Ciril Jimeno

A highly active catalyst for Huisgen 1,3-dipolar cycloadditions based on the tris(triazolyl)methanol-Cu(I) structure.

A new tris(1-benzyl-1H-1,2,3-triazol-4-yl)methanol ligand 3 has been prepared by a triple Cu(I)-catalyzed alkyne-azide 1,3-dipolar cycloaddition (CuAAC). Ligand 3 forms a stable complex with CuCl, which catalyzes the Huisgen 1,3-dipolar cycloaddition on water or under neat conditions. Low catalyst loadings, short reaction times at room temperature, and compatibility with free amino groups make 3.CuCl an outstanding catalyst for CuAAC.

Covalently immobilized tris(triazolyl)methanol–Cu(I) complexes: highly active and recyclable catalysts for CuAAC reactions

Tris(1-benzyl-1H-1,2,3-triazol-4-yl)methanol (3), a highly efficient ligand for CuAAC reactions, has been immobilized onto Merrifield resins through different strategies. The SN2-supported Cu complex (8) is stable in water and under air; it is active at low catalyst loadings (1 mol%) and at low concentration (down to 0.125 M) in both aqueous and purely organic media. Resin 8 can be repeatedly reused in 1 : 1 MeOH–water for short reaction times (4 h) with the only precaution of Cu(I) reloading every five cycles.

Synthesis of functional cobalt nanoparticles for catalytic applications. Use in asymmetric transfer hydrogenation of ketones

Long chain carboxylic acids functionalized at the ω position with chiral amino alcohol fragments have been used to stabilize cobalt nanoparticles prepared by thermal decomposition of Co2(CO)8. The first examples of chirally modified cobalt nanoparticles have been prepared in this manner and used as magnetically decantable ligands in the Ru-catalyzed asymmetric transfer hydrogenation of ketones.

Structural optimization of enantiopure 2-cyclialkylamino-2-aryl-1,1-diphenylethanols as catalytic ligands for enantioselective additions to aldehydes.

The structural optimization of a family of modular, enantiopure beta-amino alcohol ligands with a common 2-amino-2-aryl-1,1-diphenylethanol skeleton, whose stereogenicity was introduced through the Jacobsen epoxidation of 1,1-diphenyl-2-arylethylenes, has led to the identification of a small set of optimal catalysts with enhanced activity and enantioselectivity in the addition of alkylzinc and arylzinc reagents to aldehydes. Criteria for the discrimination between apparently analogous, highly enantioselective ligands are proposed.

The dual-catalyzed (amino alcoho/Lewis acid) enantioselective addition of diethylzinc to N-diphenylphosphinoyl imines

Abstract Optimal structural characteristics within a family of (2 R ,3 R )-1-alkoxy-3-dialkylamino-3-phenyl-2-propanols have been determined for maximum enantioselectivity in the addition of diethylzinc to N -diphenylphosphinoyl imines (1-alkoxy = trityloxy; 3-dialkylamino = piperidino). The simultaneous use of silylating agents acting as Lewis acids to induce rate acceleration has been investigated, allowing the identification of triisopropylsilyl chloride and tert -butyldiphenylsilyl chloride as the most efficient mediators in terms of rate enhancement and enantiomeric excess of the resulting phosphinamides.

Covalent Heterogenization of Asymmetric Catalysts on Polymers and Nanoparticles

The development of enantioselective processes involving the use of catalytic species covalently bonded onto polymers and nanoparticles has gained a considerable importance over the last decade, as sustainability concerns have deeply influenced the practice of chemistry. In this review, an overview is given of the different strategies followed for the covalent immobilization of ligand–metal assemblies (for metal catalysis) and catalytic organic molecules (for organocatalysis) onto organic polymers and nanoparticles, paying special attention to the factors that control catalytic activity and enantioselectivity. Efforts devoted to the development of continuous flow processes with immobilized catalysts of these types are also reviewed.

Intramolecular hydrogen bonding guides a cationic amphiphilic organocatalyst to highly stereoselective aldol reactions in water

A novel amphiphilic guanidine organocatalyst, efficient for asymmetric aldol reactions of ketones in water at neutral pH, is disclosed. The reaction presented a clear substrate dependence depicting a free energy linear correlation with ee. Intramolecular hydrogen bonding in the acylguanidine moiety was identified as the key structural motif.

Two distinct conformations of GABA locked by embedding in the bicyclo[3.1.0]hexane core structure.

Bicyclo[3.1.0]hexane and diverse heteroanalogues containing nitrogen, oxygen, or sulfur atoms in the five-membered ring have been recognized as interesting core structures of small molecules with diverse biological activities. They have been used as conformationally locked analogues of nucleoside building blocks and as intrinsically interesting building blocks in numerous other applications. They have been reported as intermediates in natural compound synthesis, or as constituents of bioactive compounds, 19] novel materials, and catalysts. Methanoproline 1, a naturally occurring inhibitor of proline metabolism, and 3-azabicyclo[3.1.0]hex-6-ylamine 2, a constituent of the potent broad-spectrum antibiotic trovafloxacin, are particularly prominent examples. They led to the design of the hybrid structure 3 as a conformationally locked basic amino acid analogue. Other ways to embed amino acid units such as glutamate into the bicyclo[3.1.0]hexane scaffold are illustrated by structure 4 or its corresponding 2-oxaand 2-thia-analogues 5 and 6 (Figure 1). Such compounds or further functionalized derivatives have been described by various research groups 22] and have resulted in highly potent metabotropic glutamate receptor antagonists or agonists. In all these examples, an extended conformation of the glutamate moiety was attempted and achieved. To the best of our knowledge, the prototypic 2aminobicyclo[3.1.0]hexane-6-carboxylic acid 7 a and its C2 epimer 8 a have not yet been prepared. Both contain an embedded g-aminobutyric acid (GABA) unit. Based on the structural results obtained for the bicyclic glutamate analogues, 6, 7] the GABA unit in 7 a,b should be locked in a fully extended conformation. In contrast, the corresponding C2 epimer 8 a,b should lock the GABA unit in a distinctly different conformation, depending on the conformational robustness of the bicyclic core system. A bicyclo[3.1.0]hexane core structure with or without embedded heteroatoms in the five-membered ring could, in principle, adopt three distinct conformations. An envelope conformation with an essentially planar five-membered ring (see Figure 2 b) is typically encountered for five-membered rings with conjugated exocyclic double bonds (e.g. , lactones, lactams, anhydrides, imides). For saturated (hetero)bicyclo[3.1.0] systems, five-membered ring envelope conformations are expected due to the structural constraints by the annelated cyclopropane unit (exerting a similar constraint as an endocyclic double bond), with the flap either anti (chair-type, Figure 2 a) or syn (boat-type, Figure 2 c) to the cyclopropane unit.

TEMPO-mediated, room temperature synthesis of pure CoO nanoparticles

Treatment of dicobalt octacarbonyl with TEMPO in THF at room temperature, in the presence of oleic acid as the sole additive, leads to the formation of monodisperse nanoparticles (ca. 3.0 nm diameter) of CoO; the particles agglomerate in solution at room temperature into aggregates, and this property has been used for the controlled preparation of hybrid materials.

Hafnia–Silica Cryogels: Solvent‐Assisted Textural and Catalytic Control in the Citronellal Cyclization

A series of hafnia–silica mixed oxides of HfO2(SiO2)8 stoichiometry were prepared by a sol–gel method followed by freeze‐drying. Two hafnium precursors, Hf(OiPr)4 and Hf(OtBu)4 were examined under a variety of aqueous–alcoholic systems. A decisive dependence of the alcoholic solvent on the gel formation and the surface and porosity of the final materials was found, which in turn were key to the enhancement of catalysis. Hence, acid hydrolysis and gelification of Hf(OiPr)4 in tert‐butyl alcohol, followed by lyophilization, yielded a material with the highest mesoporosity and specific surface area. This catalyst behaved most efficiently in the acid‐catalyzed cyclization of citronellal to isopulegol at room temperature. Furthermore, this cryogel also presented combined Lewis acidity and hydrogen bonding that resulted in higher diastereoselectivity for the above reaction. These results highlight the effect of how the textural and, therefore catalytic, properties of the cryogels depend decisively on the solvents chosen for their synthesis.