Mesoporous Metal Complex–Silica Aerogels for Environmentally Friendly Amination of Allylic Alcohols

Two series of mesoporous hybrid iron(III) complex–silica aerogels were prepared in one-pot synthesis by using the sol–gel coordination chemistry approach. The use of the ligands 3-(2-aminoethylamino)propyltrimethoxysilane and 2-(diphenylphosphino)ethyltriethoxysilane, both with terminal triethoxysilyl groups, were used to incorporate metal complexes in situ into the framework of silica, through their co-condensation with a silicon alkoxide during the aerogel formation. This methodology yielded optically translucent hybrid mesoporous gels with homogeneous metal incorporation and excellent textural properties. The catalytic performance of these materials was tested in the direct amination of allylic alcohols in water as a target reaction, with activities comparable or even higher than those corresponding to the homogeneous iron(III) complex. Furthermore, these catalysts were stable and maintained their catalytic activity after six reaction cycles.

Organocatalytic Asymmetric α-Chlorination of 1,3-Dicarbonyl Compounds Catalyzed by 2-Aminobenzimidazole Derivatives

Bifunctional chiral 2-aminobenzimidazole derivatives 1 and 2 catalyze the enantioselective stereodivergent α-chlorination of β-ketoesters and 1,3-diketone derivatives with up to 50% ee using N-chlorosuccinimide (NCS) or 2,3,4,4,5,6-hexachloro-2,5-cyclohexadien-1-one as electrophilic chlorine sources.

Impregnated palladium on magnetite as catalyst for direct arylation of heterocycles

Palladium impregnated on magnetite is an efficient, cheap and easy to prepare catalyst for the direct arylation of heterocycles. Good yields are afforded under relatively mild conditions and a broad substrate scope is evident. The catalyst is regioselective in many cases, affording arylated products, at the C2- or C3-position (depending of the heterocycle used). The methodology can be extended to prepare chromenes through an intramolecular direct arylation reaction. Some evidence is provided for two catalyst deactivation pathways, which prevents efficient recycling.

Cross-dehydrogenative coupling reaction using copper oxide impregnated on magnetite in deep eutectic solvents

The synthesis of different tetrahydroisoquinolines using choline chloride : ethylene glycol as a deep eutectic solvent (DES) and copper(II) oxide impregnated on magnetite as a catalyst has been accomplished successfully. The copper catalyst amount is the lowest loading ever reported. The presence of DES showed to be essential since the reaction in the absence of this medium did not proceed. A direct proportional relationship was found between the conductivity of DES medium and the yield obtained. The DES and the catalyst could be reused up to ten times without any detrimental effect on the yield of the reaction, with the aerobic conditions making the protocol highly sustainable, where the only waste is water.

Pursuing Chemical Efficiency by Using Supported Organocatalysts for Asymmetric Reactions under Aqueous Conditions

Over the past decade, a great effort has been made by the chemical community to improve the efficiency of organic transformations and allow sustainable processes. Merging the use of supported and recyclable organocatalysts and aqueous conditions for the asymmetric synthesis of valuable molecules, has led to outstanding contributions in the area of green chemistry. Recent progresses in the field include the implementation of these methodologies in the large scale production of chiral molecules using automated flow chemistry.

Bio-renewable enantioselective aldol reaction in natural deep eutectic solvents

Among the deep eutectic solvents (DES), natural deep eutectic solvents (NADES) formed by D-glucose and racemic malic acid are suitable media to perform the enantioselective L-proline catalyzed intermolecular aldol reaction, creating simultaneously and selectively a C–C bond and a new stereocenter. The scope of the reaction was found to be broad, with products being obtained with good levels of diastereo- and enantioselectivities. Furthermore, when the reaction was performed at a large scale, the catalyst together with the reaction media can be recovered by simple water extraction and reused at least three times affording similar results. Therefore, the use of NADES as reaction media to carry out a VOC-free selective process has been demonstrated for the first time. The process is clean, cheap, simple and scalable and meets most of the criteria to be considered as a sustainable and bio-renewable process, with the reaction media and catalyst arising directly from Nature.

Palladium(II) oxide impregnated on magnetite as a catalyst for the synthesis of 4-arylcoumarins via a Heck-arylation/cyclization process

Heck-arylation/cyclization was achieved using heterogeneous palladium(II) oxide impregnated on magnetite catalyst (2.5 mol%) with a lower catalyst loading than that reported for similar processes. Ethanol was used as a non-toxic and bio-renewable solvent. Good yields were afforded using a broad range of substrates (40–98%). The catalyst could be partially recycled, and analyses confirmed the almost total reduction of palladium(II) oxide to palladium(0) as well as the iodine poissoning effect, which is the main barrier to complete recyclability.

La Reacreditación en el Grado de Biología de la Facultad de Ciencias de la Universidad de Alicante

Implantación de los nuevos Grados, como sustitución de las Licenciaturas en los estudios universitarios, lleva consigo un proceso de Reacreditación, consistente en la revisión de una serie de parámetros de calidad, a realizar una vez terminada su implantación. Este proceso se ha desarrollado en tres ámbitos principales: la Gestión del Título, los Recursos de los que se dispone y, por último, los Resultados, y tiene como fin principal evaluar si los resultados obtenidos son adecuados para garantizar la continuidad de la impartición del Grado. El equipo de trabajo que ha llevado a cabo la revisión y ha puesto en marcha los procesos de mejora en el Grado de Biología de la Facultad de Ciencias de la Universidad de Alicante ha sido la Comisión de Título. La revisión que dicha Comisión ha realizado se ha centrado en evaluar la adquisición de competencias por parte de los estudiantes, en los recursos humanos y materiales que soportan el desarrollo del título, y en el análisis de la evolución de los resultados del mismo. Toda la información generada en este grupo de trabajo, ha sido volcada a la aplicación “AstUA” con la que se gestionan los programas de calidad de toda la Universidad de Alicante.

On the reactivity of naphthalene and biphenyl dianions: tying up loose ends concerning an SN2-ET dichotomy in alkylation reactions

Naphthalene and biphenyl dianions are interesting compounds that can be obtained by double reduction of the corresponding arenes in solution with certain alkali metals. These dianions are highly reactive and rather elusive species with very high laying and highly delocalized electrons. They share many aspects of the reactivity of the alkali metal they originated from and consequently behave primarily as strong electron transfer (ET) reagents. We report here kinetic evidence for a different type of reactivity in their alkylation reactions with alkyl fluorides. By using cyclopropylmethyl fluoride (c-C3H5CH2F) as a very fast radical probe, we were able to settle that this alkylation does not involve the classical electron transfer reaction followed by radical coupling between diffusing radicals, but supports the alternative SN2 concerted mechanism, discerning thus this mechanistic SN2-ET dichotomy.

A comparative study of hydroxyl- and carboxylate-functionalized imidazolium and benzimidazolium salts as precursors for N-heterocyclic carbene ligands

The preparation of imidazolium and benzimidazolium salts with hydroxyl or carboxylate functions has been achieved using straightforward synthetic pathways. These salts in combination with palladium(II) acetate give active catalytic systems for Suzuki reaction. A comparative study has been performed, which has revealed that both the heterocycle and the functional group are important for the catalytic activity and stability of the catalyst.

Synthesis of 3,5-Disubstituted Isoxazoles and Isoxazolines in Deep Eutectic Solvents

The synthesis of different 3,5-disubstituted isoxazoles and related isoxazolines using choline chloride:urea as deep eutectic solvent (DES) in a one-pot three step reaction has been accomplished successfully. The use of highly nucleophilic functionalized DES did not affect the process where highly electrophilic reagents or intermediates are involved. The presence of DES showed to be essential since the reaction in absence of this media did not proceed. The DES media could be reused up to five times without a detrimental effect on the yield of the reaction. To exemplify the synthetic potential of this methodology, the reaction was scaled up to the gram scale without any noticeable problem. Finally, different isoxazoles were easily transformed into β-aminoenones.

Reduction of 1,2-dicarbonyl compounds and of their N-phenylimine derivatives by sodium cyanide under aprotic conditions

Some aromatic 1,2-dicarbonyl compounds, i.e. 9,10-phenanthrenequinone, acenaphthenequinone and benzil, and their corresponding N-phenyl monoimines, have been reduced, using dry acetonitrile as the solvent, in the presence of sodium cyanide as a reducing agent. Comparative potentiostatic preparative-scale electrolysis is described.

Direct synthesis of β-ketophosphonates and vinyl phosphonates from alkenes or alkynes catalyzed by CuNPs/ZnO

Copper nanoparticles (CuNPs) supported on ZnO have been shown to effectively catalyze the direct synthesis of β-ketophosphonates from alkenes or alkynes, and that of vinyl phosphonates from alkynes and diethylphosphite, under air and in the absence of any additive or ligand. When using alkynes as starting materials, the selectivity proved to be dependent on the nature of the alkyne. Thus, alkynes conjugated with an aromatic ring or a carbon–carbon double bond gave β-ketophosphonates as the main reaction products, whereas aliphatic alkynes or alkynes conjugated with a carbonyl group led to the formation of the corresponding vinyl phosphonates.

Copper Nanoparticles in Click Chemistry

Conspectus: The challenges of the 21st century demand scientific and technological achievements that must be developed under sustainable and environmentally benign practices. In this vein, click chemistry and green chemistry walk hand in hand on a pathway of rigorous principles that help to safeguard the health of our planet against negligent and uncontrolled production. Copper-catalyzed azide–alkyne cycloaddition (CuAAC), the paradigm of a click reaction, is one of the most reliable and widespread synthetic transformations in organic chemistry, with multidisciplinary applications. Nanocatalysis is a green chemistry tool that can increase the inherent effectiveness of CuAAC because of the enhanced catalytic activity of nanostructured metals and their plausible reutilization capability as heterogeneous catalysts. This Account describes our contribution to click chemistry using unsupported and supported copper nanoparticles (CuNPs) as catalysts prepared by chemical reduction. Cu(0)NPs (3.0 ± 1.5 nm) in tetrahydrofuran were found to catalyze the reaction of terminal alkynes and organic azides in the presence of triethylamine at rates comparable to those achieved under microwave heating (10–30 min in most cases). Unfortunately, the CuNPs underwent dissolution under the reaction conditions and consequently could not be recovered. Compelling experimental evidence on the in situ generation of highly reactive copper(I) chloride and the participation of copper(I) acetylides was provided. The supported CuNPs were found to be more robust and efficient catalyst than the unsupported counterpart in the following terms: (a) the multicomponent variant of CuAAC could be applied; (b) the metal loading could be substantially decreased; (c) reactions could be conducted in neat water; and (d) the catalyst could be recovered easily and reutilized. In particular, the catalyst composed of oxidized CuNPs (Cu2O/CuO, 6.0 ± 2.0 nm) supported on carbon (CuNPs/C) was shown to be highly versatile and very effective in the multicomponent and regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles in water from organic halides as azido precursors; magnetically recoverable CuNPs (3.0 ± 0.8 nm) supported on MagSilica could be alternatively used for the same purpose under similar conditions. Incorporation of an aromatic substituent at the 1-position of the triazole could be accomplished using the same CuNPs/C catalytic system starting from aryldiazonium salts or anilines as azido precursors. CuNPs/C in water also catalyzed the regioselective double-click synthesis of β-hydroxy-1,2,3-triazoles from epoxides. Furthermore, alkenes could be also used as azido precursors through a one-pot CuNPs/C-catalyzed azidosulfenylation–CuAAC sequential protocol, providing β-methylsulfanyl-1,2,3-triazoles in a stereo- and regioselective manner. In all types of reaction studied, CuNPs/C exhibited better behavior than some commercial copper catalysts with regard to the metal loading, reaction time, yield, and recyclability. Therefore, the results of this study also highlight the utility of nanosized copper in click chemistry compared with bulk copper sources.

Recent Advances in the Direct Nucleophilic Substitution of Allylic Alcohols through SN1-Type Reactions

Direct nucleophilic substitution reactions of allylic alcohols are environmentally friendly, since they generate only water as a byproduct, allowing access to new allylic compounds. This reaction has, thus, attracted the interest of the chemical community and several strategies have been developed for its successful accomplishment. This review gathers the latest advances in this methodology involving SN1-type reactions.