Studies towards the total synthesis of lycoposerramine A. Synthesis of a model for the tetracyclic core

Lycoposerramine A (1) is a pentacyclic alkaloid isolated in 2001 by Takayama and co-workers. A concise synthesis of a model compound 8 for the tetracyclic core of this natural product is described. Key steps include the desymmetrising free-radical cyclisation of compound 7 to give compound 18 and spirocyclisation of compound 26 to give compound 8. Earlier approaches using a novel high-yielding stereoselective anionic cyclisation of a cyclohexa-1,4-diene are also reported.