Jean-François Soulé

Powerful Amide Synthesis from Alcohols and Amines under Aerobic Conditions Catalyzed by Gold or Gold/Iron, -Nickel or -Cobalt Nanoparticles

Considering the importance of the development of powerful green catalysts and the omnipresence of amide bonds in natural and synthetic compounds, we report here on reactions between alcohols and amines for amide bond formation in which heterogeneous gold and gold/iron, -nickel, or -cobalt nanoparticles are used as catalysts and molecular oxygen is used as terminal oxidant. Two catalysts show excellent activity and selectivity, depending on the type of alcohols used. A wide variety of alcohols and amines, including aqueous ammonia and amino acids, can be used for the amide synthesis. Furthermore, the catalysts can be recovered and reused several times without loss of activity.

Regioselectivity in palladium-catalysed direct arylation of 5-membered ring heteroaromatics

In recent years, palladium-catalysed arylation of heteroaromatics via C–H bond activation has become a popular method for generating carbon–carbon bonds. For this reaction, a wide variety of heteroaromatics such as (benzo)furans, (benzo)thiophenes, pyrroles, indoles, thiazoles, oxazoles, imidazoles, pyrazoles or triazoles can be employed. In most of these heterocycles, several reactive C–H bonds are present. If specific C–H bonds of such heteroarenes can be coupled with arenes, this becomes one of the most simple methods to access bi(hetero)arenes. In the past few years, several results using modified and improved catalysts and new reaction conditions have been reported permitting better control of the regioselectivity of such arylations. For example, initially only C2- or C5-arylated thiophenes were accessible via palladium-catalysed direct arylation, whereas now regioselective C3- or C4-arylations are possible when appropriate reaction conditions are used. In this review, the influence of the reactants, catalysts and reaction conditions on the regioselectivity of palladium-catalysed arylation of heteroaromatics is reported. The recent progress in the regioselectivity control now allows the synthesis of a wide variety of complex molecules using only a few steps, and will certainly provide simpler access to new heteroaryl derivatives in the next years.

Synthesis of (Poly)fluorobiphenyls through Metal‐catalyzed CH Bond Activation/Arylation of (Poly)fluorobenzene Derivatives

In recent years, palladium‐catalyzed direct arylation of (hetero)aromatics with aryl halides through a CH bond activation has become a popular method for generating carbon–carbon bonds. A wide variety of heteroaromatics such as furans, thiophenes, thiazoles, or even pyridines can be employed to prepare arylated heterocycles. Conversely, the formation of biphenyl derivatives through CH bond activation has attracted less attention, owing to the lower reactivity of CH bonds of most benzene derivatives. However, over the last few years several new results using modified and improved catalysts and reaction conditions, especially using polyfluorobenzene derivatives, have been reported permitting the synthesis of fluoro‐containing biphenyl derivatives at synthetically useful yields. As fluoro‐substituents on benzene rings appear to present a very specific effect, which promote such couplings, we summarize here the various methods allowing the synthesis of fluoro‐containing biaryls by metal‐catalyzed so called “direct arylation” of (poly)fluorobenzene derivatives. For most of these reactions, aryl halides have been used as the coupling partners, though a several examples employing other coupling partners, such as tosylates or boronic acids, are also known. Moreover, the reaction can be performed with several metal catalysts. This methodology allows the synthesis of complex molecules containing fluorine atoms in only a few steps, and will certainly give the access to a very wide variety of new fluorinated biphenyls useful to both material and biochemists.

Size of Gold Nanoparticles Driving Selective Amide Synthesis through Aerobic Condensation of Aldehydes and Amines

Metal nanoparticles (NPs) have attracted much attention in many fields due to their intrinsic characteristics. It is generally accepted that smaller NPs (1.5-3 nm) are more active than larger NPs, and reverse cases are very rare. We report here the direct aerobic oxidative amide synthesis from aldehydes and amines catalyzed by polymer-incarcerated gold (Au) NPs. A unique correlation between imine/amide selectivity and size of NPs was discovered; Au-NPs of medium size (4.5-11 nm) were found to be optimal. High yields were obtained with a broad range of substrates, including primary amines. Au-NPs of medium size could be recovered and reused several times without loss of activity, and they showed good activity and selectivity in amide formation from alcohols and amines.

Copolymer-incarcerated nickel nanoparticles with N-heterocyclic carbene precursors as active cross-linking agents for Corriu-Kumada-Tamao reaction.

We have developed heterogeneous polymer-incarcerated nickel nanoparticles (NPs), which catalyze cross-coupling reactions. The matrix structure of these catalysts incorporates both N-heterocyclic carbenes (NHCs) as ligands and Ni-NPs, thanks to a new design of cross-linking agents in polymer supports. These embedded NHCs were detected by field gradient swollen-resin magic angle spinning NMR analysis. They were successfully applied to Corriu-Kumada-Tamao reactions with a broad substrate scope including functional group tolerance, and the catalyst could be recovered and reused several times without loss of activity.

Remarkable stereoselectivity in intramolecular Borono-Mannich reactions: synthesis of conduramines.

An unprecedented intramolecular Petasis condensation provides a novel approach to biologically important conduramines. The compounds are produced with an exclusive anti stereoselectivity for the newly created β-amino alcohol motif. The stereochemical outcome of the reaction is opposite to the one usually observed in the intermolecular reaction.

Direct Amidation from Alcohols and Amines through a Tandem Oxidation Process Catalyzed by Heterogeneous‐Polymer‐Incarcerated Gold Nanoparticles under Aerobic Conditions

We describe herein a highly elegant and suitable synthesis of amide products from alcohols and amines through a tandem oxidation process that uses molecular oxygen as a terminal oxidant. Carbon-black-stabilized polymer-incarcerated gold (PICB-Au) or gold/cobalt (PICB-Au/Co) nanoparticles were employed as an efficient heterogeneous catalyst depending on alcohol reactivity and generated only water as the major co-product of the reaction. A wide scope of substrate applicability was shown with 42 examples. The catalysts could be recovered and reused without loss of activity by using a simple operation.

Eco‐Friendly Solvents for Palladium‐Catalyzed Desulfitative CH Bond Arylation of Heteroarenes

Herein, we report the Pd-catalyzed regioselective direct arylation of heteroarenes in which benzenesulfonyl chlorides are used as coupling partners through a desulfitative cross-coupling that can be performed in diethyl carbonate (DEC) or cyclopentyl methyl ether (CPME) as green and renewable solvents or even in neat conditions instead of dioxane or dimethylacetamide (DMA). Under these solvent conditions, the reaction proceeds with a wide range of heteroarenes. C2- or C5-arylated products were obtained with furan and pyrrole derivatives. Benzofuran was also arylated regioselectively at the C2-position, whereas the reaction proceeds selectively at the C3- or C4-positions if thiophenes and benzothiophenes are used. Moreover, in some cases, especially with 1-methylindole, solvent-free conditions afforded better regioselectivities and/or yields than the reaction performed in the presence of solvents.

Environmentally-Safe Conditions for a Palladium-Catalyzed Direct C3-Arylation with High Turn Over Frequency of Imidazo[1,2-b]pyridazines Using Aryl Bromides and Chlorides.

Pd(OAc)2 was found to catalyze very efficiently the direct arylation of imidazo[1,2-b]pyridazine at C3-position under a very low catalyst loading and phosphine-free conditions. The reaction can be performed in very high TOFs and TONs employing as little as 0.1-0.05 mol % catalyst using a wide range of aryl bromides. In addition, some electron-deficient aryl chlorides were also found to be suitable substrates. Moreover, 31 examples of the cross couplings were reported using green, safe, and renewable solvents, such as pentan-1-ol, diethylcarbonate or cyclopentyl methyl ether, without loss of efficiency.

Reactivity of 2,1-Benzisoxazole in Palladium-Catalyzed Direct Arylation with Aryl Bromides

The Pd‐catalyzed direct arylation of 2,1‐benzisoxazole with aryl bromides to access 3‐arylbenzoisoxazoles proceeds in moderate‐to‐high yields with 1 mol % Pd(OAc)2 or 2 mol % PdCl(C3H5)(dppb) (dppb=1,4‐bis(diphenylphosphino)butane) as the catalysts and KOAc as an inexpensive base. A wide variety of (hetero)aryl bromides have been employed successfully. Moreover, arylations followed by benzisoxazole ring opening allowed the preparation of 2‐aminobenzophenones in only two steps.