Biomedical subjects

Olivier Hamelin

Publications and source records attributed to Olivier Hamelin.

5 recordsLinked to original sources

PubMed2005

Activation of oxaziridines by lewis acids: application in enantioselective sulfoxidation.

The preparation of new and easily accessible chiral N-alkyloxaziridines for asymmetric sulfides oxidation was investigated. Most significantly, we report here that inert N-alkyloxaziridines can be activated by Lewis acids to achieve a fast, selective, and efficient oxygen atom transfer to sulfides. Asymmetric sulfoxidation by three new chiral oxaziridines (two of them were structurally characterized by X-ray analysis) afforded enantioselectivities ranging from 22% to 63% ee with the simplest aryl alkyl sulfides.

Journal Article↗

PubMed2004

Crystallization-induced asymmetric transformation of chiral-at-metal ruthenium(II) complexes bearing achiral ligands.

Recently, we observed that the enantiopure Lambda form of the tributylammonium salt of the chiral anion tris[tetrachlorobenzene-1,2-bis(olato)]phosphate, also named Trisphat, was able to induce an efficient resolution of a Delta,Lambda racemic mixture of cis-[Ru(dmp)2(NCCH3)2](PF6)2 (dmp=2,9-dimethyl-1,10-phenanthroline) due to the spontaneous and selective precipitation of the heterochiral pair [Delta-Ru(dmp)2(CH3CN)2][Lambda-Trisphat]2. We report here that the combination of such a stereoselective precipitation process and irradiation results in the quantitative conversion of the initial [Ru(dmp)2(NCCH3)2]2+ racemate into only one of the two enantiomers. This is the first example in inorganic chemistry of an asymmetric transformation that leads to a chiral complex with no chiral ligand. Finally, three new racemic ruthenium bis(diimine) complexes, namely [Ru(dmp)2(NCCH3)Py](PF6)2 (Py=pyridine), [Ru(dmp)2(1,3-diaminopropane)](PF6)2, and [Ru(dmp)2(ethylenediamine)](PF6)2 were synthesized. For all of them, crystallization-induced asymmetric transformation proved to be an efficient way of obtaining the corresponding optically active chiral-at-metal complexes in high yields and with excellent stereoselectivities.

Journal Article↗

PubMed2003

Catalytic asymmetric sulfoxidation by chiral manganese complexes: acetylacetonate anions as chirality switches.

Three manganese(II) complexes, namely [Mn(1)(ClO(4))(2)] (3), [Mn(1)(acac)(2)] (4), and [Mn(2)(1)(acac)(4)] (5), were isolated from solutions of Mn(ClO(4))(2) or Mn(acac)(2), and an easily accessible diimine ligand (1S,2S)-N,N'-bis-pyridin-2-ylmethylene-cyclohexane-1,2-diamine (1). Their structure was determined by X-ray crystallography, and these complexes proved to be catalysts for asymmetric sulfide oxidation by H(2)O(2). Enantiomeric excesses ranging from 5% to 62% were obtained with a variety of aryl alkyl sulfides. We also observed an interesting "chirality switch" effect by the achiral acac anion reversing the enantioselectivity of the complex [Mn(1)(ClO(4))(2)] from the S to the R sulfoxide enantiomer.

Journal Article↗

PubMed2003

"Chiral-at-Metal" octahedral ruthenium(II) complexes with achiral ligands: a new type of enantioselective catalyst.

cis-[Ru(dmp)(2)(CH(3)CN)(2)][PF(6)](2) (dmp = 2,9-dimethyl-1,10-phenanthroline), complex 1[PF(6)](2), exists in two enantiomeric forms, Delta and Lambda. During treatment with the chiral anion tris[tetrachlorobenzene-1,2-bis(olato)]phosphate(V), also named Trisphat, in dichloromethane it has been possible to selectively precipitate each enantiomer, associated with Trisphat in the form of the heterochiral pair. This enantiomerically pure compound has been characterized in solution by UV-visible, CD, ESI-MS, and NMR spectroscopy and by X-ray crystallography in the solid state. Trisphat was also used as an NMR chiral shift reagent to determine the enantiomeric excess of the complex preparations. The "chiral-at-metal" ruthenium complex has been evaluated as a catalyst for the oxidation of sulfides to sulfoxides by hydrogen peroxide. The reactions displayed a low but significant level of enantioselectivity (18% ee in the case of 4-bromophenyl methyl sulfide). Our results thus provide the first demonstration that the chiral information carried by a stereogenic metal center can be catalytically transferred to molecules during stereoselective oxidation.

Journal Article↗

PubMed2002

First comprehensive bakkane approach: stereoselective and efficient dichloroketene-based total syntheses of (+/-)- and (-)-9-acetoxyfukinanolide, (+/-)- and (+)-bakkenolide A, (-)-bakkenolides III, B, C, H, L, V, and X, (+/-)- and (-)-homogynolide A, (+/-)-homogynolide B, and (+/-)-palmosalide C.

Cycloaddition of dichloroketene with dimethylcyclohexenes has been used as the key reaction in an efficient, general approach to the bakkanes. New methods and methodologies that have been developed in this work include spiro beta-methylene-gamma-butyrolactonizations, a vicinal dicarboxylation, an angelic ester preparation, a transesterification, an epoxy ketone double reduction, and a retro aldol-aldol approach to low-energy aldol isomers.

4-Butyrolactone↗