Reaktionen von Dihalogencarbenen mit Enoläthern

Nerdel, Friedrich; Buddrus, Joachim; Brodowski, Walter; Hentschel, Peter; Klamann, Dieter; Weyerstahl, Peter

doi:10.1002/jlac.19677100106

Cited by 31 publications

(6 citation statements)

References 23 publications

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“…The formation of hemiacetals 8 was eliminated by reduction of 4b at 40 °C, but this tended to be at the expense of the formation of more 7b . The presence of the oxepane 9 as a minor component of the product mixture obtained from the reduction of substrate 4f was confirmed by comparison of observed data with those previously reported …”

Section: Resultssupporting

confidence: 86%

Formation of Some Oxygen-Containing Heterocycles by Radical Cyclization: The Stereochemical Influence of Anomeric Effects

Beckwith

Page

1998

J. Org. Chem.

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The influence of the anomeric effect on radical cyclization has been examined by determining the stereochemical outcome of the ring closure of 10 suitably substituted radicals. The stereochemistry of the products formed from the acyclic precursors 4a-f indicates that for suitably constituted radicals anomeric interactions stabilize pseudoaxially substituted transition structures 14 thus affording products with stereochemistry the reverse of that normally observed.In recent times, the use of free radical reactions for chemical synthesis has grown steadily in popularity as the processes which govern and control their outcomes have become better understood. 1 Intramolecular addition reactions of suitably constituted alkenyl radicals and related species are particularly interesting since they readily afford a variety of ring systems commonly found in many natural products. 1 The advantages offered by such reactions generally include high regioselectivity, modest to good stereoselectivity, 1-5 and high chemoselectivity. [1][2][3][4][5] The highly regioselective exo-cyclization of the hex-5-enyl radical has been intensively studied. The accurate determination of its kinetics 6 has underpinned its widespread use as a mechanistic probe and as a radical clock. 7 Most monosubstituted hex-5-enyl radicals also undergo regioselective exo-cyclization while conforming to the general stereochemical guideline that 1-or 3-substituted radicals afford predominantly cis-disubstituted products, while 2-or 4-substituted radicals give mainly transdisubstituted products. 5 It is now generally accepted that the cyclization behavior of simple hex-5-enyl systems reflects the stereoelectronic demands of the transition structure. [2][3][4][5] The hypothesis that the strain energy engendered in attaining the optimum orbital overlap for 1,6-ring closure outweighs the steric and thermodynamic factors which would otherwise favor six-membered ring formation 2-5 has received support from theoretical analyses 8 and the modeling of transition structures by a combination of molecular orbital and molecular mechanics calculations. 8 These calculations confirm the original hypothesis that the transition structure for 1,5-exo-cyclization of hex-5-enyl radicals and related species resembles cyclohexane in its chair form. 2-5 Hence the stereoselectivity exhibited in the ring closure of monosubstituted hexenyl radicals and related species is seen to arise from the propensity of cyclizations to proceed through the more stable pseudoequatorially substituted cyclohexane-like conformation of the transition structure rather than through its less stable pseudoaxially substituted conformer. 8 Since calculations of the relative selectivities of the cyclized products tend to be overestimated when only axially substituted chairlike structures are considered, it appears that boatlike transition structures might also be involved in some reactions. 4,8 Cyclizations of hex-5-enyl type radicals containing heteroatoms have also been studied. 1,9,10 In general such spec...

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Section: Resultssupporting

confidence: 86%

Formation of Some Oxygen-Containing Heterocycles by Radical Cyclization: The Stereochemical Influence of Anomeric Effects

Beckwith

Page

1998

J. Org. Chem.

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“…as in the case of the carene-type molecules of our studies. There are then two possible hydrogen shift possibilities remaining: either those of the aforementioned junction hydrogens or, as in the Makosza mechanism, the hydrogen on the carbon α to cyclopropane, which earns its acidity from the "hyperconjugation" to the cyclopropane [14][15][16].…”

Section: Dear Editormentioning

confidence: 99%

On a novel dihalocyclopropane– dihalomethylvinyl rearrangement:Additional mechanistic evidence

Jankowski

BouLaouz²,

Díaz-Torres³

2005

Journal of Spectroscopy

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“…Cette ènone monoterpénique est largement utilisée en industrie pharmaceutique, agroalimentaire et cosmétique ainsi qu'en médecine traditionnelle [5][6][7]. Plusieurs travaux sont orientés vers l'étude de l'activité biologique des huiles essentielles extraites de différentes plantes dont le constituant majoritaire est la R-(+)-pulégone [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], tandis que d'autres ont utilisé la R-(+)-pulégone comme intermédiaire dans la synthèse d'un bon nombre de produits [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43].…”

Section: Introductionunclassified

Synthèse de nouveaux dérives de la R-(+)-pulégone par la technique de four à micro-onde en milieu sec et étude de leur impact sur les champignons attaquant la pomme dans les entrepôts de stockage

Oubair¹,

Fihi²,

Mazouz³

2016

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Dans ce travail on a réalisé la condensation de la R-(+)-pulégone avec une série d’aryaldéhyde en présence d’hydrure de sodium. L’activation par micro-ondes dans des conditions sans solvant, a été applique dans le protocole de synthèse. Le processus est très efficace. Il permet en quelques minutes de préparer de nouveaux dérivés de la pulégone avec des rendements remarquables. Les analyses spectroscopiques à savoir RMN 1H, 13C et IR permet d’envisager les structures des nouveaux produits synthétisés. Ainsi on a étudié l’impact de ces nouveaux produits sur la croissance mycélienne des souches des champignons P. expansum, Alternariat sp et R. stolonifer, isolées des pommes pourries en post-récolte.

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Reaktionen von Dihalogencarbenen mit Enoläthern

Cited by 31 publications

References 23 publications

Formation of Some Oxygen-Containing Heterocycles by Radical Cyclization: The Stereochemical Influence of Anomeric Effects

Formation of Some Oxygen-Containing Heterocycles by Radical Cyclization: The Stereochemical Influence of Anomeric Effects

On a novel dihalocyclopropane– dihalomethylvinyl rearrangement:Additional mechanistic evidence

Synthèse de nouveaux dérives de la R-(+)-pulégone par la technique de four à micro-onde en milieu sec et étude de leur impact sur les champignons attaquant la pomme dans les entrepôts de stockage

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