A highly enantioselective phase-transfer catalyzed epoxidation of enones with a mild oxidant, trichloroisocyanuric acidElectronic supplementary information (ESI) available: experimental details. See http://www.rsc.org/suppdata/cc/b3/b308042k/

Ye, Jinxing; Wang, Yongcan; Liu, Renhua; Zhang, Guofu; Zhang, Qing; Chen, Jiping; Liang, Xinmiao

doi:10.1039/b308042k

Cited by 54 publications

(17 citation statements)

References 15 publications

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“…In the presence of 10 mol % of chiral catalyst A2, the asymmetric epoxidation of enones under non-aqueous solid-liquid conditions provided the epoxy ketones in 73 ± 93% ees and 76 ± 94% yields. Although the ees are similar to or slightly lower than those obtained under liquid-liquid conditions, [8] the yields are good in almost all cases. Coupled with the fact that the product separation is more convenient excluding the wet viscid isocyanuric acid, we believe that this new non-aqueous procedure holds considerable promise for the future applications.…”

Section: Full Papersmentioning

confidence: 81%

“…[10] This process can take place under basic conditions as well and produce aqueous hypochlorite salt, which is a mild oxidant for the asymmetric epoxidation of a,b-enones under liquid-liquid phase-transfer catalytic conditions. [8] Interestingly, we found that this epoxidation could occur under non-aqueous conditions when using solid potassium hydroxide instead of its aqueous solution, and the reaction procedure is more convenient for product separation excluding the wet viscid isocyanuric acid.…”

Section: Introductionmentioning

confidence: 99%

“…Recently, we have recognized that trichloroisocyanuric acid (TCCA) can serve as an efficient alternative to these oxidants for the asymmetric epoxidation of a,b-enones with a high enantioselectivity. [8] TCCA is a cheap, safe, inexpensive and efficient reagent for the oxidation of ethers, thioethers, aldehydes, acetals and alcohols. [9] The decomposition of TCCA under acidic or neutral conditions produces hypochlorous acid.…”

Section: Introductionmentioning

confidence: 99%

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Trichloroisocyanuric Acid: A Convenient Oxidation Reagent for Phase‐Transfer Catalytic Epoxidation of Enones under Non‐Aqueous Conditions

Wang

Chen

et al. 2004

Adv Synth Catal

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Trichloroisocyanuric acid (TCCA) is a cheap, safe and readily available alternative to the commonly used hydrogen peroxide and hypochlorite for the phase-transfer catalytic epoxidation of a,benones under non-aqueous conditions. A variety of chalcone derivatives give the corresponding epoxides with quantitative conversion and satisfactory yields in just a few hours under mild conditions. An asymmetric variant of the epoxidation can be carried out in the presence of chiral N-anthracenylmethylcinchonidine bromide catalyst giving 73 ± 93% ees and 76 ± 94% yields.

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Section: Full Papersmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Trichloroisocyanuric Acid: A Convenient Oxidation Reagent for Phase‐Transfer Catalytic Epoxidation of Enones under Non‐Aqueous Conditions

Wang

Chen

et al. 2004

Adv Synth Catal

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“…A somewhat limited applicability of this system was observed with less-reactive enones, such as those which bore an alkyl group at the carbonyl position and which required long reaction times so [46]. Subsequently, trichloroisocyanuric acid (TCCA) was shown to be an alternative for use with catalyst 46, as a safe and inexpensive oxygen source [47]. Corey suggested a model to account for the formation of the (αS, βR)-enantiomer of the product in the epoxidation of trans-chalcones promoted by catalyst 46 (Figure 9.8).…”

Section: Phase-transfer Catalystsmentioning

confidence: 99%

Asymmetric Epoxidations of α,β‐Unsaturated Carbonyl Compounds

Lattanzi

2010

Catalytic Asymmetric Conjugate Reactions

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The asymmetric epoxidation of alkenes is a fundamental process in organic synthesis, and unquestionably the most exploited approach to synthesize epoxides [1]. Alternative useful strategies to access these molecules concern the enantioselective alkylidenation of carbonyl compounds by ylides [2] and the Darzens condensation [3]. Enantioenriched epoxides are important targets of biological and pharmaceutical interest. Moreover, their high synthetic potential as intermediates is exemplified by the stereoselective ring opening with nucleophiles, which affords a variety of compounds with two contiguous chiral centers, the absolute configuration of which can be controlled [4].During the past few decades, metal-based electrophilic asymmetric methodologies of epoxidation have been successfully developed and found widespread application in multistep synthesis; these include: the Sharpless' epoxidation of allylic alcohols mediated by the Ti/tartrate system [5]; and the Jacobsen's and Katsuki's epoxidation of unfunctionalized alkenes by using Mn-and Ti-/Salen complexes [6]. More recently, chiral Ru-Pt and Fe-Pt complexes have proved to be effective in the enantioselective epoxidation of disubstituted aromatic and challenging terminal unfunctionalized alkenes [7]. Impressive results have been achieved by the groups of Yang [8] and Shi [9] for the electrophilic organocatalyzed asymmetric epoxidation of a great variety of olefins such as trisubstituted, disubstituted trans-alkenes, terminal alkenes, dienes, and enynes (to cite the most relevant examples), and by the in situ generation of dioxiranes derived from chiral ketones. Within the context of asymmetric epoxidation catalyzed by organic promoters, notable achievements have also been attained by using chiral oxaziridines [10], oxaziridinium salts [11], amines [12], and peptide-based peracids [13].The epoxidation of α,β-unsaturated carbonyl compounds leads to the formation of another valuable class of functionalized epoxides [14], the carbonyl and epoxide groups of which can be selectively manipulated to provide enantioenriched products such as allylic epoxy alcohols, α-or β-hydroxy ketones, and α,β-epoxy esters [15]. The general approach for the epoxidation of electron-poor Catalytic Asymmetric Conjugate Reactions. Edited by Armando Córdova

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“…Recently, we have reported that a novel oxidation system, trichloroisocyanuric acid (TCCA) with an inorganic base such as potassium hydroxide, could serve as an efficient alternative for these oxidants in the epoxidation of enones with high activity and enantioselectivity under chiral phase-transfer conditions. [10] It is well known that the Claisen-Schmidt condensation (CSC) is a convenient method for the synthesis of enones. The reaction of a ketone and an aldehyde can occur under aqueous or alcoholic alkaline conditions.…”

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confidence: 99%

Convenient Preparation of Chiral α,β‐Epoxy Ketones via Claisen–Schmidt Condensation‐Epoxidation Sequence

Wang

Liang

2007

Adv Synth Catal

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A novel Clasisen-Schmidt condensationepoxidation sequence of aldehydes and ketones was developed to produce a series of chiral a,b-epoxy ketones under asymmetric phase-transfer catalytic conditions. The organocatalytic method reported here can afford chiral a,b-epoxy ketones under mild conditions with moderate to good yields and up to 96 % ee.Keywords: aldehydes; asymmetric catalysis; condensation; epoxidation; ketones; one-pot Chiral epoxides are important intermediates and precursors for further chemical transformations.[1] In recent years, a clean and efficient asymmetric phasetransfer catalytic epoxidation access to chiral a,bepoxy ketones has become particularly attractive in the development of asymmetric processes. [2][3][4][5][6][7][8][9] A series of chiral quaternary ammonium salts such as Cinchona alkaloid derivatives and N-spiro C 2 -symmetric binaphthyl derivatives have shown high catalytic efficiency and remarkable asymmetric control. In these bi-or triphase catalytic systems, a variety of oxidants such as hydrogen peroxide, sodium or potassium hypochlorite have demonstrated different reaction activities and selectivities under different reaction conditions. Recently, we have reported that a novel oxidation system, trichloroisocyanuric acid (TCCA) with an inorganic base such as potassium hydroxide, could serve as an efficient alternative for these oxidants in the epoxidation of enones with high activity and enantioselectivity under chiral phase-transfer conditions. [10] It is well known that the Claisen-Schmidt condensation (CSC) is a convenient method for the synthesis of enones. The reaction of a ketone and an aldehyde can occur under aqueous or alcoholic alkaline conditions. Since a base is needed in both condensation and epoxidation, we envisioned that it would be possible to combine the two reactions into a one-pot sequential process. We hoped that the CSC products could be directly converted to epoxy ketones through asymmetric phase-transfer catalytic epoxidation without any isolation. Such a one-pot reaction sequence is a highly efficient and economic method in organic synthesis. To the best of our knowledge, this combination of condensation and epoxidation process has not been reported before. We herein present our results on the one-pot CSC-asymmetric epoxidation reaction to access chiral a,b-epoxy ketones. The aldehyde and ketone were treated with aqueous potassium hydroxide to yield the enone. TCCA and chiral quaternary ammonium salt were then added to this mixture to afford the corresponding a,b-epoxy ketone with moderate to high yield and satisfactory enantioselectivity (Scheme 1).Scheme 1. Claisen-Schmidt condensation-epoxidation sequence for the preparation of chiral a,b-epoxy ketones.

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A highly enantioselective phase-transfer catalyzed epoxidation of enones with a mild oxidant, trichloroisocyanuric acidElectronic supplementary information (ESI) available: experimental details. See http://www.rsc.org/suppdata/cc/b3/b308042k/

Cited by 54 publications

References 15 publications

Trichloroisocyanuric Acid: A Convenient Oxidation Reagent for Phase‐Transfer Catalytic Epoxidation of Enones under Non‐Aqueous Conditions

Trichloroisocyanuric Acid: A Convenient Oxidation Reagent for Phase‐Transfer Catalytic Epoxidation of Enones under Non‐Aqueous Conditions

Asymmetric Epoxidations of α,β‐Unsaturated Carbonyl Compounds

Convenient Preparation of Chiral α,β‐Epoxy Ketones via Claisen–Schmidt Condensation‐Epoxidation Sequence

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