Perchloric acid treatment of sarcophytoxide, a marine cembranoid possessing an epoxide, brought about epoxideketone rearrangement affording ketones. When the reaction time was long (22 h), a minor ketone that was antipodal to the ketone obtained in a short-time (10 min) reaction was formed. These puzzling findings, considering that the starting epoxide had three asymmetric carbons, were interpreted by surveying the structures of other ketonic products. The stereochemistry of a major ketone, which had been wrongly assigned, was corrected by extensive analyses of NMR spectra. The correct stereochemistry indicated that the epoxide-ketone rearrangement took a course via a cationic intermediate.

Treatment of sarcophytoxide (I) with perchloric acid affords ketone (+)-III or its antipodal ketone (-)-III depending on the reaction time. This curious phenomenon is interpreted by assuming the epimerization of the doubly allylic C-O linkage at C-2 of starting cembranoid (I). -(NII, K.; TAGAMI, K.; KIJIMA, M.; MUNAKATA, T.; OOI, T.; KUSUMI*, T.; Bull. Chem.