Synthesis of Heterocycles by Intramolecular Nucleophilic Substitution at an Electron-Deficient sp2 Nitrogen Atom

2-Aryl(arylsulfony1)-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ones and 3-arylimino-6,7-dihydroimidazo[2,1-c][1,2,4]thiadiazoles have been synthesized by intramolecular nucleophilic substitution reactions at the electron-deficient sp(2) nitrogen atom of 2-(hydroxyimino)imidazolidine O-sulfonate. The displacement of the sulfate leaving group by both nitrogen and sulfur anionic nucleophiles proceeds exothermically by in-plane S(N)2 sigma nucleophilic substitution.