Synthesis of Heterocycles by Intramolecular Nucleophilic Substitution at an Electron-Deficient sp2 Nitrogen Atom
作者:Jarosław Sączewski、Maria Gdaniec
DOI:10.1002/ejoc.200901520
日期:2010.4
1-c][1,2,4]thiadiazoles have been synthesized by intramolecularnucleophilicsubstitution 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 nucleophilicsubstitution.
The course of reaction of aryl and heteroaryl sulfonamides with diphenylcarbonate (DPC) and 4-dimethylaminopyridine (DMAP) was found to depend on the pKa of the sulfonamide used. Aryl sulfonamides with pKa ~ 10 gave 4-dimethylamino-pyridinium arylsulfonyl-carbamoylides, while the more acidic heteroaryl sulfonamides (pKa ~ 8) furnished 4-dimethylaminopyridinium heteroarylsulfonyl carbamates. Both the carbamoylides and carbamate salts reacted with aliphatic and aromatic amines with the formation of appropriate aryl(heteroaryl)sulfonyl ureas, and therefore, can be regarded as safe and stable substitutes of the hazardous and difficult to handle aryl(heteroaryl)sulfonyl isocyanates.