Pd(II)-Catalyzed ortho-C-H Olefination/Dearomatization of N-Aryl Ureas: An Approach to Imine Derivatives.

An unprecedented approach for the synthesis of imine derivatives was achieved via a Pd(II)-catalyzed dearomatization reaction of N-aryl ureas with internal alkynes. The corresponding spirocyclic imine derivatives were obtained with 20 examples in good to excellent yields. Mechanistic investigation indicated that an interesting 1,3-palladium migration process led to the α-regioselective dearomatization when 2-naphthyl ureas were used as the substrates.

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.