Use of a Traceless Activating and Directing Group for the Construction of Trifluoromethylpyrazoles: One‐Pot Transformation of Nitroolefins and Trifluorodiazoethane

We disclose an efficient one‐pot transformation of trifluorodiazoethane and higher perfluorinated homologues with various nitroolefins. This method takes advantage of the nitro group as a traceless activating and directing group (TADG) that is released in the aromatization step to produce 4‐substituted 3‐perfluoroalkyl pyrazoles with complete regioselectivity. The potential of this method is further demonstrated by the synthesis of penthiopyrad. Leaves discreetly when the job is done: A one‐pot reaction of trifluorodiazoethane and higher perfluorinated homologues with various nitroolefins takes advantage of the nitro group as a traceless activating and directing group that is released in the aromatization step to produce 4‐substituted 3‐perfluoroalkyl pyrazoles with complete regioselectivity (see scheme). The method was applied to the synthesis of the fungicide penthiopyrad.