Transition structures and exo/endo stereoselectivities of concerted [6 + 4] cycloadditions with density functional theory |
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Authors: | E Goldstein Brett R Beno K N Houk |
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Institution: | (1) Department of Chemistry, California State Polytechnic University at Pomona, 3801 W. Temple Avenue, Pomona, CA 91768, USA, US;(2) Department of Chemistry and Biochemistry, University of California. at Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1569, USA, US |
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Abstract: | Density functional theory transition structures were located for three concerted 6 + 4] cycloaddition reactions involving
cis-hexatriene and butadiene, cyclopentadiene and cycloheptatriene, and cyclopentadiene and tropone. Geometries, energies, and
entropies were computed at the Becke3LYP/6-31G* level. The activation energy of the concerted 6 + 4] cycloaddition of hexatriene
and butadiene is 33.3 kcal/mol, about 8 kcal/mol above the activation energy of the butadiene plus ethylene 4 + 2] cycloaddition.
The endo concerted 6 + 4] transition state is 1.1 kcal/mol higher than the exo. The 6 + 4] reaction of cyclopentadiene and
cycloheptatriene has a barrier of 25.9 kcal/mol, while the cyclopentadiene–tropone barrier drops to 20.7 kcal/mol.
Received: 3 December 1998 / Accepted: 18 February 1999 / Published online: 7 June 1999 |
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Keywords: | : Secondary orbital interactions B3LYP Diels Alder reaction |
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