system. In particular, an acidic pillared clay selectively promoted this transformation. The bicyclic core of the halimanic framework is synthesized in optically active form by an acid-induced rearrangement of a homodrimanic epoxide. The substrate can follow two different pathways under acidic treatment. Using fluorosulfonic acid as a promoter at low temperature favors ring contraction to a perhydrindanic
An enantiospecific synthesis of the nor-sesquiterpene austrodoric acid 1, recently isolated from an Antarctic marine mollusk, has been achieved. The synthetic strategy was based on the ring contraction of a suitable homo-drimanic epoxide,3, easily obtained from commercial (+)-sclareolide 4. The absolute configuration of natural austrodoric acid, not determined previously, has been now established by analyzing the CD profile of synthetic 1, which was the same as the natural compound. (C) 2003 Elsevier Ltd. All rights reserved.