine-catalyzed asymmetric hydrogenation, the enantioselectivity of the product is higher than that obtained by using a typical chiral diamine. Such an easy and direct modification of the chiral ligand has the potential to facilitate the optimization of the steric effect of chiral ligands in asymmetric catalysis.

Stereochemical Consequences of Threefold Symmetry in Asymmetric Catalysis: Distorting C3 Chiral 1,1,1‐Tris(oxazolinyl)ethanes (“Trisox”) in CuII Lewis Acid Catalysts

The underlying conceptual differences in exploiting two- and threefold rotational symmetry in the design of chiral ligands for asymmetric catalysis have been addressed in a comparative study of the catalytic performance of bisoxazoline (BOX) and tris(oxazolinyl)ethanes (trisox) containing copper(II) Lewis acid catalysts. The differences become apparent in constructing new catalysts by systematically "deforming" the stereodirecting ligand by inverting chiral centres or replacing chiral by achiral oxazolines. The catalytic alpha-amination of ethyl 2-methylacetoacetate with dibenzyl azodicaboxylate, which occurs with high enantioselectivity for both Ph(2)-BOX and Ph(3)-trisox copper catalysts, has been employed as the test reaction. In the trisox-copper complex [Cu(II)(iPr(3)-trisox)(kappa(2)-O,O'-MeCOCHCOOEt)](+)[BF(4)](-) (1), which was characterised by X-ray diffraction, two of the oxazoline groups are coordinated to the central copper atom, whilst the third oxazoline unit is dangling with the N-donor pointing away from the metal centre. A similar arrangement is found for the stereochemically "mixed" C(1)-trisox complex [Cu(II){(Ph(3)-trisox(R,S,S)}(kappa(2)-O,O'-MeCOCHCOOEt)(H(2)O)](+)[ClO(4)](-) (2), in which the phenyl substituents adopt a first coordination sphere meso arrangement. The almost identical selectivity of the Ph(3)-trisox(R,R,R)- and Ph(2)-BOX(R,R)-derived catalysts is as expected from the proposed model of the active catalyst based on a partially decoordinated podand. The behaviour of the "desymmetrised" trisox-Cu catalysts may be rationalised in terms of a general steady-state kinetic model for the three possible active bisoxazoline-copper species, which are expected to be in rapid exchange with each other in solution. This applies to both the trisox derivatives with stereochemically inverted and achiral oxazoline rings. The study underscores previous observations of superior performance of the catalysts bearing C(3)-chiral stereodirecting ligands as compared to systems of lower symmetry.

Novel benzoferrocenyl chiral ligands: Synthesis and evaluation of their suitability for asymmetric catalysis

Four benzoferrocenyl phosphorus chiral ligands were conveniently prepared in good overall yields. These ligands were found to be stable in solid form and in solution. Two of the four ligands were resolved by chiral HPLC. Unlike a reported bis(phosphino-η 5-indenyl)iron(II) complex, in which the indenyl ligands undergo ring flipping through an η 1-intermediate, these two ligands were found to be configurationally stable in solution and in solid state. The suitability of these ligands for enantioselective catalysis was assessed in studies on allylic alkylation reactions. When the two less sterically hindered ligands were used, excellent chemical yields were obtained, but the other two more sterically hindered ones gave lower yields. When the two enantiopure ligands were used, enantioselectivity of up to 51% ee was observed. These findings suggest that benzoferrocene derivatives may be used as chiral ligands for asymmetric catalysis.

Vibrational circular dichroism DFT study on bicyclo[3.3.0]octane derivatives

The absolute configurations of four bicylco[3.3.0]octane derivatives: endo-bicyclo[3.3.0]octane-2,6-diol, endo-2,6-diacetoxybicyclo[3.3.0]octane, endo-bicyclo[3.3.0]octane-2,6-dione and bicyclo[3.3.0]octa-2,6-dien-2,6-bistriflate were studied by vibrational circular dichroism (VCD). These chiral derivates are of interest as intermediates in the asymmetric synthesis of enantiomerically pure natural products and chiral ligands for asymmetric catalysis. VCD has been used to determine the absolute configuration of each compound, proving the capability of VCD for molecules with several stereogenic centres. IR and VCD spectra have been simulated at the B3LYP/6-31G ∗ level for all possible diastereomers. Based on the agreement between the experimental and the calculated spectrum, the stereochemistry of each compound could be assigned. The predicted absolute configurations are found to agree with literature data.

Substituent Electronic Effects in Chiral Ligands for Asymmetric Catalysis

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Synthesis of 4-diphenylphosphanylmethyl- and 4-phenylthiomethyl-1,4-methano-11,11-dimethyl-1,2,3,4-tetrahydroacridine: new N–P and N–S camphor-derived chiral ligands for asymmetric catalysis

A new procedure has been developed for the preparation of camphor-annulated quinoline with different substituents on the 1-methyl group of the (+)-camphor backbone. Amongst them, two new N–P and N–S ligands, namely the 4-(diphenylphosphanylmethyl)- and 4-(phenylthiomethyl)-1,4-methano-11,11-dimethyl-1,2,3,4-tetrahydroacridine, have been employed in asymmetric palladium-catalyzed allylic substitution.

Ten Years of Research on NOBIN Chemistry

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Ten Years of Research on NOBIN Chemistry

2-Amino-2-hydroxy-1,1-binaphthyl (NOBIN, 3) can be considered as the analogue of 1,1-bi-2- naphthol (BINOL, 1) and 1,1-bi-2-naphthylamine (BINAM, 2) in terms of its functionality and scaffold. Since the first report on the synthesis of NOBIN by Kocovsky, the chemistry of NOBIN has been developed rapidly in the last decade. This article summarizes its synthesis, modification and application of its derivatives as the chiral ligands in asymmetric catalysis. The methods for the preparation of enantiopure NOBIN included asymmetric cross-coupling reaction of 2-naphthol and 2-naphthylamine, optical resolution of its racemic form and transformation from enantiopure BINOL. A variety of chiral ligands could be easily obtained by simple transformation from NOBIN. Their application in various asymmetric reactions, such as diethyl zinc addition to aldehydes, allylation of aldehydes, allylic substitutions, 1,4-addition to α,β-unsaturated ketones, aldol-type reaction, Diels-Alder and hetero-Diels-Alder reactions, transfer hydrogenation of ketones, cyclopropanation, phase-transfer catalysis of alkylations, ring-opening/cross metathesis, α-vinylation/arylation of ketones and Suzuki coupling reactions, clearly demonstrated that NOBIN has become one type of privileged scaffold for construction of various chiral ligands for asymmetric catalysis. Keywords: cross coupling, optical resolution, alkylation, asymmetric catalysis, binaphthyl, diethyl zinc addition, conjugate addition, cyclopropanation, transfer hydrogenation, aldol reaction

Design of Chiral Ligands for Asymmetric Catalysis

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Design of Chiral Ligands for Asymmetric Catalysis: From C2‐Symmetric P,P‐ and N,N‐Ligands to Sterically and Electronically Nonsymmetrical P,N‐Ligands

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Design of chiral ligands for asymmetric catalysis: from C2-symmetric P,P- and N,N-ligands to sterically and electronically nonsymmetrical P,N-ligands.

For a long time, C(2)-symmetric ligands have dominated in asymmetric catalysis. More recently, nonsymmetrical modular P,N-ligands have been introduced. These ligands have been applied successfully in various metal-catalyzed reactions and, in many cases, have outperformed P,P- or N,N-ligands.

Design of Chiral Ligands for Asymmetric Catalysis

Design of Chiral Ligands for Asymmetric Catalysis

The use of a chiral borate counteranion as a 1H NMR shift reagent for cationic copper(I) complexes

The chiral borate counteranion bis[(R)-1,1′-bi-2-naphtholato]borate (1–) has been found to be a competent chiral 1H NMR shift reagent for cationic copper(I) complexes. This has been demonstrated by the addition of the Cu(NCMe)4+ salt of 1– to two classes of common chiral ligands in asymmetric catalysis: 2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl (tol-BINAP) (2) and 2,2′-isopropylidenebis(4-phenyl-2-oxazoline) (3). In the case of ligand 2, the addition of 1 equiv. of either (R,R)-2 or (S,S)-2 to Cu(NCMe)4+1– results in well-resolved 1H NMR resonances for the two enantiomers. Examination of standard solutions of non-enantiopure 2 shows that the copper complex can be an effective NMR shift reagent of a wide range of enantiomeric compositions. Cu(NCMe)4+1– also generates distinct 1H NMR resonances for the two separate enantiomers of 2,2′-isopropylidenebis(4-phenyl-2-oxazoline) (3). However, attempts to employ this copper salt as a chiral NMR shift reagent for rac-3 led to the discovery of a new and unexpected equilibrium: [(R,R)-3]Cu+ + [(S,S)-3]Cu+ [Formula: see text] [(R,R)-3][(S,S)-3]Cu+ + Cu+. Key words: chiral counteranion, copper, chiral NMR shift reagent, ion pairing.

Diastereoselective Synthesis of Chiral Non‐Racemic 2‐Substituted 2‐Boranatophosphino Ethanoic Acid: A Potential Intermediate to Chiral Ligands for Asymmetric Catalysis.

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Reinventing Phenanthroline Ligands — Chiral Derivatives for Asymmetric Catalysis?

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Diastereoselective synthesis of chiral non-racemic 2-substituted 2-boranatophosphino ethanoic acid: a potential intermediate to chiral ligands for asymmetric catalysis

Chiral α-amidophosphine boranes 7a– b can be diastereoselectively alkylated, using a phenylglycinol derivative as a chiral inducer, to furnish α-substituted α-amidophosphine boranes 8– 12 with up to 99% diastereoisomeric excess. Selective reduction of the amidophosphine boranes afforded optically pure β-boranatophosphine-alcohol 13. The latter one can then be oxidized in boronatophosphine acid 14.

Reinventing Phenanthroline Ligands − Chiral Derivatives for Asymmetric Catalysis?

AbstractOver the last three decades, the rational design of chiral ligands for asymmetric catalysis has increasingly replaced the trial‐and‐error approach. A well‐known analytical reagent, 1,10‐phenanthroline, is now being employed as a template for the development of chiral ligands. In most cases these heterocyclic ligands have been functionalized in the peripheral region utilizing three prevailing ligand templates. Chiral groups are either introduced in the 2‐, 3‐, 8‐ and/or 9‐position (I, II) or are incorporated by ring fusion to phenanthroline (III). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Alternative Synthesis of α‐Substituted β‐Amidophosphines by [1,4]‐Addition. A New Route to Chiral Ligands.

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Readily Available Carbohydrate‐Derived Imines and Amides as Chiral Ligands for Asymmetric Catalysis.

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Alternative synthesis of α-substituted β-amidophosphines by [1,4]-addition. A new route to chiral ligands

Phosphine–borane can be diastereoselectively added to chiral α,β-unsaturated amides 3 , using amino-alcohols as chiral inducers, leading to α-substituted β-amidophosphine boranes 4 with up to 74% diastereomeric excess. Selective deprotection afforded optically pure carboxylic derivatives 5 which are key intermediates for the synthesis of various potential chiral ligands for asymmetric catalysis.