Asymmetric Synthesis of the Biologically Active Compounds by the Diastereoselective Acetal Formation Reaction

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The hydroxyl group on the side chain at C2-position of 1, 3-cyclohexanedione derivatives discriminates carbonyl group on the ring to produce the hemiketal stereoselectively depending on its absolute configuration. The intramolecular ketals were afforded as almost single compound from the hemiketals. When the hemiketals were converted to the intermolecular ketals, the other ketone was selected. Namely, the optically active compounds, which contain the different absolute configuration at the quaternary carbon center, could be synthesized from the single molecule. Although the hydrogen bonding plays the important role for the diastereoselective hemiketal formation reaction, it was also clarified that the steric demand is more important for the different kind of substrates. The asymmetric synthesis of BCD ring system of (+)-cepharamine and (+)-lycopladine A were also accomplished utilizing the diastereoselective hemiketal formation reactions as a key step.