UUmann ether synthesis

UUmann ether synthesis. The original Ullmann ether synthesis9 involved melting the salt of a phenol with an aryl bromide in the presence of copper metal. Yields are low. Williams et al.10 found that the reaction can be carried out at lower temperatures by using as solvent pyridine, which forms a complex with copper salts (cuprous chloride preferred), which provides catalysis for the reaction reflux temperature is then sufficient. 

As noted in the introduction to this section, UUmann also reported the formation of biaryl ethers from phenol and phenyl bromide in the presence of copper and a base. This UUmann ether synthesis has been used extensively to prepare biaryl ethers. " However, the original reaction conditions involved high temperatures (150-200 C), neat phenol or highly polar aprotic solvents, and stoichiometric amounts of copper complexes. The yields for the reactions of unactivated aryl halides were often low. Conditions with catalytic amounts of copper at lower temperatures with broader scope have now been developed. 

UUmann diphenyl ether synthesis. Copper or one of its salts or oxides has been used to effect this reaction between an aromatic halide and a phenol. Cava... 

Sjwyer and coworkers have developed an efficient alternative UUmann synthesis of diaryl ethers, diaryl thioethers, and diarylamines using the SnAt reaction. Phenol, thiophenol, or aniline reacts v/ith an appropriate aryl halide, In the presence of KF-aliunina and 18-crovm-6 In acetonitrile or DMSO to give the corresponding diaryl ether or diaryl thio ether as shovm In Eqs. 9.6 and 9.7. ... 

---