1‐Chloro‐2‐azapropenylium and 1‐chloro‐2,4‐diazabutenylium salts. Intermediates for the synthesis of pyrido[1,2‐ a ]‐1,3,5‐triazinium salts

1‐Chloro‐1,3‐bis(dimethylamino)‐3‐phenyl‐2‐azaprop‐2‐en‐1‐ylium perchlorate obtained from the reaction of phosphorus oxychloride‐ N,N ‐dimethylbenzamide complex and dimethylcyanamide reacts with 2‐amino‐4‐methylpyridine to yield 8‐methyl‐4‐dimethylamino‐2‐phenylpyrido[1,2‐ a ]‐1,3,5‐triazinium perchlorate ( 8 ). The structure is established by X‐ray crystallography. Various suitably substituted pyridines react similarly to afford the corresponding pyrido[1,2‐ a ]‐1,3,5‐triazinium salts. The intermediates obtained from several secondary amides give identical products when treated with the same pyridines. The limitations of this procedure are investigated.