Cyclic meso-ionic compounds. Part 22. Meso-ionic derivatives of the imidazo[1,2-a]pyridinium system and the unexpected synthesis of stable pyridinium dinitromethylides

Abstract

The chemistry of 1,3-diazolium-4-olates (1) has been extended by the synthesis of representatives of a new type (2) of bicyclic meso-ionic system. N-Methylation of the imidazo[1,2-a]pyridine (3) gave the salt (11) which reacted smoothly with appropriate nucleophilic reagents yielding the meso-ionic hetero-cycles (9) and (12)–(15). Nitration of the lactam (10) did not give the expected nitro-derivative (8), but instead a novel pyridinium dinitromethylide (16) was produced. The planar and orthogonal conformations of pyridinium ylides in the solid state are discussed.