Hydroesterification of Vinylarenes Catalyzed by Palladium Complexes of Dialkylmonoaryl- and Monoalkyldiarylphosphines

Hydroesterification of vinylarenes using a mixture of PdCl2 and monodentate phosphorus ligands as a catalyst was studied. As ligands, menthyldiphenylphosphine (MDPP), neomenthyldiphenylphosphine (NMDPP), and dicyclohexyl(phenyl)phosphine (Cy2PPh) were effective to obtain branched esters with high regioselectivity under the moderate reaction conditions without additives such as acids. Not only electronic effects but also steric effects of the cycloalkyl groups were revealed to be significant in order to achieve high catalytic activity. When (S)-2-dicyclopentylphosphino-2′-methoxy-1,1′-binaphthyl was used for the asymmetric hydroesterification of 2-methoxy-6-vinylnaphthalene, (S)-naproxen methyl ester was obtained with 53% ee.