Carbon dioxide was used not only as a reaction medium but also as a renewable C₁ feedstock for the palladium catalyzed coupling reaction of butadiene and carbon dioxide. By utilization of nitrile modified phosphine ligands, in the liquid phase complete butadiene conversion and selectivity for the formation of (3E)-3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one (1) up to 47% were achieved. Phase equilibrium considerations were used for process development in order to realize single-phase conditions for the reaction. In contrast to a CO₂ enriched phase composition, variation of the density only enables moderate conversion rates also with single-phase conditions and without further catalyst modification.