A total synthesis of (±)-carpesiolin (3) is reported starting from the hydroazulenone (2), which is a key intermediate of helenanolide synthesis. For the introduction of the C6 to C8 functionalities, 2 was converted to the epoxy-alcohol (5). Its structure was confirmed by chemical and spectroscopic evidence. After construction of the γ-lactone ring, the tert-butyl protective group was removed from the ester (15) by acid-catalyzed thermolysis. However, this reaction was unexpectedly accompanied by concomitant 1, 3-acyl migration with inversion of the configuration at C4 to yield the hydroxy-ester (16), whose structure was established by analysis of its proton magnetic resonance spectrum and some chemical reactions. After manipulation of the protective group to give the tetrahydropyranyl ether (18), its conversion to (±)-carpesiolin was achieved by (i) introduction of the exo-methylene group onto the lactone ring, (ii) oxidation to the cyclopentanone (24), and (iii) deprotection of the C6 hydroxyl group.
报道了(±)-carpesiolin(3)的全合成,起始于氢化阿基伦酮(2),该化合物是helenanolide合成的关键中间体。为了引入C6至C8的功能团,将2转化为环氧醇(5)。其结构通过
化学和光谱证据得到证实。构建γ-lactone环后,通过酸催化热裂解去除了酯(15)中的叔丁基保护基团。然而,该反应意外伴随着1, 3-酰基迁移,并使C4的构型反转,从而生成了羟基酯(16),其结构通过质子磁共振谱和一些
化学反应的分析得以确认。经过保护基团的操作,得到四氢
吡啶醚(18),其转化为(±)-carpesiolin的过程通过以下步骤实现:(i) 向内酯环引入exo-亚甲基基团,(ii) 氧化为
环戊酮(24),以及(iii) 去保护C6羟基。