Abstract Synthetic emodin bianthrone is separated into meso-and (±)-diastereomers which are identified by means of an asymmetric pmr shift reagent. They behave differently on mild oxidation. Both give protohypericin accompanied by an anthraquinone fraction but, whereas the major anthraquinone from the meso is emodin, the (k) gives chiefly the bianthraquinonyl, skyrin. This difference is accounted for in terms of the geometry of oxidative coupling. ...
