Synthese und Charakterisierung der 8 isomeren, im Ring B mono‐ bzw. dihydroxylierten Royleanone

Synthesis and Characterization of the 8 Stereoisomeric Royleanones with One or Two Hydroxy Groups in Ring B The partial syntheses of 6α, 7α‐dihydroxyroyleanone ( 6a ), 6α, 7β‐dihydroxyroyleanone ( 7a ) and 6β, 7β‐dihydroxyroyleanone ( 9a ) are described. Thus, all in ring B mono‐ and dihydroxylated royleanones are now known (see [2–11]), being fully characterized by extensive spectroscopic, chiroptic and chromatographic (HPLC.) methods. An opening of the epoxyroyleanone 11a yields cis ‐ and trans ‐diols together with their corresponding mono‐ and di‐ O ‐acetyl derivatives. We postulate a reversible addition of the acetate ion at C(8) of the quinone system, followed by a neighbouring group participation of this O ‐acetyl group.