Aryl with arylcopper reagents

Moreover, functionalized arylcopper reagents have been reported as appropriate nucleophiles with alkenyl and dienyl sulfonates (Table 5.3, entries 14—18) [18]. Although aryl sulfonates showed little reactivity towards arylcopper reagents, alkenyl sulfonates proved to be much more reactive under the described reaction conditions. 

P-Arylation of electron-deficient alkenes. Aryl radicals are generated from aryl halides by reaction with the CrCh-ethylenediamine complex, and the mode of addition is similar to that of arylcopper reagents. 

Heterocycle openings. a,p-Epoxy silanes fiimish P-hydroxy silanes due to the attack of cuprate reagents at the a-carbon. The regioselectivity for the reaction of methyl ( J-4,5-epoxypent-2-enoate with arylcopper is dependent on the presence or absence of BF,. The S 2 pathway giving the a-aryl esters becomes significant with the added Lewis acid. The Sf 2 products are observed in the reaction of epoxy vinyl sulfoxides with... 

Cross-coupling reaction of arylcopper reagents with aryl halides... 

Arylcopper intermediates can be generated from organolithium compounds, as in the preparation of cuprates.95 These compounds react with a second aryl halide to provide unsymmetrical biaryls in a reaction that is essentially a variant of the cuprate alkylation process discussed on p. 680. An alternative procedure involves generation of a mixed diarylcyanocuprate by sequential addition of two different aryllithium reagents to CuCN, which then undergo decomposition to biaryls on exposure to oxygen.96 The second addition must be carried out at very low temperature to prevent equilibration with the symmetrical diarylcyanocuprates. 

Similarly to the alkyl derivatives, the most common route for arylcopper compounds is the reaction of a copper halide and aryllithium compounds (Equation (4)). Organocuprates with aryl groups are obtained by using an appropriate excess of the lithium reagent. Magnesium aryls have also been employed in transmetallation reactions with Cu(l) salts to yield both arylcopper compounds and arylcuprates (Equations (5) and (6)). 

In some instances, the unsymmetrical coupling reaction of an arylcopper(I) reagent with the aryl halide can be carried out without the or/Ao-coordinating substituents. It has been shown that 2-thienylcopper(l) and 2-furylcopper(l) readily couple with iodobenzene or 4-iodoanisole to give 2-phenylthiophene (50%) and 2-(4-methoxy... 

The reaction apparently involves free-radical mechanism, but arylcopper compounds take a part, at least under certain reaction conditions, as clearly demonstrated through Cohen s concise results [99,100]. The reaction was discovered as a side-reaction during probes of the Gatterman synthesis of aryl halides from diazonium salts and copper(l) halides. Probably the most known example is very practical preparation of diphenic acid (57) starting from anthranilic acid (58). The reaction is usually conducted by adding an aqueous diazotized anthranilic acid solution (diazonium salt 59) to the copper(l) reagent, in situ obtained by reduction of CUSO4 with an equimolar amount of hydroxylaminc in aqueous sodium hydroxide solution, to produce diphenic acid with a 80-90% yield [99,100], Scheme 25. 

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