Functionalization Of Calix Research Articles

Direct C−H Functionalization of Calix[n](het)arenes (n=4,6): A Brief Update

AbstractCalix[4]arenes are, probably, the mostly explored macrocycles in the supramolecular chemistry. By means of the synthetic modification/functionalization of the upper or lower rims, as well as meso‐positions, the “host‐guest” properties of these macrocycles can be modulated in order to accommodate the guest molecules of various sizes and nature for supramolecular and coordination chemistry, and to perform various functions for materials science and for biomedical applications. In this review, we wish to highlight the most prospective synthetic approaches for the direct C−H functionalization of calixarene core with various functional moieties. Depending on the nature of the functional moiety these calix[4]arenes can serve as drug carriers and nano‐containers for the recognition, encapsulation or storage of bioactive molecules and for many other applications. Current review article deals with the recent examples of C(H)‐functionalization of calix[4]arenes, as well as selected patterns of direct C(H)‐modification of some calix[6]arenes and calix[4]pyrroles.

<italic>Meso</italic> position functionalized calix[<italic>n</italic>]arenes and pillar[<italic>n</italic>]arenes and their applications

With the rapid development of macrocyclic chemistry, the functionalization of calix[ n ]arenes, pillar[ n ]arenes and other methylene linked macrocycles at their meso positions has drawn much attention. These modified macrocyclic derivatives have new functions on the basis of not changing their original properties. Not only more functional groups can be introduced, but also their applications, such as drug delivery, chemical detection, fluorescent system fabrication, are further improved due to the self-assembly behavior of host and guest. Based on the comprehensive analysis of the current research on the modification of calix[ n ]arenes and pillar[ n ]arenes at meso position, this review systematically summarizes the modification methods, the changes of the modified structures, and applications. The opportunities and challenges of its future development have been discussed.

Amidofluorene-appended lower rim 1,3-diconjugate of calix[4]arene: synthesis, characterization and highly selective sensor for Cu(2.).

Functionalization of calix[4]arene with amidofluorene moieties at the lower rim led to formation of the 1,3-diconjugate of calix[4]arene L as a novel fluorescent chemosensor for Cu2+. The receptor molecule L exhibited a pronounced selectivity towards Cu2+ over other mono and divalent ions. The formation of the complex between L and Cu2+ was evaluated by absorption, fluorescence and 1H NMR spectroscopy. The sensor L showed a remarkable color change from colorless to purple and a fluorescence quenching only upon interaction with Cu2+. The 1:1 stoichiometry of the obtained complex has been determined by Job’s plot. The association constant determined by fluorescence titration was found to be 1.8 × 106 M−1. The sensor showed a linear response toward Cu2+ in the concentration range from 1 to 10 µM with a detection limit of 9.6 × 10−8 M.

ChemInform Abstract: Novel Routes for the Synthesis of Upper Rim Amino and Methoxycarbonyl Functionalized Calix(4)arenes Carrying Other Types of Functional Groups.

The selective functionalization of calix[4]arenes 1 by iodination at the upper rim in the presence of other functionalities is described. The resulting (partly) iodinated calix[4]arenes 2 are good starting materials for the preparation of both the corresponding carboxylic ester and amino derivatives 3 and 6, respectively.

Wide-rim functionalization of calix[4]arene: The di- and tetraisocyanocalix[4]arene assembling ligands and their silver(I) polymers and oligomers

The 5,11- and 5,17-diisocyano-25,26,27,28-tetra-n-propoxycalix[4]arene bridging ligands (calix(NC)2) have been prepared in four steps with 34 and 30% global yields, respectively. Their corresponding Ag(I) complexes have been prepared from the direct reaction of the ligand with AgBF4 and are characterized from various spectroscopic and physical techniques. The MALDI-TOF spectra indicate the presence of polymers or oligomers of the type {Ag(calix(NC)2)(BF4)}n. The compounds have been characterized further from TGA, DSC, and XRD and compared with the oligomeric species 5,11,17,23-tetraisocyano-25,26,27,28-tetra-n-propoxycalix[4]arene silver(I) (as a BF4– salt).Key words: silver, calix[4]arene, polymer, isocyanide, photosensitive, thermal gravimetric analysis.

A New Tubular Arrangement of a Dimethylsilyl Bridged Calix[4]resorcinarene

The functionalization of calix[4]resorcinarene 1 (R 1=H, R 2=Me) with dichlorodimethylsilane leads to the formation of the dimethylsilyl-bridged cavitand 2 which, during the work up of the reaction product, encapsulates a molecule of water 2·H2O crystallizes in the C2/c system (a = 23.892 Å, b = 8.493 Å, c = 43.035 Å, β = 100.05°, reflections: 5385, 2376 (F>4.0 [sgrave](F)), R=9.17%, calculated density=1.213 Mg/m3) with eight molecules per unit cell. The main feature of the crystal packing is the alternating pairs of up-down disposed cavitands along the c direction and well developed columns in the b direction. The molecules of water are completely encapsulated, but there are some close contacts with the methylene bridge from the upper molecule. Molecular orbital calculations show that the lowest energy conformer of cavitand 2 is that with all four silicon atoms oriented inward and the energies of the other conformers are so high that they cannot be accessed at normal temperature. Ab initio calculated electrostatic potentials correlate well with the relative positions of the cavitands in the crystal structure.

Synthesis and functionalization of calix[4]arene-based carceplexes

New calix[4]arene-based carceplexes are obtained via solvent or doped inclusion; chemical modification of calix[4]arene-based carcerands can be used to modify the rotational behaviour of the incarcerated guest.

New artificial receptors from selectively functionalized calix[4]arenes

Abstract The development of new synthetic methods for the monoalkylation of calix[4]arenes at the lower rim allows the synthesis of a new class of trihydroxamate siderophores. Three chelating hydroxamic acid units are introduced through a sequence of reactions which blocks the macrocycle in the cone conformation. The new ligands obtained form neutral 1:1 complexes (FeL) with iron (III), which are stable in EtOH/H2O 9:1 at pH 2–7. Calix[4]arene bis-crown ethers are prepared by exploiting the selective 1,2-(proximal) functionalization of calix[4]arenes at the lower rim. These ligands are, however, less effective in complexing alkali metal cations compared with the 1,3-calix[4]arene crown-ethers which, in their partial cone structure, offer a better shielding for the complexed cations. Rigid upper rim-bridged calix[4]arenes potentially useful for the inclusion of neutral molecules are prepared by exploiting the selective 1,3-diformylation of calix[4]arene at the upper rim. Finally a new chloromethylation met...

Functionalization of calix[4]arenes by alkylation with 2-(chloromethyl)pyridine hydrochloride

The syntheses, structures, and conformations of nine of the 13 possible [(2-pyridylmethyl)oxyl]calix[4]arene conformers obtainable by direct substitution on calix[4]arenes 1a,b are described. The conformer distribution in the exhaustive 0-alkylation of 1a,b with 2-(chloromethyl)pyridine hydrochloride (PicCl.HCl) in N,N-dimethylformamide (DMF) is strongly affected by the base applied: NaH induces only cone conformers, while K 2 CO 3 or Cs 2 CO 3 lead preferentially to partial cone and/or 1,3-alternate conformers, depending on the para substituent of the starting calix[4]arene