Ullmann coupling copper® bromide

We investigated the catalytic performance of the CU2O coated copper nanoparticles for Ullmann coupling reactions. When the coupling reactions using aryl bromides such as 2-... 

Ullmann coupling reactions of perfluoroaryl ttnd -heteioaiyl iodides and bromides with copper proceed readily. ... 

The replacement of copper by other metals in the Ullmann reaction usually results in milder and more efficient pathways. The common use of Pd in conjunction with copper in the Ullmann coupling can be seen in many examples. Nicolaou et al. utilized such modifications in their total synthesis of kinamycins C, F, and J. Bromide 9 underwent coupling with iodide 10 to give aldehyde 11 in a satisfactory 83% yield. 

The coupling of aryl halides with copper is called the Ullmann reaction.m The reaction is of broad scope and has been used to prepare many symmetrical and unsymmetrical biaryls.187 When a mixture of two different aryl halides is used, there are three possible products, but often only one is obtained. For example, picryl chloride and iodobenzene gave only 2,4,6-trinitrobiphenyl.188 The best leaving group is iodo, and the reaction is most often done on aryl iodides, but bromides, chlorides, and even thiocyanates have been used. 

The homo-coupling Ullmann reaction can be performed at room temperature or bellow by metallation of suitable substrates such as relatively acidic arenes or aryl hahdes with the -BuLi (or other strong bases) followed by addition of Cu(II) salts [28], Aryllithium reagent undergoes transmetallation with the Cu(II) salts to form diarylcopper(II) which is prone to rapid reductive elimination of the biaryl with extrusion of a copper nrirror. Benincori and coworkers [28] described an efficient procedure for the homo-coupling reaction of bromide 21 via diarylcopperfll) 22 under very mild reaction conditions, where the 3,3 -bibenzo[b]thiophene (23) was obtained in 56% yield. Scheme 4. 

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