NMR Spectroscopic and Theoretical Studies on Tautomerism and Isomerism of Perfluoroalkyl‐Substituted 1,5‐Benzodiazepines

Abstract

The tautomerism and isomerism of several ethyl 2-(4-(perfluoroalkyl)dihydro-2H-benzo(naphtho)[b] [1,4]diazepin-2-ylidene) acetates were investigated by 1 H-, 13 C-, 15 N-and 19 F-NMR spectroscopy and DFT computations. Depending on the polarity and basicity of the solvent a different behaviour was observed. In CDCl 3 , (D 6 )acetone and CD 3 CN solution two chelate hydrogen bonded tautomers, the enaminoimine and the diaminodiene, were found to exist. In the polar and more basic solvents (D 6 )DMSO and (D 7 )DMF two further species, the chelate ring-opened isomers, were detected. The ratio of the isomers is influenced by the solvents and the substituents at the chelate ring. The chelate enaminoimine is favoured in the less polar chloroform, whereas the chelate diaminodiene predominates with increasing polarity of solvents. The length of the perfluoroalkyl chain and the substituents of the phenyl ring do not influence the isomeric equilibrium as much as the chlorine atom in 4-position.