Denmark Scott E, Baiazitov Ramil Y, Nguyen Son T
Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, IL 61801, USA.
Tetrahedron. 2009 Aug 15;65(33):6535-6548. doi: 10.1016/j.tet.2009.05.060.
An asymmetric synthesis of the ABCD ring system of daphnilactone B is described. The synthesis features a tandem, double intramolecular, [4+2]/[3+2] cycloaddition of a highly functionalized, enantiomerically enriched nitroalkene to generate a pentacyclic nitroso acetal. The cycloaddition establishes six contiguous stereogenic centers including the critical CD ring junction that bears two quaternary stereogenic centers. Hydrogenolysis of the nitroso acetal followed by amide reduction and cyclization provided the AB rings. The methyl substituent on the A ring was installed in the correct configuration via hydrogenation of an exocyclic olefin in the final step.
本文描述了瑞香内酯B的ABCD环系的不对称合成。该合成的特点是将一个高度官能化、对映体富集的硝基烯烃进行串联、双分子内的[4+2]/[3+2]环加成反应，以生成一个五环亚硝基缩醛。该环加成反应构建了六个连续的立体中心，包括带有两个季碳立体中心的关键CD环连接点。亚硝基缩醛经氢解，随后进行酰胺还原和环化反应，得到AB环。在最后一步，通过环外烯烃的氢化反应，以正确的构型引入了A环上的甲基取代基。
