title: Oligoene-Based π-Helicenes or Dispiranes? Winding up Oligoyne Chains by a Multiple Carbopalladation/Stille/(Electrocyclization) Cascade.
abstract: A domino approach consisting of up to five consecutive steps to access either highly substituted dispiranes or π-helicenes from oligoyne chains is reported. The domino sequence consists of several carbopalladation reactions, a Stille cross-coupling to obtain the helicenes, and, depending on the steric demands of the helicene, a final 6π-electrocyclization to afford the dispiranes. Formally, the latter transformation contravenes the Woodward-Hoffmann rules, as revealed by X-ray crystallography of the dispirane. Additionally, the racemization barrier of the (Z,Z,Z)-triene-based helicene has been determined by a kinetic analysis and compared with results from density functional theory calculations. Characteristic points on the reaction coordinate were further analyzed according to their relaxed force constants (compliance constants).
authors.affiliation: Institut für Organische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig (Germany).
authors.forename: Bastian
authors.initials: B
authors.lastname: Milde
authors.affiliation: Institut für Organische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig (Germany).
authors.forename: Markus
authors.initials: M
authors.lastname: Leibeling
authors.affiliation: Institut für Anorganische Chemie, Georg-August-Universität Göttingen, Tammannstraße 4, 37077 Göttingen (Germany).
authors.forename: Alexander
authors.initials: A
authors.lastname: Hecht
authors.affiliation: Institut für Anorganische und Analytische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig (Germany).
authors.forename: Peter G
authors.initials: PG
authors.lastname: Jones
authors.affiliation: Institut für Anorganische Chemie, Georg-August-Universität Göttingen, Tammannstraße 4, 37077 Göttingen (Germany).
authors.forename: Arne
authors.initials: A
authors.lastname: Visscher
authors.affiliation: Institut für Anorganische Chemie, Georg-August-Universität Göttingen, Tammannstraße 4, 37077 Göttingen (Germany).
authors.forename: Dietmar
authors.initials: D
authors.lastname: Stalke
authors.affiliation: Institut für Organische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig (Germany).
authors.forename: Jörg
authors.initials: J
authors.lastname: Grunenberg
authors.affiliation: Institut für Organische Chemie, Technische Universität Braunschweig, Hagenring 30, 38106 Braunschweig (Germany). d.werz@tu-braunschweig.de.
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Werz
keywords: carbopalladation; dispiranes; domino reactions; helicenes; synthetic methods