Dramatic solvent effect on the diastereoselectivity of Michael addition: study toward the synthesis of the ABC ring system of hexacyclinic acid.

During our studies toward the synthesis of the ABC ring system of hexacyclinic acid, we have observed a dramatic influence of the solvent on both our key steps. The diastereoselectivity of the intermolecular Michael addition could be totally reversed by changing the polarity of the solvent, and trifluoroethanol was found to be the optimal solvent for the following Mn(III)-promoted radical cyclization.