Two-Phase Total Synthesis of Taxanes: Tactics and Strategies

This Perspective goes into the fine details of our laboratory's quest to answer a longstanding fundamental question: Could any new approach to terpene synthesis, perhaps one patterned on biosynthesis, enable a divergent synthetic approach to the taxane family of natural products? We targeted Taxol, the flagship taxane, as the upper limit of chemical complexity and employed two-phase terpene synthesis logic as the guiding strategy. The first synthesis target was taxadiene, the lowest oxidized member of the taxane family, followed by three site-selective allylic oxidations at C5, C10, and C13, which led to the two-phase synthesis of taxuyunnanine D. Successful C9 oxidation enabled access to a wider range of taxanes, which was demonstrated by the two-phase synthesis of decinnamoyltaxinine E and taxabaccatin III. The final two sp³ C-H oxidations at C1 and C7 were attained by dioxirane-mediated C-H oxidation and an oxidation relay based on judicious substrate design, culminating in a two-phase synthesis of Taxol. The purpose of this Perspective is to articulate strategies and tactics developed for the two-phase synthesis of taxanes, whose lessons can be potentially extrapolated to medicinal chemistry endeavors in the taxane family, as well as to the synthesis of other terpene families.