Triflic Anhydride (Tf2O): An Efficient Catalyst for Electrophilic Activation of Amides

Abstract Tf 2 O (trifluoromethanesulfonic anhydride) as an electrophilic reagent has been increasingly attracting the attention of researchers over the last decade due to its capability in synthesizing a variety of N ‐heterocycles through activation of amides. This activation is associated with the formation of intermediates such as enolonium, imino/iminium, nitrilium and keteniminium triflate ions and isocyanate species which can lead to the synthesis of different types of N ‐heterocycles depending on the nature of the intermediates. In this review, we have summarized and classified the latest research in this area (from 2012 on) based on the type of intermediates produced from the triflic anhydride‐catalyzed activation of amides. The findings are classified into five main categories, namely enolonium, imino/iminium, nitrilium and keteniminium intermediates ions and isocyanate species.