Re-examining the mechanisms of competing pericyclic reactions of 1,3,7-octatriene

Osvaldo Gutierrez; Jason G Harrison; Ryan P Pemberton; Dean J Tantillo

doi:10.1002/chem.201201193

Re-examining the mechanisms of competing pericyclic reactions of 1,3,7-octatriene

Chemistry. 2012 Aug 27;18(35):11029-35. doi: 10.1002/chem.201201193. Epub 2012 Jul 26.

Authors

Osvaldo Gutierrez¹, Jason G Harrison, Ryan P Pemberton, Dean J Tantillo

Affiliation

¹ Department of Chemistry, University of California-Davis, Davis, CA 95616, USA.

PMID: 22836223
DOI: 10.1002/chem.201201193

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.