Christophe Bour

• PhD
• Professor (Associate) at University of Paris-Saclay

A series of 4‐sulfoximinocyclopent‐2‐en‐1‐ones was prepared in 35 to 99% yield through a calcium(II)‐catalyzed aza‐Piancatelli reaction, including in enantioenriched form. Depending on their substitution pattern, diverse diastereoselective chemical transformations can be applied to these scaffolds, allowing access to cyclopentane derivatives. This...

A series of enantioenriched substituted tetrahydropyrrolo[3,2‐c]azepine products possessing an axial chirality were synthesized in 63–99% yield through a gold(I)‐catalyzed hydroarylation. DFT calculations rationalized the reactivity observed for the formation of such complex molecular frameworks and guided our choice in the pyrrole N‐substituent to...

Difluoromethylene-skipped enones have been readily obtained from arylvinyltriflates and aryldifluoroenoxysilanes. While these useful compounds are difficult to synthesize by the classical aldol/dehydration approach, the use of a squaramide/Li+ catalyst allows their direct formation via a vinyl carbocation paired with a weakly coordinating perfluori...

The formation of a rare type of diphosphazenium cation is described. Its synthesis features a unique oxidative dealkylation of an iminophosphorane-phosphole by a silver(I) salt. DFT study of this compound...

An overlooked pericyclic reaction between allyl alcohols and alkenes to form carbonyl compounds is analyzed. It combines the characteristic features of the Alder-ene reaction and of the oxy-Cope rearrangement. This oxy-ene reaction could be involved in biosynthetic pathways.

The concept of alkynophilicity is revisited with group 13 MX3 metal salts (M = In, Ga, Al, B; X = Cl, OTf) using M06-2X/6-31+G(d,p) calculations. This study aims at answering why some of these salts show reactivity toward enynes that is similar to that observed with late-transition-metal complexes, notably Au(I) species, and why some of them are in...

9,10-Dihydroacridines are frequently encountered as key scaffolds in OLEDs. However, accessing those compounds from feedstock precursors typically requires multiple steps. Herein, a modular one-pot synthesis of 9,10-dihydroacridine frameworks is achieved through a reaction sequence featuring a selective ortho-C alkenylation of diarylamines with ary...

Correction for 'Bimolecular vinylation of arenes by vinyl cations' by Zhilong Li et al., Chem. Commun., 2020, 56, 6507-6510, DOI: 10.1039/D0CC02300K.

An efficient ortho-C-alkylation of unprotected anilines with a variety of styrenes and alkenes using an univalent cationic indium(I) catalyst is reported. Mechanistic studies revealed that the reaction likely proceeds via a tandem hydroamination/Hofmann-Martius rearrangement. The high compatibility between cationic indium(I) complex and primary ani...

The catalytic activity of cationic NHC‐ZnII and NHC‐AlIII (NHC=N‐heterocyclic carbene) complexes in reactions that require the electrophilic activation of soft C−C π bonds has been studied. The former proved able to act as a soft π‐Lewis acid in a variety of transformations. The benefit of the bulky IPr NHC ligand was demonstrated by comparison wit...

The synthesis and structural features of several families of unsolvated molecular complexes of the heavy alkaline earths (Ae = calcium, strontium and barium) supported by bis(phenolate)s or bis(fluoroalkoxide)s are described. These dianionic, multidentate ligands are built around diaza-macrocycles that contain either five or six N- and O-heteroatom...

Aniline derivatives are frequently encountered in molecules of industrial relevance such as dyes or antioxidants, which make the development of synthetic methods for the functionalization of these privileged structures highly sought-after. A general protocol for the hydroarylation of electronically diverse alkenes with anilines would be ideal to pr...

The reactivity of 7‐alkynycycloheptatrienes tethered to an aryl group under π‐acid catalysis has been studied. A variety of useful cyclic products were synthesized via Au(I)‐catalyzed skeletal reorganization, Cu(II)‐catalyzed hydroarylation, or Brønsted acid‐catalyzed tandem hydroarylation/Friedel‐Crafts reaction. We also report a rare type of skel...

Styrene derivatives can be easily synthesized from vinyl triflates and arenes under mild reaction conditions, using [Li][Al(OC(CF 3 ) 3 ) 4 ] as a catalyst and LiHMDS as a base. This transformation is likely to...

The GaCl3-mediated Friedel-Crafts alkylation of benzene by methyl chloride has been studied by means of DFT computations at the M062X/6-311+G(2d,2p) level of theory. The role of superelectrophilic Ga2Cl6 homodimers has been confirmed and explained. The results are in line with the observation of second order rate dependence in GaCl3-mediated Friede...

Herein, we report the preparation of bridged tetrahydrobenzo[b]azepines, which was accomplished through an aza‐Piancatelli cyclization/Michael addition sequence in a one‐pot fashion from readily available precursors. It is noteworthy that a general method to access these scaffolds was hitherto unprecedented. Additionally, the multifaceted aspects o...

Brücken bauen: Mit einem neuen, einheitlichen Ansatz lassen sich 2‐Furylcarbinole mithilfe von Aminen als Nucleophilen unter milden Bedingungen in verbrückte Tetrahydrobenzo[b]azepine und verwandte verbrückte Verbindungen umwandeln. Die Methode ist verträglich mit vielfältigen funktionellen Gruppen und sehr gut geeignet zur Herstellung dicht funkti...

The first examples of a catalytic tandem process involving a ring-closing carbonyl-olefin metathesis and a transfer hydrogenation are described. 1,4-Cyclohexadiene has been used as an H2 surrogate to reduce the cyclic alkenes formed after the metathesis step. The same cationic gallium(III) complex, [IPr·GaCl2][SbF6], performs the two steps with fun...

We report a catalytic tandem process involving a ring-closing carbonyl-olefin metathesis and a transfer hydrogenation. 1,4-Cyclohexadiene has been used as H₂surrogate to reduce the cyclic alkenes formed after the metathesis step. The same NHC-stabilized cationic gallium(III) complex, [IPr _˙ GaCl₂][SbF₆],...

Homogenous gold catalysis has emerged as a powerful tool in organic synthesis, but many mechanistic questions in that area remain unanswered. The ability of diffusion-ordered NMR spectroscopy (DOSY) to investigate interactions between substrates, to study molecular assemblies, and to characterize reactive intermediates makes it a powerful technique...

γ-Aryl enol acetates are easily obtained from diacetoxy alkenes and electron-rich arenes at room temperature using GaCl3 as catalyst. The products can then be converted into β-aryl aldehydes. This method represents the first broadly applicable catalytic version of the Scriabine reaction. DFT computations shed light on the mechanism of this transfor...

A new method has been developed for the preparation of 3-bromo-1-phenylallenes from 7-alkynylcycloheptatrienes and N-bromosuccinimide. Trisubstituted bromoallenes were obtained at room temperature in moderate to excellent yields. Functionalization of the carbon-bromine bond via Pd- or Cu-catalyzed cross-coupling reactions easily provided substitute...

Diffusion-ordered NMR spectroscopy (DOSY) is a powerful method for the analysis of mixtures. Classic DOSY methods require several minutes of acquisition, and we show here that DOSY experiments can be recorded in less than one second for the challenging case of solution mixtures in low-viscosity solvents. The proposed method relies on a spatial enco...

The borrowing hydrogen strategy has been applied to the ethylation of imines, using an air-stable iron complex as precatalyst. This approach opens new perspectives in this area, as it allows the synthesis of unsymmetric tertiary amines from readily available substrates and ethanol as C2-building block. A variety of imines bearing electron-rich arom...

The borrowing hydrogen strategy has been applied to the ethylation of imines, using an air-stable iron complex as precatalyst. This approach opens new perspectives in this area, as it allows the synthesis of unsymmetric tertiary amines from readily available substrates and ethanol as C2-building block. A variety of imines bearing electron-rich arom...

Transformations of alkene and alkyne substrates relevant to π‐Lewis acid catalysis have been performed using low‐valent Ga(I) species for the first time. [Ga(I)(PhF) 2 ] ⁺ [Al(OR F ) 4 ] ⁻ and gallium dichloride (i. e. [Ga(I)] ⁺ [GaCl 4 ] ⁻ ) proved to be efficient catalysts for cycloisomerizations, Friedel‐Crafts reactions, transfer hydrogenations...

A compound that isomerizes into distinct products depending on the Lewis or Brønsted acid catalyst used is disclosed. One product can only be obtained with the softest pi-acids such as Au, Pt, Ga or In complexes. Another is formed only with harder pi-acids such as Ag or Cu salts. The formation of the third one requires even harder pi-acids or proto...

Five new tartrate-containing Keplerate compounds have been synthesized and characterized in the solid state and in solution. These characterizations evidenced the total replacement of inner sulfate ligands by L- or D-tartrate ligands in aqueous medium under heating during several days. To our knowledge these compounds correspond to the first Kepler...

The title cationic gallium(iii) complexes are shown to be useful in homogeneous molecular catalysis. They have been used in catalytic reactions involving the activation of alcohols, alkynes and alkenes towards the addition of various nucleophiles (H2O, ROH, carbonyls, arenes, hydrides, etc.). The mechanism of the transformations of alkynes and alke...

Two new cationic dinuclear gold(I) complexes, [Au2(μ(P,N)-5)2]X2-in which X=NTf2 (7; Tf=trifluoromethanesulfonate) or SbF6 (8) and 2-(diphenylphosphanyl)benzonitrile (5) is a P,N-bridging donor-have been synthesized and structurally characterized. These air-stable species and their dimeric and polymeric analogues possessing 1′-(diphenylphosphanyl)-...

1,3-Dienyl β-keto esters are cyclised into bicyclolactones using the Bi(OTf)3/TfOH catalytic system. This reaction represents a rare case of simultaneous C-C and C-O bond formation at positions 1 and 3 of a 1,3-diene. Application to the synthesis of ramulosin is presented.

The cell division cycle 25 phosphatases (CDC25A, B, and C; E.C. 3.1.3.48) are key regulator of the cell cycle in human cells. Their aberrant expression has been associated with the insurgence and development of various types of cancer, and with a poor clinical prognosis. Therefore, CDC25 phosphatases are a valuable target for the development of sma...

An efficient synthesis of polysubstituted 2-alkenylfurans using Ca(NTf2)2/KPF6 as a catalytic mixture is described. It is based on the cycloelimination of readily available propargyl alcohols tethered to β-keto esters under dry conditions to avoid competitive Meyer–Schuster rearrangement. The furan can be further functionalized in situ by a calcium...

ortho-Oligo(phenylene)ethynylenes (o-OPEs) stapled with enantiopure 2,3-dihydroxybutane diethers have highly intense circular dichroism (CD) spectra and excellent circular polarized luminescence (CPL) responses (glum values up to 1.1 × 10⁻²), which are consistent with homochiral helically folded structures. In the presence of Ag(i), a change in the...

The intramolecular condensation of β-keto esters to give propargyl alcohols is described. The substrates have two electrophilic sites and two nucleophilic sites. The site selectivity can be fully controlled. In the presence of a calcium-based catalyst and under anhydrous conditions, O-addition products are isolated. On the other hand, traces of wat...

The use of copper salts as additives in Au(I)-catalyzed reactions allows the gradual delivery of [LAu]⁺ from a reservoir of stable LAuX. With the Au/Cu catalytic system, it becomes possible to carry out gram-scale reactions in a small amount of solvent, even at elevated temperature, without observing the formation of Au(0). Since then, we have work...

On the basis of DFT computations and experimental results, we show that the presence of the ester group in the backbone of organic substrates can influence the mechanism of metal-catalyzed carbocyclization reactions. The non-innocent role of the ester functionality in lowering the activation barrier of the key step of the gallium- and indium-cataly...

Direct alkenylation of a variety of alcohols with vinylboronic acids has been accomplished using the air-stable calcium(II) complex Ca(NTf2)2 under mild conditions with short reaction times. For reluctant transformations, an ammonium salt was used as an additive to circumvent the reactivity issue. Cross-coupling: Direct alkenylation of a variety of...

Cationic gold(I) complexes are soft Lewis acids that are able to trigger numerous types of nucleophilic attack onto alkenes, allenes, and alkynes (π-acid catalysis). In this account, we initially summarize the novel methods that we have developed to generate such catalysts by silver-free activation of ligated gold(I) chlorides. The advantages of th...

Optimized reaction conditions including 1,4-cyclohexadiene as hydrogen source in combination with a gallium carbene complex catalyst allow hydrogenative cyclization, hydroarylation, and reduction of olefins.

[IPr•InBr2][SbF6] (2) (IPr = 1,3-bis(2,6-diisopropylphenyl) imidazol-2-ylidene) has been synthetized and characterized in the solid state. This complex proved to be a very active catalyst for hydroarylations, transfer hydrogénations, and cycloisomerizations.

By reacting IPr⋅InBr3 with AgSbF6 in dichloroethane at room temperature, we could obtain single crystals comprising [{(IPr⋅InBr3 )(Ag⋅(CH2 Cl)2 )}2 ][SbF6 ]2 (1) and two identical HSbF6 units. It is presumed that the reaction gave rise to [IPr⋅InBr3-x ][SbF6 ]x (x=1, 2, or 3) which reacted with adventitious water to give HSbF6 and [IPr⋅InBr3-x (OH)...

The first gallium- and calcium-catalyzed Meyer-Schuster rearrangements are described. Under substrate control, the incipient conjugated ketones can be trapped intramolecularly by β-keto esters or amides to yield cyclic products after aldol condensation or endo-Michael addition. An interesting additive effect that promotes the latter tandem process...

While the coordination chemistry of gallium is very rich, only a few applications of organo-gallium compounds as catalysts for molecular transformations have been reported. Nevertheless, some studies containing both families of X-ray characterized species and their catalytic activity allow the establishment of a structure-activity and a structure-s...

We report a rare case of alkene transfer hydrogenation using a main-group compound instead of a transition-metal complex as catalyst. We disclosed that 1,4-cyclohexadiene can be used as H2 surrogate towards olefin reduction in the presence of [IPrGaCl2][SbF6]. Hydrogenative cyclizations have also been carried out because this cationic gallium compl...

Complexes of type [LAuCl] (L=phosphine, phosphite, NHC and others) are widely employed in homogeneous catalysis, however, they are usually inactive as such and must be used jointly with a halide scavenger. To date, this role has mostly been entrusted to silver salts (AgSbF6, AgPF6, AgBF4, AgOTf, etc.). However, silver salts can be the source of dea...

Enantioselective intramolecular additions of [small beta]-ketoamides to unactivated alkenes have been accomplished by means of gold catalysis. Chiral LAuCl complexes have been activated by various Lewis acids (Cu, Ag, Ga, In, Si, Bi etc.). The influence of these activators on the stereoselectivity has been studied.

Fluorine-bridged NHC-gallium(III) complexes of the type IPr center dot GaCl2(mu-F)EFn-1 [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, and EFn = SbF6 or BF4] have been synthesized and characterized in solution and in the solid state. The [BF4](-) adduct readily decomposes into gallium fluorides of the type [IPr center dot GaClmF3-m] (m =...

Chiral gold(i) phosphite complexes are readily prepared modularly from 3,3[prime or minute]-bis(triphenylsilyl)-1,1[prime or minute]-bi-2-naphthol. These chiral gold(i) phosphite complexes are very reactive precatalysts for the [4+2] cycloaddition of aryl-substituted 1,6-enynes with enantiomeric ratios ranging from 86 : 14 up to 94 : 6.

Six new molecular GaCl3 adducts of electron rich compounds of the carbone (carbodiphosphorane, tetraaminoallene) and cyclic alkyl amino carbene (CAAC) families have been synthesized and characterized by X-ray crystallography. The sum of their Cl-Ga-Cl angles has been compared to those of 20 other complexes exhibiting various oxygen-, nitrogen-, pho...

The right combination: Cu(I) and Cu(II) salts can advantageously replace silver additives in Au(I) -catalyzed reactions. On the basis of reactivity studies and NMR experiments, it is believed that anion metathesis between CuYn (Y=OTf, BF4 , PF6 , SbF6 ) and [R3 PAuCl] takes place to give [R3 PAu]Y. As this process is slow, there is no fast decay of...

A molecular donor-acceptor adduct has been isolated by the reaction of the N-heterocyclic carbene 1,3-dimethyl imidazol-2-ylidene (diMe-IMD) with GaCl(3). In contrast, the structurally related, yet much more nucleophilic, 1,3-dimethyl-2-methylene-2,3-dihydro-1H-imidazole (diMe-MDI) gave rise to ion pairs of type [L(2)GaX(2)][GaX(4)], where X = Cl,...

Ga-neration X: Well-defined neutral and cationic gallium(III) halide complexes have been synthesized and evaluated in catalysis. Both the (NHC)GaX(3) /AgSbF(6) catalytic mixture and isolated (NHC)GaX(2) (+) species function as exquisite π-Lewis acids in typical GaX(3) -catalyzed reactions. The cationic complexes are more active than GaX(3) and yet...

GaGa dancers welcome cationic Ga catalysts in the family of π‐Lewis acids. While most members of this family are complexes of noble metals, the carbophilicity of this main‐group element could be exploited in tandem reactions involving activation of alkynes and alkenes toward nucleophilic attack. The cationic species are stabilized by a strongly coo...

Neutral gold(I)-phosphate complexes (I) are synthesized from the corresponding silver precursors and evaluated for their catalytic potential in the activation of alkyne substrates.

Electrophilic gold(I) catalyst 6 competes with GaCl(3) as the catalyst of choice in the synthesis of fluoranthenes by intramolecular hydroarylation of alkynes. The potential of this catalyst for the preparation of polyarenes is illustrated by a synthesis of two functionalized decacyclenes in a one-pot transformation in which three C-C bonds are for...

Gold(I) forms neutral complexes with binol phosphates that are unreactive in the catalytic cyclisation of enynes. Reaction in protic solvents or activation by silver(I) restores the catalytic activity.

Carbodiphosphoranes [C(PR3)2] are divalent carbon(0) derivatives which can be used as ligands to form either M←C(PR3)2 or (M)2← C(PR3)2 species. They were computationally predicted to be even stronger electron donors than N-heterocyclic carbenes. We have introduced hexaphenylcarbodiphosphorane [C(PPh3)2] for the first time in gold catalysis in orde...

Access to enantiopure synthetic platforms that can generate key intermediates for salvinorin A analogues through diastereoselective Diels–Alder cycloaddition between an enantiopure sulfinylquinone and semicyclic dienes is described.

Acyclic 1,7- and 1,8-enynes with the alkyne moiety directly connected to the asymmetric carbon of an ethyl acetal have been obtained in two steps from the corresponding aldehydes. Ring-closing metathesis of these enynes delivered the corresponding six- and seven-membered cyclic 1,3-dienes in moderate-to-excellent yields. A competitive ethylene inse...

Complexes [AuCl{C(NHR)(NHR′)}] and [AuCl{C(NHR)(NEt2)}] (R = tBu, p-Tol, Xylyl, p-C6H4COOH, p-C6H4COOEt, R′ = Me, nBu, iPr, nheptyl, p-Tol) have been prepared by reaction of the corresponding isocyanogold complexes [AuCl(CNR)] with either primary amines or diethylamine. All the prepared carbenes are reactive and highly selective catalysts for skele...

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Complexes [AuCl{C(NHR)(NHPy-2)}] (Py-2 ) 2-pyridyl; R ) Me, tBu, nBu, iPr, nheptyl) have been prepared in amodular way from [AuCl(CNPy-2)]. The carbene moiety has a hydrogen-bond supported heterocyclic structure similar to the nitrogen heterocyclic carbenes in the solid state, and in CH2Cl2 or acetone solution, which is open in the presence of MeOH...

Gerüstbau mit Edelmetallen: Gold- und Platinkatalysatoren vermitteln die Titelreaktion von 1,6-Eninen (siehe Schema: [M]=Metallkatalysator, Z=C(CO2Me)2, R=elektronenschiebende Gruppe). Für diese Umwandlung wird ein offenes carbokationisches Intermediat vorgeschlagen.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Two new palladium catalyzed cascade reactions involving a 4-exo-dig cyclocarbopalladation are described. These processes are shown to convert bromoenediynes and bromodienynes into strained aromatic compounds in a single step.

The cyclizations of enynes substituted at the alkyne gives products of formal [4+2] cyclization with Au(I) catalysts. 1,8-Dien-3-ynes cyclize by a 5-exo-dig pathway to form hydrindanes. 1,6-Enynes with an aryl ring at the alkyne give 2,3,9,9a-tetrahydro-1H-cyclopenta[b]naphthalenes by a 5-exo-dig cyclization followed by a Friedel-Crafts-type ring e...

The 4-exo-dig and 5-exo-dig cyclocarbopalladations have been efficiently used to produce molecular complexity in a straightfor-ward manner. Strained 1,2-cyclobutanediols are rapidly obtained under microwave irradiation in high yields. In many cases, the cyclocarbo-palladation cascade reaction is associated with a 6 or 8p electrocyclic reaction. Dur...

The 4-exo-dig and 5-exo-dig cyclocarbopalladations have been efficiently used to produce molecular complexity in a straightforward manner. Strained 1,2-cyclobutanediols are rapidly obtained under microwave irradiation in high yields. In many cases, the cyclocarbopalladation cascade reaction is associated with a 6 or 8π electrocyclic reaction. Durin...

Treatment of acyclic gamma-bromopropargylic diols with tributyl-stannylated alkynes under palladium catalysis and microwave irradiation conditions gives high yields of the bis(alkylidene)cyclobutanediol derivatives and cyclobutenediols through an efficient 4-exo-dig cyclocarbopalladation. The cyclization is general with a wide variety of alkyne der...

For Abstract see ChemInform Abstract in Full Text.

A DFT/B3LYP model study has been carried out on the cyclocarbopalladation and on an unusual 1,5 vinyl to aryl palladium shift which are the two first steps of a cyclocarbopalladation-Stille coupling tandem reaction of various gamma-bromopropargylic-1,2 diols with alkenyls or alkynyl stannanes catalyzed by Pd(PPh(3))(4). From the calculations, the a...

A new cyclization and C-H activation/Stille cross-coupling reaction on a nonactivated aromatic has been discovered. The reaction is regioselective and controlled by the stannylated reagent. Labeling experiments have been performed that provide evidence for a complete transfer of the deuterium through the coordination sphere of palladium. [reaction:...

[13450-90-313450-90-3] GaCl3 (MW 179.03) InChI = 1S/3ClH.Ga/h3*1H;/q;;;+3/p-3InChIKey = UPWPDUACHOATKO-UHFFFAOYSA-K(used as a Lewis acid or a precursor of organogallium reagents)Physical Data: mp 77.9 °C; bp 201.3 °C; d 2.47 g cm−3.Solubility: soluble in hexane, benzene, diethyl ether, ethanol, and other organic solvents as well as water.Form Suppl...