The absolute configurations of (–)-angolensin and some related 1,2-diarylpropanes

(-)-Angolensin has been converted into (+)-(2S)-1-(2,4-dimethoxyphenyl)-2-(4-methoxyphenyl)propane, an analogue of (+)-(2S)-1-(2,4,6-trimethoxyphenyl)-2-(3,4-dimethoxyphenyl)propane. The stereochemistry of angolensin is thereby correlated with that of catechin and epicatechin. Oxidation of (+)-(2S)-1-(2-hydroxy-4-methoxyphenyl)-2-(4-methoxyphenyl)propane gave (+)-3-(4-methoxyphenyl)- butyric acid, in agreement with the established absolute configuration of (-)-angolensin. The (+)-butyric acid was also prepared by resolution of the synthetic racemate with quinine, and by homologation of (-)-2-(4-methoxyphenyl)propionic acid.