Presence Of Chiral Catalyst Research Articles

Direct Asymmetric Arylation of Imines

AbstractThe Friedel‐Crafts reaction represents one of the most efficient tools for the formation of carbon‐carbon bonds and direct derivatization of aromatic compounds. Asymmetric arylation of imines involving Friedel‐Crafts reaction has received much interest recently. The present review summarizes the works on the asymmetric arylation of imines by different approaches including Friedel‐Crafts reaction and their development to date. The review is divided into three main sections: addition reaction of arenes to imines in the presence of chiral catalysts; addition reaction of arenes to imines containing chiral tails and asymmetric coupling reaction of aryl boronic acids and imines.magnified image

Transition Metal Catalyzed Aerobic Asymmetric Coupling of 2-Naphthols

Optically pure 1,1′-bi-2-naphthol (BINOL) and its derivatives are among the most widely used chiral ligands and auxiliaries for asymmetric synthesis. These molecules also occur as scaffolds for various biologically active compounds. Direct oxidative coupling of 2-naphthols in the presence of chiral catalysts provides a powerful strategy for the synthesis of optically pure 1,1′-bi-2-naphthols (BINOLS). In 1978, Wynberg with co-workers discovered that a copper salt with chiral auxiliary mediates the oxidative coupling of 2-naphthols, which can be taken as the starting point for further progress in this area. Over the last decades, a number of efficient and stereoselective catalyst systems have been developed. This mini-review surveys the aerobic asymmetric oxidative coupling of 2-naphthols catalyzed by transition metal complexes reported since 1995.

Recent advances in organocatalytic enantioselective transfer hydrogenation.

The organocatalytic reduction of C[double bond, length as m-dash]C and C[double bond, length as m-dash]N double bonds with biomimetic reductants, e.g. Hantzsch 1,4-dihydropyridine esters and benzothiazolines, is reviewed. Very high yields and stereoselectivities have been achieved with a variety of catalysts, including chiral amines, thioureas and phosphoric acids, even with loadings equivalent to those of transition metal-catalyzed reactions in some cases. Reductive amination reactions and the dearomatization of heteroaromatic substrates are the subject of more than one half of the contributions. Of lately, methodologies based on kinetic resolution, cascade reactions involving transfer hydrogenation and the development of novel reductants have become prominent in an area which brings great prospects for the future of target oriented-synthesis.

ChemInform Abstract: Catalytic Enantioselective 1,4‐Iodofunctionalizations of Conjugated Dienes.

AbstractTreatment of unsaturated oximes and hydrazones with NIS in the presence of chiral catalysts (I) gives optically active isoxazolines and pyrazolines.

ChemInform Abstract: Organocatalyzed Enantioselective Aldol Reaction of 1H‐Pyrrole‐2,3‐diones.

AbstractCross aldol reaction between 4,5‐dioxopyrroles (I) and ketones (II) and (IV) in the presence of chiral catalysts is investigated.

ChemInform Abstract: γ‐Hydroxy‐α,β‐acetylenic Esters: Asymmetric Syntheses and Applications

AbstractReview: 77 refs.

Copper(I)-Catalyzed Substitution Reactions of Propargylic Amines: Importance of C(sp)−C(sp3) Bond Cleavage in Generation of Iminium Intermediates

Substitution reactions of propargylic amines proceed in the presence of copper(I) catalysts. Mechanistic studies showed that C(sp)-C(sp(3)) bond cleavage assisted by nitrogen lone-pair electrons is essential for the reaction, and the resulting iminium intermediates undergo amine exchange, aldehyde exchange, and alkyne addition reactions. Because iminium intermediates are key to aldehyde-alkyne-amine (A(3)) coupling reactions, this transformation is effective not only for reconstruction of propargylic amines but also for chiral induction of racemic compounds in the presence of chiral catalysts.

γ-Hydroxy-α,β-acetylenic esters: asymmetric syntheses and applications

γ-Hydroxy-α,β-acetylenic esters are versatile synthetic precursors to many organic compounds. This paper reviews the synthesis of chiral γ-hydroxy-α,β-acetylenic esters by asymmetric reduction of γ-oxo-α,β-acetylenic esters, enantioselective addition to aldehydes in the presence of chiral catalysts, and diastereoselective addition to chiral aldehydes. The preparation of racemic γ-hydroxy-α,β-acetylenic esters is also included. Examples are provided for the application of γ-hydroxy-α,β-acetylenic esters in organic synthesis.

Asymmetric intramolecular Pd(II)-catalysed amidocarbonylation of unsaturated amino alcohols

The first example of an asymmetric carbonylative bicyclisation of racemic N-protected 1-amino-pent-4-ene-3-ols (±) -1 catalysed by palladium(II) with chiral bis(oxazoline) ligands was investigated. The kinetic resolution of (±) -1 in the presence of chiral catalyst, p-benzoquinone in acetic acid under carbon monoxide atmosphere afforded enantiomerically enriched derivatives of 2-oxa-6-azabicyclo[3.3.0]octan-3-ones ( R, R) -2 and ( S, S) -2, respectively.

Synthesis and application of chiral monoesters derived from cyclohex-4-ene-1,2-dicarboxylic acid and bicyclo[2.2.1]-hept-5-ene-2,3-dicarboxylic acid

Optically active alkyl and cycloalkyl hydrogen cyclohex-4-ene-1,2- and bicyclo[2.2.1]hept-5-ene- 2,3-dicarboxylates were synthesized by asymmetric Diels-Alder reactions in the presence of chiral catalyst. The cycloadducts were found to possess antimicrobial activity.

Kinetic Resolution of Racemic Carboxylic Acids Using Achiral Alcohols by the Promotion of Benzoic Anhydrides and Tetramisole Derivatives: Production of Chiral Nonsteroidal Anti‐Inflammatory Drugs and Their Esters

AbstractA variety of optically active carboxylic esters were produced by kinetic resolution of racemic carboxylic acids by using achiral alcohols, benzoic anhydrides, and Birman's tetramisole‐type catalysts. Bis(α‐naphthyl)methanol is a very effective reagent for producing the corresponding esters with high ee values in the presence of 4‐methoxybenzoic anhydride (PMBA) as the coupling reagent by promotion of benzotetramisole derivatives (BTM, α‐Np‐BTM, and β‐Np‐BTM). This protocol directly provides chiral carboxylic esters from free carboxylic acids and achiral alcohols by utilizing a transacylation process to generate the mixed anhydrides from the acid components with benzoic anhydride derivatives in the presence of chiral catalysts.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Asymmetric Diels-Alder reaction between acrylates and cyclopentadiene in the presence of chiral catalysts

Asymmetric Diels-Alder reaction between cyclopentadiene and alkyl and cycloalkyl acrylates in the presence of new chiral catalysts, BBr3·MentOEt, AlCl2OMent, BBr2OMent, and BBr(OMent)2, was studied. Optically active bicyclo[2.2.1]hept-2-ene-5-carboxylates were synthesized. The influence of the reaction conditions on the total and optical yields and on the stereoselectivity of the adducts synthesized was examined.

Enantioselective Synthesis of (R)- and (S)-α-Alkylcysteines via Phase-Transfer Catalytic Alkylation

We reported efficient enantioselective synthetic methodologies for (R)-alpha-alkylcysteines and (S)-alpha-alkylcysteines. The phase-transfer catalytic alkylation of 2-phenyl-2-thiazoline-4-carboxylic acid tert-butyl ester and 2-o-biphenyl-2-thiazoline-4-carboxylic acid tert-butyl ester, in the presence of chiral catalysts (1 or 2), gave the corresponding alkylated products, which could be hydrolyzed to provide (R)-alpha-alkylcysteines (67->99% ee) and (S)-alpha-alkylcysteines (66-88% ee), respectively.

Metal Chelations in Asymmetric Diels—Alder Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Metal Chelations in Asymmetric Diels-Alder Reaction

In the presence of chiral catalysts, Diels-Alder reaction of a N-acryloyl chiral dienophile with cyclopentadiene gave the corresponding endo norbornenecarboxamide with high diastereoselectivity. In the reaction, 8-membered chelation was effective enough to distinguish transoid and cisoid conformation in the presence of divalent Lewis acid catalysts, such as TiCl 4 .

Cis, TransStereochemistry and Asymmetric Induction in the Synthesis of Epoxides from Aryl Aldehydes and Phenacyl Halides in a Two-Phase System in the Presence of Chiral Phase-Transfer Catalysts

Abstract Reactions under phase-transfer conditions in the presence of chiral catalysts constitute an actractive route to optically active epoxides.