CsF-Mediated Reaction of Trifluorodiazoethane with 3‑Nitroindoles Enables Access to Trifluoromethylpyrazolo[4,3‑b]indoles

A mild and metal-free strategy for the construction of trifluoromethylated pyrazolo[4,3-b]indoles through the reaction of N-substituted 3-nitroindoles with trifluorodiazoethane is reported. This operationally simple transformation involves a [3 + 2] cycloaddition of trifluorodiazoethane with 3-nitroindole, followed by the elimination of the nitro group to furnish pyrazole-fused indoles. The synthetic utility of this method is further demonstrated by applying it to other heterocycles, such as 3-nitrobenzothiophene and 2-nitrobenzofuran.本文报道了一种温和无金属的合成策略，可通过N-取代3-硝基吲哚与三氟重氮乙烷（trifluorodiazoethane）的反应构建三氟甲基化吡唑并[4,3-b]吲哚（trifluoromethylated pyrazolo[4,3-b]indoles）。该操作简便的转化过程先经历三氟重氮乙烷与3-硝基吲哚的[3+2]环加成反应，随后经硝基消除得到吡唑稠合吲哚类产物。本方法的合成实用性进一步通过拓展至其他杂环底物得以验证，例如3-硝基苯并噻吩（3-nitrobenzothiophene）与2-硝基苯并呋喃（2-nitrobenzofuran）。