Substituted pyridines from isoxazoles: scope and mechanism
Substituted pyridines from isoxazoles: scope and mechanism
复制标题
异恶唑取代吡啶：范围和机制
DOI：
10.1039/d2ob00779g
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发表时间：
2022
影响因子：
3.2
通讯作者：
Odom, Aaron L.
中科院分区：
文献类型：
--
作者：
Lee, Seokjoo;Jena, Rashmi;Odom, Aaron L.
用烯胺处理异恶唑会导致逆电子需求杂狄尔斯-阿尔德反应，在 TiCl4(THF)2 和钛粉存在下产生取代的吡啶。该反应具有高度区域选择性，通过 GC/MS 观察到产物仅具有单一异构体，并且能够耐受许多常见官能团。通过计算检查该转化，发现 TiCl4（或类似的路易斯酸）可能起到催化反应的作用。在最初的[4 + 2]-环加成之后，恶氮杂-[2.2.1]-双环可能在胺损失之前产生环打开，得到N-氧化物。用TiCl4和钛粉还原后得到吡啶。
Treatment of isoxazoles with enamines leads to an inverse electron-demand hetero-Diels–Alder reaction that produces substituted pyridines in the presence of TiCl4(THF)2 and titanium powder. The reaction is highly regioselective with only a single isomer of the product observed by GC/MS and tolerant of many common functional groups. The transformation was examined computationally, and it was found that TiCl4 (or a similar Lewis acid) likely acts to catalyze the reaction. After the initial [4 + 2]-cycloaddition, the oxaza-[2.2.1]-bicycle produced likely ring opens before amine loss to give an N-oxide. The pyridine is then obtained after reduction with TiCl4 and titanium powder.