FULL PAPER DOI:10.1002/ejic.201301450 Boron Macrocycles Based on Multicomponent Assemblies using (3-Aminophenyl)boronic Acid and Pentaerythritol as Common Reagents; Molecular Receptors toward Lewis Bases Norma A. Celis, [a] Carolina Godoy-Alcántar, [a] Jorge Guerrero-Álvarez, [a] and Victor Barba* [a] Keywords: Multicomponent reactions / Molecular recognition / Sensors / Macrocycles / Boronates Four cyclic boronate esters were synthesized by using a multicomponent reaction from (3-aminophenyl)boronic acid, pentaerythritol, and aldehyde derivatives [isophthalaldehyde (1), dialdehyde A (2), (3-formylphenyl)boronic acid (3), and (2,4-difluoro-3-formylphenyl)boronic acid (4)]. All four reac- tions lead to the formation of macrocyclic compounds in good yields of more than 70 %. The cavities of the compounds con- sist of 29-, 30- and 40-membered rings, and the macrocyclic structures contain two (2) and four (1 and 3–4) boron atoms as Lewis acids. Additionally, the molecules contain eight (1) Introduction Boronic acids have been reported to rapidly and revers- ibly react with alcohols, forming boronates. [1,2] Actually, the reaction with diols leads to the formation of highly stable cyclic esters. The best interaction is obtained with 1,2- and 1,3-diols to form five- and six-membered rings, respectively, although the stability for the latter cyclic esters is somewhat lower than the five-membered counterparts. [3] Owing the easy synthesis and thermal stability of boronate esters, such compounds have been formed even under mechanochemis- try conditions. [4] It is known that the boronate ester linkage functions as tecton of supramolecular architectures. In fact, the self-assembly of well-defined structures allows the for- mation of macrocycles, [1,5–8] capsules, [9,10] and polymers. [11] Due to the ready recognition of the diol motif by boronic acids, the use of boronate ester systems has been explored as sensors for diol derivatives involving saccharides. [12–17] Pentaerythritol forms stable boronate cyclic esters when reacted with arylboronic acids, and this reaction constitutes an important strategy for the construction of macrocyclic compounds. For instance, Aldridge described the condensa- tion of pentaerythritol with 1,1'-ferrocendiboronic acid [a] Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, C.P. 62209, Cuernavaca, Morelos, México E-mail: vbarba@uaem.mx http://www.ciq.uaem.mx/nosotros/victor-barba.html Eur. J. Inorg. Chem. 2014, 1477–1484 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1477 and six (2–4) donor atoms (N,O) within the macrocyclic struc- ture, thus constituting a ditopic cavity. X-ray analysis of 2 and 3 revealed the whole conformation within the trigonal planar geometry for the boron atoms and the inclusion of neutral guest molecules, chloroform for 2 and benzene for 3. Titration of the receptors with triethylamine, pyridine, and tetrabutylammonium fluoride show that the Lewis acids are available for interaction with Lewis bases. The interaction was follow by 11 B NMR and UV/Vis spectroscopy. leading to the formation of a macrocyclic boronate ester by using a simple one-step synthesis. [18] In 2008, Severin [19] and Nitschke [20] showed the formation of macrocycles through the [4+2+2] multicomponent condensation of arylboronic acids, pentaerythritol, and diaminobenzene. Furthermore, Severin [19] proved that the additional utilization of a metal- ligand coordination fragment could assist the boronic acid based macrocyclic formation wherein twelve building blocks were involved. The esterification reaction combining aryldiboric acids with pentaerythritol is an important process for polymeric product formation. Indeed, self-repairing polymers have been developed by using the well-know reversible nature of the B–O bonds. [21] In addition, boron polymers incorporat- ing Lewis acid centers have been used to form hybrid mate- rials with gold-nanoparticles that exhibit catalytic activities for the reduction of nitroaromatic compounds. [22] The pres- ence of Lewis acid boron centers in macrocyclic or poly- meric systems allows their potential use as molecular recep- tors for Lewis bases. The construction of macrocyclic and polymeric struc- tures with boronic acids generally involves the self-assembly of boronate esters containing N-donor groups, in which tri- gonal-planar boronic esters are Lewis acidic compounds that form adducts with the N-donor fragments. [23,24] The strength of the resulting dative B–N bonds determine the stability of the compounds and it is strongly influenced by steric and electronic factors. [25] Thus, the combination of