Carbon Ullmann coupling reactions

The biaryl synthesis by Ullmann coupling, as well as a large number of related coupling reactions, constitutes another type of copper-mediated or -catalyzed reaction used extensively for the formation of carbon-carbon and carbon-heteroatom bonds. These transformations have been reviewed recently17,177,177a,177b and will not be discussed in detail here. 

Vinylic halides can be coupled to give 1,3-butadienes (134) by treatment with activated copper powder in a reaction analogous to the Ullmann reaction (13-11). " This reaction is stereospecific, with retention of configuration at both carbons. Vinyhc halides can also be coupled with Zn—NiCl2, " " and with -BuLi in ether in the presence of MnCl2. " The coupling reaction with vinyltin reagents and vinyl halides occurs with a palladium catalyst. " ... 

The 1,4-conjugate addition of triorganoindium to enones is promoted by a catalytic amount of Ni(COD)2 (Scheme 8.71) [100], Allylindium reagents can be used in Pd-catalyzed cross-coupling reaction with aryl halides (Scheme 8.72). The Pd-catalyzed allylic substitution of allyl carbonate produces 1,5-dienes (Scheme 8.73) [101]. The indium-mediated palladium-catalyzed Ullmann-type reductive coupling of aryl halides proceeds in aqueous media under air (Scheme 8.74) [102]. 

Coupling reactions. Nanosized copper is a good catalyst for Ullmann ether synthesis, using CS2CO3 as base in MeCN at 50-60°. Carbon-supported copper in the presence of 1,10-phenanthroline shows similar activities with the aid of microwave irradiation. A -Arylation of A-heterocycles (benzimidazole, triazole,...) by ArSi(OR)3 is mediated by Cu-FeCls and TBAF in the air. ... 

Silyl enol ethers (CHj = CROSiMe3) react with cyanuryl chloride and replace only one chlorine with a carbon substituent (CH2COR R = cyclopropyl, 70 /o, R = Ph, 90 /o). Friedel-Crafts arylation <83KGS1125,92EUP497734>, the Ullmann reaction of 2-iodo-1,3,5-triazine to form 2,2 -bis-1,3,5-triazine <82NKK1425>, and a palladium-catalyzed cross-coupling reaction of 2-substituted 4,6-dichloro-... 

Several copper-catalyzed 7 -arylation reactions of imidazole have been published. The coupling of arylboronic acids with imidazole in the presence of binuclear bis-p,-hydroxy copper (11) complexes in air has been carried out at ambient temperature without the need for base <04TL7659>. A variety of A -arylimidazoles were prepared in excellent yields through the cross-coupling of arylboronic acids with imidazole in methanol or water with copper(I) chloride <04CC188>. Copper(II) oxide-coated nanoparticles were used catalytically in the Ullmann coupling of imidazole with various aryl chlorides with cesium carbonate in dimethyl sulfoxide <04CC778>. 

Palladium-catalyzed reductive couplings are among the most important carbon-carbon bond forming reactions in modem synthetic organic chemistry (18). These reactions are generally air sensitive. Recently we found that, in water, palladium catalysts are air-stable. Under such conditions several important palladium catalyzed reactions are more reactive and proceed smoothly at room temperature. For example, a zinc mediated Ullmann-type coupling provides high yield of the products catalyzed by palladium in water and under air-atmosphere (eq. 10) (79). 

Copper was used in carbon-carbon bond formation reactions for the first time in 1904 [140] in the well-known Ullmann reaction which involved aromatic halides. Very recent work has reported the use of activated copper (Cu ) in homo-coupling and cyclization reactions of a, co-dihaloalkanes [141],... 

The synthetic and kinetic regularities of the amino-Claisen rearrangement were studied for the transformation of 2,5-dimethyl-Af-(pent-3-en-2-yl)aniline." The products are obtained via conversion of a binary r-complex formed by the reaction of N-alkenylaniline hydrochloride with the hydrochloride of the solvent (2,5-dimethylaniline). Spirocyclic oxindoles have been prepared from iodoindoles via a sequential intramolecular Ullmann coupling and Claisen rearrangement." Nucleophilic ort/io-propargylation of aryl sulfoxides has been reported to occur by intermolecular delivery of the nucleophile to sulfur followed by an intramolecular relay to carbon in a... 

Intramolecular carbon-nitrogen bond formation may result from the Ullmann coupling of l,3-bis(2-iodoaryl)propan-2-amines catalysed by copper. Using (i )-BINOL, l,l -Bi-2-naphthol, ligands, the enantioselective formation of indolines and 1,2,3,4-tetrahydroquinolines was achieved. Copper catalysis has also been used in the intramolecular formation of imidazobenzimidazole derivatives. The reaction is likely to involve the formation of intermediates, such as (16), which on aerobic oxidation yield the product. There is evidence for an intramolecular 0- -N Smiles rearrangement, as... 

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). 

Vinylic halides can be coupled to give 1,3-butadienes by treatment with activated copper powder in a reaction analogous to the Ullmann reaction (13-14). " This reaction is stereospecific, with retention of configuration at both carbons. 

Substitution reactions at aromatic carbon (see also Reduction reactions, Ullmann ether coupling, specific reactions such as Nitration) Arene(tricarbonyl)chromium complexes, 19... 

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