Synthesis of functionalized o-, m-, and p-terphenyl derivatives by consecutive cross-coupling reactions of triazene-substituted arylboronic esters

Triazene-substituted arylboronic esters were prepared readily from the corresponding aryl magnesium derivatives and shown to function as a new class of donor-acceptor-substituted coupling reagents. The selective functionalization of these aromatic derivatives led to a wide variety of terphenyl derivatives in which the original bifunctional unit (often further substituted with another functional group) formed the central aromatic ring. The functionalized terphenyl derivatives were formed in two efficient cross-coupling steps from the triazene-substituted boronic esters: Suzuki cross-coupling with an aryl halide was followed by BF₃·OEt₂-induced palladium-catalyzed coupling of the diazonium salt generated in situ from the triazene with an arylboronic acid.