title: Possibility of [1,5] sigmatropic shifts in bicyclo[4.2.0]octa-2,4-dienes.
abstract: The thermal equilibration of the methyl esters of endiandric acids D and E was subject to a computational study. An electrocyclic pathway via an electrocyclic ring opening followed by a ring flip and a subsequent electrocyclization proposed by Nicolaou [ Nicolaou , K. C. ; Chen , J. S. Chem. Soc. Rev. 2009 , 38 , 2993 ], was computationally explored. The free-energy barrier for this electrocyclic route was shown to be very close to the bicyclo[4.2.0]octa-2,4-diene reported by Huisgen [ Huisgen , R. ; Boche , G. ; Dahmen , A. ; Hechtl , W. Tetrahedron Lett. 1968 , 5215 ]. Furthermore, the possibility of a [1,5] sigmatropic alkyl group shift of bicyclo[4.2.0]octa-2,4-diene systems at high temperatures was explored in a combined computational and experimental study. Calculated reaction barriers for an open-shell singlet biradical-mediated stepwise [1,5] sigmatropic alkyl group shift were shown to be comparable with the reaction barriers for the bicyclo[4.1.0]hepta-2,4-diene (norcaradiene) walk rearrangement. However, the stepwise sigmatropic pathway is suggested to only be feasible for appropriately substituted compounds. Experiments conducted on a deuterated analogous diol derivative confirmed the calculated (large) differences in barriers between electrocyclic and sigmatropic pathways.
authors.affiliation: Center for Molecular Modeling, Ghent University , Technologiepark 903, 9052 Zwijnaarde, Belgium.
authors.forename: Hannelore
authors.initials: H
authors.lastname: Goossens
authors.forename: Johan M
authors.initials: JM
authors.lastname: Winne
authors.forename: Sebastian
authors.initials: S
authors.lastname: Wouters
authors.forename: Laura
authors.initials: L
authors.lastname: Hermosilla
authors.forename: Pierre J
authors.initials: PJ
authors.lastname: De Clercq
authors.forename: Michel
authors.initials: M
authors.lastname: Waroquier
authors.forename: Veronique
authors.initials: V
authors.lastname: Van Speybroeck
authors.forename: Saron
authors.initials: S
authors.lastname: Catak
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D001643:Bridged Bicyclo Compounds / Q000737:chemistry*; D015394:Molecular Structure; D013816:Thermodynamics
chemical_list: D000475:Alkenes; D001643:Bridged Bicyclo Compounds; C000601915:bicyclo(4.1.0)hepta-2,4-diene; C000599071:bicyclo(4.2.0)octa-2,4-diene