Computational Study of the Cyclization of 5-Hexenyl, 3-Oxa-5-hexenyl and 4-Oxa-5-hexenyl Radicals

Title:
Computational Study of the Cyclization of 5-Hexenyl, 3-Oxa-5-hexenyl and 4-Oxa-5-hexenyl Radicals
Authors:
Matlin, Albert; Leyden, Matthew C.
Abstract:
The intramolecular cyclization of 5-hexenyl radicals continues to be an important synthetic method for the construction of five-membered rings. The synthetic utility arises from the high degree of regioselectivity to give predominantly cyclopentyl products in high yield under mild conditions. Recently we reported product cyclization studies on 4-oxa perturbed 5-hexenyl radical. In this paper we report our results from a computational study (UB3LYP and UCCSD(T)) of the cyclization of a series of 5-hexenyl and 3- and 4-oxa-5-hexenyl radicals. Three highly conserved cyclization transitions states (exo-chair, exo-boat and endo-chair) were located for 10 acyclic radicals. Activation en-ergies were calculated for the three modes of cyclization for each radical. Calculated values for the exo/endo cycliza-tion ratios had a high level of agreement with experiment and predictions were offered for two cases that have not been experimentally tested. The increased percentage of exo-cyclization with 3- and 4-oxa substitution is the result of an increase in the energy difference between the exo- and endo-chair transition states compared to the hydrocarbon sys-tems. The decreased rate of cyclization of the 4-oxa compounds is primarily due to the stabilization of the initial acy-clic radical by the vinyl ether linkage. The increase in the rate of cyclization with 3-methyl substitution is due to the increased conformational energy of the starting acyclic radical.
Citation:
Matlin, Albert R. and Matthew C. Leyden. 2013. “Computational Study of the Cyclization of 5-Hexenyl, 3-Oxa-5-hexenyl and 4-Oxa-5-hexenyl Radicals.” International Journal of Organic Chemistry 2013(3): 169-175.
Publisher:
Scientific Research Publishing
DATE ISSUED:
2013-09
Department:
Chemistry
Type:
article
PUBLISHED VERSION:
10.4236/ijoc.2013.33021
PERMANENT LINK:
http://hdl.handle.net/11282/309711

Full metadata record

DC FieldValue Language
dc.contributor.authorMatlin, Alberten_US
dc.contributor.authorLeyden, Matthew C.en_US
dc.date.accessioned2013-12-23T16:16:06Z-
dc.date.available2013-12-23T16:16:06Z-
dc.date.issued2013-09en
dc.identifier.citationMatlin, Albert R. and Matthew C. Leyden. 2013. “Computational Study of the Cyclization of 5-Hexenyl, 3-Oxa-5-hexenyl and 4-Oxa-5-hexenyl Radicals.” International Journal of Organic Chemistry 2013(3): 169-175.en_US
dc.identifier.issn2161-4687en_US
dc.identifier.urihttp://hdl.handle.net/11282/309711-
dc.description.abstractThe intramolecular cyclization of 5-hexenyl radicals continues to be an important synthetic method for the construction of five-membered rings. The synthetic utility arises from the high degree of regioselectivity to give predominantly cyclopentyl products in high yield under mild conditions. Recently we reported product cyclization studies on 4-oxa perturbed 5-hexenyl radical. In this paper we report our results from a computational study (UB3LYP and UCCSD(T)) of the cyclization of a series of 5-hexenyl and 3- and 4-oxa-5-hexenyl radicals. Three highly conserved cyclization transitions states (exo-chair, exo-boat and endo-chair) were located for 10 acyclic radicals. Activation en-ergies were calculated for the three modes of cyclization for each radical. Calculated values for the exo/endo cycliza-tion ratios had a high level of agreement with experiment and predictions were offered for two cases that have not been experimentally tested. The increased percentage of exo-cyclization with 3- and 4-oxa substitution is the result of an increase in the energy difference between the exo- and endo-chair transition states compared to the hydrocarbon sys-tems. The decreased rate of cyclization of the 4-oxa compounds is primarily due to the stabilization of the initial acy-clic radical by the vinyl ether linkage. The increase in the rate of cyclization with 3-methyl substitution is due to the increased conformational energy of the starting acyclic radical.en_US
dc.language.isoen_USen_US
dc.publisherScientific Research Publishingen_US
dc.identifier.doi10.4236/ijoc.2013.33021-
dc.subject.departmentChemistryen_US
dc.titleComputational Study of the Cyclization of 5-Hexenyl, 3-Oxa-5-hexenyl and 4-Oxa-5-hexenyl Radicalsen_US
dc.typearticleen_US
dc.identifier.journalInternational Journal of Organic Chemistryen_US
dc.subject.keywordRadical cyclizationsen_US
dc.subject.keywordActivation energiesen_US
dc.subject.keywordUB3LYPen_US
dc.subject.keywordUCCSD (T)en_US
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