Ethanol-promoted reductive homocoupling reactions of aryl halides catalyzed by palladium on carbon (Pd/C)

Homocoupling reactions of aryl bromides or iodides proceeded smoothly with palladium on carbon (Pd/C) catalyst, ethanol and base in dimethyl sulfoxide (DMSO) to afford exclusively symmetric biaryls in good to excellent yields. Ethanol was first used as a reducing agent in situ to reduce the Pd2+/C species into Pd-0/C active species to complete the catalytic redox cycle. It was found that ethanol can promote the Pd/C-catalyzed reductive homocoupling of aryl iodides and bromides efficiently in the presence of base. A reaction mechanism has been put forward and discussed. Copyright (C) 2010 John Wiley & Sons, Ltd.