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

Abstract

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.