Terminal Acetylenic Iminium Salts: Cycloaddition Reactions with Azides Leading to 1,2,3‐Triazoles and Bicyclic 1,2,3‐Triazolium Salts

Terminal acetylenic iminium triflate salts [HC≡C‐C(R)=N + Me 2 TfO – ] represent very potent dipolarophiles which undergo [3+2] cycloadditions with aryl and benzyl azides at very mild and uncatalyzed conditions, yielding 1,4‐disubstituted 1,2,3‐triazoles with complete regioselectivity. Addition of nucleophiles at the iminium group of the cycloadducts leads to diverse 1‐aryl‐(or benzyl‐)‐4‐dimethylaminomethyl‐1,2,3‐triazoles. The first formed cycloaddition adducts subsequently react with a second molecule of the acetylenic iminium salt by a consecutive Michael addition/1,5‐cyclization to form 2,4‐dihydropyrrolo[1,2‐ c ][1,2,3]triazol‐7‐ium triflates. Further transformations of the latter salts are described, among them the conversion into a mesoionic carbene, isolated as a monomeric silver(I) complex.