2‐Azaallenium salts from the reaction of 1‐oxa‐3‐azabutatrienium salts with cyanamides and carbodiimides

1‐Oxa‐3‐azabutatrienium salts 2 react with disubstituted cyanamides under [2 + 2 + 2] cycloaddition affording the 2‐(alkylideneamino)‐4,6‐diamino‐1,3,5‐oxadiazinium salts 7a – o , which can be regarded as oxy‐substituted 2‐azaallenium salts. Addition of methanol leads to the oxadiazinium salts 8a, d, p . From 2n and dimethylcyanamide the 2‐azaallenium salt 11 was obtained, which must be formed by an [1,5] isocyanatotropic rearrangement. Most butatrienium salts 2 react with two equivalents of carbodiimides R 1 N C N CHR   2 2to form the 2‐azaallenium salts 17a – k . The reaction mechanism includes an [1,5] hydride shift. Bulky substituted butatrienium salts 2 add three molecules of diisopropylcarbodiimide to give the 1,3,5‐triazinium salts 20n, o . X ‐Ray structural analyses for 7a and 17a are reported.