Diversity of Reactions of Isomeric Aminopyridine N ‐Oxides with Chloronitropyridines: An Experimental and Theoretical Study

Reaction of 2‐aminopyridine N ‐oxides 1a , 1b , 1c , 1d with chloronitropyridine 7a gave 2‐[(pyridin‐2‐yl)amino]pyridine N ‐oxides 8a , 8b , 8c and 9 in good yield. The reactions of 4‐ and 3‐aminopyridine N ‐oxides 12a , 12b and 24 with 7a , 7b , 7c proceed in the different manner involving initial formation of the intermediary 1‐pyridyloxypyridinium salts 13a , 13b , 13c , 13d and 26 , which rearrange to 4‐[(5‐nitropyridin‐2‐yl)amino]pyridine N ‐oxide 22 and 1‐(3‐aminopyridin‐2‐yl)pyrid‐2‐one derivatives 27a , 27b , respectively. However, N‐protected 2‐aminopyridine N ‐oxides 17 gave quaternary 1‐pyridyloxypyridinium salts 18a , 18b , which upon treatment with aqueous ammonia afforded 2‐[(pyridin‐2‐yl)amino]pyridine N ‐oxides 8a and 20 . Quantum chemical calculations at the DFT/B3LYP/6‐311++G(d,p) level were performed to explain the differences in properties of the frontal orbitals and atomic charge distribution in isomeric aminopyridine N ‐oxides.