N-Triflination of pyrazolones: a new method for N–S bond formation

Abstract

A simple method, which takes place quickly in 5 min, is developed for the N-triflination of pyrazolones using CF₃SO₂Na (Langlois reagent) and phenyliodine(III)bis(trifluoroacetate) (PIFA). This reaction takes place at the imine nitrogen centre instead of the more reactive C4-position, forming a new N–S bond. A variety of pyrazolone derivatives were subjected to the reaction. Unlike the previous reports on sulfenylation or sulfonylation of pyrazolone, wherein the corresponding C–S bond is formed, this new method leads to the formation of the hetero–hetero atom bond (N–S bond) at room temperature.