Conformational analysis. 40. Conformation of 1-methyl-1-phenylcyclohexane and conformational energies of the phenyl and vinyl groups

Eliel, Ernest L.; Manoharan, Muthiah

doi:10.1021/jo00322a056

Cited by 125 publications

(70 citation statements)

References 2 publications

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“…(2) have determined -AGOcH,cH, to be 1.68 + 0.06 kcallmol. Due to the obvious difficulties in the present work of measuring K precisely, our uncertainty is at least a factor of two higher than that quoted in the recent work (2). Nevertheless, it appears that direct determination of -AG0cH=cH2 leads to a smaller value than that obtained from a 1,Cdisubstituted derivative.…”

Section: $contrasting

confidence: 62%

“…Recently there has been renewed interest in determining the conformational preference of the vinyl group in substituted cyclohexanes (2). From low temperature I3C nmr studies of cis-4-methyl-1-vinylcyclohexane, the conformational free energy of the vinyl group, (-AG°CH=CH,), has been determined to be 1.68 + 0.06 kcallmol, only slightly smaller than the currently accepted value of 1.75 + 0.06 kcallmol for the CH, group (3).…”

Section: Introductionmentioning

confidence: 99%

“…Ideally one would prefer to have a direct measure of the conformational preference for a given functionality in the monosubstituted cyclohexane. In the recent report (2) it is stated that the conformational equilibrium in vinylcyclohexane is too one-sided to be measured directly. Considering the early success of high field I3C nmr in studying methylcyclohexane (I), however, we deemed it worthwhile to search for the axial conformer of vinylcyclohexane using the same technique.…”

Section: Introductionmentioning

confidence: 99%

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Low temperature carbon-13 magnetic resonance detection of axial conformers in vinyl- and formylcyclohexane: a deshielding γ–gauche effect

Buchanan¹

1982

Can. J. Chem.

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Using 50.3 MHz 13C nmr at 173 K, distinct resonances for axial conformers of vinyl- and formylcyclohexane have been obtained. Substituent effects for axial and equatorial substitution of these groups have been derived. A deshielding γ–gauche effect was found for the axial substituent carbon of formylcyclohexane, a result attributed to the high preference for rotamers in which the formyl proton does not sterically interfere with syn-axial protons at C-3 and C-5 of the ring. Conformational free energies for the vinyl and formyl groups have been estimated to be 1.49 and 0.84 kcal/mol respectively.

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Section: $contrasting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Low temperature carbon-13 magnetic resonance detection of axial conformers in vinyl- and formylcyclohexane: a deshielding γ–gauche effect

Buchanan¹

1982

Can. J. Chem.

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“…First, a change in the 5-substituent from methyl to phenyl resulted in a decrease in selectivity, which was contrary to the result predicted from the A-values. This result is supported by the fact that in the equilibrium of l-methyl-lphenylcyclohexane conformers, the methyl group prefers the equatorial position by 0.3 kcal/mol (27,28; see also ref. 12).…”

Section: Factors Influencing Diastereoselectivitymentioning

confidence: 69%

“…Substrates 25 and 26, which have a 5-ethyl and a 5-isopropyl group, respectively, were synthesized by the introduction of the alkyl groups through the copper-catalyzed conjugate addition (13) of Grignard reagents to 2-penten-5-olide (20) and the subsequent transformations were similar to those described above (Scheme 5). To synthesize the 5-phenyl substrate 30 the requisite 3-phenyl-6-valerolactone (28) was prepared by the NaBH4 reduction of 3-phenylglutaric anhydride (27). To synthesize the 5-tert-butyl substrate 35, since the anhydride corresponding to 27 could not be obtained by the Michael reaction of methyl 4,4-dimethyl-2-pentenoate with dimethyl malonate, the other method shown in Scheme 6 was used.…”

Section: Synthesis Of Cyclization Substratesmentioning

confidence: 99%

Folding strain stereocontrol in cyclohexane ring formation by means of an intramolecular ester enolate alkylation reaction

Tokoroyama¹,

Kusaka²

1996

Can. J. Chem.

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Diastereoselectivity in the cyclization of ethyl 7-bromo-2-methylheptanoates with an additional substituent at various positions in the chain, by LDA treatment, was investigated in connection with the concept of folding strain stereocontrol. Cyclization of 3-, 4-, and 6-methyl-substituted substrates revealed high selectivity, which demonstrates the prevalence of folding strain stereocontrol and the usefulness of this approach for stereoselective ring construction. In particular, reactions of the latter two substrates resulted in the stereodivergent preparation of diastereomeric 1,3-dimethylcyclohexanecarboxylates. In the case of the 5-methyl-substituted substrate, the selectivity of ring closure was only moderate. 'H and '" NMR spectroscopic data were useful for determining the conformation of 1-methylcyclohexanecarboxylate derivatives. The origin of the diastereoselectivity was examined through the qualitative comparison of the strain in the diastereomeric folding in the transition state. Various factors that might affect stereoselectivity were examined in the cyclization of 5-substituted substrates to better understand this concept. As predicted, the selectivity increased as the substituent became bulkier: Ph < M e = Et < i-Pr < t-Bu. The effects of other factors -solvent, base counter cation, and leaving group -on selectivity agree with results predicted from the reactivity-selectivity relationship.Key words: folding strain stereocontrol; diastereoselectivity in ring-closure reaction; remote asymmetric induction; ethyl 2-methylcyclohexanecarboxylate derivatives, 'H and 13c NMR; stereoselective synthesis of substituted cyclohexane derivatives.Resume : Dans le cadre de travaux sur le concept du stCrCocontr6le par le plissement des chahes, on a CtudiC la diastCrCosClectivitC de la cyclisation, sous l'influence du LDA, de 7-bromo-2-mCthylheptanoates d'Cthyle portant un substituant additionnel dans diverses positions. Les cyclisations des substrats substituCs par des groupes mCthyles en positions 3 , 4 ou 6 se produisent avec une grande sClectivitC; ceci met en Cvidence la prkvalence du stCrCocontr6le par le plissement de la chaine et dCmontre 1'utilitC de cette approche pour la formation stCrCosClective de cycles. Ceci est particulibrement vrai avec les deux derniers substrats qui conduisent a la prCparation stCrCoconvergente des 1,3-dimCthylcyclohexanecarboxylates diastCrCombres. Dans le cas du substrat portant un groupe mCthyle en position 5, la sClectivitC de la formation du cycle n'est que modCrCe. Les donnCes de la spectroscopie RMN du 'H et du I3c se sont avCrCes utiles pour la dktermination de la conformation des dCrivCs 1-mCthylcyclohexanecarboxylates. On a CtudiC l'origine de la diastCrCosClectivitC par le biais d'une comparaison qualitative de la tension dans le plissement diastCrCombre dans 1'Ctat de transition. Dans le but de mieux comprendre ce concept, on a examin6 divers facteurs pouvant affecter la stCrCosClectivitC lors de la cyclisation de substrats substituCs en position 5. Tel qu'on ...

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A comparison of conformational energies calculated by several molecular mechanics methods

et al. 1996

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Several commonly used molecular mechanics force fields have been tested for accuracy in conformational energy calculations. Differences in performance between the force fields are discussed for different classes of structures. MMFF93 and force fields based on the MM2 or MM3 functional form are found to perform significantly better than other force fields in the test, with average conformational energy errors around 0.5 kcal/mol. CFF91 also reaches this accuracy for the subset in which fully determined parameters are used, but it doubles the overall error due to use of estimated parameters. Harmonic force fields generally have average errors exceeding 1 kcal/mol. Factors influencing accuracy are identified and discussed. 0 1996 by John Wiley & Sons, Inc. different programs can be run on personal computers or small workstations. The problem today in routine work is not so much how to perform the calculation as what force field to use. A few years ago, two of us participated in a compafison of some of the most popular force fields at that time.' However, the last few years have seen the advent

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Conformational analysis. 40. Conformation of 1-methyl-1-phenylcyclohexane and conformational energies of the phenyl and vinyl groups

Cited by 125 publications

References 2 publications

Low temperature carbon-13 magnetic resonance detection of axial conformers in vinyl- and formylcyclohexane: a deshielding γ–gauche effect

Low temperature carbon-13 magnetic resonance detection of axial conformers in vinyl- and formylcyclohexane: a deshielding γ–gauche effect

Folding strain stereocontrol in cyclohexane ring formation by means of an intramolecular ester enolate alkylation reaction

A comparison of conformational energies calculated by several molecular mechanics methods

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