Ullman reaction

Ullman reaction The synthesis of diaryls by the condensation of aromatic halides with themselves or other aromatic halides, with the concomitant removal of halogens by a metal, e.g. copper powder thus bromobenzene gives diphenyl. The reaction may be extended to the preparation of diaryl ethers and diaryl thio-ethers by coupling a metal phenolate with an aryl halide. 

An aiyl methane- or toluenesulfonate ester is stable to reduction with lithium aluminum hydride, to the acidic conditions used for nitration of an aromatic ring (HNO3/HOAC), and to the high temperatures (200-250°) of an Ullman reaction. Aiyl sulfonate esters, formed by reaction of a phenol with a sulfonyl chloride in pyridine or aqueous sodium hydroxide, are cleaved by warming in aqueous sodium hydroxide. ... 

NONA was prepd in a mixed Ullman reaction using picryl chloride, 13 dichloro-2,4,6-trinitrobenzene and electrolytic Cu dust ... 

The Ullman reaction has long been known as a method for the synthesis of aromatic ethers by the reaction of a phenol with an aromatic halide in the presence of a copper compound as a catalyst. It is a variation on the nucleophilic substitution reaction since a phenolic salt reacts with the halide. Nonactivated aromatic halides can be used in the synthesis of poly(arylene edier)s, dius providing a way of obtaining structures not available by the conventional nucleophilic route. The ease of halogen displacement was found to be the reverse of that observed for activated nucleophilic substitution reaction, that is, I > Br > Cl F. The polymerizations are conducted in benzophenone with a cuprous chloride-pyridine complex as a catalyst. Bromine compounds are the favored reactants.53,124 127 Poly(arylene ether)s have been prepared by Ullman coupling of bisphenols and... 

Cu-mediated Ullman reaction has been used for the polymerization of dihaloaryls. For example, see ref. 3. This type of polymerization as well as other transition-metal-mediated reactions that involve radicals in the polymerization process is not included in this chapter. 

Uniformly labeled 2,4-dichlorophenol- C (purchased from New England Nuclear Corp, Boston, Mass.) was used in the tracer preparation. This provided a label at all carbon positions in the dibenzo-dioxin structure. 2,7-Dichlorodibenzo-p-dioxin- C after initial cleanup by fractional sublimation, contained approximately 5% of an impurity, detected by thin layer chromatography (TLC) which gave mass peaks at 288, 290, 292, and 294 in the mass spectrometer, consistent with a trichloro-hydroxydiphenyl oxide. This is probably the initial condensation product of the Ullman reaction and is most likely 2-(2,4-dichlorophenoxy)-4-chlorophenol. It was removed easily by extractions with aqueous... 

The Ullman reaction, discovered in 1903,2 is the prototype cross-coupling method for the synthesis of aryl ether... 

Apart from nucleophilic substitution reactions, the chemistry of the halo derivatives of the 7r-deficient heterocycles is fairly similar to that of aromatic halides. Thus, heterobiaryls can be prepared by the Ullman reaction, and Grignard reagents and organolithium compounds can be prepared, although in many instances, and especially with Grignard reagents,... 

The procedure described here is by far the most efficient synthesis of terpyridine. Previous preparations include the dehydrogenation of pyridine with ferric chloride, the Ullman reaction of 2-bromopyrid1ne and 2,6-dibromopyridine,5 the action of copper on 2-bromopyridine and 6-bromo-2,2 -... 

Table I. (continued) Ambient Temperature Ullman Reaction... 

In a modified Graebe-Ullman reaction, pyridylbenzotriazole 223 was converted to a-carboline 224 in an efficient manner but in moderate yield (Scheme 38) <20060L415>. Microwave irradiation was the energy source for both a-carboline synthesis and the preparation of 223. The advantages of this procedure are that the starting materials are commercially available and lower reaction times are used resulting in fewer undesirable side products. The style of microwave oven, amount of pyrophosphoric acid, power level, and time were all optimized. 

Ullman reaction conditions have also been used in the synthesis of biflavanoids. Heating of 3-haloflavones in the presence of copper powder provided biflavones in good yield <1993SC1075>. Isoflavone and derivatives, for example 425, can be prepared efficiently by the Suzuki cross-coupling of 3-bromo and 3-iodochromones 424 with arylboronic acids (Scheme 71) <1988BCJ3008, 1989CPB529>. 

The mixed Ullman reaction in which two haloarenes couple in the presence of copper powder is still commonplace in industrial process, but the catalyzed cross-coupling reactions appear to be more productive and provide reliable results in synthesis of unsymmetrical biaryls (Scheme 30). The isomeric michel-... 

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