Stereochemical Investigation of Macrocyclic Bisbibenzyls with a Stereogenic Center at One of the Ethylene Bridges

Abstract 7′‐Hydroxyriccardin C ( 1 ) and marchantin E ( 2 ), two macrocyclic bisbibenzyls with a stereogenic center at the ethylene bridge from Chinese liverworts, were investigated stereochemically. Compound 1 was found to be optically active and occurred as a pair of dynamically interchangeable atropisomers at room temperature due to the low barrier of rotation around the biaryl bond, while 2 was a racemic mixture, which was successfully resolved by chiral HPLC into two enantiomers. Their absolute configurations were unequivocally assigned by analysis of temperature‐dependent NMR spectra, X‐ray crystallographic diffraction, and comparison of experimental and calculated ECD data.