Division of Organic Chemistry, National Chemical Laboratory (CSIR) , Pune 411 008, India.
J Org Chem. 2018 Jan 5;83(1):382-387. doi: 10.1021/acs.joc.7b02773. Epub 2017 Dec 22.
Starting from dimethyl (E)-2-{[(1-tert-butoxycarbonyl)-1H-indol-3-yl]methylene}succinate and (R)-2,2,5,5-tetramethyl-1,3-dioxolane-4-carbaldehyde, facile synthesis of (-)-epi-claulansine D was accomplished via condensation and two intramolecular cyclizations. The (-)-epi-claulansine D in the solid state exists in a metastable form, and after an induction period of 30-90 days, it underwent complete epimerization to exclusively deliver the desired natural product (-)-claulansine D in quantitative yield. The witnessed inversion of C-centrochirality in the solid state is conceptually novel and takes place for relatively higher crystal stability reasons. Base-catalyzed ring expansion of both (±)/(-)-epi-claulansine D and (±)/(-)-claulansine D resulted in (±)/(+)-epi-claulansine C in very good yields.
从二甲基（E）-2-{[(1-叔丁氧羰基)-1H-吲哚-3-基]亚甲基}琥珀酸酯和（R）-2,2,5,5-四甲基-1,3-二氧戊环-4-甲醛出发，通过缩合和两个分子内环化，轻松合成了（-）-表克劳兰辛 D。（-）-表克劳兰辛 D 在固态中以亚稳态存在，经过 30-90 天的诱导期后，它完全外消旋化，以定量产率得到所需的天然产物（-）-克劳兰辛 D。在固态中观察到 C-中心手性的反转在概念上是新颖的，并且由于相对较高的晶体稳定性而发生。（±）/（-）-表克劳兰辛 D 和（±）/（-）-克劳兰辛 D 的碱催化环扩张以非常好的收率得到了（±）/（+）-表克劳兰辛 C。
