Bridgehead nitrogen heterocycles. VI. The reaction of 1‐amino‐ and 1,2‐diaminopyridinium salts with β‐dicarbonyl compounds

1,2‐Diaminopyridinium iodide underwent reaction with ethyl acetoacetate to form 1,4‐dihydro‐2‐methyl‐4‐oxopyrido[1,2‐ a ]pyrimidin‐1‐ium iodide, and with acetyl acetone it gave 2,4‐dimethylpyrido[1,2‐ a ]pyrimidin‐5‐ium iodide. Though 2‐acetylcyclohexanone gave the corresponding 5‐methyl‐1,2,3,4‐tetrahydropyrido[1,2‐ a ]quinazolin‐11‐ium iodide, no reaction was observed with 2,6‐dimethyl‐3,5‐heptanedione, 1‐benzoylacetone, 1,3‐diphenyl‐1,3‐propanedione and its p ‐methoxyphenyl derivative. However, 1‐aminopyridinium iodide and acetyl acetone in the presence of base gave 3‐acetyl‐2‐methylpyrazolo[1,5‐ a ]pyridine and 1‐amino‐2‐methylpyridinium iodide yielded the corresponding 3‐acetyl‐2,7‐dimethylpyrazolo[1,5‐ a ]pyridine. With ethyl acetoacetate, the latter salt formed 3‐ethoxycarbonyl‐2,7‐dimethylpyrazolo[1,5‐ a ]pyridine but with 2,6‐dimethyl substituents in the pyridine ring no condensation occurred. Reaction of 1‐amino‐2‐methylpyridinium iodide with benzaldehyde gave N ‐benzalimino‐2‐methylpyridinium iodide which, on treatment with base, resulted in the formation of 2‐picoline and benzonitrile, providing a convenient method of deamination.