Copper-mediated oxidative [3 + 2]-annulation of nitroalkenes and pyridinium imines: efficient synthesis of 3-fluoro- and 3-nitro-pyrazolo[1,5-<i>a</i>]pyridines
作者:Vladimir A. Motornov、Andrey A. Tabolin、Yulia V. Nelyubina、Valentine G. Nenajdenko、Sema L. Ioffe
DOI:10.1039/c9ob02668a
日期:——
efficient route to pyrazolo[1,5-a]pyridines by Cu(OAc)2-promoted oxidative [3 + 2]-annulation of nitroalkenes with in situ generated pyridinium imines is developed. The reaction with α-fluoronitroalkenes enables the first preparative synthesis of 3-fluoro-pyrazolo[1,5-a]pyridines. Cycloaddition with α-unsubstituted nitroalkenes provides access to 3-nitro-pyrazolo[1,5-a]pyridines in excellent yields. A broad
开发了通过Cu(OAc)2促进硝基烯烃与原位生成的吡啶鎓亚胺的氧化[3 + 2]环化反应制备吡唑并[1,5-a]吡啶的有效途径。与α-氟硝基烯烃的反应使得能够进行3-氟-吡唑并[1,5-a]吡啶的第一制备合成。与α-未取代的硝基烯烃进行环加成反应,可以以优异的产率获得3-硝基-吡唑并[1,5-a]吡啶。展示了广阔的转型范围。富电子和电子不足的硝基烯烃以及不同的氨基吡啶鎓盐都可以用于组装目标吡唑并[1,5-a]吡啶。通过本方法成功地制备了相关的氮杂杂环,即吡唑并[1,5-a]吡嗪和吡唑并[1,5-b]哒嗪。讨论了反应的可能机理。