Conversion of 2-methyl-4-styrylquinolines into 2,4-distyrylquinolines: synthesis, and spectroscopic and structural characterization of five examples

Four new 2,4-distyryl­quino­lines and one 2-styryl-4-[2-(thio­phen-2-yl)vin­yl]quinoline have been synthesized using indium trichloride condensation reactions between aromatic aldehydes and the corresponding 2-methyl­quino­lines, which were themselves prepared using Friedländer annulation reactions between mono- or diketones and (2-amino­phen­yl)chalcones: the products have all been fully characterized by spectroscopic and crystallographic methods. 2,4-Bis[(E)-styr­yl]quino­line, C₂₅H₁₉N, (IIa), and its di­chloro analogue, 2-[(E)-2,4-di­chloro­styr­yl]-4-[(E)-styr­yl]quino­line, C₂₅H₁₇Cl₂N, (IIb), exhibit different orientations of the 2-styryl unit relative to the quino­line nucleus. In each of the 3-benzoyl analogues {2-[(E)-4-bromo­styr­yl]-4-[(E)-styr­yl]quinolin-3-yl}(phen­yl)methanone, C₃₂H₂₂BrNO, (IIc), {2-[(E)-4-bromo­styr­yl]-4-[(E)-4-chloro­styr­yl]quinolin-3-yl}(phen­yl)methanone, C₃₂H₂₁BrClNO, (IId), and {2-[(E)-4-bromo­styr­yl]-4-[(E)-2-(thio­phen-2-yl)vin­yl]quinolin-3-yl}(phen­yl)methanone, C₃₀H₂₀BrNOS, (IIe), the orientation of the 2-styryl unit is similar to that in (IIa), but the orientation of the 4-aryl­vinyl units show considerable variation. The thio­phene unit in (IIe) is disordered over two sets of atomic sites having occupancies of 0.926 (3) and 0.074 (3). There are no hy­dro­gen bonds of any kind in the structure of (IIa), but in (IId), a single C—H...O hy­dro­gen bond links the mol­ecules into cyclic centrosymmetric R22(20) dimers. A combination of C—H...N and C—H...π hy­dro­gen bonds links the mol­ecules of (IIb) into a three-dimensional framework structure. A combination of three C—H...π hy­dro­gen bonds links the mol­ecules of (IIc) into sheets, and a combination of C—H...O and C—H...π hy­dro­gen bonds forms sheets in (IIe). Comparisons are made with the structures of some related compounds.