Fully substituted acyclic enolates are valuable intermediates for the enantioselective construction of α-quaternary carbonyl compounds, yet reliable control of enolate geometry—particularly for aldehydes—remains difficult under conventional deprotonation conditions. β-Oxy vinylbenziodoxoles (VBXs), accessible through two complementary pathways, provide stereodefined acyclic enolate precursors that retain alkene geometry through subsequent cross-coupling and carbonate formation. These VBXs undergo configuration-retentive Sonogashira coupling, enabling modular installation of alkynyl substituents. Subsequent conversion to allyl enol carbonates furnishes ketone- and aldehyde-type enolate surrogates with defined E/Z configuration. Under Pd/Trost-ligand conditions, these carbonates participate in enantioselective decarboxylative allylic alkylation to deliver α-quaternary ketones and aldehydes in high yields and enantioselectivities. The decisive role of enolate geometry is demonstrated by the opposite sense of asymmetric induction for E- and Z-isomers of the carbonate precursor. The resulting alkynyl-substituted products are readily diversified through manipulation of the allyl, alkynyl, and carbonyl groups.