Palladium-catalyzed unsymmetrical aryl couplings in sequence leading to o-teraryls: dramatic olefin effect on selectivity.

Selectively substituted o-teraryls are obtained by palladium/norbornene-catalyzed reaction of aryl iodides, aryl bromides and aryl boronic acids in ordered sequence; high selectivity is attained thanks to the addition of diethyl maleate acting as palladium ligand.