The synthesis of triarylmethanes was evaluated in the presence of various Br & oslash;nsted and Lewis acids under the same stoichiometric conditions. An efficient silver(I)-catalyzed synthesis of triarylmethanes is reported. The reaction offers low catalyst loadings and quasi-stoichiometric conditions (1-1.2 equiv. of electrophile) to access to symmetrical and unsymmetrical TRAMs in moderate to excellent yields (35 examples). Broad substrate scope was observed, including compatibility with ester and cyano groups. After a broad screening of Br & oslash;nsted and Lewis acids, AgNTf2 was shown to catalyze the synthesis of symmetrical and unsymmetrical triarylmethanes (TRAMs) in moderate to excellent yields (30-99 % yield, 35 examples) with the tolerance of ester and cyano groups. image

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The first examples of tandem oxidative dearomatizations of 9,10-diphenylanthracene atropisomers with ortho,ortho'- formyl substituents are presented. In the presence of KMnO4, their stereoselective tandem double oxidation and spirocyclization mainly afford the syn or anti dearomatized 9,10-diphthalide anthracenes. Using Pinnick's reagent and depending on the conditions, the oxidation can mainly lead to the corresponding syn or anti diacids in good yields or to three oxidation products. An unprecedented further oxidative ring expansion toward dibenzo[b,e]oxepines is also reported.

In switchable molecular recognition, 1 O2 stimulus responsive receptors offer a unique structural change that is rarely exploited. The employed [4+2] reaction between 1 O2 and anthracene derivatives is quantitative, reversible and easily implemented. To evaluate the full potential of this new stimulus, a non-macrocyclic anthracene-based host was designed for the modular binding of cations. The structural investigation showed that 1 O2 controlled the atropisomerism in an on/off fashion within the pair of hosts. The binding studies revealed higher association constants for the endoperoxide receptor compared to the parent anthracene, due to a more favoured preorganization of the recognition site. The fatigue of the 1 O2 switchable hosts and their complexes was monitored over five cycles of cycloaddition/cycloreversion.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Chiral trifluoromethyl alcohol groups were introduced at the hindered ortho positions of 9,10-diphenylanthracenes to investigate their effects on the physical properties and reactivity towards oxidative dearomatization. In such compact structures, the position in different quadrants and the preferred orientation of the -CH(OH)CF3 groups were determined by the relative and absolute configurations of each stereoisomer, respectively. As a consequence, the stereochemistry governs the organization of the H-bonded molecules in single crystals (homochiral dimers vs ribbon), whereas in chlorinated solvents, they all behave as discrete compounds. Concerning their reactivity, the stereospecific dearomative oxidation of these molecules leads to 9,10-bis-spiro-isobenzofuran-anthracenes, when using organic single-electron transfer oxidants. The chiroptical properties of the alcohols and the corresponding dearomatized products were compared and showed an important modulation of the intensity.

We describe the first thiourea-catalyzed C-F bond activation. The use of a thiourea catalyst and Ti(OiPr)4 as a fluoride scavenger allows the amination of benzylic fluorides to proceed in moderate to excellent yields. Preliminary results with S- and O-based nucleophiles are also presented. DFT calculations reveal the importance of hydrogen bonds between the catalyst and the fluorine atom of the substrate to lower the activation energy during the transition state.

Gold has been considered an inert metal in catalysis until the seminal work of Teles and Hashmi unveiled the potential of homogeneous gold catalysis. Acting as a Lewis acid, numerous gold complexes are now considered as robust and versatile catalysts that efficiently activate carbon–carbon π bonds toward nucleophilic attack. Since the last decade, an emerging field exploits the redox potential of gold through Au(i)/Au(iii) catalytic cycles, using organic oxidants or using light-related processes. The latter approach is covered by this photochemistry lecture which reports the different strategies used: the photophysical behaviour of gold complexes, cooperative gold catalysis/photoredox chemistry (named dual gold/photoredox catalysis) and light-triggered gold catalysis with mono- and dinuclear complexes (named gold photoredox catalysis). Each approach of light-assisted gold catalysis is presented with a general mechanism followed by the organic transformation scopes.

The combination of metal catalyst and inorganic silica frameworks provides a greener approach to recyclable catalysis. In this study, three phosphine-gold chloride complexes have been successfully covalently grafted onto chiral silica nanohelices. The resulting 3D ensembles showed chiroptical properties that allowed the monitoring of the supported ligands. The heterogeneous gold chloride catalysts in cooperation with silver triflate exhibited high reactivity in various reactions, especially in the spirocyclization of aryl alkynoate esters, for which a catalytic loading of 0.05 mol % could be employed. The heterogeneous catalysts could be easily recovered and recycled seven or eight times without any loss of efficiency. By adding more silver triflate, 25 cycles with full conversion were achieved owing to a complex catalytic system based on silica and metallic species.

Molecular cages 1a and 2a incorporating a 9,10-diphenylanthracene (DPA) chromophore were synthesized through a templated ring-closure metathesis approach that allows variation in cavity size through the introduction of up to three different pillars. Reversible Diels-Alder reaction between the DPA moiety and photogenerated singlet oxygen smoothly converted 1a and 2a to the corresponding endoperoxide cages 1b and 2b, which are converted back to 1a and 2a upon heating. Endoperoxide formation constitutes a reversible covalent signal that combines structural changes in the interior of the cage with introduction of two additional coordination sites. This results in a large modulation of the binding ability of the receptors attributed to a change in the location of the preferred binding site owing to the added coordination by the endoperoxide oxygen lone pairs. Cages 1a and 2a form complexes with sodium and cesium whose association constants are modified by 4-20 fold for Na+ and 200-450 fold for Cs+ upon conversion to 1b and 2b. DFT calculations show that in the anthracene form, cages 1a and 2a can bind 2 metal cations in their periphery so that each cation is coordinated by 4 oxygens and one amine nitrogen, whereas the endoperoxide cages 1b and 2b bind cations centrally in a geometry that favors coordination to the endoperoxide oxygens.

The bis-ortho-thioether 9,10-bis[(o-methylthio)phenyl]anthracene was synthesized as a syn-atropisomer, as revealed by X-ray diffraction. This alkylaryl thioether ligand (L) formed different macrocyclic complexes by coordination with silver(I) salts depending on the nature of the anion: M2L2 for AgOTf and AgOTFA, M6L4 for AgNO3. A discrete M2L complex was obtained in the presence of bulky PPh3AgOTf. These silver(I) complexes adopted similar structures in solution and in the solid state. As each sulfur atom in the ligand is prochiral, macrocycles L2M2 were obtained as mixtures of diastereoisomers, depending on the configurations of the sulfur atoms coordinated to silver cations. The X-ray structures of the two L2·(AgOTf)2 stereoisomers highlighted their different geometry. The catalytic activity of all silver(I) complexes was effective under homogeneous conditions in two tandem addition/cycloisomerization of alkynes using 0.5–1 mol % of catalytic loading.

Since the late seventies, the search for new molecular receptors has been constant in perfecting the affinity and selectivity of recognition in different media. At present, a renewed interest in (host:guest) chemistry focuses on the molecular detection of specific targets such as biological, pollutant, toxic or explosive species. This review of triphenylene-based receptors outlines their recent contribution to molecular recognition. Two main structural approaches were investigated to transform a simple triphenylene moiety into a host for neutral aromatic compounds or cations, by tailoring multivalent molecules provided with or without a flatten cavity. The properties of different receptors are presented along with the latest synthetic methods to prepare high-value triphenylenes and the perspectives in the field of sensing. In addition, the role of functionalized triphenylenes in extended (host:guest) systems is illustrated by the main examples of discotic liquid crystals and porous coordination polymers involving this polyaromatic compound. (C) 2019 Elsevier Ltd. All rights reserved.

This review focuses on the recognition and the detection of the acetylcholine neurotransmitter by artificial receptors, in water and buffered water. The design of water-soluble hosts and the advanced devices based on this (host: ACh) chemistry are also presented. [GRAPHICS] .

Synthetic hydrogen-bonding receptors are described, which incorporate a central electroactive ferrocene moiety grafted with two adjacent bis(amido)pyridine motifs and an aliphatic tether (14 and 18 methylene units for 1 and 2, respectively) completing the macrocycle. The crystallographic structure, barbiturate guest-binding studies and electrochemical data are provided for the more strongly-binding macrocycle 2. [GRAPHICS] .

Complexes formed between AuCl3 and thioether ligands underwent a photoinduced reductive elimination under homogeneous conditions in dichloromethane and toluene solutions to afford the corresponding Au-I complexes. All the gold(III) complexes were rapidly reduced to the gold(I) chloride complexes under 365 nm irradiation or ambient light while being thermally stable below 55 degrees C. The mechanism of photoreduction through Cl-2 elimination is discussed based on a kinetic study and the chemical trapping of chlorine species: Cl-2, radical Cl-., and possibly Cl+. The catalytic activities of the gold(III) chloride complexes and the corresponding gold(I) complexes obtained by in situ reduction were evaluated in the cyclization of N-propargylic amides to oxazoles. The merits of such photoreducible complexes in homogeneous gold catalysis are illustrated by a cascade reaction catalyzed by thioether gold complexes that affords a 4H-quinolizin-4-one in high yields.

The use of supramolecular interactions to control the reactivity of excited states is discussed with emphasis on covalent bond formation and catalysis. The latter is shown to apply both to the synthesis of organic compounds as well as to the preparation of inorganic materials.

Three crystallographic structures highlight the acid-base half-equivalence point of hydrogen-bond donor (thio)amido-benzimidazoles induced by fluoride or benzoate salts with concomitant hydrogen-bonding and deprotonation as a merged synergic process.

Hydrogen-bonding catalysts based on (thio)amidoindole moieties were evaluated in the presence of anions as potent anion receptors and/or acidic partners involved in acid–base reactions. In particular, we focused on their behavior at the acid–base half-equivalence point in the presence of basic anions such as fluoride and benzoate salts. Among three isolated X-ray structures, an amidoindole in the presence of fluoride and hexafluorophosphate salts formed, at the acid–base half-equivalence point, an unprecedented sandwich complex between two receptors and a PF6– anion.

The synthesis and application of protonated phosphazeniums as hydrogen-bond donor groups was demonstrated in the solid state and in solution. In particular, their catalytic activity was shown in the activation of the carbonyl group within cyclic esters, using a benchmark reaction, that is, in the ring-opening polymerization of lactide and valerolactone, in the presence of a basic co-catalyst. The reactions proceed differently depending on monomers and/or phosphazenium salts. The impact of catalysts and reactants steric hindrance upon the outcome of the reaction is then highlighted and discussed.

The hydrogen-bonding activation of C=O bonds by azaphosphatranes was explored in a model reaction, i. e., the ring-opening polymerization of lactide. The polymerization process was controlled, and allowed the preparation of polylactides with narrow dispersity under mild conditions (20 degrees C, 24 h, 10 mol-% catalyst loading). Interestingly, the steric hindrance of azaphosphatranes, as globular rigid structures, prevents any undesired interaction with the tertiary amine cocatalysts, as shown by X-ray analysis and semi-empirical calculations. In contrast to their organocatalytic activity in the CO2/epoxide reaction, all of the phosphonium derivatives tested were found to be efficient catalysts in this ROP benchmark reaction.