Stereoselective hydrogenation of lignin degradation model compounds

Di-mu-chloro-bis(eta(4)-1,5-hexadiene)dirhodium(I) in a two-phase hexane-aqueous medium catalyzes the diastereoselective H-2-hydrogenation of lignin degradation model compounds 4-propylphenol, 2-methoxy-3-propylphenol, and 2,6-dimethoxy-3-propylphenol. The all-cis diastereomer is obtained selectively when the phenolic hydroxy group is protected as a methyl ether or when a model compound possessing two methoxy substituents adjacent to the phenolic hydroxy group is used. The relative stereochemistries of the hydrogenated products are established by X-ray crystal structure analysis and (or) H-1 NMR.