Facile palladium-catalyzed homocoupling of aryl halides using 1,4-butanediol as solvent, reductant and O,O-ligand

A mild, efficient and environmentally friendly method for the synthesis of biaryl compounds via palladium-catalyzed reductive homocoupling of aryl halides in 1,4-butanediol (1,4-DBO) has been developed. In this catalyst system, green solvent-1,4butanediol is used not only as solvent, but also as reductant and O,O-ligand,and therefore no extra reducing agents and ligands are required. Moreover, the weak coordinate effect brings 1,4-butanediol close to the palladium and accelerates the process of electron transfer in a four-membered ring transition state and hence promotes the reduction and catalytic process. A variety of biaryl compounds have been synthesized via this protocol rapidly with low loading of palladium catalyst under mild conditions in air.