4-Styrylquinolines from cyclocondensation reactions between (2-aminophenyl)chalcones and 1,3-diketones: crystal structures and regiochemistry.

Structures are reported for two matched sets of substituted 4-styryl­quino­lines which were prepared by the formation of the heterocyclic ring in cyclo­condensation reactions between 1-(2-amino­phen­yl)-3-aryl­prop-2-en-1-ones with 1,3-dicarbonyl com­pounds. (E)-3-Acetyl-4-[2-(4-meth­oxy­phen­yl)ethen­yl]-2-methyl­quino­line, C21H19NO2, (I), (E)-3-acetyl-4-[2-(4-bromo­phen­yl)ethen­yl]-2-methyl­quino­line, C20H16BrNO, (II), and (E)-3-acetyl-2-methyl-4-{2-[4-(tri­fluoro­meth­yl)phen­yl]ethen­yl}quino­line, C21H16F3NO, (III), are isomorphous and in each structure the mol­ecules are linked by a single C—H⋯O hydrogen bond to form C(6) chains. In (I), but not in (II) or (III), this is augmented by a C—H⋯π(arene) hydrogen bond to form a chain of rings; hence, (I)–(III) are not strictly isostructural. By contrast with (I)–(III), no two of ethyl (E)-4-[2-(4-meth­oxy­phen­yl)ethen­yl]-2-methyl­quino­line-3-carboxyl­ate, C22H21NO3, (IV), ethyl (E)-4-[2-(4-bromo­phen­yl)ethen­yl]-2-methyl­quino­line-3-carboxyl­ate, C21H18BrNO2, (V), and ethyl (E)-2-methyl-4-{2-[4-(tri­fluoro­meth­yl)phen­yl]ethen­yl}quino­line-3-carboxyl­ate, C22H18F3NO2, (VI), are isomorphous. The mol­ecules of (IV) are linked by a single C—H⋯O hydrogen bond to form C(13) chains, but cyclic centrosymmetric dimers are formed in both (V) and (VI). The dimer in (V) contains a C—H⋯π(pyrid­yl) hydrogen bond, while that in (VI) contains two independent C—H⋯O hydrogen bonds. Comparisons are made with some related structures, and both the regiochemistry and the mechanism of the heterocyclic ring formation are discussed.