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Emmanuel Lacôte

Publications and source records attributed to Emmanuel Lacôte.

15 recordsLinked to original sources
PubMed2006

Production and reactions of organic-soluble lanthanide complexes of the monolacunary Dawson [alpha1-P2W17O61]10- polyoxotungstate.

The incorporation of lanthanides into polyoxometalates provides entry to new classes of potentially useful materials that combine the intrinsic properties of both constituents. To utilize the [alpha1-Ln(H2O)4P2W17O61]7- species in applications of catalysis and development of luminescent materials, the chemistry of this family of lanthanide polyoxometalates in organic solvents has been developed. Organic-soluble polyoxometalate-lanthanide complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] (Ln = La(III), Sm(III), Eu(III), Yb(III)) were prepared and characterized by elemental analysis, acid-base titration, IR, 31P NMR, and mass spectrometry. The synthetic procedure involves a cation metathesis reaction in aqueous solution under strict pH control. A solid-liquid-phase transfer protocol yielded a unique species (TBA)8K3[Yb(alpha1-YbP2W17O61)2] with three ytterbium ions and two [alpha1-P2W17O61]10- polyoxotungstates. A centrosymmetric dimeric complex [{alpha1-La(H2O)4P2W17O61}2]14- was crystallized from aqueous solution and characterized by X-ray diffraction. ESI mass spectral analysis of the complexes TBA5H2[alpha1-Ln(H2O)4P2W17O61] shows that similar dimers exist in organic solution, in particular for the early lanthanides. Fragmentation in the mass spectrometer of the complexes from dry acetonitrile solution involves double protonation of an oxo ligand and loss of one water molecule. Low mass tungstate fragments combine into [(WO3)n]2- (n = 1-5) ions and their condensation products with phosphate. Reaction of TBA5H2[alpha1-Eu(H2O)4P2W17O61] with 1,10-phenanthroline or 2,2'-bipyridine showed an increase of the europium luminescence. This result is explained by the formation of a ternary complex of [alpha1-Eu(H2O)4P2W17O61]7- and two sensitizing ligands.

Cations↗
PubMed2006

Improved method for the iodine(III)-mediated preparation of aryl sulfonimidates.

[reaction: see text] One-pot hypervalent iodine-mediated oxidations of arylsulfinamides to arylsulfonimidates is reported. Contrary to the case of alkylsulfinamides, use of iodosobenzene was not satisfactory. The reaction worked best with diacetoxyiodosobenzene (DIB) and a mild base (MgO). The influence of substituents on the iodine(III) reagent arene has been examined.

Journal Article↗
PubMed2005

Recent advances in the use of phosphorus-centered radicals in organic chemistry.

This tutorial review aims at presenting recent contributions dealing with organic chemistry of organophosphorus radicals. The first part briefly lays out the physical organic background of such intermediates. In a second part the use of organophosphorus radicals possessing a P-H bond that can undergo homolytic cleavage as alternative mediators is detailed. The third part is focused on radical additions of phosphorus-centered radicals to unsaturated compounds, an old reaction that is being rejuvenated. Lastly, radical eliminations of phosphorus-centered radical are introduced in the fourth part. Most of the latter are relatively novel reactions, and have never been reviewed previously.

Chemistry, Organic↗
PubMed2005

Efficient preparation of functionalized hybrid organic/inorganic Wells-Dawson-type polyoxotungstates.

Hybrid organic/inorganic Wells-Dawson polyoxotungstates have been prepared through addition of functionalized tricholorostannanes to lacunary alpha(2)- and alpha(1)-[P(2)W(17)O(61)](10-). Coupling of amines and alcohols to polyoxotungstate platforms led to new structures in good yields. Coupling of chiral amines to the previously unknown organotin-substituted alpha(1) derivatives allowed the isolation of diastereomers, which feature in some cases split (1)H, (13)C, and (31)P NMR spectra. This is the first example of NMR observation of a single pair of diastereomers in the alpha(1)-Wells-Dawson series. It opens the way to potential resolution of those chiral polyoxotungstates.

Journal Article↗
PubMed2004

Efficient copper-mediated reactions of nitrenes derived from sulfonimidamides.

[reaction: see text] Sulfonimidamides lead efficiently to nitrenes and have been converted to sulfimides, sulfoximines, and aziridines in good yields, through a copper-mediated multicomponent reaction. The stereogenic sulfur atom and the trivalent nitrogen atom present in the molecules open the way to asymmetric synthesis, whose first results are presented.

Journal Article↗
PubMed2004

A radical show.

Explore the source record for details and available documents.

Journal Article↗
PubMed2004

Reactivity of beta-lactamido N-sulfonyl radicals.

[reaction: see text] A new class of N-substituted radical has been studied. Obtained from the corresponding chlorides, beta-lactamido N-sulfonyl radicals were allylated and added onto electron-rich olefins. It has been shown that the radicals do not undergo desulfonylation and are electrophilic in nature.

Journal Article↗
PubMed2004

Iodine(III)-mediated preparations of nitrogen-containing sulfur derivatives: dramatic influence of the sulfur oxidation state.

Reaction of sulfonamides with iodosobenzene leads to phenyliodinanes. A new catalysis reaction of the decomposition of these products in the presence of sulfoxides that allows the smooth synthesis of sulfoximines has been evidenced and studied: copper(II) salts were used to prepare compounds 4 a-j and 5 b, d, f, j, k from the corresponding, easily prepared, sulfoxides. The reactions proceed with retention of configuration at the sulfur center, and copper(II) triflate is the best candidate for the catalyst for the imination. Switching from sulfonamides to sulfinamides in the preparation of the starting iodinanes completely alters the reaction pathway: iodinanes are no longer accessible, and sulfonimidates 7 a-j are obtained instead. This behavior can be rationalized by the increase in pK(a) brought about by the removal of one oxygen atom from the sulfur center. Sulfonimidates are interesting molecules with varied applications. Optimization of their one-pot synthesis has been achieved by carrying out the reaction in acetonitrile. The stereochemical study has shown that the transformation proceeds with global retention of the configuration at the sulfur center, albeit with erosion of the enantiomeric purity. A model accounting for this outcome is proposed. In addition, the presence of oxidized sulfonamide by-products has been explained, and this latter pathway becomes the sole one when alcohol is replaced by water. Good yields of the oxidized products are obtained.

Journal Article↗
PubMed2002

The practical synthesis of a novel and highly potent analogue of bryostatin.

Macrocycle 1 is a new highly potent analogue of bryostatin 1, a promising anti-cancer agent currently in human clinical trials. In vitro, 1 displays picomolar affinity for PKC and exhibits over 100-fold greater potency than bryostatin 1 when tested against various human cancer cell lines. Macrocycle 1 can be generated in clinically required amounts by chemical synthesis in only 19 steps (LLS) and represents a new clinical lead for the treatment of cancer.

Antineoplastic Agents↗
PubMed2002

A new practical one-pot access to sulfonimidates.

Sulfonimidates were prepared from sulfinamides and iodosobenzene in a very mild one-pot procedure in good to excellent yields. This reaction allows quick and efficient access to a class of molecules of important synthetic as well as biological and industrial interest. [reaction: see text]

Journal Article↗
PubMed2002

Stereoselective transition metal-catalyzed and radical polycyclizations.

This short review presents a selection of metal-mediated and radical polycyclizations reported during the past two years. Palladium-catalyzed domino processes, cobalt-mediated cycloadditions and Pauson-Khand reactions catalyzed by rhodium are described. Ruthenium and platinum are shown as powerful metal catalysts in cyclizations, ring-closing metathesis and cycloisomerizations. Finally, recent examples of radical cascades, and their synthetic applications, are selected for their ability to build polycyclic compounds.

Animals↗