An efficient protocol was developed to construct functionally dense quaternary carbons with concomitant formation of a new Csp(3)-Csp(3) bond via Pd-catalyzed decarboxylative transformation of vinyl cyclic carbonates. This redox-neutral catalytic system features stereocontrolled formation of multisubstituted allylic scaffolds with an aldehyde functionality generated in situ, and it typically can be performed at room temperature without any additives. DFT calculations provide a rationale toward the selective formation of these compounds and reveal a complex mechanism that with the help of microkinetic models is able to reproduce the nontrivial dependence of the identity of the product on the nature of the substituents in the substrate.