Search results for "Catalysis"

Synthesis of novel 1,2,5,6-tetrahydro-4H-pyrrolo[3,2,1-ij]quinolines via benzotriazole methodology

2001

Abstract Pyrroloquinolines have been synthesized reacting 1-(benzotriazol-1(2)-ylmethyl)indolines with unactivated and electron-rich alkenes in the presence of p-toluenesulfonic acid catalyst. Mixtures of the expected diastereomers were obtained and some of them separated in their respective components. X-Ray diffraction along with two-dimensional NMR experiments was needed to assist the determination for both the structures of the precursors and products.

Efficient Synthesis of 1,4,7-Triazacyclononane and 1,4,7-Triazacyclononane-Based Bifunctional Chelators for Bioconjugation

2014

The reaction of diethylenetriamine with chloroacetaldehyde yielded a bicyclic aminal intermediate for the synthesis of 1,4,7-triazacyclononane (TACN), a macrocyclic polyamine the derivatives of which find applications as catalysts, bleaching agents, and chelators for medical imaging. This new synthetic protocol outperforms the synthetic methods described so far because it does not involve any cyclization step. Moreover, this aminal intermediate allowed access to a new family of TACN derivatives functionalized on the carbon skeleton, for example, C-aminomethyl-TACN. This novel compound is a precursor of valuable bifunctional chelating agents for nuclear medicine, in particular, for the prepa…

Synthesis of Natural Products By Rhodium-Mediated Intramolecular C-H Insertion

1998

The strategic advantages of the Rh-mediated intramolecular C–H insertion, which has been used as the key step in several natural product syntheses, are described here. The most recent such synthesis is the elegant route to (+)-morphine shown below.

ChemInform Abstract: Dual Hydrogen-Bond/Enamine Catalysis Enables a Direct Enantioselective Three-Component Domino Reaction.

2011

A dual system, composed of an enantioselective enamine catalyst and a multiple-hydrogen-bond catalyst achieves the three-component enantioselective aldehyde—nitroalkene—aldehyde domino reaction using either two similar or two different aldehydes.

Support effect on the catalytic performance of Au/Co3O4–CeO2 catalysts for CO and CH4 oxidation

2008

Gold-based catalysts supported on Co3O4, on CeO2 and on mixed Co3O4-CeO2 oxides were prepared by co-precipitation. They were tested in the catalytic oxidation of CO and CH4, in separate tests, and their activities were compared with that of the bare oxides. Tests of CH4 oxidation were performed in two consecutive runs in order to evaluate the catalysts stability. The effect of SO2 in the reactant mixture was investigated. The fresh and spent catalysts were analsed by XRD, BET, TPR and XPS techniques. Among the fresh catalysts, Au supported on CeO2 was the most active in CO oxidation whereas Au supported on Co3O4 was the most active for methane total oxidation. Synergy between the two oxides…

Giant Crown-Shaped Polytungstate Formed by Self-Assembly of CeIII-Stabilized Dilacunary Keggin Fragments

2010

Single crystals of Na40K6[Ni(H2O)6]3 [K@K7Ce24Ge12W120O456 (OH)12(H2O)64]· 178H2O are synthesized by addition of KCl to a NaOAc/AcOH buffer solution containing Ce(NO3)3, GeO2, Na2WO4, and NiCl2 followed by slow evaporation at room temperature (24% yield).

A Simple Organocatalytic Enantioselective Synthesis of Pregabalin

2009

This paper describes a new procedure for the enantioselective synthesis of the important anticonvulsant drug Pregabalin, which shows biological properties as the (S) enantiomer only. The key step of the synthetic sequence is the Michael addition reaction of Meldrum's acid to a nitroalkene mediated by a quinidine derived thiourea. A variety of novel catalysts bearing different groups at the thiourea moiety were synthesized and tested. The most successful catalyst that incorporates a trityl substituent provided up to 75 % ee of (S)-4. The conjugate addition reaction was carried out on a multigram scale with low loadings of catalyst (10 mol-%). Moreover, the catalyst can be recycled showing th…

The Preparation of 1,3-Divinylparabanic Acid (1,3-Divinylimidazoletrione) and its 4-Imino Derivative

1962

ChemInform Abstract: One-Pot Synthesis of Pyrrole-2-carboxylates and -carboxamides via an Electrocyclization/Oxidation Sequence.

2015

An electrocyclic ring closure is the key step of an efficient one-pot method for the synthesis of pyrrole-2-carboxylates and -carboxamides from chalcones and glycine esters or amides. The 3,4-dihydro-2H-pyrrole intermediates generated in situ are oxidized to the corresponding pyrroles by stoichiometric oxidants or by catalytic copper(II) and air in moderate to high yields. A wide range of functional groups are tolerated, and further combination with an in situ bromination gives access to polyfunctional pyrrole scaffolds.

Discrete supramolecular donor-acceptor complexes

2009

The renewed interest in noncovalently associating electroactive molecules arises in part from the quest for new organic materials that convert solar energy into electrical/ chemical equivalents. In this context, the formation of charge-separated states is a key prerequisite. Charge-transfer events triggered by light have been studied in supramolecular donor–acceptor systems based on hydrogen bonds and coordinative metal bonds. Although many of the most widely utilized electroactive fragments feature large pconjugated surfaces, to date the use of p–p aromatic interactions has mainly been limited to the construction of semi-infinite ensembles of chromophores either to achieve charge transport…