Copper(I)-catalysed homo-coupling of aryldiazonium salts: synthesis of symmetrical biaryls

Copper(I) triflate acts as an efficient stoichiometric reagent for the homo-coupling of aryldiazonium salts bearing electron-withdrawing group(s), to yield symmetrical biaryls in acetonitrile under mild reaction conditions. Aryldiazonium salts bearing electron-donating groups undergo the reaction by using catalytic amounts of a copper complex prepared in situ from copper(II) triflate and 2,2′-bipyridine with metallic copper as an ultimate reductant.

(i) 1.5 equiv CuOTf; MeCN; 0 °C-rt; overnight; R=EWG(s); (ii) 20 mol % Cu(OTf)2, bpy; 3 equiv Cu; MeCN; rt; overnight; R=H or EDG(s); 15 examples; yields: 7-96%.