An Organocatalytic Cascade Strategy for the Enantioselective Construction of Spirocyclopentane Bioxindoles Containing Three Contiguous Stereocenters and Two Spiro Quaternary Centers
作者:Wangsheng Sun、Gongming Zhu、Chongyang Wu、Liang Hong、Rui Wang
DOI:10.1002/chem.201200478
日期:2012.5.29
A rapid and efficient organocatalyticcascade sequence for the direct construction of spirocyclopentanebioxindoles has been carried out by using a chiral squaramide catalyst in the presence of a base. This process constitutes a powerful approach to the preparation of biologically important bispirooxindoles in high enantioselectivities (see scheme).
Construction of Tetracyclic 3-Spirooxindole through Cross-Dehydrogenation of Pyridinium: Applications in Facile Synthesis of (±)-Corynoxine and (±)-Corynoxine B
A facile and straightforward method was developed to construct the fused tetracyclic 3-spirooxindole skeleton, which exists widely in natural products. The formation of the tetracyclic 3-spirooxindole structure was achieved through a transition-metal-free intramolecular cross-dehydrogenative coupling of pyridinium, which were formed in situ by the condensation of 3-(2-bromoethyl)indolin-2-one derivatives with 3-substituted pyridines. As examples of the application of this new methodology, two potentially medicinal natural products, (+/-)-corynoxine and (+/-)-corynoxine B, were efficiently synthesized in five scalable steps.