New strategy for the synthesis of the taxane diterpenes: Formation of the BC-rings of taxol via a [5+2]-pyrylium ylide-alkene cyclization, ring expansion strategy
The BC-rings of taxol can be synthesized using an intramolecular [5+2]-pyrylium ylide-alkene cyclization, followed by gem-methylcyclopropanation and reductive cleavage of the internal cyclopropane bond.