Palladium-Catalyzed (Ullmann-Type) Homocoupling of Aryl Halides: A Convenient and General Synthesis of Symmetrical Biaryls via Inter- and Intramolecular Coupling Reactions

A convenient new procedure is described for both inter- and intramolecular homocoupling of aryl halides (Ullmann reaction) using catalytic palladium in the presence of hydroquinone, a homogeneous reductant. Optimal conditions for the reductive coupling include the use of a 1:1 molar ratio of Pd(OAc)2 and As(o-tolyl)3 in catalytic amounts under basic conditions.