Ullmann biaryl ether

ULLMANN BIARYL ETHER AND BIARYL AMINE SYNTHESIS / CONDENSATION... 

Modified Ullmann biaryl ether / thioether and biaryl amine synthesis ... 

Ullmann Biaryl Ether and Biaryl Amine Synthesis/Condensation 464... 

Cu-catalyzed Ullmann biaryl ether synthesis Cu-mediated synthesis of biaryl ethers by coupling aryl halides and phenols. 464... 

Palomo, C., Oiarbide, M., Lopez, R. and Gomez-Bengoa, E. (1998) Phosphazene P4-But base for the Ullmann biaryl ether synthesis. Chemical Communications, 2091-2092. 

Cycloamidation has been used extensively to prepare 17-membered cycloisodityrosines. The acyclic biaryl ether precursors were prepared by methods including the Ullmann reaction 2-5 and nucleophilic aromatic substitution (SNAr)J6 7 Since these methods have all been used intramolecularly in cyclization reactions, they will be discussed in Sections 9.5.3 and 9.5.4. Evans and co-workers employed the pentafluorophenyl ester method of macrolactamization 8] to prepare 11, an intermediate in their total synthesis of OF4949-III (7) (Scheme 2)J3 In this case, the acidic removal of a Boc group was employed to release the cyclization substrate, although hydrogenolysis of a Z group is also effective 3 ... 

Biaryl ether and amine synthesis (Ullmann 1903 Goldberg 1906) ... 

The intramolecular Ullmann condensation was used by D.L. Boqer and co-workers to form the 15-membered macrocyclic ring of the cytotoxic natural product, combretastatin D-2. This compound possesses unusual meta- and paracyciophane subunits, which are also found in a range of antitumor antibiotics. The first approach where the final step was a macrolactonization was unsuccessful, so the researchers chose to form the biaryl ether moiety as the key macrocyciization step. Methyicopper was found to mediate the cyclization and gave moderate yield of the corresponding biaryi ether. Finaiiy boron triiodide mediated demethylation afforded the natural product. 

In the laboratory of K.C. Nicolaou, a novel mild method for the preparation of biaryl ethers was developed. The di-ort/70-halogenated aromatic triazenes underwent efficient coupling with phenols in the presence of CuBr. This mild modified Ullmann condensation was utilized in the synthesis of the DOE and COD model ring systems of vancomycin. 

Carbon-oxygen bonds are formed by the Ullmann reaction (- coupling of aryl halides with copper) which has been varied in alkaloid chemistry to produce diaryl ethers instead of biaryls. This is achieved by the use of CuO in basic media (T. Kametani, 1969 R.W. Dos-kotch, 1971). 

The name Ullmann is not only associated with the biaryl synthesis (Figure 16.4, 16.5), but is also known from the synthesis of diaryl ethers (Ullmann synthesis of diaryl ethers). An example is given in the topmost reaction of Figure 16.6. Remember Side Note 5.6, where we asked the following question How can diphenyl ethers be prepared Now you are ready to give a correct answer, which is By way of Ullmann synthesis. ... 

Aryl ethers. Pd of the Ullmann m< Electron-deficient. 4rl Electron-poor phosphii aryl bromides and sodii Biaryls and diaryl reactions of aryl iodic obtained from iodoph coupling at 55-60°. 

The Ullmann reaction can be taken to refer to two different transformations. The first is the copper mediated coupling of two aryl groups to give a biaryl compound this is the classic Ullmann reaction. The second, the Ullmann-type reaction, is the nucleophilic aromatic substitution between aryl nucleophiles and aryl halides, the most common of which is the Ullmann ether synthesis. The classic Ullmann reaction will be reviewed in this chapter the reader is refered to several excellent reviews for details on the Ullmann-type reaction. " ... 

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