Supramolecular synthons in the gamma-hydroxybutenolides

The supramolecular organization in the solid state of five novel gamma-hydroxybutenolides is described. The functionalities on their framework drive the construction of the crystalline packing through weak non-covalent forces such as H-bonds, CH-pi, pi-pi and CH center dot center dot center dot O interactions. Gamma-butenolides bearing an unsubstituted aromatic or heteroaromatic ring as the side arm exhibit a helical assembly, in which the helical sense is determined by the chirality of the molecule, promoted by a three-center, bifurcated intraintermolecular H-bond. In this assembly, the aromatic residues form an "aromatic zipper" between adjacent homochiral helices. Crystal structures of gamma-butenolide with p-substituted aromatic rings exhibit dimers, promoted by mutual O-H center dot center dot center dot O=C intermolecular hydrogen-bond interactions. Finally, when the p-position of the aromatic ring is occupied by a potential H-bond acceptor substituent, such as CN group, the aromatic substituent is involved in an exclusive intermolecular H-bond in the observed crystal packing. The ability of gamma-butenolides to control the type of packing induced by the substitution pattern of their side arm makes them interesting for the engineering of novel crystalline assemblies.