title: 6,6-Dicyanopentafulvenes: electronic structure and regioselectivity in [2 + 2] cycloaddition-retroelectrocyclization reactions.
abstract: We present an investigation of the electronic properties and reactivity behavior of electron-accepting 6,6-dicyanopentafulvenes (DCFs). The electron paramagnetic resonance (EPR) spectra of the radical anion of a tetrakis(silylalkynyl) DCF, generated by Na metal reduction, show delocalization of both the charge and unpaired electron to the nitrogens of the cyano moieties and also, notably, to the silicon atoms of the four alkynyl moieties. By contrast, in the radical anion of the previously reported tetraphenyl DCF, coupling to the four phenyl rings is strongly attenuated. The data provide physical evidence for the different conjugation between the DCF core and the substituents in both systems. We also report the preparation of new fulvene-based push-pull chromophores via formal [2 + 2] cycloaddition-retroelectrocyclization reaction of DCFs with electron-rich alkynes. Alkynylated and phenylated DCFs show opposite regioselectivity of the cycloaddition, which can be explained by the differences in electronic communication between substituents and the DCF core as revealed in the EPR spectra of the radical anions.
authors.affiliation: Laboratory of Organic Chemistry, ETH Zurich, Hönggerberg, HCI, CH-8093 Zurich, Switzerland.
authors.forename: Aaron D
authors.initials: AD
authors.lastname: Finke
authors.forename: Oliver
authors.initials: O
authors.lastname: Dumele
authors.forename: Michal
authors.initials: M
authors.lastname: Zalibera
authors.forename: Daria
authors.initials: D
authors.lastname: Confortin
authors.forename: Pawel
authors.initials: P
authors.lastname: Cias
authors.forename: Govindasamy
authors.initials: G
authors.lastname: Jayamurugan
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Gisselbrecht
authors.forename: Corinne
authors.initials: C
authors.lastname: Boudon
authors.forename: W Bernd
authors.initials: WB
authors.lastname: Schweizer
authors.forename: Georg
authors.initials: G
authors.lastname: Gescheidt
authors.forename: François
authors.initials: F
authors.lastname: Diederich
mesh_terms: D003500:Cyclization; D003517:Cyclopentanes / Q000138:chemical synthesis / Q000737:chemistry*; D004583:Electrons; D008958:Models, Molecular; D015394:Molecular Structure; D013237:Stereoisomerism
chemical_list: D003517:Cyclopentanes