Accessing low-oxidation state taxanes: is taxadiene-4(5)-epoxide on the taxol biosynthetic pathway?

We have shown for the first time that taxadiene () can be epoxidised in a regio- and diastereoselective manner to provide taxadiene-4(5)-epoxide () as a single diastereoisomer, and that this epoxide can be rearranged to give taxa-4(20),11(12)-dien-5α-ol (). Furthermore, the epoxide rearranges under acidic conditions to give taxa-4(20),11(12)-dien-5α-ol (), the known bridged ether OCT () and the new oxacyclotaxane (OCT2) . Contrary to previous speculation, taxadiene-4(5)-epoxide () is susceptible to rearrangement when exposed to an iron porphyrin, and these observations justify consideration of epoxide as a chemically competent intermediate on the taxol biosynthetic pathway.