| Abstract
| - The synthesis of the spirovetivane sesquiterpenes (+)-anhydro-β-rotunol and all the diastereomersof 6,11-spirovetivadiene in enantiomerically pure form has been achieved starting from santonin.The key step is the silicon-guided acid-promoted rearrangement of a 1-trimethylsilyl-4,5-epoxyeudesmane prepared from santonin in several steps involving lactone reductive opening, conjugateaddition of TMSLi−CuCN, deoxygenation of a carbonyl group, and epoxidation. Rearrangement ofthe epoxide gave a spiro[4,5]decanediol which was used as a synthetic intermediate. From thiscompound, (+)-anhydro-β-rotunol was prepared after elimination of the primary hydroxyl groupin the side chain, followed by allylic oxidation at C8 and elimination of the tertiary hydroxyl groupin the cyclohexane ring. On the other hand, elimination of the hydroxyl group in the side chainand reduction of the hydroxyl in the cyclohexane ring gave (−)-premnaspirodiene and (−)-hinesene.The synthesis of the rest of the diastereomers for these compounds required formal inversion ofthe C5 spiro carbon. The synthesis of these compounds showed that the structure of (−)-agarospireneisolated from Scapania sp. was erroneously assigned, and it has been corrected to be identical tothat of (−)-hinesene.
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