The biomimetic synthesis of fused bispyran via Lewis acid mediated tandem oxacyclization of a 1,4,7-polyepoxide is explored. The nature of the Lewis acid promoter is critical for the endo-regioselectivity of epoxide cyclization, although anomalous apparent retention of stereochemistry is observed at some reactive centers.
biomimetic synthesis - fused polycyclic ethers - polyepoxides - regioselectivity - stereoselectivity