Studies on the biosynthesis of taxol. Synthesis of taxa-4(20),11 (12)-diene-2 alpha,5 alpha-diol

The synthesis of taxa-4(20),11(12)-diene-2 alpha ,5 alpha -diol is describe d. An improved procedure for the intramolecular Diels-Alder cycloaddition p reviously reported in our synthesis of taxa-4(5),11(12)diene has been utili zed to prepare a taxoid with oxygenation in the B and C rings. It has been established previously that taxa-4(20),11(12)-dien-5 alpha -ol is the first oxygenated intermediate on the biosynthetic pathway to Taxol. Taxa-4(20),1 1(12)-diene-2 alpha ,5 alpha -diol (5), which has been observed in a biosyn thetic conversion, is a potential candidate as the second oxygenated interm ediate on the Taxol biosynthetic pathway, has been prepared to probe the in termediacy of this substance.