Aromaticity-Dependent Regioselectivity in Pd(II)-Catalyzed C-H Direct Arylation of Aryl Ureas.

Palladium-catalyzed C-H direct arylation generally occurs on the ortho-position of directing groups. By comparing meta-arylated products of 2-naphthyl urea to ortho-arylated products of phenyl urea, the ortho- and meta-regioselectivity of aryl ureas were found to depend on the aromaticity of the corresponding aryl substituents. Thus, aromaticity is a new factor which can affect the regioselectivity in C-H direct arylation. The finding was further confirmed by regioselective direct arylation of indole and pyrrole derivatives.