Stereoselective hydrogenation of lignin degradation model compounds

Abstract

Di-µ-chloro-bis(η4-1,5-hexadiene)dirhodium(I) in a two-phase hexane–aqueous medium catalyzes the diastereoselective H2-hydrogenation of lignin degradation model compounds 4-propylphenol, 2-methoxy-4-propylphenol, and 2,6-dimethoxy-4-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) 1H NMR. Keywords: catalytic hydrogenation, diastereomer, lignin degradation model compounds, stereoselective, X-ray crystal structure.