The vinylogous anomeric effect in 3-alkyl-2-chlorocyclohexanone oximes and oxime ethers

Denmark, Scott E.; Dappen, Michael S.; Sear, Nancy L.; Jacobs, Robert T.

doi:10.1021/ja00165a034

Cited by 77 publications

(44 citation statements)

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“…[2] led to the values appearing in Table 2. These results, in contrast to earlier assertions (2,(5)(6)(7)9), show no axial preference for the methoxy substituent except in the least polar solvent, cyclohexane-d,,.…”

contrasting

confidence: 99%

On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

Fraser¹,

Faibish²

1995

Can. J. Chem.

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Abstract:The value for the equilibrium constant representing the ratio of equatorial to axial conformers for 2-methylthio-and 2-methoxycyclohexanone has been measured in five solvents using 500 MHz 'H nuclear magnetic resonance. In cyclohexane solvent, the methylthio group is found to have a large axial preference while that for the methoxy is negligible. For both compounds the equilibrium shows a strong solvent dependence.Comparison of these results with those known for the halo derivatives shows the amount of axial to increase in the order: fluoro, methoxy, chloro, bromo, and methylthio. With the aid of molecular mechanics calculations it is concluded that the order of conformational preference can be attributed to a variation in the van der Waals interaction between the substituent and the carbonyl group in the equatorial conformer.Key words: a-substituted cyclohexanones, conformation, MMX calculations, steric and dipolar effects.Resume : Utilisant la rksonance magnCtique nuclCaire du 'H a 500 MHz et opCrant dans cinq solvants, on a mesurC la valeur de la constante d'tquilibre reprksentant le rapport des conformkres Cquatorial et axial des 2-mCthylthio-et 2-mCthoxycyclohexanones. Dans le cyclohexane comme solvant, on trouve que le groupe mtthylthio a une prCfCrence axiale alors que celle du groupe mCthoxy est negligeable. Pour les deux composts, 1'Cquilibre depend fortement du solvant. Une comparaison de ces rCsultats avec ceux connus pour les dCrivCs halogCnCs montre que la quantitC de conformkre axial augrnente dans l'ordre : fluoro, mCthoxy, chloro, bromo et rntthylthio. En se basant sur des calculs de mCcanique molCculaire, on conclut que l'ordre de prCftrences conformationnelles peut Etre attribuC a une variation de l'interaction de van der Waals entre le substituant et le groupe carbonyle du conformkre Cquatorial.

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confidence: 99%

On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

Fraser¹,

Faibish²

1995

Can. J. Chem.

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“…A comparison of the chemical shifts in 13 C NMR spectra of resonances for C-6 and C-8 and the corresponding starting carbonyl compounds showed a significant strong-field shift for C-6 in 8 and 9 ('G = 14.3-15.3 ppm) (the change of shift for C-8 was about 'G 5.7 ppm). These results confirmed that the oxime had the (E)-configuration [16].…”

supporting

confidence: 76%

Synthetic transformations of higher terpenoids. XXVII.* Synthesis of 7-hydroxylabdanoids and their transformations

et al. 2012

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Allylic oxidation of phlomisoic acid and its methyl ester by selenium dioxide occurred stereoselectively to form 7D-hydroxy derivatives of labdanoids, which were oxidized by active manganese dioxide to 7-ketofuranolabdanoids. Oximation of the last by hydroxylamine hydrochloride in MeOH in the presence of NaOAc gave pure (E)-ketooximes. Beckmann rearrangement of 7-ketooximes of phlomisoic acid and its methyl ester occurred with formation of the corresponding octahydro-1H-benzoazepines.Keywords: phlomisoic acid, synthesis, 7R-hydroxy-15,16-epoxy-8(9),13(16),14-labdatrien-18-oic acid, 7-ketolabdanoids, oximes, 5-furan-3-ylethylbenzoazepines, XSA.Furan-containing labdanoids functionalized in ring B were isolated from extracts of plants that exhibit sedative and uterotonic properties and are used in folk medicine for cardiovascular disorders [2]. 7-Keto-and 7-hydroxyfurolabdanoids showed antibacterial [3], antifeedant [4], and cytotoxic activity [5]. The isolation of 8,9-secofuranolabdanoids that exhibited cytotoxicity against human tumor cells was reported [6]. Promising inhibitors of N-O synthase were recently found among labdanoids modified in ring B [7]. Therefore, it seemed interesting to synthesize modified labdanoids. Currently known approaches are most often based on transformations of available natural metabolites [8,9]. We proposed earlier methods for preparing the plant diterpenoid phlomisoic acid (1) and its ester 2 from lambertianic acid, an available metabolite of Pinus sibirica R. Major [10,11]. Herein results from a study of the transformations of furanolabdanoids 1 and 2 in ring B are reported.Allylic oxidation of 1 and 2 by SeO 2 in dioxane occurred stereoselectively to form 7D-hydroxy derivatives 3 and 4 (59 and 74% yields, respectively) (Scheme 1). This could be explained by attack of the reagent from the less hindered D-side.

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“…Data on substituted cyclohexanone oximes and oxime ethers reflect hyperconjugative effects that can be investigated by vicinal interproton coupling constants and anisotropic deshielding by the oxime oxygen 6 . More recent work 7 is also based on fluorine coupling to protons, carbon and nitrogen and includes theoretical calculations.…”

Section: Structural and Conformational Effectsmentioning

confidence: 99%

“…1 H NMR chemical shifts (ppm from internal TMS) of oximes 44-51 measured for 0.1 M solutions in DMSO-d6 …”

mentioning

confidence: 99%

NMRSpectra of Hydroxylamines, Oximes and Hydroxamic Acids

Seidl

Dias

2010

Patai's Chemistry of Functional Groups

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The vinylogous anomeric effect in 3-alkyl-2-chlorocyclohexanone oximes and oxime ethers

Cited by 77 publications

References 1 publication

On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

Synthetic transformations of higher terpenoids. XXVII.* Synthesis of 7-hydroxylabdanoids and their transformations

NMRSpectra of Hydroxylamines, Oximes and Hydroxamic Acids

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