Synthesis of a Highly Functionalised and Homochiral 2-Iodocyclohexenone Related to the C-Ring of the Polycyclic, Indole Alkaloids Aspidophytine and Haplophytine

The enzymatically-derived and enantiomerically pure (1S,2S)-3-bromocyclohexa-3,5-diene-1,2-diol (7) has been elaborated over 10 steps into cyclohexenone 8. The latter compound embodies the enantiomeric form of the C-ring associated with the hexacyclic framework of the alkaloid aspidophytine (2). As such, this work sets the stage for effecting the conversion of the enantiomeric metabolite ent-7 into compound ent-8, and thence, through previously established protocols, including a palladium-catalysed Ullmann cross-coupling reaction, into the title alkaloids.