Palladium-Catalyzed Methoxycarbonylation of 1,3-Butadiene to Methyl-3-Pentenoate: Introduction of a Continuous Process

The base-assisted Pd(cod)Cl₂/Xantphos-catalyzed methoxycarbonylation of 1,3-butadiene (BD) to methyl-3-pentenoate (MP) was explored. Mechanistic studies suggest the excessive Xantphos (beyond an equimolar amount per Pd) as well as its substitute, pyridines of proper steric and electronic functionality, do participate the catalytic cycle and significantly reduce the activation energy by accelerating the rate-limiting methanolysis step. As thus, all the reaction parameters, especially the solvents, were optimized based on the Pd(cod)Cl₂/Xantphos/4-hexylpyridine catalytic system, enabling the construction of a continuous process. Systematic optimization demonstrates that a yield of 82% of MP with a purity of 99.8% could be reached under steady-state operation.