Acid-Catalyzed Ring-Chain Tautomerism in 1,3-Diazolidines

Article abstract of DOI:10.1021/jo00377a011

Ring-chain tautomerism has been studied in 2-substituted and 1,3-disubstituted diazolidines.In trifluoroacetic acid, these heterocycles are in equilibrium with the open-chain iminium ion.For materials lacking 2 substitution, 5-10percent of the chain form is present at room temperature.Because of resonance stabilization of the positive charge, 2-aryl-substituted systems have about 30percent of the chain form.All of these ring and chain forms undergo interconversion on the NMR time scale with a free energy of activation of 16 - 18 kcal/mol.