Synthesis of Covalently-Linked exo-Calix[4]arenes

Abstract

Calix[4]arenes, or endo-calix [4]arenes, 1 have been extensively studied for the past several decades, 1 but exocalix [4]arenes 2 have only recently attracted much attention. [2][3][4] With respect to structure, an exo-calixarene, having the OH groups on the "upper rim" of the bowlshaped molecules, is actually more similar to a resorcinarene (3a) 5 or cavitand (3b) 5 than to the corresponding endo-isomer. We report here the preparation of a tetra-(propyl-substituted) exo-calix [4]arene and a study of the conformational properties of it and some covalentlylinked derivatives. Experimental SectionGeneral. All reagents used were analytical grade. DMF, CH2Cl2, and CHCl3 were distilled from CaH2. 1 H NMR spectra were recorded on a Varian VXR 300 MHz or on a Varian XL400 spectrometer. Mass spectra and high-resolution mass spectra were obtained at the Mass Spectrometry Laboratory for Biotechnology at the North Carolina State University in Raleigh. Elemental analyses were performed by Atlantic Microlabs, Norcross, GA. 2,2-Bis[4′-(allyloxy)phenyl]propane (4b).Bisphenol A (235 g, 1.00 mol), allyl chloride (330 mL, 4.00 mol), potassium carbonate (276 g, 2.00 mol), sodium iodide (6.00 g, 0.040 mol), and absolute ethanol (1.50 L) were added to a 3 L three-necked round-bottomed flask. The mixture was allowed to reflux for 24 h under argon, cooled to ambient temperature, and filtered to remove solid material. The solvent was evaporated under reduced pressure to give a brown liquid (301 g, 98%). 1 H NMR (CDCl3): δ 7.12 (dd, 4H,

Conformation, Inversion Barrier, and Solvent-Induced Conformational Shift inExo- andEndo/Exo-Calix[4]arenes

“…These groups are involved in a circular array of hydrogen bonds in which each hydroxyl group serves both as a donor and as an acceptor. In the resorcarenes the hydroxyl groups are present in extra annular ( exo ) positions of the macrocycle, and therefore these and related compounds possessing a similar disposition of the hydroxyls may be designated by the general term “ exo -calixarenes” as opposed to the “conventional” endo -calixarenes. − Although intramolecular hydrogen bonds may be formed between adjacent OH groups, no circular array of hydrogen bonds is possible in resorcarenes. The all - cis resorcarenes and the alkanediyl derivatives of 1a (e.g., 1b ) adopt cone conformations, but they differ in the conformational preferences of the alkyl groups: the alkanediyl group of 1b prefers the equatorial position, , while a tetraaxial disposition of the alkyl substituents is exclusively found in all - cis - 2a …”

“…The preparation of exo -calixarenes possessing only four exo hydroxyl groups ( 3 ) was recently described. − , X-ray diffraction studies of 3a ·CH 3 CN and 3a ·CH 2 Cl 2 indicate that the exo -calixarene exists in a cone conformation 3,5a whereas 3c and a bis(dioxamethylene) derivative exist in the crystal in a 1,2-alternate conformation. 4c,5b In solution all the exo -calixarenes 3 were found to be flexible on the NMR time scale, even at −70 °C, and since the dynamic processes could not be frozen, the solution conformation could not be unambiguously determined 4b…”

Synthesis, Modification, and Characterization of a Family of Homologues of exo-Calix[4]arene: exo-[n.m.n.m]Metacyclophanes, n,m ≥ 3

“…An exo -metacyclophane with both sets of ortho-phenolic oxygens bridged by a methylene carbon is consistent with the spectral analysis of the bis-adduct prepared from 19a . As in the case with the cone and 1,2-alternate conformation of the bis(methylene-linked) exo -calix[4]arene reported by Sorrel, it is not possible to distinguish between the cone conformation of 20a (Figure ) and 1,2-alternate conformation of 20b by their 1 H NMR spectra due to symmetry considerations. The NMR spectra of 20 exhibits only slight broadening of its protons signals over the temperature range 323−228 K (the largest change is seen in the triplets at 2.54 and 2.72 ppm, which coalesce into two broad singlets by 312 K).…”

Synthesis of eugenol‐based monomers for sustainable epoxy thermoplastic polymers

“…Numerous studies of the allylation of BPA include the use of allyl halides, allyl carbonate, allyl acetate, or allyl alcohol as allylating agents 13. [48][49][50][51] The allylation reaction of 1 with allyl halides (X = Cl, Br) is performed in strong basic media (NaOH), much like the glycidylation reaction, 48,49 whereas utilization of allyl (hydro)oxy derivatives (X = MeO[O]CO, HO) requires Pd or Ru complex catalysis (Table 2). 50,51 Some of the byproducts of this step can be the Calkylated products formed via the Claisen rearrangement due to the reaction temperature or more conventional mono-O-allylated compounds.…”