Laurent Djakovitch

Progress in palladium-based catalytic systems for the sustainable synthesis of annulated heterocycles: a focus on indole backbones

A survey highlighting the most recent palladium catalytic systems produced and their performances for progress in direct synthesis of indole backbones by heterocarbocyclization of reactive substrates is provided. The discussion is developed in relation with the principles of sustainable chemistry concerning atom and mass economy. In this respect, the general convergent character of the syntheses is of particular interest (one-pot, domino, cascade or tandem reactions), and the substrates accessibility and reactivity, together with the final waste production, are also important. This critical review clearly indicates that the development of ligand chemistry, mainly phosphines and carbenes, in the last few decades gave a significant impetus to powerful functionalization of indoles at virtually all positions of this ubiquitous backbone (118 references).

Heterogeneously catalysed Heck reaction using palladium modified zeolites

Abstract Palladium modified zeolites exhibit a high activity towards the Heck reaction of aryl bromides with styrene for small Pd concentrations (=0.2 mol%). The catalysts can be easily separated from the reaction mixture and reused without loss in activity. Leaching of active Pd species was observed in dependence on the zeolite structure. The electronic nature of the aryl bromide has a dominating effect on the reaction yield and the results observed are consistent with an oxidative addition of the aryl bromide to a Pd(0) centre via a S N Ar route.

Heck reactions between aryl halides and olefins catalysed by Pd-complexes entrapped into zeolites NaY

Abstract Palladium complexes entrapped into zeolite cages have been prepared and characterised by MAS-NMR. They exhibit a high activity towards the Heck reaction of aryl bromides with olefins for small palladium concentrations (0.1 mol%). The catalysts can be easily separated from the reaction mixture and reused after washing without loss in activity. Except for very large complexes, no limitation to the diffusion of educts in the zeolite cages was observed. As for the homogeneous Heck reaction, the electronic nature of the aryl bromides and the olefins has a dominating effect on the reaction yield and selectivity. The heterogeneous catalysts activate even aryl chlorides under standard reaction conditions.

Heck reactions catalyzed by oxide-supported palladium – structure–activity relationships

The catalytic activity and selectivity of palladium supported on various metal oxides in carbon–carbon coupling reactions of aryl bromides with styrene (Heck reaction) were investigated. The activity is determined by the nature of the oxide support and the Pd dispersion (structure–activity relationships). The relation of homogeneous (leaching) and heterogeneous mechanisms is discussed.

Direct C sp2H and C sp3H Arylation Enabled by Heterogeneous Palladium Catalysts

This review gives an overview of direct CH arylation catalyzed by heterogeneous Pd catalysts. The efficiency of the different forms of heterogeneous Pd catalysts is discussed with a critical view of the transformations attainable. If experimental evidence is provided, mechanistic considerations on the true nature of the catalysis, that is, heterogeneous versus homogeneous, are discussed as well.

Heterogeneous Transformation of Glycerol to Lactic Acid

Significant yields of lactic acid (LA) are obtained during the treatment of glycerol solution under inert gas with supported metallic catalysts under basic conditions. The nature of the atmosphere and the metal affected the activity and the selectivity of the reaction. Iridium-based catalysts are efficient for LA synthesis.

Amination of aryl bromides catalysed by supported palladium

Abstract Palladium particles immobilised onto a metal oxide support or Pd(0), Pd(II) and [Pd(NH3)4]2+ in NaY zeolite have been prepared and characterised. They exhibit a good activity towards the amination of aryl bromides using secondary amines such as piperidine and diethyl amine with a good regio-selectivity for these reactions. Low Pd concentrations (1 mol%) are required to observe a reasonable regio-selectivity. The catalysts can easily be separated from the reaction mixture (filtration) and reused without loss of activity and selectivity. The electronic nature of the aryl halides plays an important role for both the reaction yields and the regio-control of the reaction. It depends on the relation of the direct amination via a benzyne intermediate versus the Pd-catalysed route.

Recent Advances in the Synthesis of N-Containing Heteroaromatics via Heterogeneously Transition Metal Catalysed Cross-Coupling Reactions

N-containing heteroaromatics are important substructures found in numerous natural or synthetic alkaloids. The diversity of the structures encountered, as well as their biological and pharmaceutical relevance, have motivated research aimed at the development of new economical, efficient and selective synthetic strategies to access these compounds. Over more than 100 years of research, this hot topic has resulted in numerous so-called “classical synthetic methods” that have really contributed to this important area. However, when the selective synthesis of highly functional heteroaromatics like indoles, quinolones, indoxyls, etc. is considered these methods remain limited. Recently transition metal-catalysed (TM-catalysed) procedures for the synthesis of such compounds and further transformations, have been developed providing increased tolerance toward functional groups and leading generally to higher reaction yields. Many of these methods have proven to be the most powerful and are currently applied in target- or diversity-oriented syntheses. This review article aims at reporting the recent developments devoted to this important area, focusing on the use of heterogeneous catalysed procedures that include either the formation of the heterocyclic ring towards the nuclei or their transformations to highly substituted compounds.

Palladium complexes grafted onto mesoporous silica catalysed the double carbonylation of aryl iodides with amines to give α-ketoamides

A promising route for the double carbonylation of aryl iodide derivatives with secondary and primary amines to produce α-ketoamides is described using covalently immobilized palladium complexes on SBA-15 silica. Adequate adjustments of the different reaction parameters (temperature, CO pressure, nature of base, solvent, substrate…) to achieve optimal catalyst performance were made using PdCl2(PPh2)2@SBA-15 as catalytic system. High conversions (up to 80%) and excellent selectivities (up to 96%) for the double carbonylated α-ketoamide products were obtained using K2CO3 as base, MEK or DMF as solvent and a 1 mol% [Pd] catalyst. We also demonstrated that two other palladium hybrid mesoporous materials can be alternatively used, namely PdCl2(PCy2)2@SBA-15 and PdCl2(PNP)@SBA-15, without loss of activity and selectivity. Finally, catalyst recycling of PdCl2(PPh2)2@SBA-15 showed that the catalyst could be reused for up to 3 cycles without affecting catalyst performance.

First heterogeneously palladium catalysed α-arylation of diethyl malonate

Abstract Pd exchanged NaY zeolites ([Pd(0)]–, [Pd(II)]– and entrapped [Pd(NH 3 ) 4 ]) exhibit a good activity towards the α-arylation of carbonyl compounds using different para -substituted aryl bromides. Low Pd-concentrations (only 2 mol%) are required to observe interesting activity. The catalysts can easily be separated from the reaction mixture and reused without any loss in activity. For large-scale applications the alternative use of an insoluble base as K 2 CO 3 seems to be promising. The electronic nature of the aryl halides plays a limited role concerning the rate of the reaction.