In this work, we report an unusual nucleophilic allylation reaction between isatin‐derived Morita–Baylis–Hillman carbonates and simple alkenes synergistically catalyzed by tertiary phosphines and palladium complexes, through chemoselective assemblies of in situ formed onium salts and η1‐allylpalladium species, respectively. A range of 3,3‐disubstituted oxindoles were easily constructed in moderate to good yields with exclusive linear regioselectivity. Moreover, a number of control and deuterium experiments have been conducted to elucidate the catalytic mechanism.