Synthesis of azulene, a blue hydrocarbon

Abstract

Azulene is a simple, beautiful, and theoretically interesting compound with many unusual properties. For all of these reasons one might expect it to enjoy a place in the undergraduate laboratory curriculum, but it is a rare undergradu-

The Azulene Framework as a Novel Arene Bioisostere: Design of Potent Dopamine D4 Receptor Ligands Inducing Penile Erection

“…To differentiate between interactions due to the non‐alternant π‐electron system and those of the C ‐alkyl substituents, unnatural azulenes were prepared and treated with various phenylpiperazine derivatives. Starting from 2,5‐dihydrothiophene‐1,1‐dioxide, Br 2 addition gave the respective dibromide, which underwent elimination of HBr followed by [6+4]‐cycloaddition with 6‐dimethylaminofulvene to give azulene in 34 % overall yield 12. Subsequent Vilsmeier formylation led to the respective mono‐ and diformylazulenes 6 a and 6 b , depending on the reaction conditions 11.…”

Diazuleno‐s‐indacene Diradicaloids: Syntheses, Properties, and Local (anti)Aromaticity Shift from Neutral to Dicationic State

“…Alternatively,c hemists are looking into acene-like structures in which one or more six-membered benzenoid rings are replaced by non-benzenoid five-and seven-membered rings. [6] Our particular interest here is to fuse two azulene rings to an s-indacene moiety to form an ew 7-5-5-6-5-5-7 fused ring system with 28p electrons,asystem which is an analogue of heptacene but with two p electrons less (Figure 1). [5] Azulene,anon-alternant and non-benzenoid bicyclic hydrocarbon, is a1 0 p-electron isomer of naphthalene.I th as ad ipole moment of about 1.08 Db ecause of intramolecular donor (five-membered ring) and acceptor (seven-membered ring) interactions,a nd possesses unique physicochemical properties currently unattainable by benzenoid systems.…”

“…[5] Azulene,anon-alternant and non-benzenoid bicyclic hydrocarbon, is a1 0 p-electron isomer of naphthalene.I th as ad ipole moment of about 1.08 Db ecause of intramolecular donor (five-membered ring) and acceptor (seven-membered ring) interactions,a nd possesses unique physicochemical properties currently unattainable by benzenoid systems. [6] Our particular interest here is to fuse two azulene rings to an s-indacene moiety to form an ew 7-5-5-6-5-5-7 fused ring system with 28p electrons,asystem which is an analogue of heptacene but with two p electrons less ( Figure 1). Tw o isomers,t he diazuleno[2,1-a:2',1'-g]-s-indacene (DAI-1) and diazuleno[2,1-a:1',2'-h]-s-indacene (DAI-2), are investigated in this report.…”

Molecules with Linear π‐Conjugated Pathways between All Substituents: Omniconjugation

“…All of these omniconjugated systems, with rings containing an odd number of carbon atoms, are called non-alternant. [37] We have been unable to construct omniconjugated systems based on even-membered units only. Additional mathematical analysis is required to understand this topological property of omniconjugated models.…”