Selective, Metal-Free Approach to 3- or 5-CF<sub>3</sub>-Pyrazoles: Solvent Switchable Reaction of CF<sub>3</sub>-Ynones with Hydrazines
作者:Vasiliy M. Muzalevskiy、Alexander Yu. Rulev、Alexey R. Romanov、Evgeniy V. Kondrashov、Igor A. Ushakov、Vyacheslav A. Chertkov、Valentine G. Nenajdenko
DOI:10.1021/acs.joc.7b00774
日期:2017.7.21
A detailed study of the reaction of trifluoroacetylated acetylenes and aryl (alkyl) hydrazines was performed, aimed to the regioselective synthesis of 3- or 5-trifluoromethylated pyrazoles. It was found that the regioselectivity of reaction depends dramatically on the solvent nature. Highly polar protic solvents (hexafluoroisopropanol) favor the formation of 3-trifluoromethylpyrazoles. In contrast
对三氟乙酰化乙炔与芳基(烷基)肼的反应进行了详细的研究,目的在于区域选择性合成3-或5-三氟甲基化的吡唑。发现反应的区域选择性极大地取决于溶剂性质。高极性质子溶剂(六氟异丙醇)有利于3-三氟甲基吡唑的形成。相反,当反应在极性非质子溶剂(DMSO)中进行时,优先观察到它们的5-CF 3-取代的异构体的形成。或者,3-CF 3的区域选择性组装取代的吡唑可以通过两步一锅法进行。在酸性催化剂存在下三氟甲基化的炔酮与芳基(烷基)肼的反应导致形成相应的。后者可以通过用碱处理平滑地转化为3-CF 3-吡唑。该溶剂可切换程序用于制备重要药物,如Celebrex和SC-560以及其以克为单位的异构体。讨论了可能的反应机理。