A facile access to new diazepines derivatives: Spectral characterization and crystal structures of 7-(thiophene-2-yl)-5-(trifluoromethyl)-2,3-dihydro-1H-1,4-diazepine and 2-thiophene-4-trifluoromethyl-1,5-benzodiazepine

•Synthesis of 1,4-diazepine by double condensation of TTA with ethylenediamine.•Synthesis of 1,5-benzodiazepine by double condensation of TTA with o-diaminophenyl•X-ray crystal structures of both diazepines.•1,4-Diazepine exists as imine-enamine tautomer in solution and in the solid-state.•1,5-Benzodiazepine exists as diimine tautomer in solution and in the solid-state.

The one-pot double condensation reaction of 2-thenoyltrifluoroacetone (2-TTA) with ethylendiamine or o-phenylenediamine, in a 2:1 stoichiometric molar ratio, leads to the formation of 7-(thiophene-2-yl)-5-(trifluoromethyl)-2,3-dihydro-1H-1,4-diazepine 2 and 2-thiophene-4-trifluoromethyl-1,5-benzodiazepine 3, that were isolated in 56 and 53% yields, respectively. The bis(trifluoroacetamide)ethylene derivative 1 was also isolated in 32% yield as a side-product in the reaction of 2-TTA and ethylenediamine. Compounds 1–3 were fully characterized by elemental analysis, FT-IR and multinuclear (1H, 13C and 19F) NMR spectroscopy. In addition, their molecular identities and geometries have been authenticated by single-crystal X-ray diffraction analysis. The spectroscopic and structural data confirm that the 1,4-diazepine 2 and the 1,5-benzodiazepine 3 exist in the imine-enamine and diimine tautomeric forms, respectively, both in solution and in the solid-state.

Graphical abstractBoth thienyl-containing 1,4-diazepine and 1,5-benzodiazepine (illustrated) were synthetized in a one-pot double condensation reaction of 2-thenoyltrifluoroacetone with ehtylenediamine and o-phenylene diamine, respectively.Figure optionsDownload full-size imageDownload as PowerPoint slide