Stereoselective construction of an unprecedented 7-8 fused ring system in micrandilactone a by [3,3]-sigmatropic rearrangement

The 7-8 bicyclic ring system of micrandilactone A (1) with the required stereochemistry and functional groups was constructed by a Bu3Al-promoted Claisen rearrangement. Computational studies indicated that the exocyclic vinyl ether undergoes a [3,3] sigmatropic process via a chairlike transition state to afford exclusively the Z-double bond in the newly generated 8-membered ring with a high level of chirality transfer.