Diyl Trapping Reactions To Synthesize Taxol Analogs

A new and efficient entry to the ABC-ring system common to taxol and related materials has been developed. Highlights include the use of a regioselective intramolecular diyl trapping reaction to synthesize tricyclic alkene 5, the creation and oxidative cleavage of the tetrasubstituted olefin found in ketal 20a,b to afford a highly functionalized eight-membered ring (21a), and cyclization of 22, thereby providing the tricyclic core.