Search

A series of pyrroloquinolone photosensitizers bearing different halogen substituents (Cl, Br, I) on the heterocyclic framework was studied. These structures were readily prepared through a multi-step synthetic sequence involving an oxidative protocol as an important step to access the quinolone framework. Spectroscopic characterizations and computational investigations were carried out to study the dyes before and after the oxidative step. Interestingly, the fluorescence emission was significantly reduced upon oxidation. In spite of a low photostability under UV light, the pyrroloquinolone photosensitizers proved effective to produce singlet oxygen. Higher singlet oxygen quantum yields were obtained with photosensitizers bearing halogen atoms with a higher atomic number.

Photochemistry is a tremendous research field offering many synthetic possibilities to the chemists. Breakthroughs in this area have been notably driven by the implementation of new classes of photocatalysts. Within this context, Bodipy (Borondipyrromethene) dyes possess attractive chemical and physical features such as their modularity, strong absorption under visible light irradiation, good thermal and photochemical stabilities and high fluorescence quantum yields. As such, this class of compounds has found widespread applications in functionalized materials, biology, medicine or organic chemistry. From an organic-synthetic point of view, excited states of Bodipy dyes have been harnessed in electron and energy transfer reactions. This minireview collates the relevant literature on the applications of these catalysts in synthetic photochemistry and provides some perspectives of this research area.

In the past decade, the field of visible-light-mediated photocatalysis has been particularly thriving by offering innovative synthetic tools for the construction of functionalized architectures from simple and readily available substrates. One strategy that has been of interest is energy transfer catalysis, which is a powerful way of activating a substrate or an intermediate by using the combination of light and a relevant photosensitizer. This review deals with recent advances in energy transfer catalysis applied to phenols, which are ubiquitous in chemistry both as starting materials and as high-added-value products. Processes involving energy transfer from the excited photosensitizer to ground state oxygen and to phenol-containing substrates will be described.1 Introduction2 Intermolecular Processes2.1 Reactions with Singlet Oxygen2.2 [2+2] Cycloadditions3 Intramolecular Transformations4 Conclusions and Outlook

The discovery of a multiple-bond-forming process merging the singlet oxygen-mediated dearomatization of 3,4-disubstitued phenols and diastereo- and regioselective epoxidation is described. This one-pot strategy using a transition metal-free multicatalytic system comprised of rose bengal and cesium carbonate allowed the efficient formation of functionalized epoxyquinol products under mild conditions. Mechanistic investigations have been performed to shed the light on the key species involved in this transformation.

International audience; The quest for molecules able to trap, store and release singlet oxygen is of utmost interest due to their applicability in various domains such as materials science and photomedicine. The aim of this study was to prepare and to study a new family of singlet oxygen donors based on the 1,2-dihydropyridine motif. The experiments demonstrated the influence of substituents and solvents on the photooxygenation rate constants. The process can be operated reversibly by thermolysis of the in-situ formed endoperoxide leading to a release of singlet oxygen and formation of the parent 1,2 dihydropyridine compound. A bifunctional structure based on a phenalenone photosensitizer covalently connected to a 1,2 dihydropyridine module was synthesized via a multi-step sequence. Upon irradiation with blue light, singlet oxygen was produced leading to the formation of the endoperoxide intermediate. In the dark cycle, the endoperoxide underwent cycloreversion reaction affording the parent 1,2-dihydropyridine unit paving the way to a continuous production of singlet oxygen during the light/dark cycles.

French National Research Agency (ANR) ANR-18-CE07-0013-01 French National Research Agency (ANR) Universite de Nantes Centre National de la Recherche Scientifique (CNRS) FONDEQUIP EQM160099

Substrate selectivity by means of synthetic catalysts remains a challenging topic in chemistry. Here, a catalytic system combining an iodo-BODIPY photosensitizer and quinine was evaluated in the competitive photooxygenation of non-hydrogen and hydrogen-bond-donor substrates. The ability of quinine to activate hydrogen-bond-donor substrates towards photooxygenation was reported and the results were benchmarked with photooxygenation experiments in the absence of quinine.

A multicatalytic photooxygenation of substituted phenols in the presence of rose bengal and cesium carbonate under green LED light is reported. This transformation enabled the introduction of both atoms of singlet oxygen and led to the one-pot synthesis of epoxyquinols in a stereoselective way.

BIOSCREEN is a well-known simple tool for evaluating the transport of dissolved contaminants in groundwater, ideal for rapid screening and teaching. This work extends the BIOSCREEN model for the calculation of stable isotope ratios in contaminants. A three-dimensional exact solution of the reactive transport from a patch source, accounting for fractionation by first-order decay and/or sorption, is used. The results match those from a previously published isotope model but are much simpler to obtain. Two different isotopes may be computed, and dual isotope plots can be viewed. The dual isotope assessment is a rapidly emerging new approach for identifying process mechanisms in aquifers. Furthermore, deviations of isotope ratios at specific reactive positions with respect to “bulk” ratios in the whole compound can be simulated. This model is named BIOSCREEN-AT-ISO and will be downloadable from the journal homepage.

In this contribution, we describe two simple and efficient routes for the preparation of keto-aldehyde 1, a key intermediate for the synthesis of

International audience; In this contribution, we describe two simple and efficient routes for the preparation of keto-aldehyde 1, a key intermediate for the synthesis of (13)C3-androstanes and (13)C3-estranes. In the first route, the targeted aldehyde 1 was obtained in 40% overall yield from 1,4-androstadien-3,17-dione (3 mmol scale) via a two-step sequence involving a one-pot, abnormal ozonolysis/sulfur oxidation/retro-Michael/ozonolysis process. Alternatively, a second route from 4-androsten-3,17-dione, using a six-step sequence, was optimized to produce 40 mmol batches of the key intermediate 1 in 42% overall yield. At the final stage, the A-ring was reconstructed through a Wittig reaction with the 1-triphenylphosphoranylidene-(13)C3-2-propanone 2, followed by an intramolecular condensation assisted by thioacetic acid via a Michael addition/retro-Michael reaction sequence to provide 2,3,4-(13)C3-1,4-androstadien-3,17-dione.

Within the food and pharmaceutical industries, there is an increasing legislative requirement for the accurate labeling of the productʼs origin. A key feature of this is to indicate whether the product is of natural or synthetic origin. With reference to this context, we have investigated three alkaloids commonly exploited for human use: nicotine, atropine, and caffeine. We have measured by 13C nuclear magnetic resonance spectrometry the position-specific distribution of 13C at natural abundance within several samples of each of these target molecules. This technique is well suited to distinguishing between origins, as the distribution of the 13C isotope reflects the primary source of the carbon atoms and the process by which the molecule was (bio)synthesized. Our findings indicate that labeling can be misleading, especially in relation to a supplied compound being labeled as “synthetic” even though its 13C profile indicates a natural origin.

Six-membered ring fused furans containing a tetrasubstituted tertiary carbon were prepared in an unprecedented one-pot BODIPY-catalyzed domino photooxygenation/reduction process. A series of functionalized furans was synthesized from readily available 2-alkenylphenols and mechanistic studies were performed to account for the domino photosensitized oxygenation.

International audience; Position-specific isotope effects (PSIEs) have been measured by isotope ratio monitoring C-13 nuclear magnetic resonance spectrometry during the evaporation of 10 liquids of different polarities under 4 evaporation modes (passive evaporation, air-vented evaporation, low pressure evaporation, distillation). The observed effects are used to assess the validity of the Craig-Gordon isotope model for organic liquids. For seven liquids the overall isotope effect (IE) includes a vapor-liquid contribution that is strongly position specific in polar compounds but less so in apolar compounds and a diffusive IE that is not position-specific, except in the alcohols, ethanol and propan-1-ol. The diffusive IE is diminished under forced evaporation. The position-specific isotope pattern created by liquid-vapor IEs is manifest in five liquids, which have an air-side limitation for volatilization. For the alcohols, undefined processes in the liquid phase create additional PSIEs. Three other liquids with limitations on the liquid side have a lower, highly position-specific, bulk diffusive IE. It is concluded that evaporation of organic pollutants creates unique position-specific isotope patterns that may be used to assess the progress of remediation or natural attenuation of pollution and that the Craig-Gordon isotope model is valid for the volatilization of nonpolar organic liquids with air-side limitation of the volatilization rate.

International audience; Isotopic fractionation of pollutants in terrestrial or aqueous environments is a well-recognized means by which to track different processes during remediation. As a complement to the common practice of measuring the change in isotope ratio for the whole molecule using isotope ratio monitoring by mass spectrometry (irm-MS), position-specific isotope analysis (PSIA) can provide further information that can be exploited to investigate source and remediation of soil and water pollutants. Position-specific fractionation originates from either degradative or partitioning processes. We show that isotope ratio monitoring by C-13 NMR (irm-C-13 NMR) spectrometry can be effectively applied to methyl tert-butylether, toluene, ethanol and trichloroethene to obtain this position-specific data for partitioning. It is found that each compound exhibits characteristic position-specific isotope fractionation patterns, and that these are modulated by the type of evaporative process occurring. Such data should help refine models of how remediation is taking place, hence back-tracking to identify pollutant sources. (C) 2015 Elsevier Ltd. All rights reserved.

International audience; We aim at predicting the effect of structure and isotopic substitutions on the equilibrium vapour pressure isotope effect of various organic compounds (alcohols, acids, alkanes, alkenes and aromatics) at intermediate temperatures. We attempt to explore quantitative structure property relationships by using artificial neural networks (ANN); the multi-layer perceptron (MLP) and compare the performances of it with multi-linear regression (MLR). These approaches are based on the relationship between the molecular structure (organic chain, polar functions, type of functions, type of isotope involved) of the organic compounds, and their equilibrium vapour pressure. A data set of 130 equilibrium vapour pressure isotope effects was used: 112 were used in the training set and the remaining 18 were used for the test/validation dataset Two sets of descriptors were tested, a set with all the descriptors: number of C-12, C-13, O-16, O-18, H-1, H-2, OH functions, OD functions, C=O functions, Connolly Solvent Accessible Surface Area (CSA) and temperature and a reduced set of descriptors. The dependent variable (the output) is the natural logarithm of the ratios of vapour pressures (ln R), expressed as light/heavy as in classical literature. Since the database is rather small, the leave-one-out procedure was used to validate both models. Considering higher determination coefficients and lower error values, it is concluded that the multi-layer perceptron provided better results compared to multi-linear regression. The stepwise regression procedure is a useful tool to reduce the number of descriptors. To our knowledge, a Quantitative Structure Property Relationship (QSPR) approach for isotopic studies is novel. (C) 2014 Elsevier Ltd. All rights reserved.

Tramadol, previously only known as a synthetic analgesic, has now been found in the bark and wood of roots of the African medicinal tree Nauclea latifolia . At present, no direct evidence is available as to the biosynthetic pathway of its unusual skeleton. To provide guidance as to possible biosynthetic precursors, we have adopted a novel approach of retro-biosynthesis based on the position-specific distribution of isotopes in the extracted compound. Relatively recent developments in isotope ratio monitoring by 13 C NMR spectrometry make possible the measurement of the nonstatistical position-specific natural abundance distribution of 13 C (δ 13 C i ) within the molecule with better than 1‰ precision. Very substantial variation in the 13 C positional distribution is found: between δ 13 C i = −11 and −53‰. Distribution is not random and it is argued that the pattern observed can substantially be interpreted in relation to known causes of isotope fractionation in natural products. Thus, a plausible biosynthetic scheme based on sound biosynthetic principals of precursor–substrate relationships can be proposed. In addition, data obtained from the 18 O/ 16 O ratios in the oxygen atoms of the compound add support to the deductions made from the carbon isotope analysis. This paper shows how the use of 13 C NMR at natural abundance can help with proposing a biosynthetic route to compounds newly found in nature or those difficult to tackle by conventional means.

11th International Symposium on Applied Isotope Geochemistry (AIG), French Geol Survey, Orleans, FRANCE, SEP 21-25, 2015; International audience; The common practice of measuring the change in isotope ratio for the whole molecule using isotope ratio measurement by mass spectrometry leads to the loss of significant information of potential interest, since it is the position-specific fractionation which most closely reflects the effect of physicochemical processes. We have shown for MTBE, a common ground water contaminant, that isotopic quantitative C-13 NMR spectrometry can be effectively applied to obtain this position-specific data. It is found that different characteristic position-specific isotope fractionation patterns are introduced by different types of evaporative process or by oxidative degradation. (C) 2015 Published by Elsevier B.V.

The natural xanthines caffeine, theobromine, and theophylline are of major commercial importance as flavor constituents in coffee, cocoa, tea, and a number of other beverages. However, their exploitation for authenticity, a requirement in these commodities that have a large origin-based price-range, by the standard method of isotope ratio monitoring by mass spectrometry (irm-MS) is limited. We have now developed a methodology that overcomes this deficit that exploits the power of isotopic quantitative (13)C nuclear magnetic resonance (NMR) spectrometry combined with chemical modification of the xanthines to enable the determination of positional intramolecular (13)C/(12)C ratios (δ(13)Ci) with high precision. However, only caffeine is amenable to analysis: theobromine and theophylline present substantial difficulties due to their poor solubility. However, their N-methylation to caffeine makes spectral acquisition feasible. The method is confirmed as robust, with good repeatability of the δ(13)Ci values in caffeine appropriate for isotope fractionation measurements at natural abundance. It is shown that there is negligible isotope fractionation during the chemical N-methylation procedure. Thus, the method preserves the original positional δ(13)Ci values. The method has been applied to measure the position-specific variation of the (13)C/(12)C distribution in caffeine. Not only is a clear difference between caffeine isolated from different sources observed, but theobromine from cocoa is found to show a (13)C pattern distinct from that of caffeine.

The European Research Council (ERC), Advanced Investigator Award-FUNCAT and Syngenta are gratefully acknowledged for financial support. The oxidation chemistry of a range of AuI-bis(NHC) (NHC = N-heterocyclic carbene) complexes with hypervalent iodine(III) oxidants has been explored. AuI-bis(NHC) precursors have been synthesised by treatment of the corresponding [Au(NHC)Cl] derivatives with imidazol(idin)ium salts in the presence of K2CO3. The reactivity of the AuI complexes towards PhICl2 has revealed an influence of the nature of the NHC ligands present in the complex on the outcome of the oxidation reaction: small and more strongly electron-donating NHC ligands favoured the formation of a AuIII species. On the basis of these results, a AuI complex bearing two 1-butyl-3-methylimidazol-2-ylidene (BMIM) ligands has been synthesised. This complex reacted with PhICl2 and also – for the first time in Au-NHC systems – with PhI(OAc)2 and PhI(OAcF)2 (OAcF = trifluoroacetate), affording stable AuIII-(NHC)2 complexes bearing acetate ligands. Postprint

BIOSCREEN is a well-known simple tool for evaluating the transport of dissolved contaminants in groundwater, ideal for rapid screening and teaching. This work extends the BIOSCREEN model for the calculation of stable isotope ratios in contaminants. A three-dimensional exact solution of the reactive transport from a patch source, accounting for fractionation by first-order decay and/or sorption, is used. The results match those from a previously published isotope model but are much simpler to obtain. Two different isotopes may be computed, and dual isotope plots can be viewed. The dual isotope assessment is a rapidly emerging new approach for identifying process mechanisms in aquifers. Furthermore, deviations of isotope ratios at specific reactive positions with respect to "bulk" ratios in the whole compound can be simulated. This model is named BIOSCREEN-AT-ISO and will be downloadable from the journal homepage.

International audience; In forensic environmental investigations the main issue concerns the inference of the original source of the pollutant for determining the liable party. Isotope measurements in geochemistry, combined with complimentary techniques for contaminant identification, have contributed significantly to source determination at polluted sites. In this work we have determined the intramolecular C-13 profiles of several molecules well-known as pollutants. By giving additional analytical parameters, position-specific isotope analysis performed by isotope ratio monitoring by C-13 nuclear magnetic resonance (irm-C-13 NMR) spectrometry gives new information to help in answering the major question: what is the origin of the detected contaminant? We have shown that isotope profiling of the core of a molecule reveals both the raw materials and the process used in its manufacture. It also can reveal processes occurring between the contamination site `source' and the sampling site. Thus, irm-C-13 NMR is shown to be a very good complement to compound-specific isotope analysis currently performed by mass spectrometry for assessing polluted sites involving substantial spills of pollutant. (C) 2015 Elsevier B.V. All rights reserved.

Two well-defined 16-electron ruthenium hydroxide complexes were prepared and successfully used in the racemization of aromatic and aliphatic secondary alcohols. The intrinsic basicity of these new complexes permits for the exclusion of KOtBu in the racemization reaction.

The use of [(IPr)AuOH] as versatile, air- and moisture-stable pre-catalyst permits the in situ generation of the cationic gold(I) species [(IPr)Au]X after reaction with a Bronsted acid. This catalytic system presents as a main advantage the lack of use of a silver salt activator or co-catalyst which is often air-, light- and moisture-sensitive. A general gold(I)-catalyzed procedure using this in situ activation at very low catalyst loading is reported for the hydration of a broad range of internal and terminal alkynes.

The use of the versatile N-heterocyclic carbene (NHC) gold(I) hydroxide [Au(OH)(IPr)] (IPr = N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) as precursor permits the expedient synthesis of a series of cationic heteroleptic [Au(NHC)(NHC′)]+ and [Au(NHC)(PR3)]+ complexes by protonolysis with the appropriate acid salts. Complete characterization by 1H and 13C NMR spectroscopy and by single-crystal X-ray diffraction was performed in order to discern electronic and structural differences between cationic heteroleptic [Au(NHC)(NHC′)]+ and [Au(NHC)(PR3)]+ congeners.

International audience; We have developed a new method for Suzuki coupling using an NHC-stabilized palladium catalyst under solvent-free conditions using microwave activation

Isotopic fractionation of pollutants in terrestrial or aqueous environments is a well-recognized means by which to track different processes during remediation. As a complement to the common practice of measuring the change in isotope ratio for the whole molecule using isotope ratio monitoring by mass spectrometry (irm-MS), position-specific isotope analysis (PSIA) can provide further information that can be exploited to investigate source and remediation of soil and water pollutants. Position-specific fractionation originates from either degradative or partitioning processes. We show that isotope ratio monitoring by (13)C NMR (irm-(13)C NMR) spectrometry can be effectively applied to methyl tert-butylether, toluene, ethanol and trichloroethene to obtain this position-specific data for partitioning. It is found that each compound exhibits characteristic position-specific isotope fractionation patterns, and that these are modulated by the type of evaporative process occurring. Such data should help refine models of how remediation is taking place, hence back-tracking to identify pollutant sources.

[478980-04-0] C24H29ClN2Pd (MW 487.37) InChI = 1S/C21H24N2.C3H5.ClH.Pd/c1-14-9-16(3)20(17(4)10-14)22-7-8-23(13-22)21-18(5)11-15(2)12-19(21)6;1-3-2;;/h7-12H,1-6H3;3H,1-2H2;1H;/q;;;+1/p-1 InChIKey = PBWADPFFHMNMFI-UHFFFAOYSA-M (used for cross-coupling reactions, aryl amination, cyclization–trapping of bisdiene, polymerization of olefins, allylation of alkylidenes malonitriles, oxidation of secondary alcohols) Data: mp >165 °C. Solubility: acetone, CH2Cl2, partially soluble in toluene and DMSO, insoluble in water, pentane, hexane, and diethyl ether. Form Supplied in: white solid, crystal structure available.1 Preparative Methods: [Pd(IMes)(allyl)Cl] is easily obtained by reaction in a Schlenk tube of 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene with [Pd(allyl)Cl]2 in dry THF at room temperature for 1 h. Solvent is removed under reduced pressure and the product triturated with hexane and then filtered under air to provide the complex as a solid in high yield.2 Purification: crystallization from THF/hexanes solution.1 Handling, Storage, and Precautions: described as air and moisture stable. Nevertheless, the complex should be stored under an inert atmosphere.

[60259-30-5] C12H12N3P (MW 229.22) InChI = 1S/C12H12N3P/c1-2-8-13(7-1)16(14-9-3-4-10-14)15-11-5-6-12-15/h1-12H InChIKey = QEILNSNBJVMEKR-UHFFFAOYSA-N (used as ligand on several metals) Physical Data: mp 43–44 °C. Solubility: acetone, CH2Cl2, chloroform, THF, not soluble in methanol or hexane. Form Supplied in: white solid. Preparative Methods: the first synthesis was carried out by adding an ethereal solution of PCl3 to an ethereal solution suspension of 20% excess potassium pyrrolide. After 24 h, the precipitate of KCl and excess potassium pyrrolide was filtered off and the solvent removed under vacuum yielding crude tris(pyrrolyl)phosphine with yields ranging from 70% to 95%.1 Many years later, an alternative synthesis was described.2 In a flame-dried Schlenk reactor under inert atmosphere, pyrrole and triethylamine in THF are cooled to −78 °C, then PCl3 added, and the reaction mixture allowed to warm to room temperature. After heating for 24 h at 65 °C, a colorless solid appeared and was filtered and washed with THF. Filtrates were combined and taken to dryness under vacuum yielding a crystalline off-white mass. The product was dissolved in hexane and impurities removed by filtration. Concentration of the solution and cooling to −78 °C gave the product as colorless crystals (74%). Purification: crystallization from methanol solution,1 or crystallization from cold hexane.2 Spectroscopic Data: 1H (toluene d8) δ6.55 (m, 6H), 6.21 (m, 6H); 31P (toluene d8) δ79.6. Handling, Storage, and Precautions: described as air and moisture stable.

Title hydrophosphoryloxylation of alkynes proceeds smoothly in the presence of low amounts of gold catalyst (0.01—1 mol%) to selectively afford the kinetic enol phosphates (III), (V), (VII).

Ball milling of various aldehydes and ketones with hydrazines proceeds without the need for a solvent in one to three hours to give the hydrazones (III) and (VII) in quantitative yields.

Title hydrophosphoryloxylation of alkynes proceeds smoothly in the presence of low amounts of gold catalyst (0.01—1 mol%) to selectively afford the kinetic enol phosphates (III), (V), (VII).

International audience; The asymmetric alkylation of Schiff bases under basic conditions in a ball mill was performed. The starting Schiff bases of glycine were prepared beforehand by milling protected glycine hydrochloride and benzophenone imine, in the absence of solvent. The Schiff base was then reacted with a halogenated derivative in a ball mill in the presence of KOH. By adding a chiral ammonium salt derived from cinchonidine, the reaction proceeded asymmetrically under phase-transfer catalysis conditions, giving excellent yields and enantiomeric excesses up to 75%. Because an equimolar amount of starting material was used, purification was greatly simplified.

Furans and pyrroles were prepared via the gold(I)-catalyzed alkyne hydration of diynes. The use of [Au(IPr)OH] as precatalyst in a silver-free protocol permits low catalyst loadings and in situ generation of the active cationic gold species. A detailed computational study confirmed the experimental results and supports the proposed mechanism.

Gold-catalyzed cyclization of propargylic acetates (I) provides access towards acetoxyindenes (II) in high yields.

The use of [(IPr)AuOH] permits the generation of Au(I)-amine complexes by a Ag-free protocol.

The use of [(IPr)AuOH] as versatile, air- and moisture-stable pre-catalyst permits the in situ generation of the cationic gold(I) species [(IPr)Au]X after reaction with a Bronsted acid. This catalytic system presents as a main advantage the lack of use of a silver salt activator or co-catalyst which is often air-, light- and moisture-sensitive. A general gold(I)-catalyzed procedure using this in situ activation at very low catalyst loading is reported for the hydration of a broad range of internal and terminal alkynes.

Substituted indenes can be prepared after a sequence [1,3] O-acyl shift-hydroarylation-[1,3] O-acyl shift. Each step is catalyzed by a cationic NHC-Gold(I) species generated in situ after reaction between [(IPr)AuOH] and HBF(4)·OEt(2). This interesting silver-free way is fully supported by a computational study justifying the formation of each intermediate.

Furans and pyrroles were prepared via the gold(I)-catalyzed alkyne hydration of diynes. The use of [Au(IPr)OH] as precatalyst in a silver-free protocol permits low catalyst loadings and in situ generation of the active cationic gold species. A detailed computational study confirmed the experimental results and supports the proposed mechanism.

The use of [(IPr)AuOH] permits the generation of gold(I)–amine complexes by a silver-free protocol. These in situ or well-defined complexes are used in a straightforward synthetic route to substituted allenes from propargylic acetates. The catalytic activity can be modulated as a function of the nature of the ligand bound to the gold–NHC moiety.

The use of a versatile N-heterocyclic carbene (NHC) gold(I) hydroxide precatalyst, [Au(OH)(IPr)], (IPr=N,N'-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) permits the in situ generation of the [Au(IPr)](+) ion by simple addition of a Brønsted acid. This cationic entity is believed to be the active species in numerous catalytic reactions. (1)H NMR studies in several solvent media of the in situ generation of this [Au(IPr)](+) ion also reveal the formation of a dinuclear gold hydroxide intermediate [{Au(IPr)}(2)(μ-OH)], which is fully characterized and was tested in gold(I) catalysis.

The three-component reaction under solvent-less conditions affords the products generally in excellent yields and avoids purification by column chromatography.

International audience; A new solvent-free microwave-assisted procedure for the Petasis multicomponent reaction was developed. This method is the first application of the borono-Mannich reaction in solvent-free conditions and proved its applicability to various boronic acids and secondary amines. Results are very good in term of yields, with shorter reaction time than with classic methods. Because of the efficiency of the method, full conversion of the starting materials towards the expected product was achieved, starting from stoichiometric quantities of reactants, avoiding the usual solvent consuming column chromatography on silica gel. No other purification step than an aqueous washing was required.

We have developed a new method for Suzuki coupling using an NHC-stabilized palladium catalyst under solvent-free conditions using microwave activation.

International audience; A crush on sweetness ! A novel solvent-free methodology for the synthesis of peptides was developed: the coupling of an urethane protected N-carboxy anhydride (UNCA) of an aminoacid with another aminoacid derivative gave a protected dipeptide in very high yield under ball-milling conditions. The reaction is taking place in the solid state. This solvent-free synthesis was applied to the preparation of dipeptides and tripeptides, and exemplified in the preparation of Aspartame, in three steps, using the UNCA route, without any organic solvent and purification.

Various C-aryl and C-alkyl-nitrones were synthesized within 0.5–2 h via condensation of an equimolar amount of aldehydes and N-substituted-hydroxylamines under solvent-free conditions in a ball-mill apparatus. Reactions can be performed without the need of excluding air and moisture and yields the expected products with no need for further purification. The study has been complemented by Differential Scanning Calorimetry (DSC) and solid-state 13C MAS nuclear magnetic resonance experiments. We have also studied the temperature profile during the reaction. A comparative study with the corresponding solvent-free microwave activated reaction showed the superiority of the ball-milling method; 31 examples are described, including the synthesis of the anti-aging agent C-phenyl-N-tert-butyl nitrone (PBN) and one of its analogues C-2-pyridyl-N-tert-butylnitrone (2-PyBN

La chimie verte reduit les substances dangereuses et toxiques. Les solvants de reactions, generalement utilises en grande quantite, entrent dans cette categorie de substances dangereuses. Des solvants alternatifs comme l’eau ont ete proposes, mais le meilleur solvant d’un point de vue ecologique reste l’absence de solvant. Dans un procede, l’utilisation de solvants intervient a differents stades : synthese, purification et nettoyage des equipements. Les methodes presentees ici permettent la suppression des solvants dans les voies de synthese chimique.