Synthesis of the A,B,C-Ring System of Hexacyclinic Acid

<UFIGR ID="ol048720on00001">The synthesis of the A,B,C-ring system (<BO>2</BO>) of hexacyclinic acid (<BO>1</BO>) is achieved starting from a selective Diels−Alder reaction followed by vinyl cuprate addition. The diastereoselective reduction of the ketone carbonyl at C16 could be achieved with LiAlH<INF>4</INF>. An intramolecular Michael addition established the ring system stereoselectively, providing access to the selective generation of 9 out of the 14 stereocenters of hexacyclinic acid.