Taxane synthesis through intramolecular pinacol coupling at C-1-C-2. Construction and oxidative transformations of a C-aromatic taxane diene

A ten-linear-step construction of C-aromatic taxane diene 14 from ethyl isopropyl ketone, acryloyl chloride, and commercially available 8 is reported. This sequence concludes with an intramolecular pinacol coupling carried out on 13. 14 is oxidized by m-chloroperbenzoic acid and dimethyldioxirane to give 17 through intermediate epoxide 20 and by VO(acac)(2)-t-BuOOH and Mo(CO)(6)-t-BuOOH to give 13. 17 is converted efficiently into 22 upon treatment with Mo(CO)(6)-t-BuOOH, apparently through an unusual equilibration with isomeric 20, which is converted irreversibly to 22. While these oxidative transformations highlight some of the peculiar reactivity patterns characteristic of taxane-related structures, the formation of 14 through an intramolecular pinacol coupling that joins C-l and C-2 demonstrates the potential of this strategy for stereoselectively delivering advanced taxane synthesis intermediates.