Recyclable Stereoselective Catalysts

Multivalent polyglycerol supported imidazolidin-4-one organocatalysts for enantioselective Friedel-Crafts alkylations

The first immobilization of a MacMillan’s first generation organocatalyst onto dendritic support is described. A modified tyrosine-based imidazolidin-4-one was grafted to a soluble high-loading hyperbranched polyglycerol via a copper-catalyzed alkyne–azide cycloaddition (CuAAC) reaction and readily purified by dialysis. The efficiency of differently functionalized multivalent organocatalysts 4a–c was tested in the asymmetric Friedel–Crafts alkylation of N-methylpyrrole with α,β-unsaturated aldehydes. A variety of substituted enals was investigated to explore the activity of the catalytic system which was also compared with monovalent analogues. The catalyst 4b showed excellent turnover rates and no loss of activity due to immobilization, albeit moderate enantioselectivities were observed. Moreover, easy recovery by selective precipitation allowed the reuse of the catalyst for three cycles.

Nickel azamacrocyclic complex activated persulphate based oxidative degradation of methyl orange: recovery and reuse of complex using adsorbents

The use of adsorbents for the recovery and reuse of metal complex based persulphate activator is demonstrated.

Efficient and recyclable heterogeneous zinc alkyl carboxylate catalyst for the synthesis of N-phenyl carbamate from aniline and dimethylcarbonate

A heterogeneous salt catalyst with zinc alkyl carboxylate chemically bonded on silica was highly active and recyclable in the synthesis of MPC.

Ionic liquid effects on a multistep process. Increased product formation due to enhancement of all steps

An ionic liquid is shown to increase the rate of all three steps in this imine formation and the microscopic origins of such are investigated. The magnitude of this enhancement varies with the nature of the substituent, though in all cases the rate of imine formation is increased.

Syntheses and properties of phosphine-substituted ruthenium(ii) polypyridine complexes with nitrogen oxides

The substitution lability of the nitrogen oxide ligands of novel phosphine-substituted ruthenium(ii) polypyridine complexes is discussed in comparison with that of the corresponding acetonitrile complexes.

Facile one-pot fabrication of a silica gel-supported chiral phase-transfer catalyst—N-(2-cyanobenzyl)-O(9)-allyl-cinchonidinium salt

A novel silica gel-supported cinchona alkaloid-based PTC catalyst was prepared by one-pot synthesis for the first time. Excellent enantioselectivities (72.0–96.9% ee) and 80–96% yields in enantioselective α-alkylation were achieved without significant loss in the catalytic performance for five runs.

Olefin epoxidation by a (salen)Mn(iii) catalyst covalently grafted on glass beads

A newly synthesized robust (salen)Mn(iii) monolayer on glass bead substrates provides an active catalyst for asymmetric epoxidation of 6-cyano-2,2-dimethylchromene, cis-β-ethylstyrene, 1,2-dihydronaphthalene and indene.

Synthesis, immobilization and catalytic activity of a copper(II) complex with a chiral bis(oxazoline)

A chiral bis(oxazoline) bearing CH2OH groups was synthesized from a commercial bis(oxazoline) and characterized by 1H- and 13C-NMR, high resolution ESI-mass spectrometry and FTIR. The corresponding copper(II) complex was immobilized onto the surface of a mesoporous carbonaceous material (Starbon® 700) in which the double bonds had been activated via conventional bromination. The materials were characterized by elemental analysis, ICP-OES, XPS, thermogravimetry and nitrogen adsorption at 77 K. The new copper(II) bis(oxazoline) was tested both in the homogeneous phase and once immobilized onto a carbonaceous support for the kinetic resolution of hydrobenzoin. Both were active, enantioselective and selective in the mono-benzoylation of hydrobenzoin, but better enantioselectivities were obtained in the homogeneous phase. The heterogeneous catalyst could be separated from the reaction media at the end of the reaction and reused in another catalytic cycle, but with loss of product yield and enantioselectivity.

Self-assembled asymmetric catalyst engaged in a continuous-flow platform: an anti-selective catalytic asymmetric nitroaldol reaction

An anti-selective catalytic asymmetric nitroaldol reaction was manifested in a continuous-flow platform. The requisite Nd/Na heterogeneous catalyst was readily prepared by self-assembly of an amide-based chiral ligand, NdO1/5(O(i)Pr)13/5, NaHMDS, and a multiwalled carbon nanotube without covalent linkage. A stainless-steel column filled with the Nd/Na catalyst was incorporated in a flow system to promote the nitroaldol reaction with high stereoselectivity. The flow system with the heterogeneous catalyst obviated the quenching operation, and the cooling system was minimized.

Pd/C as a catalyst for completely regioselective C-H functionalization of thiophenes under mild conditions

The completely C3-selective arylation of thiophenes and benzo[b]thiophenes was achieved by using Pd/C as a heterogeneous catalyst without ligands or additives under mild reaction conditions. The practicability of this transformation is demonstrated by notable functional group tolerance and the insensitivity of the reaction to H2 O and air. This method is also applicable to nitrogen- and oxygen-containing heterocycles, yielding the corresponding C2-arylated products. Three-phase tests along with Hg-poisoning and hot-filtration tests suggest that the catalytically active species is heterogeneous in nature.

Silica nanospheres supported diazafluorene iron complex: an efficient and versatile nanocatalyst for the synthesis of propargylamines from terminal alkynes, dihalomethane and amines

A novel silica nanosperes supported diazafluorene iron complex has been fabricated and found to be effective in three-component coupling reaction of terminal alkynes, dichloromethane and amines.

Catalyst life in imidazolium-based ionic liquids for palladium-catalysed asymmetric allylic alkylation

Highlighting the reactivity of palladium species in catalytic asymmetric allylic alkylation using imidazolium-based ionic liquids.

Reversal of the enantioselectivity in aldol addition over immobilized di- and tripeptides: studies under continuous flow conditions

The reversal of the enantioselectivity in the heterogeneous asymmetric direct aldol reactions obtained over resin supported di- versus tripeptides was studied in a continuous-flow system.

Chiral metal nanoparticle-catalyzed asymmetric C-C bond formation reactions

Chiral ligand-modified metal nanoparticles possess an attractive potential for application in asymmetric synthesis. This article focuses on chiral-nanoparticle-catalyzed asymmetric C-C bond formation reactions and discusses the nature of the active species.