2.1 Intermolecular Ullmann Diaryl Ether Coupling Reactions

A set of 56 multidentate ligands with different chelating functionalities and bite angles, belonging to the structural classes of amino acids, acetic acid derivatives, phosphinites, phosphonates, imines, diimines, oximes, oxime ethers and diketones were selected for the screening (). Several of these compounds have been employed in diaryl ether syntheses before [–].

3 Synthesis of Diaryl Ethers via Nucleophilic Aromatic Substitution

Ullmann diaryl ether synthesis - copper catalysts - ionic liquids - aryl halides - phenols
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5 Diaryl Ether Synthesis via Benzyne Mechanism

Copper-catalyzed Ullmann diaryl ether synthesis has been successfully demonstrated in ionic liquids as reaction media. The copper catalysts immobilized in ionic liquid media can be reused. Product isolation can be achieved via simple extraction using organic solvents.

7 Diaryl Ether Synthesis via Oxidative Coupling

Diaryl ethers form an important class of organic compounds, both in life sciences and in the polymer industry. In general, diaryl ethers can be synthesized by means of copper-catalyzed Ullmann diaryl ether coupling, palladium-catalysed Buchwald-Hartwig reaction, nucleophilic aromatic substitution, arylboronic acid diaryl ether coupling, oxidative coupling, and nucleophilic aromatic addition to metal-arene complexes. This review covers the progress in diaryl ether synthesis since 1999, with literature coverage through September 2005.

8 Diaryl Ether Synthesis by Fischer Chromium Carbene Mediated Benzannulation
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Asymmetric Total Syntheses of Colchicine, β …

Een voorbeeld is de reactie van broombenzeen met 4-nitrofenol tot een difenyletherderivaat: Ullmann-condensatie De oorspronkelijke versie van deze reactie vereist ook minstens een stoichiometrische hoeveelheid koper, maar er zijn katalysatoren ontwikkeld op basis van koper.

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A collection of 56 multidentate ligands were screened in a model system for the Ullmann diaryl ether synthesis of electron-rich phenols and aryl bromides. Structurally diverse ligands showed a catalytic activity in the coupling, but none of the ligands showed a higher catalytic activity than N,N-dimethylglycine (L1). In the long-term screening, the ligands L2, L43 and L48 were found to exhibit only slightly lower catalytic activity than L1 in the model reaction. In conclusion, N-methylated amino acid-derived N,O-ligands, N,N-ligands with small bite angles, and N-butylimidazole proved to be the most efficient ligands for Ullmann diaryl ether formation under the tested conditions. The synthesized phosphinite-type P,N-ligands derived from 8-hydroxyquinoline performed well in the short-term screening but lost catalytic activity over time. While active ligands were found in various structural classes, even relatively small variations of the efficient ligands can lead to a dramatic loss of catalytic activity, which complicates their rational optimization. In general, strongly chelating ligands with four coordinating atoms should be avoided. Coordination of the copper atom by one N- and one N- or O-atom may be a desirable structural motif for the design of new ligands. Remarkably, published ligands used for other C-heteroatom bond-formation reactions showed unexpected low activity in our system.

Aryl ether synthesis via low-cost Ullmann coupling systems

The Ullmann condensation or Ullmann ether synthesis is a variation of the , in which a is coupled to an to create a in the presence of a compound, named after . The corresponding or aryl reaction is sometimes called Goldberg reaction, named after .

A Novel Diaryl Ether Ullmann-Type Synthesis using …

2 The classical Ullmann ether synthesis remains an important tool in diaryl ether synthesis. Despite limitations under the original conditions, such as elevated reaction temperatures, formidable purification problems, generally low yields, and the use of stoichiometric quantities of copper, recent work has revitalized this method considerably.

Stille reaction Ullmann diaryl ether synthesis ..

In the short-term screening, promising results were obtained with N,P-chelating phosphinite ligands such as L19 and L20, amino acid-derived N,O-ligands such as L2 and L3 and N,O- and N,N-ligands with a rigid backbone such as 8-aminoquinoline (L44) and 8-hydroxyquinoline (L47) ( and ). These ligands have been reported to be effective in the Cu-catalyzed diaryl ether synthesis before [,–].