Thermal Stereomutaijons and Stereochemicauy Elucidated [1 ,3]-Carbon Sigmatropic Shifts of 1-(E)-Propenyl-2-methlcyclobutanes Giving 3,4-Dimethylcyclohexenes.
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| Title: | Thermal Stereomutaijons and Stereochemicauy Elucidated [1 ,3]-Carbon Sigmatropic Shifts of 1-(E)-Propenyl-2-methlcyclobutanes Giving 3,4-Dimethylcyclohexenes. |
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| Authors: | Baldwin, John E.1 jbaldwin@syr.edu, Burrell, Richard C.1 |
| Source: | Journal of the American Chemical Society. 12/24/2003, Vol. 125 Issue 51, p15869-15877. 9p. |
| Subjects: | Stereochemistry, Isomerization, Cis-trans-isomerases, Enantiomers, Carbon, Cyclopropane |
| Abstract: | The thermal stereomutations and [1,3] carbon sigmatropic shifts shown by (+)-(1 S,2S)-trans-l-(E)-propenyl-2-methylcyclobutane and by (-)-(1S,2R)-cis-1-(E)-propenyl-2-methylcyclobutane in the gas phase at 275 °C leading to 3,4-dimethylcyclohexenes have been followed. The reaction-time-dependent data for concentrations and enantiomeric excess values for substrates and [1,3] shift products have been deconvoluted to afford rate constants for the discrete isomerization processes. Both trans and cis substrates react through four stereochemically distinct [1,3] carbon shift paths. For one enantiomer of the trans reactant the relative rate constants are k[SUBsi] = 58%, k[SUBar], = 5%, k[SUBsr] = 33%, and k[SUBai] = 4%. For a single enantiomer of the cis reactant, k[SUBsi] = 18%, k[SUBar] = 11%, k[SUBsr] = 51%, and k[SUBai] = 20%. A trans starting material reacts through orbital symmetry allowed suprafacial, inversion and antarafacial retention paths to give trans-3,4-dimethylcyclohexenes 63% of the time. A cis isomer reacts to give the more stable trans-3,4-dimethylcyclohexenes through orbital symmetry-forbidden suprafacial, retention and antarafacial, inversion paths 71 % of the time. The [1,3] carbon sigmatropic shifts are not controlled by orbital symmetry constraints. They seem more plausible rationalized as proceeding through diradical intermediates having some conformational flexibility after formation and before encountering an exit channel. The distribution of stereochemical outcomes may well be conditioned by dynamic effects. The thermal stereomutations of the 1-(E)-propenyl-2-methylcyclobutanes take place primarily through one-center epimerizations. For the trans substrate, the relative importance of the three distinction rate constants are k[SUB2] = 48%, k[SUB1] = 34%, and k[SUB12] = 18%. [ABSTRACT FROM AUTHOR] |
| Copyright of Journal of the American Chemical Society is the property of American Chemical Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
| Database: | Engineering Source |
| FullText | Text: Availability: 0 |
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| Header | DbId: egs DbLabel: Engineering Source An: 12120956 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: Thermal Stereomutaijons and Stereochemicauy Elucidated [1 ,3]-Carbon Sigmatropic Shifts of 1-(E)-Propenyl-2-methlcyclobutanes Giving 3,4-Dimethylcyclohexenes. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Baldwin%2C+John+E%2E%22">Baldwin, John E.</searchLink><relatesTo>1</relatesTo><i> jbaldwin@syr.edu</i><br /><searchLink fieldCode="AR" term="%22Burrell%2C+Richard+C%2E%22">Burrell, Richard C.</searchLink><relatesTo>1</relatesTo> – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Journal+of+the+American+Chemical+Society%22">Journal of the American Chemical Society</searchLink>. 12/24/2003, Vol. 125 Issue 51, p15869-15877. 9p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Stereochemistry%22">Stereochemistry</searchLink><br /><searchLink fieldCode="DE" term="%22Isomerization%22">Isomerization</searchLink><br /><searchLink fieldCode="DE" term="%22Cis-trans-isomerases%22">Cis-trans-isomerases</searchLink><br /><searchLink fieldCode="DE" term="%22Enantiomers%22">Enantiomers</searchLink><br /><searchLink fieldCode="DE" term="%22Carbon%22">Carbon</searchLink><br /><searchLink fieldCode="DE" term="%22Cyclopropane%22">Cyclopropane</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: The thermal stereomutations and [1,3] carbon sigmatropic shifts shown by (+)-(1 S,2S)-trans-l-(E)-propenyl-2-methylcyclobutane and by (-)-(1S,2R)-cis-1-(E)-propenyl-2-methylcyclobutane in the gas phase at 275 °C leading to 3,4-dimethylcyclohexenes have been followed. The reaction-time-dependent data for concentrations and enantiomeric excess values for substrates and [1,3] shift products have been deconvoluted to afford rate constants for the discrete isomerization processes. Both trans and cis substrates react through four stereochemically distinct [1,3] carbon shift paths. For one enantiomer of the trans reactant the relative rate constants are k[SUBsi] = 58%, k[SUBar], = 5%, k[SUBsr] = 33%, and k[SUBai] = 4%. For a single enantiomer of the cis reactant, k[SUBsi] = 18%, k[SUBar] = 11%, k[SUBsr] = 51%, and k[SUBai] = 20%. A trans starting material reacts through orbital symmetry allowed suprafacial, inversion and antarafacial retention paths to give trans-3,4-dimethylcyclohexenes 63% of the time. A cis isomer reacts to give the more stable trans-3,4-dimethylcyclohexenes through orbital symmetry-forbidden suprafacial, retention and antarafacial, inversion paths 71 % of the time. The [1,3] carbon sigmatropic shifts are not controlled by orbital symmetry constraints. They seem more plausible rationalized as proceeding through diradical intermediates having some conformational flexibility after formation and before encountering an exit channel. The distribution of stereochemical outcomes may well be conditioned by dynamic effects. The thermal stereomutations of the 1-(E)-propenyl-2-methylcyclobutanes take place primarily through one-center epimerizations. For the trans substrate, the relative importance of the three distinction rate constants are k[SUB2] = 48%, k[SUB1] = 34%, and k[SUB12] = 18%. [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Journal of the American Chemical Society is the property of American Chemical Society and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.1021/ja030516t Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 9 StartPage: 15869 Subjects: – SubjectFull: Stereochemistry Type: general – SubjectFull: Isomerization Type: general – SubjectFull: Cis-trans-isomerases Type: general – SubjectFull: Enantiomers Type: general – SubjectFull: Carbon Type: general – SubjectFull: Cyclopropane Type: general Titles: – TitleFull: Thermal Stereomutaijons and Stereochemicauy Elucidated [1 ,3]-Carbon Sigmatropic Shifts of 1-(E)-Propenyl-2-methlcyclobutanes Giving 3,4-Dimethylcyclohexenes. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Baldwin, John E. – PersonEntity: Name: NameFull: Burrell, Richard C. IsPartOfRelationships: – BibEntity: Dates: – D: 24 M: 12 Text: 12/24/2003 Type: published Y: 2003 Identifiers: – Type: issn-print Value: 00027863 Numbering: – Type: volume Value: 125 – Type: issue Value: 51 Titles: – TitleFull: Journal of the American Chemical Society Type: main |
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