Highly selective methoxycarbonylation of (R)-carvone with N-Xantphos-modified Pd-catalyst

An efficient and highly chemo/regioselective Pd-catalyzed methoxycarbonylation of biomass-based ( R )-carvone has been established. Since there are several functional groups (like keto, cyclohexenyl) beside of isopropenyl in the scaffold of ( R )-carvone, the numerous side-reactions derived from C C / C O double-bond isomerization will happen in parallel along with the required methoxycarbonylation, leading to the challenging control for the oriented generation of the targe carbonylated product. Herein, upon the careful ligand-selection and reaction condition optimization, the high conversion of ( R )-carvone (95 %) with the excellent carbonylation-selectivity (95 %) were achieved, giving 90 % yield of the desired ester while the involved side-rection were successfully suppressed. It was noted that the process proved to be very chemo-/regio-selective by using the steric bulky and rigid biphosphine of N -Xantphos ( L1 ) and MSA-acid-additive at the lower concentration.