Gold‐Catalyzed Dimerization of Diarylalkynes: Direct Access to Azulenes

Abstract

We have developed a simple gold-catalyzed procedure for the synthesis of substituted and modifiable azulenes. The azulenes are formed either by the dimerization of push-pull diarylalkynes bearing a fluorine atom in ortho or para position or by the dimerization of a symmetric electron-rich diarylalkyne. In the presence of a cationic gold catalyst, the two alkynes can form a highly reactive vinyl cation. Trapping of this high-energy intermediate by an appropriate aryl unit then delivers substituted azulenes in a single step and in a perfect atom economy.

Contorted Polycyclic Aromatic Hydrocarbons with Two Embedded Azulene Units

“…Later on, a more efficient route was described by Ziegler and Hafner, starting from cyclopentadiene and 2,4‐dinitrophenyl pyridinium chloride . Other approaches followed and even nowadays new synthetic routes to azulene and their derivatives for example, by gold catalysis are being developed . The origin of the blue color of azulene as non‐alternant isomer of the colorless naphthalene has fascinated theoretical and physical chemists dealing with it…”

Thermally-Induced Doping of the Regioregular Polythiophene Bearing Alkylene Spacered Benzene sulfonate Group at the Side Chain

“…Preparation of 3-ethynylthiophene (3) with 3-bromothiophene and (trimethylsilyl)ethyne followed by desilylation was performed by the literature method with slight modification. 6 Sonogashira-Hagihara coupling 7 of neopentyl (4-bromobenzene)sulfonate (4) 5 with 3 catalyzed by palladium/copper system afforded the disubstituted alkyne 5 in 79% yield. Hydrogenation of 5 in the presence of 10 mol% Pd/C obtained the alkylene spacered thiophene bearing benzenesulfonate 6 in 92% yield.…”

Abnormal Nucleophilic Substitution on Methoxytropone Derivatives: Steric Strategy to Synthesize 5‐Substituted Azulenes

“…There are limited ways to incorporate substituents on the azulenes caffold, which include 1) Sonogashira coupling of 6bromoazulene with the terminal alkynes followed by catalytic reduction, [19] 2) the reaction between fulvene ketene acetal and a-pyrone derivatives to yield the [6+ +4] cycloaddition adduct leading to azulenols, [20] 3) Rh-catalyzed ring expansionannulation of b'-bromo-a-diazo ketones to afford 1-azulenols; [21] 4) gold-catalyzed dimerizationo fd iaryldialkynes for the synthesis of substituted andm odifiable azulenes; [22] and 5) the synthesis of 1,1-dicyanoazulenes and subsequentf unctionalization of the seven-membered ring followed by eliminationo f HCN to give the bromo-cyanos ubstituted azulene. [23] Traditional methods for the constructiono fa na zulene scaffold include long, low-yielding synthetic procedures that, in many cases,d o not afford the desired substitution patterns.A chieving regioselectivity for the substitution on the seven-membered ring of azulenei sachallenging task due to very close reactivity of all positions.…”