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首页> 外文期刊>Chemistry: A European journal >Synthesis of 5-acetyloxazoles and 1,2-diketones from β-alkoxy-β- ketoenamides and their subsequent transformations
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Synthesis of 5-acetyloxazoles and 1,2-diketones from β-alkoxy-β- ketoenamides and their subsequent transformations

机译：由β-烷氧基-β-酮烯酰胺合成5-乙酰基恶唑和1,2-二酮及其后续转化

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摘要

Lithiated alkoxyallenes, nitriles, and carboxylic acids have been employed as precursors in a three-component reaction leading to highly substituted β-alkoxy-β-ketoenamides. Upon treatment with trifluoroacetic acid, these enamides could be easily cyclized to 5-acetyloxazole derivatives. The synthesis is very flexible with respect to the substitution pattern at C-2 and C-4 of the oxazole core. A mechanistic suggestion for the oxazole formation is presented on the basis of ~(18)O-labeled compounds and their mass spectrometric analysis. In several cases, 1,2-diketones are formed as side products or even as major components. The acetyl moiety at C-5 of the oxazole derivatives can efficiently be converted into alkenyl or alkynyl moieties, which allows a multitude of subsequent reactions. Condensation reactions of the acetyl group provided the expected oxime or hydrazone. By applying a Fischer reaction, the phenylhydrazone could be transferred into an indole, which emphasizes the potential of 5-acetyloxazoles for the preparation of highly substituted (poly)heterocyclic systems. The alkynyl group at C-2 is prone to addition reactions, providing an enamine with interesting photophysical properties. Sonogashira couplings were performed with 5-alkynyl-substituted oxazoles, furnishing the expected aryl-substituted products. This alkynyl unit was employed for the preparation of a new, star-shaped trisoxazole derivative. The ability of this multivalent compound to form self-assembled monolayers between the basal plane of highly oriented pyrolytic graphite and 1-phenyloctane was demonstrated by scanning tunneling microscopy (STM). The star-shaped compound seems to prefer the C_3-symmetric arrangement in this two-dimensional crystal. Two 1,2-diketones were smoothly converted into functionalized quinoxaline derivatives.
机译：锂化的烷氧基烯，腈和羧酸已在三组分反应中用作前体，从而导致高度取代的β-烷氧基-β-酮烯酰胺。用三氟乙酸处理后，这些酰胺很容易环化成5-乙酰基恶唑衍生物。就恶唑核心的C-2和C-4处的取代方式而言，合成非常灵活。在〜（18）O标记的化合物及其质谱分析的基础上，提出了恶唑形成的机理建议。在某些情况下，1,2-二酮可作为副产品甚至主要成分形成。恶唑衍生物的C-5处的乙酰基部分可以有效地转化为烯基或炔基部分，这允许大量随后的反应。乙酰基的缩合反应提供了预期的肟或。通过应用费歇尔反应，苯hydr可以转移到吲哚中，这强调了5-乙酰基恶唑在制备高度取代的（多）杂环体系中的潜力。 C-2处的炔基易于加成反应，提供具有有趣光物理性质的烯胺。用5-炔基取代的恶唑进行Sonogashira偶联，得到预期的芳基取代的产物。该炔基单元用于制备新的星形三tri唑衍生物。通过扫描隧道显微镜（STM）证明了这种多价化合物在高度定向的热解石墨和1-苯基辛烷的基面之间形成自组装单层的能力。在此二维晶体中，星形化合物似乎更喜欢C_3对称排列。将两个1,2-二酮顺利转化为官能化的喹喔啉衍生物。

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