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Iminodiaziridines are synthesized by (i) 1,3-dehydrochlorination with potassium tert-butoxide of N-chloroguanidines, generated in situ from N,NЈ,NЈЈ-substituted guanidines with tert-butyl hypochlorite, and (ii) base-mediated 1,3-elimination of sulfuric acid from N,NЈ,NЈЈ-substituted hydroxyguanidine O-sulfonic acids. At elevated temperatures, (alkylimino)diaziridines undergo valence isomerization by 1,3-shift, [2+1] cycloelimination to afford isocyanides and diazenes, and ring-opening elimination to yield alkylideneguanidines. NЈ-Aryl-N-hydroxyguanidine O-sulfonic acids furnish (N-arylimino)diaziridines, but no 1-aryl-3-iminodiaziridines, instead giving rearranged isomers. Precursors containing perdeuterated tert-butyl groups give rearranged products that show complete scrambling. This indicates that 1-aryl-3-iminodiaziridines are intermediates that undergo very rapid degenerate valence isomerization. Provided that the ortho-

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Keywords: EPR spectroscopy / Hydrogenation / Nitrogen heterocycles / Oxidation / RadicalsOxidation of 2-tert-butyl-3-(tert-butylamino)-2H-indazoles with lead(IV) oxide yields red, stable radicals, which can be distilled under high vacuum and recrystallized. They revert to their precursors on Pd-catalysed hydrogenation. Configuration and atomic distances were obtained by X-ray diffraction analysis. EPR hfc constants were assigned with the help

Abstract(Arylimino)diaziridines rearrange in several cascade reactions at temperatures 60–100 °C. Those that possess unoccupied ortho positions yield fluorescent 3‐amino‐2H‐indazoles and 2‐amino‐1H‐benzimidazoles. If both ortho positions are blocked by methyl groups, indazoles are not formed and deeply yellow 2‐imino‐2,3‐dihydro‐3aH‐benzimidazoles are formed, which partly dimerize through Diels–Alder reaction or regenerate the aromatic system by formal loss of CH2. In addition, one of the methyl groups of 2,6‐dimethylphenyl rings is involved in a [1,7] H shift affording orthoquinonoid intermediates which undergo 1,6‐electrocyclization to furnish 2‐amino‐3,4‐dihydroquinazolines. The formation of five‐membered ring heterocycles is interpreted in terms of valence isomerization by [1,3] N shift to yield elusive 1‐aryl‐3‐iminodiaziridines as first step. These immediately experience triaza‐Cope rearrangement to benzimidazole derivatives or electrocyclic opening of the N–C bond to generate conjugated azomethine imines (1,5‐dipoles), followed by their 1,5‐electrocyclization to indazoles. First‐order rate constants of the decay of (arylimino)diaziridines refer to the [1,3] N shifts as rate‐determining steps. They are larger than the corresponding rate constants for alkylsubstituted iminodiaziridines.