Enantioselective hydrogenation of levulinic acid esters in the presence of the RuII-BINAP-HCl catalytic system

Article abstract of DOI:10.1007/s11172-006-0125-2

The rate of hydrogenation of γ-ketoesters MeCOCH₂CH ₂COOR (R = Et, Prⁱ, Bu^t) in the presence of the chiral Ru^II-BINAP catalyst (BINAP is 2,2′- bis(diphenylphosphino)-1,1′-binaphthyl) greatly increases upon the addition of 5-10 equivalents of HCl with respect to ruthenium. In the hydrogenation of ethyl levulinate, the optically active γ-hydroxy ester initially formed would cyclize by ～95% to give γ-valerolactone with optical purity of 98-99% ee. When the Ru(COD)(MA)₂-BINAP-HCl catalytic system is used (COD is 1,5-cyclooctadiene, MA is 2-methylallyl), complete conversion of the ketoester (R = Et) in EtOH is attained in 5 h at 60°C under an H₂ pressure of 60-70 atm.