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

A mild and metal-free strategy for the construction of trifluoromethylated pyrazolo[4,3-]indoles through the reaction of -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.