Biaryl coupling copper-catalysed

Under certain reaction conditions, even activated arylmethylthioethers can be used as electrophiles in the SM reactions. Thus copper(l) 3-methylsalicylate (CuMeSal) does catalyse the cross-coupling reaction of 3-methylthio-l,2,4-triazine (248) with 2-thienyl boronic acid (249) to afford biaryl 250 in 70% yield, respectively [50], Scheme 3. 

Table 8. Palladium-catalysed homo-coupling reaction of arylboronic acids to symmetrical biaryls in the presence of copper(II) nitrate as an oxidant...

Aryltrimethyl- or tri- -butylstaimanes as common Stille reagents are also successfully homo-coupled under palladium catalysed reactions in the presence of ethyl 2,3-dibromophenylpropionate (443) [26], or more conveniently by oxidation with copper(I) salts, e.g. CuCl [27], or copper(II) salts, e.g. Cu(N03)2 3H20 [28,29], which proceed smoothly at room temperature in tetrahydrofuran or DMF to afford symmetrical biaryls in excellent 3uelds. The Cu(N03)2-mediated homo-coupling works well also with diaryldimethyl(or -butyl)stannanes [30]. Moreover, the reaction can be accomplished with a catalytic amount of copper(II) chloride or manganese(II) bromide (10 mol%) in the presence of iodine as stoichiometric oxidant [31]. For example, compound 443, acting as an oxidant, converts the phenyltri-n-butylstannane (184) to biphenyl (8) in 86% yield [26], Scheme 11. 

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