Synthesis of Sterically Hindered Biaryls via the Palladium-Catalyzed Cross-Coupling Reaction of Arylboronic Acids or their Esters with Haloarenes

Sterically hindered arylboronic acids such as mesitylboronic acid (1a) were cross-coupled with 2-substituted haloarenes in high yields in the presence of tetrakis(triphenyl-phosphine)palladium(0) and aqueous barium hydroxide in 1,2-dimethoxyethane. An alternative procedure using esters of boronic acids and tripotassium phosphate in dimethylformamide was also newly developed for the cross-coupling reaction of arylboronic acids which are sensitive to hydrolytic deboronation with aqueous base.