Dienophile twisting and substituent effects influence reaction rates of intramolecular Diels-Alder cycloadditions: a DFT study.
Intramolecular cycloadditions of 5-vinyl-1,3-cyclohexadienes were studied with B3LYP/6-31G(d) density functional calculations. The one-atom tether dictates that the Z substituent becomes exo and the E substituent becomes endo in the TS. The geometry of the cycloaddition TS is typical of a pericyclic transformation except unusual twisting of the dienophile places the endo substituent in a relatively steric-free position and the exo substituent in a highly crowded position. The experimental rate differences between isomeric pairs of vinylcyclohexadienes can be explained by comparing reactant destabilization when a bulky group occupies the Z position of the starting alkene and transition state stabilization when a bulky group is endo in the cycloaddition TS.
Khuong
Kelli S
KS
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569, USA.
Beaudry
Chris M
CM
Trauner
Dirk
D
Houk
K N
KN
D003510:Cyclohexanes / Q000737:chemistry*; D053138:Cyclohexenes; D008958:Models, Molecular; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014753:Vinyl Compounds / Q000737:chemistry*
D003510:Cyclohexanes; D053138:Cyclohexenes; D014753:Vinyl Compounds; C048401:1,4-cyclohexadiene