Studies on the Biosynthesis of Taxol. Synthesis of Taxa-4(20),11(12)-diene-2α,5α-diol

The synthesis of taxa-4(20),11(12)-diene-2α,5α-diol is described. An improved procedure for the intramolecular Diels−Alder cycloaddition previously reported in our synthesis of taxa-4(5),11(12)-diene has been utilized to prepare a taxoid with oxygenation in the B and C rings. It has been established previously that taxa-4(20),11(12)-dien-5α-ol is the first oxygenated intermediate on the biosynthetic pathway to Taxol. Taxa-4(20),11(12)-diene-2α,5α-diol (5), which has been observed in a biosynthetic conversion, is a potential candidate as the second oxygenated intermediate on the Taxol biosynthetic pathway, has been prepared to probe the intermediacy of this substance.