P-7 不斉環化-カルボニル化反応を利用した(+)-Bakkenolide Aの全合成(ポスター発表の部)

抄録

Palladium(II) catalyzed intramolecular oxy-carbonylation of terminal acetylenes is considered to be a useful method for the conversion of an acetylene unit to a β-ketoester unit utilizing neighboring group participation. Compared with the impressive development of Pd^<II> catalyzed oxidative asymmetric reactons of alkenes, those of alkynes have received scant attention. We previously reported the first examples of asymmetric cyclization-carbonylation of meso-2-alkyl-2-propargylcyclohexzne-1,3-diols 1 and 2-methyl-2-propargylcyclohexane-1,3-diones 2 catalyzed by paladium(II) with chiral bisoxzzoline (box) ligands. Herein, we report a mechanistic insight of the latter reaction, and a parallel kinetic resolution of propargyl ketols 13. In the case of 2, hemiacetal formation step plays in important role in the asymmetric induction. However, in the case of 13, enantio selectivity of the reaction depends on trhe cyclication step. The products containing quaternary carbon were converted to optically active hydrindanes, and the chiral total synthesis of (+)-bakkenolide-A was achieved.