N-heterocyclic carbenes (NHCs) was uncovered as an efficient ligand in promoting allylic C–H bond functionlizations. Notably, the catalytic [Pd(η³-cin)(IPr)Cl] complex (where cin = cinnamyl) was formed in situ from direct C–H activation of allylic precursors, and was obtained by way of one-pot strategy with available IPr·HCl and allylbenzene. The catalyst exhibits high regioselectivity and stereoselectivity of the allylic C–H alkylation with oxindoles with a broad scope.