Ullmann synthesis

Sawyer and coworkers have developed an efficient alternative Ullmann synthesis of diaryl ethers, diaryl thioethers, and diarylamines using the SNAr reaction. Phenol, thiophenol, or aniline reacts with an appropriate aryl halide, in the presence of KF-alumina and 18-crown-6 in acetonitrile or DMSO to give the corresponding diaryl ether or diaryl thioether as shown in Eqs. 9.6 and 9.7.9a... 

As an alternative to the Tauber method, 2,2 -diaminobiphenyl (509) was transformed to carbazole (1) using diazotization conditions. This reaction proceeds intra-molecularly by displacement of nitrogen. With this procedure, only moderate yields of carbazoles were obtained. The reaction is mechanistically similar to the Graebe-Ullmann synthesis (494) (Scheme 5.6). 

Transformation of 1-arylbenzotriazole (520) to carbazole (1) under thermal conditions is known as the Graebe-Ullmann synthesis (502). This transformation is very sensitive to the nature of the substituents on the benzotriazole. However, unsubstituted 1-arylbenzotriazole (520) affords carbazole in nearly quantitative yield. The required starting material, 1-arylbenzotriazole (520), is prepared by the diazotization of N-(2-aminophenyl)aniline (519) (503,504). Limited reports on the mechanism of the Graebe-Ullmann reaction have appeared. Presumably, a diradical intermediate is involved in the thermolysis of the triazole (505) (Scheme 5.9). 

Results analogous to the above have been obtained in the Ullmann synthesis of polychlorobiphenyls from polychloroiodobenzenes at 220 C when by-product polychlorodibenzofurans ( 0.1%) are produced. Routes (i) and (iii) appear to op>erate under these conditions. Thus the dichloroiodo-benzene 76 gave the tetrachlorodibenzofuran 78 by route (i), and in addition and in contrast to the results of Moron et a/., a pentachlorodibenzofuran, tentatively assigned structure 79 (Scheme 19), was detected. ... 

It is comparable to crown ethers or R4NBr for phase-transfer catalyzed aliphatic nucleophilic substitutions in addition it catalyzes aromatic nucleophilic substitutions such as the Ullmann synthesis. 

A useful reaction for investigation is the Ullmann synthesis of diaryl ethers, which has potential importance for synthesis of a number of commercial products in the agrochemical and pharmaceutical fields, but which suffers from serious drawbacks, particularly high temperatures... 

Fig. 15). Ultrasound has previously been found to effect rate enhancement in the Ullmann synthesis of biaiyls. ... 

Molina, A., Vaquero, J.J., Garcianavio, J.L. and Alvarezbuilla, J., One-pot Graebe-Ullmann synthesis of gamma-carbolines under microwave irradiation, Tetrahedron Lett., 1993, 34, 2673. 

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. ... 

Ullmann synthesis, ] 15 Unsaturated acid chlorides, acylation, 49 Uranium derivatives, 154 Uranyl ions, 108 Urea, with azothiazoles. 111 to thiazolyl urea, 56 see also Thiazolyl urea Urine, 2-aminothiazoles in, 85 metabolite in, 85... 

As a recent modification, the Graebe-Ullmann synthesis of. y-carbolines under microwave irradiation has been conducted (Scheme 37). Yields of the reaction were comparable to those obtained by conventional heating at 150-210°C (30-81% yield), but the reaction times were significantly reduced <93TL2673>. Similarly, using flash vacuum pyrolysis techniques, nitroar-ylbenzotriazoles have been converted to pyridoindoles <88BSB245>. 

Ullmann synthesis, 20, 45 n-Undecyl mercaptan, 21, 38 o-Undecylylphenol, 20, 58 -Undecylylphenol, 20, 58... 

Vttmann diaryl ether synthesis. This copper(I) derivative is recommended as the condensing reagent in the Ullmann synthesis of diaryl ethers from phenols and bromoarenes in refluxing pyridine (equation I). 

Bis(3-aminophenyl)arylene ethers are useful monomers to prepare polyimides of lower Tg s. For example, l,3-bis(3-aminophenoxy)benzene has been used as building blocks for various thermally processable PI systems. The compound was originaly synthesized by Fink [6] according to the following Ullmann synthesis under rather harsh conditions. 

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