1-ha-2-azoniaallene cations / Isocyanates / 4,5-Dihydro-5-oxo-l,2,4-triazolium salts / Cinnolinium salts / Cycloadditions / Calculations, AM1 1-Aza-2-azoniaallene salts 3, prepared in situ from geminal to give pyrazolium salts 8. According to AM1 calculations the chloroalkylazo compounds 2 with Lewis acids, react with iso-cycloadditions of 3 to isocyanates proceed in two steps via cyanates 4 to give 4,5-dihydro-5-oxo-3H-1,2,4-triazolium acylium salts 5 as intermediates. Mechanistically, the rearsalts 6 and 4,5-dihydro-5-oxo-1H-1,2,4-triazolium salts ?, re-rangements 6 + 7 resemble Wagner-Meerwein rearrangespectively. The intramolecular cyclization of 3u opens a new ments rather than pericyclic [ 1,5]-sigmatropic shifts. route to cinnolinium salts 11. Allenes 3 react with isobutene Isocyanates are mostly known for their electrophilic properties [']. However, it should be recalled that towards strong electrophiles, e.g. carbenium ions or the nitronium ion, isocyanates behave as n~cleophiles[~-~1.
In preceding paper^[^-^] we reported on the in situ preparation of 1 -aza-2-azoniaallene salts 3 and their cycloadditions to the multiple bonds of nitriles, carbodiimides, and acetylenes producing five-membered heterocycles. We now found that the strongly electrophilic salts 3 react with isocyanates 4 to furnish 1,2,Ctriazolium salts 7 (Scheme 1).