Total synthesis of (-)-8-epi-chromazonarol enabled by a unique N2H4 center dot H2O promoted intramolecular oxa-Michael cyclization reaction

An enantioselective total synthesis of the natural chroman-sesquiterpenoid (-)-8-epi-chromazonarol has been accomplished by a unique N2H4H2O promoted highly diastereo-selective oxa-Michael cyclization to construct the central chroman framework and assemble the unusual C8 stereocenter. The other salient feature of the reported synthesis involves a Stille carbonylative cross-coupling reaction to link the aryl stannane 9 and bicyclic triflate 10.