Re-examining the Mechanisms of Competing Pericyclic Reactions of 1,3,7-Octatriene |
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Authors: | Osvaldo Gutierrez Jason G Harrison Ryan P Pemberton Dean J Tantillo |
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Institution: | Department of Chemistry, University of California-Davis, 1 Shields Avenue, Davis, CA 95616 (USA). |
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Abstract: | DFT (both B3LYP and M06-2X), CASSCF, and CASPT2 calculations were used to investigate competing 3,?3] and 3,?5] sigmatropic shifts and intramolecular 4+2] cycloaddition of 1,3,7-octatriene. In accord with previous results on 1,5-hexadiene, CASSCF calculations found both stepwise and concerted pathways for the 3,?3] rearrangement. For the competing 3,?5] sigmatropic rearrangement, CASSCF and CASPT2 calculations revealed three stepwise pathways with similar barriers. UB3LYP and UM06-2X calculations predicted a different potential energy landscape: no stepwise 3,?3] pathway, only two competing 3,?5] sigmatropic shifts, and an intramolecular Diels-Alder cycloaddition/homolytic ring-opening pathway. Significant lowering of barriers for all rearrangements was predicted for some 1,3,7-octatrienes with substituents at the 4- and 7-positions. |
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