Aromatic compounds copper bromide

BROMINATION OF AROMATIC COMPOUNDS WITH ALUMINA-SUPPORTED COPPER(II) BROMIDES... 

The usual aromatic bromination are performed by free bromine in the presence of a catalyst, most often iron. However, liquid bromine is not easy to handle because of its volatile and toxic character. On the other hand, alumina-supported copper(II) bromide can be treated easily and safely as a solid brominating reagent for aromatic compounds. The advantages of this procedure using the solid reagent are simple workups, mild conditions, and higher selectivities. Products can be isolated in good yield by simple filtration and solvent evaporation, and no extraction steps are required. 

In contrast to the alkynylation of acidic C-H bonds which can also be achieved using alkynyliodonium salts, the direct C-H functionalization of aromatic compounds or olefins has never been realized with this class of reagents so far. However, after several unsuccessful attempts using palladium or copper catalysts and alkynyliodonium salts for the alkynylation of heterocycles, Waser and Brand reported in 2009 the first efficient alkynylation of indoles using TIPS-EBX 52 and AuCl as catalyst (Scheme 18) [117]. With indole, selective C3-aIkynylation was obtained. The reaction was tolerant to many functional groups such as bromides, acids, or alcohols. The method was already used in the synthesis of starting materials for Friedel-Crafts reactions of aminocyclopropanes [118] and for hydroamidation to access indole c -enamides [119]. In 2010, Nevado and de Haro demonstrated that alkynylation was also possible using directly terminal propiolic ester derivatives and (diacetoxyiodo)benzene as co-oxidant [120]. 

The 5 -(trifluoromethyl)sulfonium salt can be applied to copper-mediated trifluoromethylation. Trifluoromethylation of heteroaryl iodides with the sulfonium salt proceeds in presence of stoichiometric copper under mild condition (eqs 17 and 18). Boronic acids also react with sulfonium salt (eqs 19 and 20), though 1 equiv of NaHCOs is needed as the base. These reactions furnish corresponding trifluoromethylated products in high yield. The copper-mediated trifluoromethylation reaction advances not only with aromatic compounds, but also at a benzylic position (eq 21). Trifluoromethylation reaction of benzyl bromides with S -(trifluoromethyl) sulfonium salt provides (trifluoroethyl)arenes in high yields. 

Although It IS possible to prepare aryl chlorides and aryl bromides by electrophilic aromatic substitution it is often necessary to prepare these compounds from an aromatic amine The amine is converted to the corresponding diazonmm salt and then treated with copper(I) chloride or copper(I) bromide as appropriate... 

Most of the work on the C-N bond-forming crosscoupling reactions has concentrated on the formation of aromatic C-N bonds. Recent studies show that the application of cross-coupling reactions to alkenyl halides or triflates furnished enamines (Scheme 19) (for palladium-catalyzed reaction, see 28,28a-28d, and for copper-catalyzed reaction, see 28e-28g). Brookhart et al. studied the palladium-catalyzed amination of 2-triflatotropone 109 for the synthesis of 2-anilinotropone 110.28 It was found that the reaction of 109 proceeded effectively in the presence of racemic BINAP and a base. As a simple method for the synthesis of enamines, the palladium-catalyzed reactions of alkenyl bromide 111 with secondary amine were achieved under similar conditions.2841 The water-sensitive enamine 112 was isolated as pure compound after dilution with hexane and filtration through Celite. The intramolecular cyclization of /3-lactam 113, having a vinyl bromide moiety, was investigated by Mori s... 

Other nucieophiies, such as chloride, bromide, and cyanide, are best added as copper(l) saits. Since aromatic amines are usuaiiy made by reduction of nitro compounds, a common sequence of reactions goes like this ... 

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