Activation Parameters for Three Reactions Interconverting Isomeric 4- and 6-Deuteriobicyclo[3.1.0]hex-2-enes
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- 作者：John E. Baldwin and Edmund J. Keliher
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：January 23, 2002
- 年：2002
- 卷：124
- 期：3
- 页码：380 - 381
- 全文大小：42K
- 年卷期：v.124,no.3(January 23, 2002)
- ISSN：1520-5126
文摘
Classic investigations of thermal equilibrations between 4,4-d2- and 6,6-d2-bicyclo[3.1.0]hex-2-enes (Doering, W. von E.; Roth, W. R. Angew. Chem., Int. Ed. Engl. 1963, 2, 115-122) and among deuterium-labeled and non-racemic 2-methyl-5-isopropylbicyclo[3.1.0]hex-2-enes (
ta.gif" BORDER=0 >3-thujenes) (Doering, W. von E.; Lambert, J. B. Tetrahedron 1963, 19, 1989-1994 and Doering, W. von E.; Schmidt, E. K. G. Tetrahedron 1971, 27, 2005-2030) and bicyclo[3.1.0]hex-2-enes (Cooke, R. S.; Andrews, U. H. J. Am. Chem. Soc. 1974, 96, 2974-2980) identified three different paths leading to distinct degenerate products. The equilibrations take place through [1,3]-carbon shifts with retention,suprafacial and inversion,antarafacial stereochemistry and a two-centered epimerization resulting in enantiomerization of the bicyclic skeleton through a "ring-flip" process. Activation parameters for the rate constants kr, kf, and ki associated with these paths have now been secured: Ea 43.8, 44.3, 44.8 kcal/mol and log A 14.1, 14.2, 14.1, respectively, nearly identical values, differing by less than probable error limits, consistent with a rate-determining formation followed by a rapid partitioning of a common diradical intermediate under dynamic control.
ta.gif" BORDER=0 >3-thujenes) (Doering, W. von E.; Lambert, J. B. Tetrahedron 1963, 19, 1989-1994 and Doering, W. von E.; Schmidt, E. K. G. Tetrahedron 1971, 27, 2005-2030) and bicyclo[3.1.0]hex-2-enes (Cooke, R. S.; Andrews, U. H. J. Am. Chem. Soc. 1974, 96, 2974-2980) identified three different paths leading to distinct degenerate products. The equilibrations take place through [1,3]-carbon shifts with retention,suprafacial and inversion,antarafacial stereochemistry and a two-centered epimerization resulting in enantiomerization of the bicyclic skeleton through a "ring-flip" process. Activation parameters for the rate constants kr, kf, and ki associated with these paths have now been secured: Ea 43.8, 44.3, 44.8 kcal/mol and log A 14.1, 14.2, 14.1, respectively, nearly identical values, differing by less than probable error limits, consistent with a rate-determining formation followed by a rapid partitioning of a common diradical intermediate under dynamic control.