An efficient synthesis of privileged allylic amines has been developed via cobalt-catalyzed allylation of amides with styrenes, in which DMSO was used as both the solvent and the α-methylene source. This transformation features high yields, and selectivity for the (E)-isomer of the linear product. Through the experimental and computational investigations, a sequential K2S2O8-mediated oxidative coupling/cobalt-assisted regioselective alkene insertion/β-H elimination/alkene dissociation/hydride transfer process has also been deduced.