The continuous search for new qualities and the desirability of controlling the size, shape and the chemical features had led to the successful synthesis of various molecular containers and their complexes starting from resorcarene skeleton. The rigidified cavitands have been extended to capture in their round hug bigger and bigger molecules. By covalent synthesis many kinds of new hosts have been built, that maintain guests in their prison for more and more long time. Self assembly, driven by metal-ligand interaction, van der Waals forces, hydrophobicity and, mainly, hydrogen bonds, is at the base of capsules, a novel type of compounds with a peculiar inner phase, stereochemistry and reactivity. The amazing variety of hollow buildings with a resorcarene-based framework and often unique properties is reviewed.

The synthesis and anion binding studies of the new neutral receptor 1,1′-(2,2′-(4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-diyl)bis(2-oxoethane-2,1-diyl))bis(3-(3,5-bis(trifluoromethyl)phenyl)urea) (L1) are reported. L1 is a macrocyclic ligand containing the 3,5-trifluoromethylphenylureido-binding fragment attached as a side arm on the tetraazacyclododecane. L1 is soluble in numerous organic solvents; the binding properties of L1 towards several simple anions (G) were investigated by NMR, UV–vis and fluorescence techniques in DMSO and CH₃CN solutions. L1 is able to bind F⁻ , Cl⁻  and AcO⁻  in both solvents; in addition, it binds Br⁻  in CH₃CN. Fluoride shows the highest constant values in the halide series (F⁻  > Cl⁻  > Br⁻ ) and AcO⁻  is the most strongly bound among all the anions investigated. L1 is able to signal the presence of the anions in solution by fluorescence change; in the case of acetate, this occurs in the visible range.

A concise synthesis of (R)-4-amino-3-hydroxybutanoic acid, starting from L-malic acid, is reported. The approach is based on the conversion of the oxazolidin-2-one 9 into a full protected form of (®)-GABOB by an Arndt-Eistert reaction.

Starting from the tetrabromide 1a (cone conformation) a number of resorcin[4]arene derivatives (3a, 4a, 5a, 6a) containing an amino function in the side chains have been prepared. Preliminary investigations, including UV, NMR, and MS analyses, of mixtures of the resorcinarene and its potential guests, such as metal cations or amino acids, evidenced promising new properties, depending on the nature of the substituents. Notably, treatment of 1a with pyridine gave readily the corresponding pyridinium salt 7a, capable of interacting with Ga(III) salts in aqueous solution. The same results have been obtained starting from the tetrabromide 1b (1,2-alternate conformation) for two of the above reactions, giving derivatives 3b and 7b.