Synthesis of the Bicycloundecane Moiety (AB Ring System) of Taxanes

Article abstract of DOI:10.1021/jo00001a060

Intramolecular cycloaddition of unsaturated ketenes 15a, 15b, and 6 give the 1-vinylbicyclo<3.1.1>heptan-6-ones 16a, 16b, and 5 in 51 percent, 63 percent, and 30 percent yield.Addition of vinyllithium to these cyclobutanones at -78 deg C gives 1,2-divinylcyclobutane alkoxides that undergo oxy-Cope rearrangements to give (E)-bicyclo<5.3.1>undecenones 20a, 20b, and 27 in 57 percent, 63 percent, and 19 percent yield.These cyclooctenones contain suitable substituents and functionality for elaboration of the AB ring system of taxane diterpenes.The oxy-Cope rearrangement fails if more highly substituted alkenyllithium reagents are used; so this approach cannot be used for introduction of the C ring of taxane diterpenes.