Synthesis of the bicyclo[5.3.1]undecane moiety (AB ring system) of taxanes
摘要:
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%, 63%, and 30% yield. Addition of vinyllithium to these cyclobutanones at -78-degrees-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%, 63%, and 19% 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.