A comprehensive computational examination of transannular Diels–Alder reactions of unsubstituted C14 trienes — Barriers, template effects, and the Curtin–Hammett principle

Autor: Anthony V. Buckley, Noham Weinberg, Saul Wolfe
Rok vydání: 2001
Předmět:
Zdroj: Canadian Journal of Chemistry. 79:1284-1292
ISSN: 1480-3291
0008-4042
DOI: 10.1139/cjc-79-8-1284
Popis: A combination of MM3-level molecular mechanics calculations and PM3-level semiempirical molecular orbital calculations has been employed, in conjunction with an algorithm for the comprehensive conformational analysis of cyclic compounds, to obtain 1202 unique 1,3,9-cyclotetradecatriene conformations, distributed over the six possible geometrical isomers, and 70 unique transannular Diels–Alder transition structures leading to the six possible stereoisomeric tricyclic olefins. A kinetic analysis that takes into account all minima of a given geometrical isomer and all transition structures leading to the same tricyclic product leads to a free energy of activation that is almost the same as the free energy difference between the lowest minimum and the lowest transition structure (the Curtin–Hammett principle). A substantial template effect, mainly entropic in origin, is found when the transannular reactions are compared to the Diels–Alder reactions of the cognate 2,4-hexatrienes with the 2-butenes. Although the cyclization of the trans-cis-trans triene favours the cis-anti-cis over the trans-anti-trans product by more than 20 kcal mol–1, the situation is reversed in the acyclic reaction. A cyclic triene that can cyclize directly to a trans-anti-trans tricycle can therefore be proposed.Key words: molecular models, Deslongchamps, Takahashi, trans-anti-trans tricycle, MM3, PM3, transition states.
Databáze: OpenAIRE
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