A dearomative C4-allylation of benzyl ammoniums with allyltributylstannane by a palladium catalysis is described. A triarylphosphine-ligated palladium catalyst, which is capable of cleaving benzylic C-N bonds, realized facile dearomative reactions with C4 selectivity. Combined with precedented C2-and C3-selective functionalizations of benzyl amine derivatives, the present reaction can provide a new synthetic option for the synthesis of multi-substituted alicyclic compounds as well as aromatic compounds.