1,3-Diaza-2-azoniaallene Salts, Novel N₃-Building Blocks: Preparation and Cycloadditions to Olefins

Introduced are 1,3-diaza-2-azoniaallene salts R₁ - N = N⁺ = N - R² X^- (6) representing a new functional group. The reactive intermediates 6 are prepared by reaction of N-chlorotriazenes R¹ - N = N - NCl - R² (8) with Lewis acids. The salt 6a is stable below -50°C. It shows a strong IR band at 2018 cm^-1, equivalent aryl groups in the ¹H and ¹³C NMR spectra, and gives a correct elemental analysis. The allenes 6 undergo [4π- + 2π] cycloadditions to both electron-rich and electron-deficient olefins affording 4,5-dihydro-1,2,3-triazolium salts 11 ("1,3-dipolar cycloadditions with inverse electron demand"). The cycloadditions proceed with complete conversation of the stereochemistry of the olefins. Cycloadducts 11w, 11ai of dibutyl maleate rearrange in solution into the respective more stable trans-isomers 11v, 11ah. The structure of 11m was determined by X-ray structural analysis.

heterocumulenes - 1,3-diaza-2-azoniaallene salts - 1,3-dipolar cycloaddition with inverse electron demand - 4,5-dihydro-1,2,3-triazolium salts - X-ray structural analysis