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2,5-Dihydro-1H-pyrrole-3-carboxylates are important building blocks for the synthesis of high value pyrroles and pyrroloquinoline derivatives with interesting biological activities. The use of continuous flow allowed us to perform a key synthetic step, namely ruthenium-catalyzed ring-closing metathesis, with a residence time of 1 min at 120 °C. Dimethyl carbonate, a green solvent, was demonstrated for the first time to be an excellent solvent for this reaction in continuous flow. The continuous flow conditions proved to be general and the scale-up of this reaction was not only possible, but also highly efficient. Conversion of 10 grams of diene was realized in 37 minutes under continuous flow, yielding the desired heterocycle in 91% yield. [ABSTRACT FROM AUTHOR]

The synthesis of the four olefin metathesis precatalysts Caz-1a–d, featuring the NHC ligand N,N′-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene(SIMes) and four different phosphites (P(OiPr)3, P(OPh)3, P(OEt)3, and P(OMe)3), is reported. The complexes are readily synthesized fromcommercially available [RuCl2(3-phenylinden-1-ylidene)(pyridine)(SIMes)](Ind-III) in yields of up to 88%. These complexes adoptan unusual cis configuration between the phosphite and the NHC ligands.NMR experiments and computational studies confirm that the cis complexesare thermodynamically favored in comparison to their trans counterparts.In addition, the isomerization from trans to cis occurs via a mononuclearand non-dissociative mechanism. Among the four precatalysts, cis-Caz-1a, featuring a P(OiPr)3ligand, displays the highest activity in ring-closingmetathesis and cross-metathesis transformations. Experiments at lowcatalyst loadings demonstrated the potential of this catalyst, allowingbetter conversions than with commonly used commercially availableprecatalysts. [ABSTRACT FROM AUTHOR]

Abstract: Polyethylene glycols (PEGs) are non-toxic, biodegradable and sustainable organic solvents, which find a large application in the chemical and pharmaceutical industry. In this study, we present the ring-closing metathesis reaction (RCM) in PEG under microwave irradiation. Several benchmark substrates, yielding 5- to 6-membered rings featuring di- or tri-substituted olefins, were evaluated. This study demonstrated that PEGs are suitable solvent for olefin metathesis. However, depending on the substrate/catalyst couple, isomerization may occur. [Copyright &y& Elsevier]

The use of phosphites in second generation, ruthenium-based olefin metathesis pre-catalysts leads to an improvement in catalyst stability and activity at low catalyst loadings. [ABSTRACT FROM AUTHOR]

The synthesis, characterisation and catalytic behaviour of ruthenium indenylidene complexes bearing an N-heterocyclic carbene and triisopropylphosphite are described. [ABSTRACT FROM AUTHOR]

Review: 77 refs. [ABSTRACT FROM AUTHOR]

Ring-closing metathesis (RCM) is a powerful tool for the preparation of cyclic organic compounds. Yet, one of the major limitations of this method is the difficulty to prepare large quantities of target molecules. Herein we describe a comprehensive study regarding the gram-scale synthesis of 2-aryl-1 H -pyrrole-3-carboxylates based on the ring-closing metathesis of the corresponding β-amino esters as a key step. This study includes evaluation of solvent and catalyst as well as reaction kinetics on the RCM. After an aromatization step, this methodology allowed for an efficient generation of variously substituted and unprecedented 2-aryl-1 H -pyrrole-3-carboxylates in good yields and cost-effectiveness. The resulting molecules might serve as key building blocks for the generation of CNS-oriented compound libraries. [ABSTRACT FROM AUTHOR]