OPENING OF RING-C IN RUTHENIUM-CATALYZED REARRANGEMENTS OF 15,16-EPOXYBEYERANE DITERPENES HYDROXYLATED AT C-12

Rearrangements catalyzed by ruthenium acetylacetonate of ent-1 beta-ac etoxy-15 alpha, 16 alpha-epoxybeyeranes with axial or equatorial hydro xyl groups at C-12 were carried out. The expected rearrangement produc ts (ent-kaur-15-ene and ent-kaur-16-ene) were isolated mainly from the 12-axial-hydroxyl compound. However, when the 12-equatorial-hydroxyl group was present, it participated in a process involving ring opening and cyclization from rear to give C-12 epimerized ent-kaur-15-ene and ent-kaur-16-ene compounds, as well as ent-16(R)-kauran-12-one, via co ncerted 12-->16 hydride migration. On the basis of deuterium labeling experiments, the ring C opening and cyclization process seems to occur through an aldehyde intermediate.