Predominance of the axial conformation of 4-methoxycyclohexanone

Stolow, Robert D.; Giants, Thomas W.

doi:10.1039/c29710000528

Cited by 19 publications

(13 citation statements)

References 2 publications

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“…Although 2,6-dimethylcyclohexanones could be used as constrained models, 33,34 the resulting imines and hydrazones could be destabilized by interactions between the substituents on the nitrogen atom and the nearby methyl groups. These interactions could lead to distortion of the ring and therefore perturbations in the coupling constants.…”

Section: Resultsmentioning

confidence: 99%

Spectroscopic and X-ray Crystallographic Evidence for Electrostatic Effects in 4-Substituted Cyclohexanone-Derived Hydrazones, Imines, and Corresponding Salts

Dibble

Woerpel

2011

J. Org. Chem.

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The axial conformer of several 4-substituted cyclohexanone hydrazone salts was found to predominate in solution. Changes in the charge of the molecule and the polarity of the solvent led to changes in the conformational preference of each molecule that was consistent with electrostatic stabilization of the axial conformer. 1 H NMR spectroscopic analysis was utilized to determine the structure of cyclohexanone-derived substrates by comparison to conformationally restricted transdecalone derivatives and computational models. X-ray crystallography demonstrated that the axial configuration of a pendant benzyloxy group is the preferred conformation of an iminium ion in the solid state. The structure of a neutral hydrazone was also determined to favor the axial configuration for a pendant benzyloxy group in the solid state.

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Section: Resultsmentioning

confidence: 99%

Spectroscopic and X-ray Crystallographic Evidence for Electrostatic Effects in 4-Substituted Cyclohexanone-Derived Hydrazones, Imines, and Corresponding Salts

Dibble

Woerpel

2011

J. Org. Chem.

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“…It is more difficult to apply this analysis quantitatively to the oxidations of ketones containing polar substituents such as 1g − k since their conformational behavior is complex and influenced by the presence of the carbonyl group dipole. − Moreover, specific interactions between the substituent and the protein (i.e., hydrogen bonds) may introduce additional complications. Nontheless, the high or relatively high enantioselectivities observed for the oxidations of ketones 1i , 1j , and 1 k makes this methodology useful for preparative purposes.…”

Section: Resultsmentioning

confidence: 99%

Asymmetric Baeyer−Villiger Oxidations of 4-Mono- and 4,4-Disubstituted Cyclohexanones by Whole Cells of EngineeredEscherichiacoli

et al. 2001

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Whole cells of an Escherichia coli strain that overexpresses Acinetobacter sp. NCIB 9871 cyclohexanone monooxygenase have been used for the Baeyer-Villiger oxidations of a variety of 4-mono- and 4,4-disubstituted cyclohexanones. In cases where comparisons were possible, this new biocatalytic reagent provided lactones with chemical yields and optical purities that were comparable to those obtained from the purified enzyme or a strain of bakers' yeast that expresses the same enzyme. The efficient production of cyclohexanone monooxygenase in the E. coli expression system (ca. 30% of total soluble protein) allowed these oxidations to reach completion in approximately half the time required for the engineered bakers' yeast strain. Surprisingly, 4,4-disubstituted cyclohexanones were also accepted by the enzyme, and the enantioselectivities of these oxidations could be rationalized by considering the conformational energies of bound substrates along with the enzyme's intrinsic enantioselectivity. The enzyme expressed in E. coli cells also oxidized several 4-substituted cyclohexanones bearing polar substituents, often with high enantioselectivities. In the case of 4-iodocyclohexanone, the lactone was obtained in > 98% ee and its absolute configuration was assigned by X-ray crystallography. The crystal belongs to the monoclinic P2(1) space group with a = 5.7400(10), b = 6.1650(10), c = 11.377(2) A, b = 99.98(2) degrees, and Z = 2. Taken together, these results demonstrate the utility of an engineered bacterial strain in delivering useful chiral building blocks in an experimentally simple manner.

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“…(10) (11) The conformational preferences exerted by a single alkoxy substituent can be manifested in systems with several alkoxy groups. In our studies of carbohydrate oxocarbenium ions that serve as models for enzyme inhibitors, 67 we treated the pentose acetal 30 with allyltrimethylsilane in the presence of a Lewis acid to provide the product 31 with high diastereoselectivity (eqn 12).…”

Section: Investigations and Applications Of Electrostatically Stabili...mentioning

confidence: 99%

Electrostatic interactions in cations and their importance in biology and chemistry

2006

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Electrostatic effects exert strongly stabilizing influences on cations, in many cases controlling the conformational preferences of these cations. The lowest energy conformers are ones where the positive charge is brought closest to substituents bearing partial negative charges. These conformational biases, along with stereoelectronic effects, can control the stereoselectivity of reactions involving carbocationic intermediates.

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Predominance of the axial conformation of 4-methoxycyclohexanone

Cited by 19 publications

References 2 publications

Spectroscopic and X-ray Crystallographic Evidence for Electrostatic Effects in 4-Substituted Cyclohexanone-Derived Hydrazones, Imines, and Corresponding Salts

Spectroscopic and X-ray Crystallographic Evidence for Electrostatic Effects in 4-Substituted Cyclohexanone-Derived Hydrazones, Imines, and Corresponding Salts

Asymmetric Baeyer−Villiger Oxidations of 4-Mono- and 4,4-Disubstituted Cyclohexanones by Whole Cells of EngineeredEscherichiacoli

Electrostatic interactions in cations and their importance in biology and chemistry

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