Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012, USA.
J Am Chem Soc. 2012 Aug 15;134(32):13348-56. doi: 10.1021/ja303414a. Epub 2012 Aug 1.
Dyotropic rearrangements of fused, tricyclic β-lactones are described that proceed via unprecedented stereospecific, 1,2-acyl migrations delivering bridged, spiro-γ-butyrolactones. A unique example of this dyotropic process involves a fused bis-lactone possessing both β- and δ-lactone moieties which enabled rapid access to the core structures of curcumanolide A and curcumalactone. Our current mechanistic understanding of the latter dyotropic process, based on computational studies, is also described. Other key transformations in the described divergent syntheses of (-)-curcumanolide A and (-)-curcumalactone from a common intermediate (11 and 12 steps from 2-methyl-1,3-cyclopentanedione, respectively), include a catalytic, asymmetric nucleophile (Lewis base)-catalyzed aldol-lactonization (NCAL) leading to a tricyclic β-lactone, a Baeyer-Villiger oxidation in the presence of a β-lactone, and highly facial-selective and stereocomplementary reductions of an intermediate spirocyclic enoate. The described dyotropic rearrangements significantly alter the topology of the starting tricyclic β-lactone, providing access to complex spirocyclic cyclopentyl-γ-lactones and bis-γ-lactones in a single synthetic operation.
描述了稠合的三环 β-内酰胺的重排反应，这些反应通过前所未有的立体特异性 1,2-酰基迁移进行，提供了桥连的螺-γ-丁内酯。这种重排过程的一个独特例子涉及到一个具有β-和δ-内酯部分的稠合双内酯，这使得快速获得姜黄烷酮 A 和姜黄内酯的核心结构成为可能。我们目前基于计算研究对后一种重排过程的机制理解也进行了描述。在所描述的从共同中间体（分别从 2-甲基-1,3-环戊二酮出发的 11 步和 12 步）到（-）-姜黄烷酮 A 和（-）-姜黄内酯的发散合成中的其他关键转化，包括催化的、不对称亲核试剂（路易斯碱）-催化的烯醇-内酯化（NCAL）导致三环 β-内酰胺、在β-内酰胺存在下的 Baeyer-Villiger 氧化以及中间螺环烯酸酯的高面选择性和立体互补还原。所描述的重排反应显著改变了起始三环 β-内酰胺的拓扑结构，在单个合成操作中提供了复杂的螺环环戊基-γ-内酰胺和双-γ-内酰胺的途径。
