Lewis Acid-Catalyzed Ring-Opening Reactions of Semicyclic <i>N</i>,<i>O</i>-Acetals Possessing an Exocyclic Nitrogen Atom: Mechanistic Aspect and Application to Piperidine Alkaloid Synthesis
作者:Masaharu Sugiura、Hiroyuki Hagio、Ryoji Hirabayashi、Shū Kobayashi
DOI:10.1021/ja0170448
日期:2001.12.19
reactions of semicyclic N,O-acetals possessing an exocyclic nitrogen atom with silicon-based nucleophiles (silyl enol ethers, ketene silyl acetals, allylic silanes, and trimethylsilyl cyanide) were systematically studied for the first time. It was found that the reactions were effectively catalyzed by a Lewis acid, trimethylsilyl trifluoromethanesulfonate (TMSOTf), to afford 1,4- and 1,5-amino alcohols
首次系统地研究了具有环外氮原子的半环 N,O-缩醛与硅基亲核试剂(甲硅烷基烯醇醚、烯酮甲硅烷基乙缩醛、烯丙基硅烷和三甲基甲硅烷基氰化物)的开环反应。发现该反应被路易斯酸、三氟甲磺酸三甲基甲硅烷基酯 (TMSOTf) 有效催化,以高产率得到 1,4- 和 1,5- 氨基醇。在 3-氧官能化半环 N,O-缩醛的反应中,获得了高 1,2-syn-非对映选择性。通过1H NMR实验,观察到O-三甲基甲硅烷基化开环产物的形成作为初始产物。此外,3-苄氧基半环N,O-缩醛的非对映异构体之间的差向异构化表明作为反应中间体的无环亚胺离子物质的瞬时形成。还发现 3-乙酰氧基和 3-苄氧基 N,O-缩醛显示出较大亲核试剂提供更高顺式选择性的趋势,而 3-叔丁基二苯基甲硅烷氧基 N,O-缩醛显示出相反的趋势。这些立体化学结果可以通过假设无环亚胺离子中间体的四个过渡态模型来合理化。该反应的合成效用已在哌啶生物