Taxane diterpenes 4: Autoxidation, epimerization and isomerization for the introduction of functionality into the taxane ABC ring system

Article abstract of DOI:10.1016/S0040-4020(98)00056-8

The bicyclo[5.4.0]undecenone 4 was converted through a four step sequence involving activation, gemmethylcyclopropanation and reductive cleavage into 18α/β, containing the B/C rings of the taxanes. The A-ring has been attached to the B/C ring system by cyclization of the sulfone-ester 23α to give 24. The A-ring was modified to give 29, which underwent β- elimination of the 3,10-oxido bridge via a dianion, followed by transannular hydride shift to give the butenolide 30 and 32. Autoxidation of 30 gave 33 which was further elaborated into the transfused B/C adduct 35. The isomeric 3,10-diones trans-39 and cis-45 undergo autoxidation using t- BuOK/THF/O₂/P(OEt)₃ to give 2 and 46 respectively without B/C cis/trans isomerization.