Synthesis, and spectroscopic and structural characterization of three new styrylquinoline–benzimidazole hybrids

Three new 4-styryl­quinoline–benzimidazole hybrids have been synthesized using a reaction sequence in which 2-methyl­quinoline precursors first undergo selective oxidation by selenium dioxide to form the corresponding 2-formyl­quinoline inter­mediates, followed by oxidative cyclo­condensation reactions with benzene-1,2-diamine to yield the hybrid products. The formyl inter­mediates and the hybrid products have all been fully characterized using a combination of IR, ¹H and ¹³C NMR spectroscopy, and high-resolution mass spectrometry, and the structures of the three hybrid products have been determined using single-crystal X-ray diffraction. Ethyl (E)-2-(1H-benzo[d]imidazol-2-yl)-4-(4-chloro­styr­yl)quinoline-3-carboxyl­ate, C₂₇H₂₀ClN₃O₂, (IIIa), and ethyl (E)-2-(1H-ben­zo[d]imidazol-2-yl)-4-(2-meth­oxy­styr­yl)quinoline-3-carboxyl­ate, C₂₈H₂₃N₃O₃, (IIIb), both crystallize in the solvent-free form with Z′ = 1, but ethyl (E)-2-(1H-benzo[d]imidazol-2-yl)-4-(4-methyl­styr­yl)quinoline-3-carboxyl­ate, C₂₈H₂₃N₃O₂, (IIIc), crystallizes as a partial hexane solvate with Z′ = 3, and the ester group in one of the independent mol­ecules is disordered over two sets of atomic sites having occupancies of 0.765 (7) and 0.235 (7). The mol­ecules of (IIIc) enclose continuous channels which are occupied by disordered solvent mol­ecules having partial occupancy. In all of the mol­ecules of (IIIa)–(IIIc), the styryl­quinoline fragment is markedly nonplanar. Different combinations of N—H⋯O and C—H⋯π hydrogen bonds generate supra­molecular assemblies which are two-dimensional in (IIIb) and (IIIc), but three-dimensional in (IIIa). Comparisons are made with the structures of some related com­pounds.