title: Synthesis of [5]-, [6]-, and [7]helicene via Ni(0)- or Co(I)-catalyzed isomerization of aromatic cis,cis-dienetriynes.
abstract: An original approach to helicene frameworks exploiting atom economic isomerization of appropriate energy-rich aromatic cis,cis-dienetriynes has been developed. The new paradigm provides nonphotochemical syntheses of helicenes based on the easy, convergent, and modular assembly of key cis,cis-dienetriynes and their nickel(0)-catalyzed [2+2+2] cycloisomerization. The potential of the methodology is underlined by the syntheses of the parent [5]helicene (2), 7,8-dibutyl[5]helicene (23), [6]helicene (24), and [7]helicene (25). The approach can be adapted to prepare functionalized helicenes as exemplified by the eight-step synthesis of 7,8-dibutyl-2,3-dimethoxy[6]helicene (34). Density functional theory (DFT) calculations showed that bis[2-((1Z)-1-buten-3-ynyl)phenyl]acetylene (1) and isomeric [5]helicene (2) differ enormously in the Gibbs energy content (DeltaG = -136.6 kcal x mol(-1)) to favor highly the devised intramolecular simultaneous construction of three aromatic rings.
authors.affiliation: Institute of Organic Chemistry and Biochemistry and Center for Complex Molecular Systems and Biomolecules, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Prague 6, Czech Republic.
authors.forename: Filip
authors.initials: F
authors.lastname: Teplý
authors.forename: Irena G
authors.initials: IG
authors.lastname: Stará
authors.forename: Ivo
authors.initials: I
authors.lastname: Starý
authors.forename: Adrian
authors.initials: A
authors.lastname: Kollárovic
authors.forename: David
authors.initials: D
authors.lastname: Saman
authors.forename: Lubomír
authors.initials: L
authors.lastname: Rulísek
authors.forename: Pavel
authors.initials: P
authors.lastname: Fiedler