Synthesis and multinuclear NMR investigation of some mesoionic 3-phenyl-5-imino-1,2,3,4-oxatriazole imines

Six new derivatives of mesoionic 3-phenyl-5-imino-1,2,3,4-oxatriazole imine have been obtained and investigated by 1H, 13C, 14N, 15N and 17O NMR techniques. The 15N and 17O NMR studies reveal that mesoionic oxatriazoles imines exist in a cyclic, ‘mesoionic’ form. Two stable conformers of mesoionic 3-phenyl-5-imino-1,2,3,4-oxatriazole imines, E and Z; in comparable concentrations, have been detected for the first time in the solution by the use of low temperature NMR experiments. 1H NMR techniques and band shape analysis were applied for estimation of Z–E interconversion barrier of mesoionic 3-phenyl-5-methylimino-1,2,3,4-oxatriazole imine 6 and 3-phenyl-5-benzylimino- 1,2,3,4-oxatriazole imine 10. Some one-bond 1J(15N–13C) coupling constants have been measured using 15N enriched oxatriazole and tetrazole, as a means of the C5–N26 bond characterisation. q 2003 Elsevier B.V. All rights reserved