Bronze, Ullmann coupling

Picryl chloride has been used successfully in a number of copper-mediated Ullmann coupling reactions. 2,2, 4,4, 6,6 -Hexanitrobiphenyl has been synthesized by heating picryl chloride with copper powder. The same reaction in the presence of a hydride source (hot aqueous alcohol) yields 1,3,5-trinitrobenzene (TNB). The Ullmann reactions between picryl chloride and isomeric iodonitrobenzenes with copper bronze in DMF has been used to synthesize 2,2, 4,6-, 2,3, 4,6-, and 2,4,4, 6-tetranitrobiphenyls. ... 

The first total synthesis of taspine was accomplished by T.R. Kelly and co-workers. The central biaryl link was established by a classical Ullmann coupling using activated copper bronze. It is noteworthy that no other crosscoupling strategy was successful to make the C-C bond between the aromatic rings due to the severe steric hindrance. 

The activating effect in the Ullmann coupling reaction of aryl halides provides the electronegative groups such as nitro, alkoxycarbonyl or cyano in the orrAo-position to the halogen atom. These activating substituents present in the meta- or pura-positions do not significantly activate the aryl halide. For example, 2-nitro-bromobenzene reacts with the copper bronze more rapidly and at a lower temperature, while the... 

The use of copper bronze was used in the Ullmann coupling of protected iodoresorcinol 15 to give the symmetrical biphenyl 16. Despite the obvious steric hinderance afforded by the or// o-methoxy groups, the reaction took place in a good yield of 72%. 

A reaction which is reminiscent of the Wurtz coupling procedure, and which is particularly valuable in the syntheiss of biphenyl and its symmetrically substituted derivatives, is that of Ullmann. It involves heating an aryl halide with copper powder, or better, with activated copper bronze. 

A related reaction is the coupling of two molecules of aryl halide by metallic copper at temperatures above 100° (Ullmann). Activated copper bronze or freshly precipitated copper is used. The order of activity of the aryl halides is I > Br > Cl. Both symmetrically and unsymmetrically substituted biaryls may be prepared in fair yields. An excellent review of the literature to 1945 has been made. Most functional groups do not interfere hydroxyl, carboxyl, amino, and acetamino groups are exceptions. ... 

Copper bronze is available at paint stores it is activated by the method of Vogel. Ulbnann coupling. The Ullmann reaction can be carried out in a sealed tube at 90-115° (12 hr.) without a solvent. 2,2 -Dipyrimidine has been prepared in this way in about 45% yield. ... 

Subsequently, a series of different radical reactions were reported, such as mixed Ullmann reactions of halo- and l,l -dihaloferrocene with copper bronze [17,18], coupling reactions of lithio- and l,l -dilithioferrocene with cobalt chloride in the pres-... 

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