Hybrid Organic-Inorganic Anatase as a Bifunctional Catalyst for Enhanced Production of 5-Hydroxymethylfurfural from Glucose in Water.

Hybrid organic-inorganic anatase (hybrid-TiO2 ) is prepared by a facile hydrothermal synthesis method employing citric acid. The synthetic approach results in a high surface-area nanocrystalline anatase polymorph of TiO2 . The uncalcined hybrid-TiO2 is directly studied as a catalyst for the conversion of glucose into 5-hydroxymethylfurfural (HMF). In the presence of the hybrid-TiO2 , HMF yields up to 45 % at glucose conversions up to 75 % were achieved in water at 130 °C in a monophasic batch reactor. As identified by Ti K-edge XANES, hybrid-TiO2 contains a large fraction of fivefold coordinatively unsaturated TiIV sites, which act as the Lewis acid catalyst for the conversion of glucose into fructose. As citric acid is anchored in the structure of hybrid-TiO2 , carboxylate groups seem to catalyze the sequential conversion of fructose into HMF. The fate of citric acid bound to anatase and the TiIV Lewis acid sites throughout recycling experiments is also investigated. In a broader context, this contribution outlines the importance of hydrothermal synthesis for the creation of water-resistant Lewis acid sites for the conversion of sugars. Importantly, the use of the hybrid-TiO2 with no calcination step contributes to dramatically decreasing the energy consumption in the catalyst preparation.

Stereodivergent Mannich reaction of bis(trimethylsilyl)ketene acetals with N-tert-butanesulfinyl imines by Lewis acid or Lewis base activation, a one-pot protocol to obtain chiral ß-amino acids.

We report a one-pot synthesis of chiral ß2,2,3-amino acids by the Mannich addition of bistrimethylsilyl ketene acetals to N-tert-butanesulfinyl imines followed by the removal of the chiral auxiliary. The synthesis and isolation of pure ß-amino acid hydrochlorides were conducted under mild conditions, without strong bases and this method is operationally simple. The stereoselective reaction was promoted by two different activation methods that lead to different stereoisomers: (1) Lewis Acid (LA) catalysis with boron trifluoride diethyl etherate and (2) Lewis Base (LB) catalysis with tetrabutylammonium difluorotriphenylsilicate. The reaction presented good diastereoselectivity with LB activation and moderate to good dr with LA catalysis. The exceptions in both protocols were imines with electron donating groups in the aromatic ring.

Tuning the Lewis acid phenol ortho-prenylation as a molecular diversity tool.

A diversity-oriented approach for the synthesis of various structurally different prenylated alcohols from readily accessible and common precursors was developed. With varying approaches, this article describes some successful examples of a Friedel-Crafts alkylation using methoxyphenols and different prenyl alcohols (geraniol and (E,E)-farnesol). We demonstrated that just by varying the stoichiometry of the Lewis acid used, the course of the reaction can be shifted to produce the alkylated or the cyclized product. Eighteen unique products were obtained with good isolated yields by direct alkylation with or without a consecutive π-cationic cyclization.

Lithium chloride-mediated stereoselective synthesis of cyclopropanecarboxamides from γ,δ-epoxy malonates through a domino cyclopropanation/lactonization/aminolysis process.

The stereoselective synthesis of novel multifunctionalized cyclopropanes from γ,δ-epoxy malonates and amines mediated by LiCl under mild conditions was carried out. This domino reaction involves the initial cyclopropanation via intramolecular ring-opening of γ,δ-epoxy malonates through the cooperative catalysis of LiCl (acting as a Lewis acid) and a Brønsted base (a primary or, in selected cases, a secondary amine). The sequential events consisted of lactonization and aminolysis of the lactone ring, which ultimately furnished cyclopropanecarboxamides with different substitution patterns in good isolated yields. In all cases, a quaternary stereogenic center could be perfectly assembled, with a single diastereoisomer being obtained. This method proceeds with high atom economy, is remarkably modular and operationally simple, and tolerates a variety of functional groups. The involvement of readily available starting materials, the broad scope, and the use of a sustainable solvent (methanol or ethanol) at ambient temperature make this domino process highly effective. A reaction mechanism is proposed on the basis of the experimental observations involving the preparation and reactivity of cyclopropylidene lactones as possible intermediates of the domino process.

Regional electrophilic and nucleophilic Fukui functions efficiently highlight the Lewis acidic/basic regions in ionic liquids.

The origin of catalysis and selectivity induced by room temperature ionic liquids in several organic reactions has putatively been associated with the concept of cation effect (hydrogen bond donor ability of the ionic liquids) or anion effect (hydrogen bond accepting ability of the ionic liquids). We show that there may be cases where this a priori classification may not be correctly assigned. Cations may concentrate both Lewis acidity and basicity functions in one fragment of the ionic liquid: an effect we tentatively call bifunctional distribution of the molecular Lewis acidity/basicity. Bifunctionality on the cation is however anion dependent through electronic polarization effects. The molecular distribution of the Lewis acidity/basicity may simply be assessed by evaluating the regional Fukui function within a reference ion pair structure. The model is tested for a set of nine ionic liquids based on the 1-butyl-3-methylimidazolium cation commonly used as solvent to run organic reactions.

On the reactivity of 23-methoxycarbonyl furospirostanes.

Brønsted and Lewis acid-catalysed reactions of the 23-methoxycarbonyl furospirostanic side chain are described. While bromination, deuteration and BF(3)·Et(2)O/AcOH treatment involve regioselective F-ring opening with exclusive participation of Δ(22)-furostenic intermediates, BF(3)·Et(2)O/Ac(2)O treatment leads to irreversible E- or F-ring cleavage.