Zur oxidativen Dimerisierung von CH‐Säuren

Peek, R.; Streukens, M.; Thomas, H. G.; Vanderfuhr, AndrÉ; Wellen, U.

doi:10.1002/cber.19941270713

Cited by 8 publications

(1 citation statement)

References 22 publications

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“…Besides Br, 1411, I, [42] and Cu" salts [43] were also used as oxidation reagents. Electrochemical oxidative coupling of enolates was only reported twice [42b] [44]. The intramolecular oxidative coupling of a bis-enolate is an attractive alternative to the well known Dieckman cyclization and to the acyloin condensation and was successfully applied for the construction of three-, four-, five-, and six-membered carbocycles [45].…”

Section: Lntramolecular Oxidativementioning

confidence: 99%

Synthesis and First Applications of a New Chiral Auxiliary (tert‐butyl 2‐(tert‐butyl)‐5,5‐dimethyl‐4‐oxoimidazolidine‐1‐carboxylate)

Studer

Hintermann

Seebàch³

1995

Helvetica Chimica Acta

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Both enantiomers of teut-butyl 2-(tert-butyl)-5,5-dimethyl-4-oxoimidazolidine-1 -carboxylate (1 1 ; Bbdmoic) were prepared from L-alanine (Schemes I and 2). The parent heterocycle, 2-fert-butyl-5,5-dimethylimidazolidin-4-one (1 2; from 2-aminoisobutyramide, H-Aib-NH,, and pivalaldehyde) was also available in both enantiomeric forms by resolution with 0.0'-dibenzoyltartaric acid. The compound ( R ) -or (S)-11 was used as an auxiliary, but also as a chiral Aib building block in a dipeptide synthesis. The 3-propanoyl derivative 13 of (R)-11 was used for the preparation of enantiomerically pure 2-methyl-3-phenylpropanoic acid (enantiomer ratio (ex.) 99.5:0.5), by benzylation of the Zn-enolate (+ 14; Scheme 3 ) . Oxidative coupling of the bis-enolate derived from heptanedioic acid and (S)-11 (+23) and methanolysis of the auxiliary gave dimethyl trans-cyclopentane-l,2-dicarboxylate (26) with an e.r. of 93 :7 (Scheme 5, Fig. 5). The 3-(Boc-Gly)-Bbdmoic derivative 29 was doubly deprotonated and, after addition of ZnBr, alkylated with alkyl, benzyl, or allyl halides to give the higher amino-acid derivatives with excellent selectivities (e.r. > 99.5:0.5, Schemes 6 and 7). Michael additions of cuprates to [(E)-MeCH=CHCO]-Bbdmoic 36 occurred in high yields, but high diastereoselectivities were only observed with aryl cuprates (diastereoisomer ratio (d,r.) 99:l for R = Ph, Scheme 8). Finally, 3-(Boc-CH2)-Bbdmoic 17 was alkylated through the ester Li-enolate with primary and secondary alkyl, allyl, and benzyl halides with diastereoselectivities (ds) ranging from 91 to 98%, giving acetals of Boc-Aib-Xxx-O(r-Bu) dipeptides (Scheme 4). The effectiveness of Bbdmoic is compared with that of other chiral auxiliaries previously used for the same types of transformations.1. Introduction. -Since the first reports of chiral-auxiliary-induced stereoselective reactions in the early 20th century by McKenzie [l], many 'chiral inductors' have been developed and successfully applied in asymmetric synthesis. The chemistry of auxiliarycontrolled stereoselective reactions (covalently bound) has been reviewed by several authors [2-81. Normally, these chiral auxiliaries are derived from natural sources such as amino acids [2] [3], carbohydrates [4] [5], terpenes [6], and steroids [9]. Synthetic auxiliaries that can be recovered after a reaction have also been described [7] [8] [lo-131. In Fig. I , a collection of successfully applied chiral auxiliaries is presented.During the last ten years, we have developed various chiral building blocks, based on five-membered heterocycles, oxazolidinones [28], and imidazolidinones [29], for the preparation of enantiomerically pure natural and unnatural amino acids. In the present paper, we report the synthesis and some applications of a new chiral auxiliary which is based on the imidazolidinones.

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Section: Lntramolecular Oxidativementioning

confidence: 99%

Synthesis and First Applications of a New Chiral Auxiliary (tert‐butyl 2‐(tert‐butyl)‐5,5‐dimethyl‐4‐oxoimidazolidine‐1‐carboxylate)

Studer

Hintermann

Seebàch³

1995

Helvetica Chimica Acta

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Radicaloid‐Type Oxidative Decomposition Of Beer Bittering Agents Revealed

Huvaere

Andersen

Olsen

et al. 2003

Chemistry A European J

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trans-Isohumulones, dihydroisohumulones, tetrahydroisohumulones, and humulinones, which are important hop-derived flavor components of beer, were found, by using electrolysis of organic solutions, to be stable against oxidation, like weak acids; however, they are readily oxidized in their anionic forms as present in beer. Oxygen- and carbon-centered radicals were formed by oxidation and identified by using spin trapping under aerobic and anaerobic conditions, followed by EPR (electron paramagnetic resonance) spectroscopy. Generated radicals were reactive, most likely degrading into products lacking the tricarbonyl chromophore; this is typical of five-membered-ring hop derivatives. Thus, flavor-active beer constituents may degrade oxidatively in the absence of oxygen, thereby leading to reaction products that escape UV detection.

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Oxidation of Ketones, Aldehydes, and Carboxylic Acids

Grimshaw

2000

Electrochemical Reactions and Mechanisms in Organic Chemistry

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Zur oxidativen Dimerisierung von CH‐Säuren

Cited by 8 publications

References 22 publications

Synthesis and First Applications of a New Chiral Auxiliary (tert‐butyl 2‐(tert‐butyl)‐5,5‐dimethyl‐4‐oxoimidazolidine‐1‐carboxylate)

Synthesis and First Applications of a New Chiral Auxiliary (tert‐butyl 2‐(tert‐butyl)‐5,5‐dimethyl‐4‐oxoimidazolidine‐1‐carboxylate)

Radicaloid‐Type Oxidative Decomposition Of Beer Bittering Agents Revealed

Oxidation of Ketones, Aldehydes, and Carboxylic Acids

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