Kohei Fuchibe, Masaki Takahashi, and Junji Ichikawa
Angew. Chem. Int. Ed.
We don’t often consider the trifluoromethyl group as a reactive centre. But it is, of course, a highly polarised moiety and, under the right conditions, fluoride can act as a competent leaving group. Ichikawa and coworkers employ hydrazines as nucleophiles in two successive displacements of fluoride from vinyl trifluoromethyl adducts to give 3-fluoropyrazole scaffolds.
After testing other possible reaction pathways, they postulate that the reactive intermediate in the cyclisation step, after loss of the tosyl anion, is an azomethine ylide.