Total synthesis of aspergillides using a transannular oxy-michael strategy

Abstract

In this account, full details of our total synthetic studies on aspergillides A, B and C, which have been isolated from the marine-derived fungus Aspergillus ostianus strain 01F313, are presented. The highly diastereoselective constructions of tri-and tetra-substituted tetrahydropyrans employing intramolecular oxy-Michael (IMOM) reactions have been developed and successfully applied to the first generation total syntheses of aspergillides A and C. However, the longer reaction steps and lower overall yields prompted us to try and devise a general methodology that would be useful for a highly efficient synthesis of all the aspergillides. To this end, a biomimetic [6-exo-trig] transannular oxy-Michael (TAOM) strategy was invented and successfully and efficiently applied to the second generation total syntheses of aspergillides A, B and C. Ultimately, the cycloaddition was controlled by using more suitable conditions, and aspergillide A/B and aspergillide C/3-epi -aspergillide C were able to be synthesized from a common precursor. In addition, successful conversions of aspergillide A to aspergillide B and 3-epi -aspergillide C to aspergillide C were demonstrated for the first time during these synthetic studies.