A highly diastereoselective Pd-catalyzed carbonyl allylation of aldehydes and isatins directly using simple acyclic olefins as allylating reagents is described. This transformation is actually a sequential process consisting of a Pd-catalyzed oxidative allylic C-H borylation and an allylboration of carbonyls accelerated by phosphoric acid, wherein a wide scope of olefins could be tolerated. The oxidant is revealed to play a key role in the successful realization of the allylic C-H activation-based allylation.