sp3–sp3 carbon–carbon bonds formation using 2-alkylazoles and a bromoacrylate as the reaction partners

International audienc

Synthesis of Symmetrical and Unsymmetrical 1,3-Diheteroarylbenzenes Through Palladium-Catalyzed Direct Arylation of Benzene-1,3-disulfonyl Dichloride and 3-Bromobenzenesulfonyl Chlorides

International audienceThe palladium-catalyzed synthesis of unsymmetrical 1,3-diheteroarylbenzenes was investigated. The first synthetic pathway relies on the desymmetrization of benzene-1,3-disulfonyl dichloride through two successive palladium-catalyzed direct desulfitative arylations with two different heteroarenes. The second strategy employs the orthogonal functionalization of 3-bromobenzenesulfonylchloride using an iterative C–H bond arylation sequence, namely, palladium-catalyzed direct desulfitative arylation followed by a palladium-catalyzed direct arylation step using aryl bromide as the coupling partner. The synthesis of symmetrical 1,3-diheteroarylbenzenes was also investigate

Pd-catalysed heteroarylations of 3-bromochromen-4-one via C-H bond activation of heteroarenes.

International audienceThe palladium-catalysed direct coupling of 3-bromochromen-4-one with heteroaromatics was found to proceed in moderate to high yields. A wide variety of heteroaromatics can be coupled with this chomenone derivative using 2 mol % PdCl(C3H5)(dppb) catalyst and KOAc as the base. Moreover, the reaction tolerates a range of useful functional groups on the heteroarene

Contribution des Légumineuses à la régénération après feu des forêts de Quercus suber et Pinus halepensis du Nord-Est Algérien

The role of legumes in post-fire forest regeneration has been extensively studied in the northern Mediterranean basin but no published data are available concerning the southern part of the area. The aim of the present paper is to analyse the dynamics of the leguminous species in a Q. suber and a P. halepensis forests in northeastern Algeria during the first months after a wildfire of low intensity. The aspects of seedling demography of legumes, their contribution to total biomass and species richness were considered. No major differences were detected between the two communities. They presented similar demographic patterns: legume seedlings began to emerge very early (November) after the fire (October) and continued to increase massively with a peak in December and another in March, and a significant slowdown in January and February; in April, they resumed to gradually decrease again to reach their minimum in May and completely stop in early June. This pattern with two peaks rather than only one in seedling demography was likely due to the exceptional coldness of January and February 2005 (snow down to sea level) whereby the germination slowdown and its delay to March. Eight months after the fire (towards the end of June, as the herbaceous vegetation began to dry), the above-ground biomass of legumes reached a maximum of 37.8 ± 1.83 g/m2 in the Q. suber forest and 26.7 ± 1.63 g/m2 in the P. halepensis one. Seven months after the disturbance, in comparison with the other taxa, the legumes were floristically well represented with 19.8 ± 1.11 % and 24.3 ± 2.05 % of species in the Cork oak and the Allepo pine forests respectively. These richness values are far higher than those reported for other Mediterranean-type ecosystems (3.8 - 13.3 %) probably because of the geographic location (lower latitude) of our study area and the overgrazing pressure favouring installation of leguminous speciesLe rôle des Légumineuses dans la régénération après feu a été largement étudié sur la rive nord de la Méditerranée, mais aucune donnée n'est disponible concernant la rive sud. Le but de cet article est d'analyser la dynamique des Légumineuses dans une subéraie et une pinède à Pin d'Alep du Nord-Est Algérien durant les premiers mois après un feu de faible intensité. Les aspects de la démographie des germinations des Légumineuses, leur contribution à la biomasse totale et la richesse spécifique sont considérés. Les deux communautés ne présentent pas de différences majeures. Toutes deux montrent des modèles démographiques similaires: les germinations de Légumineuses commencent à émerger très tôt (novembre) après le feu (octobre) et continuent à s'établir abondamment avec un premier pic en décembre et un deuxième en mars, avec un ralentissement significatif en janvier et février. La germination diminue à partir d'avril pour atteindre son minimum en mai et complètement s'arrêter en début juin. Ce modèle en deux pics plutôt qu'un seul, comme déjà rapporté, serait vraisemblablement dû au froid exceptionnel durant janvier et février 2005 (neige jusqu'au niveau de la mer) d'où un ralentissement de la germination et son décalage à mars. Huit mois après l'incendie (vers la fin juin, période où la végétation herbacée commence à sécher), la biomasse aérienne des Légumineuses affiche un maximum de 37,8 ± 1,83 g/m2 dans la subéraie et 26,7 ± 1,63 g/m2 dans la pinède. Sept mois après le feu, relativement aux autres familles de plantes, les Légumineuses sont floristiquement bien représentées avec 19,8 ± 1,11 % des espèces dans la subéraie et 24,3 ± 2,05 % dans la pinède, valeurs nettement supérieures à celles rapportées pour d'autres écosystèmes de type méditerranéen (3,8 - 13,3 %), probablement en raison de la localisation géographique (basse latitude) de notre aire d'étude et la pression de surpâturage qui favorise l'installation des Légumineuses

Year and tree effect on reproductive organisation of Cedrus atlantica in a natural forest

International audienc

Year and tree effect on reproductive organisation of Cedrus atlantica in a natural stand

National audienc

Catalytic system for inhibition of amination type reaction and palladium-catalyzed direct arylation using non-protected pyrazole derivatives

International audienceThe palladium-catalysed direct arylation at C-4 of non-protected 5-aminopyrazoles was found to proceed in high yields using a variety of aryl bromides. The choice of potassium acetate as the base was found to be crucial to inhibit the amination reaction and to promote the direct arylation

Palladium-catalyzed direct arylation of free NH2 substituted thiophene derivatives

International audienceThe palladium-catalyzed direct 2- or 5-arylation of some free NH2-substituted thiophene derivatives was found to proceed in high yields using a variety of aryl bromides. In the course of these reactions, no coupling of the aryl bromide with the thiophene NH2 substituent was detected. The presence of an ester substituent on C2 of thiophene was found to be useful to block this highly reactive carbon

Palladium-Ruthenium Catalyst Complementarity Strengthens Ortho-Directed C-H Bond Arylation of 2-Arylpyrazines

International audienceWe report the Pd- or Ru-catalyzed C-H bond arylation at the ortho-position of the aryl unit of 2-arylpyrazines. The reaction proceeds with complete regioselectivity using phosphine-free Pd(OAc)(2) or [RuCl2(p-cymene](2) as the catalysts and potassium acetate as an inexpensive base. In all cases, the mono-arylation of 2-arylpyrazines was obtained even with 2,3-diphenylpyrazine. Moreover, the reaction is not sensitive to the pyrazine substitution. By selecting the proper catalytic system, a wide variety of electron-rich and -poor (hetero)aryl bromides, including bromopyridine derivatives, has been successfully employed

Quinoxaline as an integrated directing group in palladium-catalyzed ortho -C–H bond arylation of the aryl unit of 2-arylquinoxalines

International audienc