Novel conditions for the Juliá–Colonna epoxidation reaction providing efficient access to chiral, nonracemic epoxides

Geller, Thomas; Gerlach, Arne; Krüger, Christa M.; Militzer, Hans‐Christian

doi:10.1016/j.tetlet.2004.04.188

Cited by 40 publications

(11 citation statements)

References 16 publications

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“…The addition of small amounts of tetrabutylammonium bromide (TBAB) as a phase-transfer catalyst (PTC) to the heterogeneous reaction mixture resulted in a significant acceleration of the epoxidation reaction. [4] With this new protocol we could obtain complete conversion of chalcone 1 into epoxy ketone 3 with high chemo-and enantioselectivity (94% ee) within 7 minutes at room temperature. In contrast to our new procedure less than 60% conversion has been observed without TBAB under otherwise identical epoxidation conditions after 1.5 hours.…”

Section: Abstract: Amino Acids; Asymmetric Catalysis; Epoxidation; Hementioning

confidence: 95%

Scale‐Up Studies for the Asymmetric Juliá–Colonna Epoxidation Reaction

Gerlach

Geller

2004

Adv Synth Catal

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The asymmetric Juliá -Colonna epoxidation reaction under triphasic/PTC conditions has been successfully scaled-up to a one-hundred gram substrate level providing the corresponding epoxy ketone with high optical purity (up to 97% ee) and in good yield (75 -78%). The amount of polyamino acid catalyst could be reduced leading to a simplified reaction work-up. In order to minimise the overall reaction time baffled reactors with pitched-blade impellers have been employed.Keywords: amino acids; asymmetric catalysis; epoxidation; heterogeneous catalysis; phase-transfer catalysisThe poly-a-amino acid-catalysed asymmetric Juliá -Colonna epoxidation has emerged as an efficient synthetic method for the enantioselective functionalisation of a,b-unsaturated ketones. Since its discovery in 1980, [1] the heterogeneous catalyst and the oxidant/solvent system has been optimised further so that now a broad range of substrates containing a substituted enone system can be epoxidised in high yield and with high enantioselectivity.[2]Recently, we have developed a new protocol for the Juliá -Colonna epoxidation reaction under triphasic conditions [3] employing our own polyamino acid catalyst. The addition of small amounts of tetrabutylammonium bromide (TBAB) as a phase-transfer catalyst (PTC) to the heterogeneous reaction mixture resulted in a significant acceleration of the epoxidation reaction.[4] With this new protocol we could obtain complete conversion of chalcone 1 into epoxy ketone 3 with high chemo-and enantioselectivity (94% ee) within 7 minutes at room temperature. In contrast to our new procedure less than 60% conversion has been observed without TBAB under otherwise identical epoxidation conditions after 1.5 hours.Some time ago we became interested in preparing enantiomerically pure epoxy ketone 4 as a valuable synthetic intermediate. Using our newly developed triphasic/PTC conditions 4 could be obtained successfully from enone 2[5] with 97%ee on a small scale.

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Section: Abstract: Amino Acids; Asymmetric Catalysis; Epoxidation; Hementioning

confidence: 95%

Scale‐Up Studies for the Asymmetric Juliá–Colonna Epoxidation Reaction

Gerlach

Geller

2004

Adv Synth Catal

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“…An improvement of the original three-phase system of the Juliá-Colonna epoxidation was recently developed by Geller [69], whereby addition of the phase-transfer agent tetrabutylammonium bromide (TBAB) as co-catalyst in the asymmetric epoxidation of trans-chalcone caused an increase in the concentration of peroxide in the organic phase. In addition, the reaction rate was notably higher, while the epoxide was produced in >99% conversion and 94% ee in only 1.5 h. Likewise, the amount of oxidant and base could be reduced from 30 to 1.3 equiv.…”

Section: Polyamino Acidsmentioning

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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“…Although the reaction was originally performed in a triphasic solvent system [27], phase-transfer catalysis [28] or nonaqueous conditions [29] were found to increase the reaction rates considerably. The reaction can be applied to dienones, thus affording vinylepoxides with high regio-and enantioselectivity (Scheme 9.7a) [29].…”

Section: From Dienones or Unsaturated Amidesmentioning

confidence: 99%