Nano‐CuO‐Catalyzed Ullmann Coupling of Phenols with Aryl Halides under Ligand‐Free Conditions

Abstract

Nano copper oxide has been found to be a highly efficient and reusable catalyst for the C–O cross‐coupling of phenols with aryl halides under ligand‐free conditions. With DMSO as solvent, Cs2CO3 and KOH are suitable bases for the cross‐coupling reactions with phenyl iodides and bromides, respectively. Diaryl ethers with different substituted groups can be synthesized in moderate‐to‐good yields. The catalyst can be recycled at least five times without obvious loss in catalytic activity.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Graphene-oxide-supported CuAl and CoAl layered double hydroxides as enhanced catalysts for carbon-carbon coupling via Ullmann reaction

“…The molecules containing this framework have shown activity across a wide range of therapeutic applications, which include antifungal, anti-inflammatory, antirheumatic, antitumor, and antihypertensive agents [32]. The main method for the synthesis of biaryls is the Classic Ullmann Homocoupling Reaction [33] based on the transition metal-catalyzed cross-coupling reaction starting from two discrete aromatic halide entities and stoichiometric amounts of organometallic reagents, originally copper [30,[34][35][36][37][38][39]. In principle, this reaction requires harsh reaction conditions, such as large excess of phenols, high temperatures (>200 °C) and at least stoichiometric amounts of copper, which result in the production of undesirable chemical waste [40].…”

Open air O-arylation reaction of phenols with aryl halides catalyzed by polymer-anchored copper(II) complexes

“…There are many examples of immobilizers such as Cu-or Pdcatalytic systems [25][26][27][28][29]. To date, few reports described reusable copper catalytic systems for this C-O coupling that allowed the recycling of active metal; nevertheless, only some reported leaching measurements of metal toxic residues in final products [30][31][32][33]. This feature is of high importance for purity requirements especially in pharmaceutical industries.…”

Chemoselective and ligand-free synthesis of diaryl ethers in aqueous medium using recyclable alumina-supported nickel nanoparticles

“…The harsh conditions of classical Ullmann synthesis have limitations due to involvement of stoichiometric amounts of copper reagents with some extra ligands, [11][12][13][14][15][16][17][18][19][20] requirement of high temperatures along with long reaction time, 11,13-20-22 and use of moisture sensitive, costly base 11,[13][14][15][16]18,19,22 as well as employment of inert atmosphere. [11][12][13]15,16,18,[21][22][23][24] For this reason, immense efforts have been spent in past few years for the discovery of more attractive and utilitarian arylation methods. However, palladium-based protocols, although successful to some extent, have some inherent limitations such as moisture sensitivity, prohibitive cost of metal catalysts, non-commercial sophisticated phosphorated ligands, environmental toxicity and limited substrate scope.…”