Reactions and rearrangements of triterpenoids - 3-epitaraxerol and its transformation products

An interesting rearrangement has been observed with 2,14-taraxeradiene 1 us ing m-chloroperbenzoic acid. With this reagent compound 1, in methylene chl oride, affords olean-2 alpha-epoxy-12-ene-15 alpha-ol 3 (confirmed by X-ray crystallographic analysis) through the intermediate 2 alpha,14 alpha-diepo xytaraxerane 4. The latter 4 has also been isolated from the same reaction mixture. This backbone rearrangement from the Delta(14)-taraxarene skeleton 4 to Delta(12)-oleanane structure 3, with C15-alpha-ol, confirms alpha-ori entation of the epoxy ring formed at Delta(14) in 4. Subsequent opening of the intermediate oxirane at Delta(14) therefore must occurr via the generat ion of an incipient carbonium ion at C(14) to allow the migration of C(13)C H3 to C(14) from the same alpha-phase. Compound 4 also undergoes rearrangem ent to olean-12-ene-2 alpha,3 beta,15 alpha-triol 5 with boron trifluoride etherate in methylene chloride.