Henriette Molinari

Synthetic enzymes. Part 2. Catalytic asymmetric epoxidation by means of polyamino-acids in a triphase system

The asymmetric epoxidation of several chalcones and other electron-poor olefins, in the presence of catalytic amounts of poly-(S)-amino-acids in a triphase system with optical yields of up to 96% is described. The influence of the molecular structure of the catalysts and substrates, the solvent, and the temperature on the stereochemistry is discussed.

Synthetic enzymes—4 : Highly enantioselective epoxidation by means of polyaminoacids in a triphase system: influence of structural variations within the catalysts

Abstract The asymmetric epoxidation of chalcone and other electron-poor olefins in a triphase system (water-organic solvent-polyaminoacid) affords optically active oxiranes. The influence of the molecular structure of catalysts and of their secondary conformation on the enantioselectivity of the reaction has also been examined.

Asymmetric epoxidation of electron-poor olefins. V: Influence on stereoselectivity of the structure of poly-α-aminoacids used as catalysts

Abstract New poly-α-aminoacids modified at the C orN-terminal groups are synthetised and employed in the asymmetric epoxidation of chalcone. Their influence on the stereoselectivity of the reaction is studied.

Asymmetric synthesis of β-hydroxythioacetamides mediated by enantiomerically pure sulphiny1 derivatives

Abstract Enantiomerically pure P -tolyl sulphinyl-N,N-dimethylthioacetamide (1) was prepared starting from (-)-(S)-menthyl toluene- p -sulphinate. Aldol-type condensation of (1) and subsequent removal of the Sulphinyl group open an entry to optically active β-hydroxy thioacetamides in 40–90% e.e.

Highly Stereoselective Synthesis of Optically Active α,β-Epoxy Alcohols

Abstract Stereoselective zinc borohydride reduction of optically active α,β-epoxy ketones affords the corresponding alcohols with enantiomeric excess up to 95%.

Lipophilic cage ligands: synthesis, spectroscopic properties and applications

Macropolycyclic lipophilic ligands, capable of solubilizing inorganic salts in non polar organic solvents, can be efficiently used as anion activators or ion carriers through membranes. In this context we recently reported the synthesis of new lipophilic ligands 6 assisted by the template effect of sodium cation. Due to the high rigidity imposed by the short bridging chains ligands 6 form very stable sodium complexes in non—polar media, even when very hydrophilic and poorly polarizable anions are involved. This makes it easy to perform base—promoted reactions: e.g. carbanion formation from very weak carbon acids under phase-transfer conditions. X-Ray analysis of a sodium perchlorate complex showed that the cation is embedded in a on—symtric cubic cage. The assignment of all resonances of H and C NMR spectra was achieved by using two-dimensional techniques. At room temperature the free ligan1d3 is in a fast conformational equilibrium as shown by a C NMR investigation at variable temperature. However, in the sodium perchlorate complex only the portion of the molecule on the side of the alkyl group is affected by lowering the temperature, while the remaining part showed no conforma— tional change down to -60°C. Ligands 6 were obtained by continuous extraction with n-hexane from an aqueous solution of their methoxide or fluoride sodium complexes. This allowed the preparation an the+ stuy of complexes with different metal cations, as K , Ag , Cu etc..

Heterogeneous phase-transfer catalysts: high efficacy of catalysts bonded by a long chain to a polymer matrix

Heterogeneous phase-transfer catalysts, such as phosphonium salts and crown-ethers, immobilized on a polystyrene matrix, show an increase in activity approaching that of the corresponding non-immobilized catalysts, when they are bonded with a long spacer chain to the polymeric support.

Heterogeneous phase-transfer catalysts: onium salts, crown ethers, and cryptands immobilized on polymer supports

Typical phase-transfer catalysts, namely organophilic onium salts, crown ethers, and cryptands, when immobilized on a polymer matrix retain most of their catalytic activity, thus permitting catalyst recycling by simple filtration from the reaction medium.

A novel co-ordination mode of nitric oxide. Synthesis and crystal structure of the [{Re3(µ-H)3(CO)10}2(µ4-η2-NO)]– anion

Reaction of [Re3(µ-H)4(CO)10]– with NOBF4 in CH2Cl2 gives the [{Re3(µ-H)3(CO)10}2(µ4-η2-NO)]– anion, containing a nitrosyI group which holds together two triangular cluster moieties by bridging one edge of each triangle through both the N and O atoms.

13C NMR Investigation of the properties of the anion [Re3(μ-H)3(CO)10]2− in solution

Abstract 13 C NMR measurements were performed on [Re 3 (μ-H) 3 (CO) 10 ] 2− at various temperatures and field strengths. Selective decoupling allowed assignments of the carbonyl resonances. Spin-lattice relaxation time measurements indicated that two mechanisms, scalar coupling and chemical shielding anisotropy, contribute to the relaxation of carbon-13. Variable temperature experiments revealed that more than one mechanism is responsible for the fluxional behaviour.