Structurally-unusual calix[4]arene derivatives generated by intra- and intermolecular McMurry reactions

Upper rim-bridged calixarenes

Calix[n]arenes represent a very attractive family of macrocyclic compounds with many potential supramolecular applications. Due to their well-established chemistry and many different synthetic strategies, enabling practically any derivatization of the basic skeleton, calixarenes are among the very popular building blocks used for the design and construction of various receptors, sensors and other sophisticated supramolecular systems. Regio- and/or stereo-selective derivatization of calixarenes currently represents a very extensive set of reactions, the overview of which would fill many thick books. Therefore, this review deals with only a small part of the above-mentioned reactions, specifically describes possible ways of bridging the upper rim of calixarenes, often leading to interesting rigidified structures, and also briefly mentions the potential use of these compounds.

Weak intermolecular interaction directed assembly of calix[4]arene derivatives

Dimer and tetramer structures of cone-di-formyl-calix[4]arene 16 were formed through weak intermolecular interactions.

Assembly of calix[4]arene carboxylic acid derivatives by hydrogen bonding

Crystallisation of seven calix[4]arene derivatives leads to the formation of a “head-to-head” or “head-to-tail” dimer motif through hydrogen bonding.

Upper-Rim Monofunctionalisation in the Synthesis of Triazole- and Disulfide-Linked Multicalix[4]- and -[6]arenes

Covalently linked multiple calixarenes are valued in supramolecular chemistry. This work reports an easy and versatile synthetic route to covalently linked double and triple calix[4]arene and calix[6]arenes by a novel DMF-controlled selective alkylation of a convenient and readily available upper-rim dimethylaminomethyl-substituted tetrahydroxy and hexahydroxy calix[4]arene and -[6]arenes. Synthetic routes to upper-rim functionalised redox active disulfide-linked double-, tetra- and peptidohybrid-calixarenes employing either redox chemistry (CH₂ SH) or thiolates (CH₂ S^- ) are also opened up from the same key starting material.

Stilbene-Bridged tert-Butylcalix[4]arene as Photoswitchable Molecular Receptors

Using a designed control of conformations of tert-butylcalix[4]arene between cone and pinched cone, a highly selective receptor for small electron-deficient molecules with photoswitching binding ability was attained. [reaction: see text]

Synthesis and Conformational Study of the First Triply Bridged Calix[6]azatubes

[reaction: see text] The first C(3)(v)- and D(3)(h)-symmetrical triply bridged calix[6]azatubes were prepared in good yields from the known 1,3,5-tris-methylated calix[6]arene through an efficient [1 + 1] macrocyclization reaction. A remarkably regioselective hexa ipso-nitration reaction led to a calix[6]azatube substituted at the wide rim in alternate position by tBu and nitro groups. A (1)H NMR study showed that, whereas the parent bis-calix[6]arenes self-include their methoxy groups, thereby closing their inner tube, the nitro-substituted calix[6]azatube undergoes a conformational change with the expulsion of the methoxy groups, hence presenting a three-dimensional structure open for host-guest applications.

Synthesis, Conformation, and Complexation of Novel 25,26,27,28- Tetrahydroxy-5,11:17,23-bis[[2,2‘-thioxydi(o-phenylene)dithioxy]- diphenylthio]calix[4]arene

Calix[4]arenes 1a,b having an electron-donating group, i.e., OH and OMe, at the lower rim reacted with thianthrene cation radical perchlorate in CH3CN at room temperature to give the corresponding thianthrenium perchlorates 3a,b in excellent yields. Treatment of 3a,b comprising a mixture of conformational isomers with NaSH.xH2O in DMF at reflux afforded the sulfur-containing cyclized compounds 4a,b, respectively. Compound 4a having a cone conformation consisted of two conformational isomers in a ratio of 0.077:1. Temperature-dependent 1H NMR study in DMF showed that conformational isomerization between the two isomers occurred with energy barriers of 14.97 and 14.10 kcal/mol at 100 and 110 degrees C, respectively. The Jobs plot of 4a against Ag+ picrate indicated that compound 4a strongly produced a 1:2 complex with Ag+ ions. Molecular mechanics calculations indicated that the conformation of the energy-minimized 4a-2Ag+ picrate complex had two crushed pyramidal geometries made up of Ag+ ion and four sulfur atoms, i.e., S1, S2, S4, S5 and S6, S7, S9, S10, respectively.

Selective synthesis and isolation of all possible conformational isomers of proximally para-disubstituted calix[4]arene

All six possible conformational isomers of the proximally p-dibrominated calix[4]arene tetraalkyl ether, 1a-f*, were selectively synthesized by appropriate control of stereochemistry during di-O-alkylation reactions of 5,11-dibromocalix[4]arene syn-dialkyl ethers, namely, 5,11-dibromo-27,28-dihydroxy-25,26-dipropoxy-, 5,11-dibromo-25,26-dihydroxy-27,28-dipropoxy-, 5,11-dibromo-25,28-dihydroxy-26,27-propoxy-, and 5,11-dibromo-26,28-dihydroxy-25,27-dipropoxycalix[4]arenes. Their conformations were confirmed by (1)H and (13)C NMR spectroscopy and are cone for 1a (u(Br)(Pr), u(Br)(Pr), u(H)(Pr),u(H)(Pr)), partial cone for 1b (u(Br)(Pr), d(Br)(Pr), u(H)(Pr),u(H)(Pr)) and 1d (u(Br)(Pr), u(Br)(Pr), u(H)(Pr),d(H)(Pr)), 1,2-alternate for 1c (u(Br)(Pr), u(Br)(Pr), d(H)(Pr),d(H)(Pr)) and 1e (u(Br)(Pr), d(Br)(Pr), d(H)(Pr),u(H)(Pr)), and 1,3-alternate for 1f (u(Br)(Pr), d(Br)(Pr), u(H)(Pr),d(H)(Pr)). Although both 1c and 1e are in the 1,2-alternate conformation, the conformation of 1e was found to be strongly distorted and distinct from that of 1c.