1,3-Diaza-2-azoniaallene salts: cycloadditions to alkynes, carbodiimides and cyanamides

1,3-Diaza-2-azoniaallene salts 2 react with alkynes 6 to furnish 1,2,3-triazolium salts 7a–m. According to AM1 calculations, these reactions are concerted [3 + 2] cycloadditions (1,3-dipolar cycloadditions with inverse electron demand). The structure of the triazolium salt 7e has been confirmed by X-ray crystallographic analysis. With N,N′-dialkylcarbodiimides 9 the heteroallene salts 2 undergo cycloaddition to furnish 1,3,4,5-tetra-substituted 4,5-dihydrotetrazolium salts 11, which on heating in acetonitrile eliminate an alkene to afford 1,3,5-tri-substituted tetrazolium salts 12. Furthermore, it has been found that heteroallene salts 2 react with N,N-dialkylcyanamides 13 to give 1,3,5-tri-substituted tetrazolium salts 15. Here, AM1 calculations suggest stepwise cycloaddition mechanisms via intermediate nitrilium salts 10 and 14 respectively.