Bench-Stable\n2‑Halopyridinium Ketene Hemiaminals\nas Reagents for the Synthesis of 2‑Aminopyridine Derivatives

2-Chloro-1-(1-ethoxyvinyl)pyridinium triflate and several\nother\nbench-stable <i>N</i>-(1-alkoxyvinyl) 2-halopyridinium triflates\nhave been developed as reagents for the synthesis of valuable 2-aminopyridine\nscaffolds via unusually mild S<sub>N</sub>Ar substitutions with amine\nnucleophiles. Advantages of this approach include an operationally\nsimple mix-and-stir procedure at room temperature or mild heat and\nambient atmosphere and without the need for transition metal catalysts,\ncoupling reagents, or high-boiling solvents. The stable <i>N</i>-(1-ethoxyvinyl) moiety serves as a dual S<sub>N</sub>Ar-activating\ngroup and pyridine <i>N</i>-protecting group that can be\ncleaved under thermal, acidic, or oxidative conditions. Preliminary\nresults of other nucleophilic substitutions using oxygen-, sulfur-,\nand carbon-based nucleophiles are also demonstrated.