Alkynylazulenes as Building Blocks for Highly Unsaturated Scaffolds

Abstract

Recently developed routes to the synthesis of mono‐ and polyethynylated azulenes and their transformations into linear oligoazulenes with ethynyl and butadiynyl bridges as well as azulenyl‐substituted benzenes, cyclobutadiene complexes, and azulene‐substituted tetracyanobutadienes are reviewed. The utility of ethynylazulene derivatives for the synthesis of azulene‐substituted heterocycles has also been reviewed.

Recent advances in the functionalization of azulene through Rh‐, Ir‐, Ru‐, Au‐, Fe‐, Ni‐, and Cu‐catalyzed reactions

“…Furthermore, the reactivity of mono‐ and poly[(azulenyl)ethynyl]benzene derivatives to [2 + 2] cycloaddition/cycloreversion reactions with TCNE and TCNQ resulted in buta‐1,3‐dienes as a new class of charge‐transfer chromophores. [ 9 ]…”

“…Furthermore, the reactivity of mono-and poly[(azulenyl)ethynyl]benzene derivatives to [2 + 2] cycloaddition/cycloreversion reactions with TCNE and TCNQ resulted in buta-1,3-dienes as a new class of charge-transfer chromophores. [9] Pd-catalyzed cross-coupling under Sonogashira conditions, Corey-Fuchs or Seyferth-Gilbert reaction [119] for the conversion of aldehydes into acetylenes, or the reaction of chloroazulenes with lithium acetylide in liquid ammonia all result in efficient ethynylation of azulene at the five-membered or seven-membered ring. Jarszak-Tyl et al [120] recently reported solvent-free C H alkynylation of azulenes via simple mortar grinding of substrates with aluminum oxide.…”

“…In this regard, we recently detailed current progress in Pd-catalyzed azulene functionalization (Figure 1). [9,10] Palladium-catalyzed Suzuki-Miyaura cross-coupling of organoboranes and the Stille-Migita reaction of organostannanes were included in our recent review, as were C C bondforming reactions by Hiyama (Si), Kumada-Tamao-Corriu (Mg), Sonogashira (Cu and C(sp) atoms), and Negishi (Zn, Al, and Zr). [11,12] Pd-catalyzed direct arylation reaction between an organic (hetero)aromatic halide and a (hetero)arene containing at least one Dedicated to the memory of Professor Klaus Hafner C(sp 2 ) H bond, which does not require the use of an organometallic reagent, was also reviewed.…”

Intense absorption of azulene realized by molecular orbital inversion

“…8 These substituted acenes are also attracting attention because of their ability to absorb visible light, which enables them to be used as photoreduction catalysts. 9,10 Furthermore, azulene [11][12][13][14][15][16][17][18][19][20] is a structural isomer of naphthalene, with relatively high HOMO and low LUMO energy levels due to its unique polarisation structure (Fig. 1a), and it is also known as a redox-active molecule compared to naphthalene, anthracene, pyrene and so on.…”