Some biogenetic-type transformations of neoclerodane diterpenoids from Scutellaria species

Treatment of scutebaicalin (1) with K-t-BuO yielded both the (13S)- and (13R)-8 beta,13-epoxyclerodanes 2 and 3, respectively, by a Michael-type heterocyclization reaction. Identical treatment of scutalpin B (4) gave the corresponding (11E)-11-deacetoxy-12-dehydro derivative 5 by an elimination reaction. Side chains at C-9, such as those of compounds 1-5, are frequent among the neoclerodanes found in Scutellaria species, and these transformations suggest a plausible biogenetic pathway for these diterpenoids.