title: Rearrangement of vinyl allene oxide geometric isomers to cyclopentenones. Further computational insights with biologically relevant model systems.
abstract: Pathways for the rearrangement of the E and Z isomers of allyl- and methyl-substituted vinyl allene oxides to stereodefined cyclopentenones have been studied by DFT computations. Regardless of the reactant geometry, cis-configured cyclopentenones are found to be formed in a stepwise cascade comprising as key steps the ring opening of the oxirane to give an oxidopentadienyl diradical, its isomerization, and electrocyclization. An allyl substituent at the Csp3atom of the starting vinyl allene oxide induces opposite effects on the activation energies for ring opening: a decrease owing to assistance by homoconjugation for the out motion and an increase due to the stereoelectronic stabilization of the reactant. As a result, allyl- and methyl-substituted vinyl allene oxides exhibit comparable activation energies. Only model systems with crotyl substituents afford lower activation energies than the methyl counterparts due to the additional stabilization of the forming charge deficiency at a secondary carbon by homoconjugation. Moreover, upon homoconjugative interaction reactants of Z geometry are predicted to undergo cyclization more readily than the E isomers. The results with Z-crotyl substituent are congruent with the spontaneous rearrangement of natural vinyl allene oxide derived from α-linolenic acid to a racemic cis-cyclopentenone (12-oxo-PDA).
authors.affiliation: Departamento de Química Orgánica, Facultade de Química and Centro de Investigacións Biomédicas (CINBIO), Universidade de Vigo, Lagoas-Marcosende, 36310 Vigo, Spain. qolera@uvigo.es.
authors.forename: Adán B
authors.initials: AB
authors.lastname: González-Pérez
authors.affiliation: Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, P.O. Box 30, 420111 Kazan, Russia.
authors.forename: Alexander
authors.initials: A
authors.lastname: Grechkin
authors.affiliation: Departamento de Química Orgánica, Facultade de Química and Centro de Investigacións Biomédicas (CINBIO), Universidade de Vigo, Lagoas-Marcosende, 36310 Vigo, Spain. qolera@uvigo.es.
authors.forename: Ángel R
authors.identifier: http://orcid.org/0000-0001-6896-9078
authors.initials: ÁR
authors.lastname: de Lera
mesh_terms: D000466:Alkadienes / Q000737:chemistry*; D003517:Cyclopentanes / Q000138:chemical synthesis* / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D010087:Oxides / Q000737:chemistry*; D011789:Quantum Theory; D013237:Stereoisomerism
chemical_list: D000466:Alkadienes; D003517:Cyclopentanes; D010087:Oxides; C013905:cyclopentenone