title: Oxidative transformation to naphthodithiophene and thia[7]helicenes by intramolecular Scholl reaction of substituted 1,2-bis(2-thienyl)benzene precursors.
abstract: We present here a strategy to synthesize a variety of substituted naphthodithiophene building blocks through DDQ/acid-mediated oxidative cyclizations. The versatility of the Scholl reaction using the DDQ/acid system was demonstrated by the preparation of a novel substituted tetrathia[7]helicene where three new C-C bonds were formed in a one-pot procedure. The new DDQ/acid method was compared to the known strategies such as FeCl3 oxidation and oxidative photocyclization. By protecting the 1,2-bis(2-thienyl)benzene precursors, it is possible to direct the intermediates to controlled cyclization and effectively suppressing the polymerization. The highly reactive α-position of the terminal thiophenes can allow for further functionalization. The efficient preparation of a variety of naphthodithiophene building blocks, the extension to a nonphotochemical synthesis of [n]helicenes, and the ease of isolation of the products are arguments for the use of DDQ/acid system for this Scholl reaction.
authors.affiliation: Molecular Design and Synthesis, Department of Chemistry, Katholieke Universiteit Leuven , Celestijnenlaan 200F, B-3001 Leuven, Belgium.
authors.forename: Deepali
authors.initials: D
authors.lastname: Waghray
authors.forename: Christiaan
authors.initials: C
authors.lastname: de Vet
authors.forename: Konstantina
authors.initials: K
authors.lastname: Karypidou
authors.forename: Wim
authors.initials: W
authors.lastname: Dehaen