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. Fused ring products could also be obtained to further prove this migration process.