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The ring opening by the cleavage of the C(sp$^3$)–O bond of 2-hydroxybutyrolactone with (ethylthio)trimethylsilane was effectively catalysed by indium triiodide. Screening the reaction conditions allowed optimizing the ring opening. The effect of the nucleophile/catalyst ratio on the reaction efficiency has also been demonstrated. After optimization, 2-hydroxy-4-(ethylthio)butyric acid was isolated with an excellent yield (85%), thus making this method useful for the preparation of methionine analogues.

The BH3‐mediated reduction of P‐stereogenic hydroxyalkylphosphine oxides was investigated by Density Functional Theory calculations. By combining theoretical approaches with experimental observations, we explored two mechanisms that account for its stereospecificity, implying an inversion of the configuration at the phosphorus atom. One mechanism proceeds through a cyclic intermediate in which the coordination of borane to the oxygen atoms lowers the BH3.THF‐attack barrier. However, the free energy barrier for this combined process is too high for a reaction feasible at room temperature. The calculations rather support a second mechanism that proceeds through from the same cyclic intermediate and the in‐situ formation of BH4− as reducing agent. [ABSTRACT FROM AUTHOR]

A rhodium(III)‐based catalytic system has been used to develop a C−H bond activation of benzaldehyde derivatives and subsequent functionalization with dioxazolones in order to afford imides. The importance of the nature of the directing group to perform selectively the aldehydic C−H bond activation has been highlighted. The scope investigation showed that this transformation could be applied to various dioxazolones and many benzaldehyde derivatives as well as an acrolein derivative. Derivatization reactions of the imide products demonstrated the synthetic utility of this rhodium‐catalyzed aldehydic C−H amidation. [ABSTRACT FROM AUTHOR]

The racemization mechanism of tert‐butylphenylphosphido‐borane is investigated experimentally and theoretically. Based on this converging approach, it is shown, first, that several phosphido‐borane molecular species coexist at the time of the reaction and, second, that one particular of both initially assumed reactive routes most significantly contribute to the overall racemization process. From our converging modeling and experimental measurement, it comes out that the most probable species to be here encountered is a phosphido‐borane‐Li (THF)2 neutral solvate, whose P‐stereogenic center monomolecular inversion through a Y‐shaped transition structure (ΔrG°≠: 81 kJ mol−1) brings the largest contribution to the racemization process. [ABSTRACT FROM AUTHOR]

From achiral imidazolinium salts, chiral transition metal complexes containing an N‐heterocyclic carbene (NHC) ligand were prepared (metal = palladium, copper, silver, gold, rhodium). Axial chirality in these complexes results from the formation of the metal‐carbene bond leading to the restriction of rotation of dissymmetric N‐aryl substituents about the C–N bond. When these complexes exhibited a sufficient configurational stability, a resolution by chiral high‐performance liquid chromatography (HPLC) on preparative scale enabled isolation of enantiomers with excellent enantiopurities (>99% ee) and good yields. A study of the enantiomerization barriers revealed the effect of the backbone nature as well as the type of transition metal on its values. Nevertheless, the evaluation of palladium‐based complexes in asymmetric intramolecular α‐arylation of amides demonstrated that the ability to induce an enantioselectivity cannot be correlated to the configurational stability of the precatalysts. [ABSTRACT FROM AUTHOR]

Verkade's superbases, entrapped in the cavity of enantiopure hemicryptophane cages, have been synthesized with enantiomeric excess (ee) superior to 98%. Their absolute configuration has been determined by using electronic circular dichroism (ECD) spectroscopy. These enantiopure encaged superbases turned out to be efficient chiral derivatizing agents for chiral azides, underlining that the chirality of the cycloveratrylene (CTV) macrocycle induces different magnetic and chemical environments around the phosphazide functions. [ABSTRACT FROM AUTHOR]

Access to hydroxy-functionalized P-chiral phosphine-boranes has become an important field in the synthesis of P-stereogenic compounds used as ligands in asymmetric catalysis. A family of optically pure α and β-hydroxyalkyl tertiary phosphine-boranes has been prepared by using a three-step procedure from readily accessible enantiopure adamantylphosphinate, obtained by semi-preparative HPLC on multigram scale. Firstly, a two-step one-pot transformation affords the enantiopure hydroxyalkyl tertiary phosphine oxides in good yields and enantioselectivities. The third step, BH3-mediated reduction, allows the formation of the desired phosphine-boranes with excellent stereospecifity. The mechanistic study of this reduction provides new evidence to elucidate the crucial role of the pendant hydroxy group and the subsequent activation of the PO bond by the boron atom. [ABSTRACT FROM AUTHOR]

In this paper we describe the synthesis of functionalised mesoporous organosilicas containing a mannitol derivative in the framework. For this purpose, a bis-silylated precursor 3,4-Di-O-[3-(triethoxysilylpropyl)carbamate]-1,2:5,6-di-O-isopropylidene-D-mannitol was prepared by coupling of 1,2:5,6-di-O-isopropylidene-D-mannitol with 3-(triethoxysilylpropyl)isocyanate. The framework-functionalised materials were obtained in one step by the “direct synthesis” method which consists of a co-hydrolysis and polycondensation of a bis-silylated mannitol precursor with tetraethylorthosilicate (TEOS) in the presence of a non-ionic triblock co-polymer (P123) as structure-directing agent. Interestingly, deprotection of the 1,2,5,6 OH functional groups occurred during the material synthesis. The obtained solids were characterized by 13C and 29Si CP-MAS NMR, N2adsorption-desorption, powder X-ray diffraction, TEM and elemental analysis. We have shown that, the OH functional groups, which are released during the synthesis of the mesoporous silica, can be used for chelation of ions and stabilisation of nanoparticles. The subsequent growth of gold (0) nanoparticles in the wall has been investigated and evidenced. [ABSTRACT FROM AUTHOR]

2-Ferrocenyl- and 2-phenyl-N-n-butylbenzimidazoles were synthesized to evaluate the influence of the benzimidazole functional group upon their directed lithiation. The regiochemistry of lithiation was studied, as well as the effect of stabilization of the lithiated species by diamine coordination using tetramethyl-ethylenediamine and (-)-sparteine. The lithiations were followed by reaction with a variety of electrophiles to give the disubstituted 2-ferrocenyl- and 2-phenyl-N-n-butylbenzimidazoles compounds. This study showed that despite a simple n-butyl function on the benzimidazole, directed lithiation was readily achieved with high regiocontrol on the ferrocenyl and phenyl groups. (-)-Sparteine failed to provide asymmetric induction in the ferrocene system, and its inefficiency is explained by intramolecular coordination of the lithiated species by the benzimidazole nitrogen, which is preferred over sparteine coordination. [ABSTRACT FROM AUTHOR]