Supramolecular synthons in the gamma-hydroxybutenolides

Abstract

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–π, π–π and CH⋯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 intra-intermolecular 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⋯O[double bond, length as m-dash]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

New Developments of the Principle of Vinylogy as Applied to π-Extended Enolate-Type Donor Systems

“…The hydrophobic amplification of weak interactions between catalyst and substrates under “on-water” conditions inspired the De Rosa group to search for new supramolecular entities able to promote a distereoselective on-water VMAR. In 2017 these efforts ended up with the design of the simple tetraminocalix[4]arene C23c ( Scheme 138 ), 356 , 357 bearing weak H-bond-donor NH 2 functionalities, capable to promote the VMAR of TMSOF 496a with polyfunctionalized α-keto esters 512 , to afford δ-hydroxybutenolides (±)- 513 in good yields (up to 99%) and acceptable diastereoselectivities.…”

Supramolecular Organocatalysis in Water Mediated by Macrocyclic Compounds

“…Recently, calix[n]arene scaffolds adorned with a supramolecularly interacting group such as thiourea moiety have been used as organocatalysts for Vinylogous Mukaiyama Aldol reaction (VMAR) between 2-(trimethylsilyloxy)furan 82 and α-ketoesters 81 under “on-water” conditions (Figure 13A ). The reaction is a useful protocol to obtain functionalized γ-butenolides, which are valuable building blocks for many biologically active compounds and, recently interesting for the engineering of new crystalline assemblies (De Rosa et al, 2009 , 2017a ). It was shown that the catalytic ability of the calixarenes 85 and 86 was closely related to their remarkable hydrophobicity and their recognition abilities toward the reactants through hydrogen—bonding interactions with a thioureido group at the upper rim.…”