Qi-Yu Zheng

Halide Recognition by Tetraoxacalix[2]arene[2]triazine Receptors: Concurrent Noncovalent Halide–π and Lone-pair–π Interactions in Host–Halide–Water Ternary Complexes†

Anion recognition has attracted much attention because of its importance in biological and environmental sciences. A large number of synthetic host molecules have been synthesized for the purpose of anion complexation. Noticeably, almost all synthetic anion receptors were designed to exploit hydrogen bonding, electrostatic interactions, hydrophobic effects, and coordination to metal ions. In recent years, however, there has been a growing interest in anion–p interactions, the interaction between an anion and an electron-deficient p-arene species. A number of theoretical studies, for example, have reported the noncovalent interactions of anions with aromatic compounds such as perfluoro-, nitro-, and cyano-substituted benzene, pyridine, pyrazine, and triazine derivatives. Experimental evidence to support the purely noncovalent anion–p interaction with charge-neutral arenes, however, is very rare. A recent study indicated indeed that the noncovalent anion–p interaction contributed less significantly than hydrogen bonding to the formation of the complex chloride–p-C6FnH6 n (n= 0– 5). Heteroatom-bridged heteroaromatic calixarenes are an emerging type of novel macrocyclic molecules. Because of their electronic nature, some heteroatoms, such as nitrogen, can adopt different configurations to form varying degrees of conjugation with adjacent heteroaromatic rings, resulting in macrocyclic heteroatom-linked heteroaromatic calixarenes with conformations and sizes different to those of conventional calixarenes. They have recently been utilized as versatile host molecules in supramolecular chemistry. As a typical example of heteroatom-bridged heteroaromatic calixarenes, tetraoxacalix[2]arene[2]triazine 1 (Scheme 1) has been reported to adopt a pre-organized 1,3-alternate conformation, yielding a cleft formed by two p-electron deficient triazine rings. We envisioned that this pelectron-deficient cavity would act as a receptor to interact with anions through p–anion interactions. Herein, we report halide recognition by tetraoxacalix[2]arene[2]triazine host molecules, and considerable substituent effects of the triazine on the halide–p interaction. Most astonishingly, X-ray crystallography revealed the concurrent formation of noncovalent p–halide and p–lone-pair electron interactions between water, chloride, or bromide, and the dichlorosubstituted tetraoxacalix[2]arene[2]triazine host. By means of spectrophotometric measurements, we examined the interaction of halides with dichloro-substituted tetraoxacalix[2]arene[2]triazine 1, a macrocycle readily accessible in large scale and good yield from the coupling of resorcinol and cyanuric acid chloride, under very mild conditions. As illustrated in Figure 1 (top), a new absorption band formed at 302 nm in the UV/Vis spectrum of 1 upon titration with tetrabutylammonium fluoride. Interaction of 1 with tetrabutylammonium fluoride also led to quenching of the host molecule emission signal at 304 nm with the concomitant emergence of a new fluorescence emission at 452 nm (Figure 1 (bottom)). These spectral changes were not caused by the cation or by moisture in the sample, as the control experiments using tetrabutylammonium perchlorate or water as a titrant showed no influence on either the absorption or the emission spectrum of 1. We then investigated the spectrophotometric titration of 1 with tetrabutylammonium chloride and tetrabutylammonium bromide. Under identical conditions, the outcomes of titration with chloride and bromide were very different to that for the titration with fluoride. For example, addition of chloride or bromide did not affect the UV/Vis spectrum of the host Scheme 1. Dichloro-substituted tetraoxacalix[2]arene[2]triazine 1 and its transformations into 2 and 3. a) H2, Pd/C, NaOAc/HOAc, 50 8C, 12 h, 82%. b) Me2NH·HCl, K2CO3, THF, 70 8C, 9 h, 65%.

Manganese‐Catalyzed Dehydrogenative [4+2] Annulation of NH Imines and Alkynes by CH/NH Activation

Described herein is a manganese-catalyzed dehydrogenative [4+2] annulation of NH imines and alkynes, a reaction providing highly atom-economical access to diverse isoquinolines. This transformation represents the first example of manganese-catalyzed CH activation of imines; the stoichiometric variant of the cyclomanganation was reported in 1971. The redox neutral reaction produces H2 as the major byproduct and eliminates the need for any oxidants, external ligands, or additives, thus standing out from known isoquinoline synthesis by transition-metal-catalyzed CH activation. Mechanistic studies revealed the five-membered manganacycle and manganese hydride species as key reaction intermediates in the catalytic cycle.

A new fluorescent chemosensor for Fe3+ and Cu2+ based on calix[4]arene

A novel fluorescent compound derived from calixarene which possesses two 3-alkoxy-2-naphthoic acid moieties has been synthesized in moderate yield. In H2O/CH3OH (1:1), its fluorescent intensity was quenched sharply in the presence of Cu2+ or Fe3+, and the degree of quenching was related to the pH of the solution. Other metal ions, such as Co2+, Ni2+, Zn2+, Mn2+, Mg2+ and Ba2+ did not affect its fluorescent spectra. This research may provide a new fluorescent probe for Cu2+ and Fe3+.

Visible light-induced 3-sulfenylation of N-methylindoles with arylsulfonyl chlorides

The synthesis of 1-methyl-3-(arylthio)-1H-indoles has been achieved by the photoredox reaction of N-methylindoles with readily available arylsulfonyl chlorides in moderate yields.

Synthesis of large macrocyclic azacalix[n]pyridines (n = 6 - 9) and their complexation with fullerenes C(60) and C(70).

Large methylazacalix[n]pyridines (n = 6-9) were synthesized effectively from the Pd-catalyzed macrocyclic fragment coupling reactions between alpha,omega-dibrominated and alpha,omega-diaminated linear oligomers. As macrocyclic host molecules, they formed a 1:1 complex with fullerenes C(60) and C(70) with association constants ranging from 3 x 10(4) to 1 x 10(5) M(-1).

A new fluorescent chemosensor for transition metal cations and on/off molecular switch controlled by pH

Abstract A new fluorescent chemosensor with imidazole as ionophore was synthesized by the selective derivation of calixarene, which can effectively recognize Cu 2+ and Zn 2+ leading to different fluoroscopic behaviors in CH 3 OH–H 2 O. This system could be considered as a molecular switch. By modulating the pH of the solution, on–off–on fluorescent switching is carried out upon combinatory addition of acid, base and Cu 2+ .

Reversal of nucleophilicity of enamides in water: control of cyclization pathways by reaction media for the orthogonal synthesis of dihydropyridinone and pyrrolidinone Clausena alkaloids.

A highly efficient, metal-free, and divergent method for the synthesis of 3,4-dihydropyridin-2-one and pyrrolidin-2-one Clausena alkaloids and their analogs is reported. While the oxirane-containing enamides underwent the TFA-mediated 6-endo-enamide-epoxide cyclization reaction in Bu(t)OH to produce homoclausenamides, an unprecedented nucleophilic reaction occurred at the alpha-carbon of enamides in water to yield 5-endo-enamide-epoxide cyclization products in excellent yields. The reversal of nucleophilicity of enamides in intramolecular cyclization is discussed in terms of steric and electronic effects of the oxirane-containing enamides.

An Organocatalytic, δ‐Regioselective, and Highly Enantioselective Nucleophilic Substitution of Cyclic Morita–Baylis–Hillman Alcohols with Indoles

The direct substitution of alcohols with carbon and heteroatom nucleophiles without prederivatization is a significant chemical transformation owing to its green, economical, and environmentally benign properties where water is generated as the only side product. Recently, researchers in the area of organocatalysis has made great progress in organic synthesis. While multiform organocatalysts can be successfully used in various addition reactions with carbonyl, imine, activated alkene, and others compounds, the enantioselective nucleophilic substitution of alcohols catalyzed by organocatalysts is rare. Because positively charged intermediates would be involved, it is a great challenge to exert enantioselective control in the nucleophilic substitution of alcohols. 5] Recently, the Morita–Baylis–Hillman (MBH) adducts have attracted much attention in organic syntheses as valuable synthons and starting materials owing to their easy availability and versatile functionalities bearing allylic hydroxy and Michael acceptor units. The reaction of MBH alcohols with a nucleophile could proceed through either conjugate addition, or allylic substitution through dehydration to afford aor g-substituted products (Scheme 1) Enantioselective reactions of MBH adducts with various O, N, and C nucleophiles have been achieved to provide the nucleophilic substitution products. These reactions have been carried out through transition-metal catalysis with palladium, and organocatalysis with chiral phosphine and tertiary amine compounds. However, none of these asymmetric transformations directly uses MBH alcohols. Furthermore, the hydroxy group is not a good leaving group because free OH may participate in the asymmetric induction. Iminium activation is one of the most important methods in organocatalysis. Inspired by the efficient enantioselective control of Michael acceptors by iminium activation, we proposed that iminium activation might be used in the nucleophilic substitution of MBH adducts derived from enones. A suitable catalyst should also contain an acid moiety to activate the hydroxy group of MBH alcohols. Herein, we report the enantioselective reaction of cyclopent2-enone-derived MBH alcohols with indoles catalyzed by chiral 9-amino-9-deoxyepiquinine in combination with an acid. This approach yields an unexpected d-regioselective product with good to excellent enantioselectivity. Initially, the reaction of MBH alcohol 1 a with indole 2a was carried out in dichloromethane (Scheme 2). It was reported that catalysts based on chiral primary amines could

Synthesis of new chromogenic calix[4]crowns and molecular recognition of alkylamines

Abstract A new type of calix[4]crown containing ester group 3 has been synthesized and selectively nitrated to give 4 or ipso-nitrated to give 6. By nitration a novel calixcrown 5 containing a quinone segment was obtained. These nitrated calixcrowns have been used as chromogenic hosts for complexing alkylamines and the factors affecting recognition are discussed.

A novel 1D independent metal–organic nanotube based on cyclotriveratrylene ligand

A novel nanotubular metal–organic framework [Cu3L2(EtOH)(Py)2(H2O)2]·9DEF·8H2O (CTV-Cu) was prepared by assembly of the rigid, trigonal pyramidal ligand tri-(4-carboxy-phenyl)-trimethoxycyclobenzylene (H33L) and Cu(NO3)2·3H2O viasolvothermal reaction. The Cu(II) ions in the crystal serve as square and linear molecular building blocks, thus forming a framework with ternary topology. One single open-ended nanotube contains two identical orthogonally interpenetrated two-nodal nets. This framework exhibits permanent microporosity and relatively high surface area.