Rieke copper, reactions

For the highly reaetive eopper metal forms, e.g. Rieke copper, oxidative addition to aryl halide occurs readily at room temperature or below [27]. At these temperatures oxidative addition of the resultant arylcopper(l) compound to the second molecule of aryl halide, or decomposition to biaryl proceeds very slowly or not at all. The arylcopper(l) compounds can then be homo-coupled or react with the aryl halides to form biaryl as the temperature is raised. In the classical Ullmann reaction employing... 

With special techniques for the activation of the metal—e.g. for removal of the oxide layer, and the preparation of finely dispersed metal—the scope of the Refor-matsky reaction has been broadened, and yields have been markedly improved." The attempted activation of zinc by treatment with iodine or dibromomethane, or washing with dilute hydrochloric acid prior to use, often is only moderately successful. Much more effective is the use of special alloys—e.g. zinc-copper couple, or the reduction of zinc halides using potassium (the so-called Rieke procedure ) or potassium graphite. The application of ultrasound has also been reported. ... 

The hydrogenation of fatty acids or fatty esters is of industrial importance for the production of fatty alcohols. Usually, the hydrogenation is performed in slurry-phase or fixed-bed reactors over copper-chromium oxide catalyst at elevated temperature and pressure.37 Rieke et al. investigated the hydrogenation of methyl dodecanoate over copper-chromium oxide at 280°C and 13.8 MPa H2, in order to study the side reactions that occur during hydrogenation.37 On the basis of the potential reaction routes described by Rieke et al., the pathways leading to C12 alcohol and various byproducts are summarized in Scheme 10.2, with exclusion of the formation and reactions of acetals. It has been found that both catalytic activity and selectivity correlated well with the crystallinity of the copper-chromium ox-... 

Wurtz-Ullmann processes can be carried out with copper or zinc, prepared by the sonochemical Rieke method. Lindley et al examined the fundamental aspects of the copper-induced reaction of 2-nitro iodobenzene (Eq. 44). 9 Almost quantitative yields are obtained with only a fourfold excess of copper flakes at 60 C in DMF under probe sonication, with a rate multiplied by a factor of ca. 50. 

Reaction Procedure (Scheme 4.4) Aryl bromide (1.0 mmol) in THF (2 mL) was added to Rieke zine (4 mL, 5 g/100 mL suspension in THF). After the addition, the reaetion mixture was heated at reflux and then concentrated in vacuo. The aryl zine was dissolved in DMA (4 mL) and transferred via cannula onto a solid copper(i) bromide-dimethyl sulfide complex (20 mg, 0.1 mmol). Oxidant (147 mg, 0.5 mmol) in DMA (2 mL) was then added and the solution was kept stirring for 1 h at room temperature. The reaction mixture was filtered through a plug of silica eluting with hexane and EtOAc. The filtrate was concentrated in vacuo and the residue purified by flash eolumn chromatography on silica gel. 

Rieke has demonstrated that the generation of active metals can be readily achieved by in situ reduction of the corresponding metallic salts with lithium naphthalenide [5]. Many copper(i) salts can be reduced under such conditions and the choice of the optimum reaction conditions is essential for the success of the insertion reaction [6]. The presence of phosphine ligands leads to highly active copper(O)-powder. The use of BUjP Cul as copper(i) salt is especially well suited and allows the subsequent opening of epoxides (Scheme 9.1). 

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