(2E)-2,4-Pentadienoic Acid Methyl Ester-d3 is the isotope labelled analog of (2E)-2,4-Pentadienoic Acid Methyl Ester (P268360); the methyl ester derivative of (2E)-2,4-Pentadienoic Acid (P268350) used as a reagent in the synthesis of opp-Dibenzoporphyrins as light-harvesters for Dye-Sensitized Solar Cells (DSSCs). Also used as a reagent in the preparation of allyl chlorides and allylboronates as substrates for stereoselective palladium-catalyzed allyl-allyl cross-coupling.