Catalytic Asymmetric Epoxidation Research Articles

Catalytic Asymmetric Sulfur Ylide Mediated Epoxidation of Carbonyl Compounds

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.

Catalytic Asymmetric Epoxidation of Enones and Related Compounds

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.

Highly Enantioselective Epoxidation of 2‐Methylnaphthoquinone (Vitamin K3) Mediated by New Cinchona Alkaloid Phase‐Transfer Catalysts

In the area of catalytic asymmetric epoxidation, the highly enantioselective transformation of cyclic enones and quinones is an extremely challenging target. With the aim to develop new and highly effective phase-transfer catalysts for this purpose, we conducted a systematic structural variation of PTCs based on quinine and quinidine. In the total of 15 new quaternary ammonium PTCs, modifications included, for example, the exchange of the quinine methoxy group for a free hydroxyl or other alkoxy substituents, and the introduction of additional elements of chirality through alkylation of the alkaloid quinuclidine nitrogen atom by chiral electrophiles. For example, the well-established 9- anthracenylmethyl group was exchanged for a "chiral" anthracene in the form of 9-chloromethyl-[(1,8-S;4,5-R)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene. The asymmetric epoxidation of vitamin K(3) was used as the test reaction for our novel PTCs. The readily available PTC 10 (derived from quinine in three convenient and high-yielding steps) proved to be the most enantioselective catalyst for this purpose known to date: At a catalyst loading of only 2.50 mol %, the quinone epoxide was obtained in 76 % yield and with 85 % ee (previously: < or =34 % ee), using commercial bleach (aqueous sodium hypochlorite) as the oxidant. To rationalize the sense of induction effected by our novel phase-transfer catalysts, a computational analysis of steric interactions in the intermediate chlorooxy enolate-PTC ion pair was conducted. Based on this analysis, the sense of induction for all 15 novel PTCs could be consistently explained.

Catalytic Asymmetric Epoxidation of α,β‐Unsaturated Esters with Chiral Yttrium—Biaryldiol Complexes.

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.

Towards a Greener Epoxidation Method: Use of Water‐Surfactant Media and Catalyst Recycling in the Platinum‐Catalyzed Asymmetric Epoxidation of Terminal Alkenes with Hydrogen Peroxide

AbstractRemarkable improvements in enantioselectivity as well as recycle were observed in the catalytic asymmetric epoxidation of terminal alkenes with a chiral, electron‐poor platinum(II) catalyst with hydrogen peroxide as terminal oxidant in water‐surfactant media.

Catalytic Asymmetric Epoxidation of α‐Methyl α,β‐Unsaturated Anilides as Ester Surrogates.

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.

Rare-Earth-Metal-Catalyzed Asymmetric Epoxidation of α,β-Unsaturated Anilides

Catalytic asymmetric epoxidation is a very efficient tool for the construction of pharmaceutically important building blocks (see review). In the present paper, the authors extended their work on rare-earth-metal-catalyzed epoxidation reactions to α-substituted α,β-unsaturated anilides (J. Am. Chem. Soc. 1997, 119, 2329-2330; J. Am. Chem. Soc. 2001, 123, 2725-2732).

Variable Synthesis of the Optically Active Thiotetronic Acid Antibiotics Thiolactomycin, Thiotetromycin, and 834‐B1

In seven steps: The antibiotic (+)-thiolactomycin was synthesized in seven steps and with 16 % overall yield from 4-acetoxy-2-methyl-2-buten-1-al, an intermediate of the industrial synthesis of vitamin A. Key transformations were the catalytic asymmetric Sharpless epoxidation of an ethoxycarbonyl-substituted pentadienol (93 % ee) and a regio- and stereoselective thiolysis of the resulting epoxide (see scheme).

Catalytic Asymmetric Epoxidation of α,β‐Unsaturated Esters with Chiral Yttrium–Biaryldiol Complexes

The full details of the asymmetric epoxidation of alpha,beta-unsaturated esters catalyzed by yttrium complexes with biaryldiol ligands are described. An yttrium-biphenyldiol catalyst, generated from Y(OiPr)3-biphenyldiol ligand-triphenylarsine oxide (1:1:1), is suitable for the epoxidation of various alpha,beta-unsaturated esters. With this catalyst, beta-aryl alpha,beta-unsaturated esters gave high enantioselectivities and good yields (< or = 99% ee). The reactivity of this catalyst is good, and the catalyst loading could be decreased to as little as 0.5-2 mol % (the turnover number was up to 116), while high enantiomeric excesses were maintained. For beta-alkyl alpha,beta-unsaturated esters, an yttrium-binol catalyst, generated from Y(OiPr)3-binol ligand-triphenylphosphine oxide (1:1:2), gave the best enantioselectivities (< or = 97% ee). The utility of the epoxidation reaction was demonstrated in an efficient synthesis of (-)-ragaglitazar, a potential antidiabetes agent.

Catalytic Asymmetric Epoxidation of α-Methyl α,β-Unsaturated Anilides as Ester Surrogates

Catalytic asymmetric epoxidation of α-methyl α,β-unsaturated carboxylic acid derivatives was achieved using anilide as a template. The Pr(Oi-Pr)3-6,6′-Ph-BINOL complex (10 mol%) with a Ph3P(O) (30 mol%) additive promoted the epoxidation of anilides in up to 99% yield and 88% ee. For α-methyl-β-Ph α,β-unsaturated anilide, the Gd(Oi-Pr)3-6,6′-I-BINOL complex (10 mol%) with Ar3P(O) (30 mol%, Ar = 4-methoxyphenyl) was suitable, giving epoxide in 87% yield and 78% ee.

Catalytic Asymmetric Epoxidation of α,β‐Unsaturated N‐Acylpyrroles as Monodentate and Activated Ester Equivalent Acceptors.

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.

Non‐Aqueous Iminium Salt Mediated Catalytic Asymmetric Epoxidation.

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.

Catalytic Asymmetric Epoxidation of Chalcones under Poly(ethylene glycol)‐Supported Cinchona Ammonium Salt Catalyzed Conditions.

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.

Stereodivergent Syntheses of Conduramines and Aminocyclitols

[reaction: see text] The diastereomers of 6-amino-cyclohex-3-ene-1,2-diols 1 (4-deoxy-3-conduramines), key building blocks for the syntheses of a large range of natural products, have been enantioselectively prepared. Diastereoselective dihydroxylation of the compounds provided a new family of aminocyclitols 2 (deoxyinosamines). The key reactions of our syntheses are Sharpless catalytic asymmetric epoxidation, diastereoselective addition of vinylmetal reagents to the aldehydes, and ring-closing metathesis (RCM).

Non-aqueous iminium salt mediated catalytic asymmetric epoxidation

A range of substituted dihydroisoquinolinium salts has been tested in the catalytic asymmetric epoxidation of simple alkenes using our newly developed non-aqueous conditions employing tetraphenylphosphonium monoperoxysulfate (TPPP) as oxidant, giving ees of up to 97%.

Catalytic asymmetric epoxidation of α,β-unsaturated N-acylpyrroles as monodentate and activated ester equivalent acceptors

Abstract Catalytic asymmetric epoxidation of α,β-unsaturated N-acylpyrroles as monodentate and activated ester equivalent acceptors is described. A Sm(O-i-Pr)3/(R)-H8-BINOL complex promoted the epoxidation reaction to afford products in high yield (up to quant) and high enantiomeric excess (up to >99.5% ee). Reaction proceeded smoothly using cumene hydroperoxide (CMHP) with low explosive hazard, and completed within 0.2–0.5 h with 5 mol % catalyst. Catalyst loading was successfully reduced to as little as 0.02 mol %. The N-acylpyrrole properties as well as efficient synthesis of α,β-unsaturated N-acylpyrroles are also described.

Practical Synthesis of Shi′s Diester Fructose Derivative for Catalytic Asymmetric Epoxidation of Alkenes.

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.

Arabinose‐Derived Ketones as Catalysts for Asymmetric Epoxidation of Alkenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Practical Synthesis of Shi's Diester Fructose Derivative for Catalytic Asymmetric Epoxidation of Alkenes

[reaction: see text] A practical synthesis of Shi's diester 3 for catalytic asymmetric epoxidations has been developed. The catalyst has been prepared in multigram quantities from D-fructose in four steps with a 66% overall yield. Efficiency, cost, and selectivity aspects of the reagents involved for its preparation have been taken care of during its preparation. The workup procedures have been simplified to the bare minimum, rendering a very practical preparation method. The well-known high efficiency of this catalyst 3 in the epoxidation of alpha,beta-unsaturated carbonyl compounds has also proved to be high in unfunctionalized alkenes.

Catalytic Asymmetric Epoxidation of α,β‐Unsaturated Esters Using an Yttrium‐Biphenyldiol Complex.

We succeeded in a catalytic asymmetric epoxidation reaction of α,β-unsaturated esters via a conjugate addition of an oxidant using 2−10 mol % of the yttirium-chiral biphenyldiol catalyst. A variety of substrates with β-aryl and β-alkyl substituents were epoxidized efficiently, yielding the corresponding α,β-epoxy esters in up to 97% yield and 99% ee.