481 research outputs found

    Organocatalysis in total synthesis

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    Synthesis of interesting β-nitrohydrazides through a thiourea organocatalysed aza-Michael addition

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    The synthesis of antimicrobial β-nitrohydrazides, as the target product of our reaction, is reached for the first time under organocatalytic enantioselective conditions. We accomplish this goal by using a thiourea organocatalysed aza-Michael addition reaction of hydrazide to nitroalkenes, furnishing final products with good yields and good enantiomeric ratios. The developed methodology is one of the rare examples of catalytic reactivity using hydrazide where the reaction proceeds through its N2 atom. Our developed strategy extends the generality of this area of research due to the difficulties of designing new nitrogen nucleophiles with high activity, and in addition, this is one of the scarce examples where nitroalkenes and chiral thioureas have been used in asymmetric organocatalytic aza-Michael addition reactions. © 2014 The Royal Society of Chemistry.We thank the Spanish Ministry of Economía y Competitividad (MICINN. Madrid. Spain. Project CTQ2010-19606) and the Government of Aragón (Zaragoza. Spain. Research Group E-10) for financial support of our research.Peer Reviewe

    Thiourea-catalyzed addition of indoles to aliphatic β,γ-unsaturated α-ketoesters

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    Communication.A thiourea-catalyzed addition reaction with indoles to aliphatic β,γ-unsaturated α-ketoesters has been developed. The easily accessible thiourea aminoindanol derivative makes this approach an interesting alternative for the use of these aliphatic substrates, very scarcely employed in previously reported procedures, highlighting the complementarity of the strategy presented here. The final adducts, which are valuable intermediates for synthesizing the corresponding α-amino acid or α-hydroxy acid derivatives, are obtained in good yields and enantiomeric excess under mild reaction conditions.We thank the Ministry of Science and Innovation (MICINN. Madrid. Project CTQ2013-44367-C2-1-P) and the University of Zaragoza (JIUZ-2014-CIE-07) for financial support of our research.Peer reviewe

    Organocatalytic Enantioselective Henry Reactions

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    This is an open access article distributed under the Creative Commons Attribution License.A large number of interesting organocatalytic enantioselective protocols have been explored and successfully applied in the last decade. Among them, the Henry (nitroaldol) reaction represents a powerful carbon-carbon bond-forming procedure for the preparation of valuable synthetic intermediates, such as enantioenriched nitro alcohols, which can be further transformed in a number of important nitrogen and oxygen-containing compounds. This area of research is still in expansion and a more complex version of this useful process has recently emerged, the domino Michael/Henry protocol, affording highly functionalized cycles with multiple stereogenic centers.We thank the Spanish Ministry of Science and Innovation (Projects CTQ2009-09028 and CTQ2010-19606) and the Government of Aragón (Project PI064/09 and Research Groups, E-10) for financial support of our research. E. M.-L. thanks CSIC for a JAE-Doc postdoctoral contract. R. P. H. thanks the Aragón I + D Foundation for her permanent position.Peer Reviewe

    Catalysis-free synthesis of thiazolidine–thiourea ligands for metal coordination (Au and Ag) and preliminary cytotoxic studies

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    The reaction of propargylamines with isothiocyanates results in the selective formation of iminothiazolidines, aminothiazolines or mixed thiazolidine–thiourea compounds under mild conditions. It has been observed that secondary propargylamines lead to the selective formation of cyclic 2-amino-2-thiazoline derivatives, while primary propargylamines form iminothiazoline species. In addition, these cyclic thiazoline derivatives can further react with an excess of isothiocyanate to give rise to thiazolidine–thiourea compounds. These species can also be achieved by reaction of propargylamines with isothiocynates in a molar ratio of 1 : 2. Coordination studies of these heterocyclic species towards silver and gold with different stoichiometries have been carried out and complexes of the type [ML(PPh3)]OTf, [ML2]OTf (M = Ag, Au) or [Au(C6F5)L] have been synthesised. Preliminary studies of the cytotoxic activity in lung cancer cells have also been performed in both ligands and complexes, showing that although the ligands do not exhibit anticancer activity, their coordination to metals, especially silver, greatly enhances the cytotoxic activity

    Stereoselective three-step one-pot cascade combining Amino- and Biocatalysis to access Chiral y-Nitro Alcohols

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    he combination of small-molecule catalysis and enzyme catalysis represents an underexploited area of research with huge potential in asymmetric synthetic chemistry due to both compatibility of reaction conditions and complementary reactivity. Herein, we describe the telescopic synthesis of chiral nitro alcohols starting from commercially available benzaldehyde derivatives through the one-pot three-step chemoenzymatic cascade combination of a Wittig reaction, chiral-thiourea-catalysed asymmetric conjugate addition, and ketoreductase-mediated reduction to access the corresponding target compounds in moderate to excellent overall isolated yields (36–80 %) and high diastereomeric and enantiomeric ratios (up to >97 : 3). This represents the first example of the combination of an organocatalysed asymmetric conjugate addition via iminium ion activation and a bioreduction step catalysed by ketoreductases

    Metal-organic frameworks (MOFs) bring new life to hydrogen-bonding organocatalysts in confined spaces

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    Hydrogen-bonding organocatalysis has emerged as a promising biomimetic alternative to Lewis acid catalysis. Urea, thiourea and squaramide moieties represent the most common hydrogen-bond donors used for the preparation of these catalysts. However, their significant tendency to undergo self-quenching (self-aggregation) often decreases their solubility and reactivity. Recently, scientists have found a promising way around this problem by immobilizing the hydrogen-bonding organocatalysts on metal–organic frameworks (MOFs). Along with advantageous modular synthesis and recycling properties, the tunable porosity and topology of MOFs also allows fast mass transport and/or interactions with substrates. Herein, we highlight the existing examples dealing with the fabrication and testing of hydrogen-bonding organocatalyst-containing MOFs, providing also our vision for further advances in this area. The results derived from these studies will likely serve as inspiration for the future development of superior hydrogen-bonding organocatalysts to accomplish in confined spaces chemical transformations that are either slow or unaffordable under standard homogeneous conditions

    Crossed intramolecular Rauhut−Currier-type reactions via dienamine activation

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    Trabajo presentado como póster al 3.Tag der Chemie celebrado en Dortmund (Alemania) en 2010.The intramolecular Rauhut−Currier reaction creates a carbon−carbon bond between two tethered Michael acceptors. Previous asymmetric versions have relied on 1,4-additions of chiral nucleophilic catalysts. Herein, we investigate a novel strategy that involves the formation of electron rich dienamines as key intermediates. Our methodology provides an efficient entry to the iridoid framework.Financial support was provided by the DFG (SPP1179), the Fonds der Chemischen Industrie (Dozentenstipendium to M. C.), the Alexander von Humboldt Foundation (fellowship to E. M.-L.) and the Aragón I+D Foundation and the Spanish Ministry of Science and Innovation (Programa Nacional de Movilidad de Recursos Humanos del Plan Nacional de I-D+I 2008-2011) and CSIC (PIE 200880I260) (R. P. H.).Peer Reviewe

    Self-Assembly of Hollow Organic Nanotubes Driven by Arene Regioisomerism

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    Arene regioisomerism in low-molecular-weight gelators can be exploited as a tool to modulate the micro-structures of the corresponding xerogel networks by using the three different possible substitution patterns ortho, meta and para. This aromatic regioisomer-driven strategy has been used with a cholesterol-based gelator to prepare hollow self-assembled organic nanotubes (S-ONTs) with inside and outside diameters of ca. 35 and 140 nm, respectively. Electron microscopy imaging and theoretical calculations were employed to rationalize the formation mechanism of these S-ONTs. From the three possible regioisomers, only the ortho-disubstituted cholesteryl-based gelator showed the optimal angle and distance between substituents to afford the formation of the cyclic assemblies required for nanotube growth by assembling 30–40 units of the gelator. This study opens fascinating opportunities to expand the synthesis of controllable and unique microstructures by modulating geometrical parameters through aromatic regioisomers.Deutsche ForschungsgemeinschaftUniversität RegensburgFundación BBVAMinisterio de Economía, Industria y CompetitividadGobierno de Aragón-Fondo Social EuropeoExtreme Science and Engineering Discovery EnvironmentMinisterio de Ciencia, Innovación y Universidade

    Self-assembled fibrillar networks of a multifaceted chiral squaramide: supramolecular multistimuli-responsive alcogels

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    Chiral N,N'-disubstituted squaramide 1 has been found to undergo self-assembly in a variety of alcoholic solvents at low concentrations leading to the formation of novel nanostructured supramolecular alcogels. The gels responded to thermal, mechanical, optical and chemical stimuli. Solubility studies, gelation ability tests and computer modeling of a series of structurally related squaramides proved the existence of a unique combination of non-covalent molecular interactions and favorable hydrophobic/hydrophilic balance in 1 that drive the anisotropic growth of alcogel networks. The results have also revealed a remarkable effect of ultrasound on both the gelation kinetics and the properties of the alcogels
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