Una nueva aproximación a la síntesis de heterociclos pirrolofusionados basada en la reacción de amidación de alquinos asistida por el reactivo de yodo hipervalente PIFA

458 p.

Metal-Free Polymethyl Methacrylate (PMMA) Nanoparticles by Enamine "Click" Chemistry at Room Temperature

"Click" chemistry has become an efficient avenue to unimolecular polymeric nanoparticles through the self-crosslinking of individual polymer chains containing appropriate functional groups. Herein we report the synthesis of ultra-small (7 nm in size) polymethyl methacrylate (PMMA) nanoparticles (NPs) by the "metal-free" cross-linking of PMMA-precursor chains prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization containing beta-ketoester functional groups. Intramolecular collapse was performed by the one-pot reaction of beta-ketoester moieties with alkyl diamines in tetrahydrofurane at r.t. (i.e., by enamine formation). The collapsing process was followed by size exclusion chromatography and by nuclear magnetic resonance spectroscopy. The size of the resulting PMMA-NPs was determined by dynamic light scattering. Enamine "click" chemistry increases the synthetic toolbox for the efficient synthesis of metal-free, ultra-small polymeric NPs.

Reactions of small molecules facilitated by metal-acceptor interactions

The role of metal-acceptor interactions arising from M–BR3 and M–PR3 bonding is discussed with respect to reactions between first-row transition metals and N2, H2, and CO. Thermally robust, S = 1/2 (TPB)Co(H2) and (TPB)Co(N2) complexes (TPB = tris(2- (diisopropylphosphino)phenyl)borane) are described and the energetics of N2 and H2 binding are measured. The H2 and N2 ligands are bound more weakly in the (TPB)Co complexes than in related (SiP3)M(L) complexes (SiP3 = tris(2- (diisopropylphosphino)phenyl)silyl). Comparisons within and between these two ligand platforms allow for the factors that affect N2 (and H2) binding and activation to be delineated. The characterization and reactivity of (DPB)Fe complexes (DPB = bis(2- (diisopropylphosphino)phenyl)phenylborane) in the context of N2 functionalization and E–H bond addition (E = H, C, N, Si) are described. This platform allows for the one-pot transformation of free N2 to an Fe hydrazido(-) complex via an Fe aminoimide intermediate. The principles learned from the N2 chemistry using (DPB)Fe are applied to CO reduction on the same system. The preparation of (DPB)Fe(CO)2 is described as well as its reductive functionalization to generate an unprecedented Fe dicarbyne. The bonding in this highly covalent complex is discussed in detail. Initial studies of the reactivity of the Fe dicarbyne reveal that a CO-derived olefin is released upon hydrogenation. Alternative approaches to uncovering unusual reactivity using metal- acceptor interactions are described in Chapters 5 and 6, including initial studies on a new π-accepting tridentate diphosphinosulfinyl ligand and strategies for designing ligands that undergo site-selective metallation to generate heterobimetallic complexes.

Investigations of group IVA transition metal mediated carbon-carbon bond forming reactions

Zirconocene aldehyde and ketone complexes were synthesized in high yield by treatment of zirconocene acyl complexes with trimethylaluminum or diisobutylaluminum hydride. These complexes, which are activated by dialkylaluminum chloride ligands, inserted unsaturated substrates such as alkynes, allenes, ethylene, nitriles, ketenes, aldehydes, ketones, lactones, and acid chlorides with moderate to high conversion. Insertion of aldehyde substrates yielded zirconocene diolate complexes with up to 20:1 (anti:syn) diastereoselectivity. The zirconocene diolates were hydrolyzed to afford unsymmetrical 1,2-diols in 40-80% isolated yield. Unsymmetrical ketones gave similar insertion yields with little or no diastereoselectivity. A high yielding one-pot method was developed that coupled carbonyl substrates with zirconocene aldehyde complexes that were derived from olefins by hydrozirconation and carbonylation. The zirconocene aldehyde complexes also inserted carbon monoxide and gave acyloins in 50% yield after hydrolysis.

The insertion reaction of aryl epoxides with the trimethylphoshine adduct of titanocene methylidene was examined. The resulting oxytitanacyclopentanes were carbonylated and oxidatively cleaved with dioxygen to afford y-lactones in moderate yields. Due to the instability and difficult isolation of titanocene methylidene trimethylphoshine adducts, a one-pot method involving the addition of catalytic amounts of trimethylphosphine to β,β-dimethyltitanacyclobutane was developed. A series of disubstituted aryl epoxides were examined which gave mixtures of diastereomeric insertion products. Based on these results, as well as earlier Hammett studies and labeling experiments, a biradical transition state intermediate is proposed. The method is limited to aryl substituted epoxide substrates with aliphatic examples showing no insertion reactivity.

The third study involved the use of magnesium chloride supported titanium catalysts for the Lewis acid catalyzed silyl group transfer condensation of enol silanes with aldehydes. The reaction resulted in silylated aldol products with as many as 140 catalytic turnovers before catalyst inactivation. Low diastereoselectivities favoring the anti-isomer were consistent with an open transition state involving a titanium atom bound to the catalyst surface. The catalysts were also used for the aldol group transfer polymerization of t-butyldimethylsilyloxy-1-ethene resulting in polymers with molecular weights of 5000-31,000 and molar mass dispersities of 1.5-2.8. Attempts to polymerize methylmethacrylate using GTP proved unsuccessful with these catalysts.

Heterogeneous catalytic activity on Mn, Fe and Co-based metalloporphyrinic Solid Coordination Frameworks (SCFs)

Comunicación al congreso 1st European Conference on Metal Organic Frameworks and Porous Polymers, celebrado en Postdam del 11 al 14 de octubre de 2015

Optical properties and electrical bistability of CdS nanoparticles synthesized in dodecanethiol

We reported the synthesis of CdS semiconductor nanoparticles using a simple one-pot reaction by thermolysis of cadmium acetylacetonate in dodecanethiol. Optical measurements of the as-obtained CdS nanoparticles revealed that their optical properties were closely related to surface effects. Based upon the cocktail of poly (N-vinylcarbazole) (PVK) and CdS nanoparticles, a bistable device was fabricated by a simple solution processing technique. Such a device exhibited a remarkable electrical bistability, which was attributed to the electric field-assisted charge transfer between PVK and the CdS nanoparticles capped by dodecaethiol. The conduction mechanism changed from an injection-controlled current to a bulk-controlled one during switching from OFF-state to ON-state.

苯乙酮、氨甲酸酯参与的直接Mannich反应

Mannich反应是有机化学中最重要的碳-碳键形成反应，其产物是合成手性胺的通用中间体。间接Mannich反应使用不稳定的预制烯醇等当体，以未修饰的酮为给体的直接方法将增强Mannich反应的效率。针对低活性苯乙酮、氨甲酸酯参与的直接Mannich反应，研究工作将更具挑战性。 在前期实验中，我们发现Lewis酸-NbCl5可高效催化苯乙酮、芳香醛、芳香胺三组分直接Mannich反应，反应在环境温度下进行，高收率获得Mannich碱。这是以苯乙酮参与的Mannich反应中，实现催化量Lewis酸催化的首次报道。该方法高效且操作简单。但就底物而言，对易去保护、低活性的氨甲酸酯类底物收率较低。我们设想Brønst酸可解决此类底物问题。令人高兴的是，杂多酸可高效催化芳香酮、芳香醛、氨甲酸酯三组分直接Mannich反应，反应在环境温度下进行，高收率获得N-保护的β-氨基酮。该方法底物范围广泛，普适性强且催化剂便宜。 基于杂多酸在苯乙酮、氨甲酸酯为底物直接Mannich反应中的高效性，我们设想杂多酸与功能化的手性有机小分子-手性伯胺组装可解决催化剂回收问题，同时实现不对称催化。实验结果表明，非共价键固载手性伯胺不能有效催化苯乙酮为底物的直接Mannich反应，无论是对映选择性还是收率均较低。随后，我们以丙二酸酯及α-氨基砜为底物，以增强底物活性，同时绕开亚胺的不稳定性。辛可宁伯胺以氢键双活化底物，有效催化原位产生氨甲酸酯类亚胺与丙二酸酯的Mannich反应，高收率获得Mannich碱，ee值中等。 我们采用逐步解决问题的策略解决Mannich反应中的部分问题并在Lewis酸催化、Brønst酸催化、非共价键固载手性伯胺催化及手性伯胺氢键催化的直接Mannich反应中做出了有益探索。 The Mannich reactions are among the most fundamental carbon-carbon bond forming reactions in organic chemistry, and the reaction products are versatile intermediates in the synthesis of chiral amines. The indirect Mannich reaction uses preformed enolate equivalents. However the preformed enolates are unstable. Thus, a direct methodology based on unmodified ketone donors would enhance the efficiency of the Mannich reaction. Especially researches for the directed Mannich reactions of acetophenone, carbamate, which own lower activities, will be more challengeable. In the initial experiments, we found an efficient Lewis acid-NbCl5 which could catalyze three-component Mannich-type reaction of acetophenone, aromatic aldehydes and aromatic amines at ambient temperature in high yields. This is the first report that use catalytic amount of Lewis acid in the Mannich reactions of .acetophenone. The method reported is not only simple to operate but also efficient. However, as far as amines are concerned, the substrates of carbamates which can be deprotected more easily and less reactive than amines give low yields. We envisaged that Brønsted acid would resolve this problem. Pleasingly, heteropoly acids (HPA) efficiently catalyzed one-pot three-component Mannich reactions of aryl aldehydes, aryl ketones, and carbamates at ambient temperature and afforded the corresponding N-protected β-amino ketones in good to excellent yields. This method provides a novel and improved modification of three-component Mannich reactions in terms of a wide scope of aldehydes, ketones and carbamates, economic viability. Based on the high efficiency of heteropoly acids in the Mannich reaction of acetophenone and carbamates, we envisaged that if HPA were combined with functionalized chiral organocatalysts–chiral primary amines the assemblies may be able to act as recoverable asymmetric organocatalysts. The results of exprimentals showed that noncovalently supported heterogeneous chiral primary amine couldn’t effectively catalyze the Mannich reactions which own two the substrate of acetophenone regardless of enantioselectivity and yield. Then, we employed malonates and α-amido sulfones as substrates to enhance reactivity of substrates and circumvent the instability of imines. A moderately enantioselective and highly yield Mannich reaction with in situ generation of carbamate-protected imines from stable α-amido sulfones catalyzed by cinchonine primary amine catalyst was developed. It is noteworthy that cinchonine primary amine can dual activate substrates through H-bond activation and thus promote the reaction. We applied step-by-step-strategy to resolve some problems in the Mannich reactions and did some instructive explorations in Lewis acid catalysis, Brønst acid catalysis, noncovalently supported heterogeneous chiral primary amine catalysis and chiral primary amine as hydrogen-bond catalysis.

Synthesis of substituted pyridyl ureas by selenium dioxide-catalyzed carbonylation

A series of commercially useful substituted pyridyl ureas have been synthesized via selenium dioxide-catalyzed reductive carbortylation of substituted nitrobenzene or substituted nitropyridine with amine as co-reagent and carbon monoxide as carbonyl reagent instead of phosgene in one-pot reaction. The recycling reusability of catalyst was also tested. It was also found that selenium dioxide-catalyzed reductive carbonylation of nitroaromatics exhibited reaction-controlled phase-transfer phenomena of the catalyst. (C) 2003 Elsevier B.V. All rights reserved.

Hydrothermal stability and catalytic activity of aluminum-containing mesoporous ethane-silicas

Aluminum was incorporated into the mesoporous framework of ethane-silica by one-pot condensation of Al(OiPr)(3) with 1,2-bis(trimethoxysilyl)ethane using octadecyltrimethylammonium chloride as surfactant. Powder X-ray diffraction patterns, nitrogen sorption analysis, and TEM results reveal the formation of an ordered mesoporous material with uniform porosity. Al-27 MAS NMR confirms the incorporation of aluminum in the framework. The synthesized materials exhibit extremely high hydrothermal stability in boiling water (no obvious change of mesostructure and textural properties was observed even after refluxing in water for 100 h), which could be mainly contributed to the ethane-bridged mesoporous framework. The aluminum-containing mesoporous ethane-silicas are efficient catalysts for the alkylation of 2,4-di-tert-butylphenol by cinnamyl alcohol to yield a flavan.

Efficient and divergent synthesis of cyclophosphamide analogues from 2-arylamino-3-acetyl-5, 6-dihydro-4H-pyrans

A facile and efficient one-pot synthesis of substituted cyclophosphamidic chlorides and their analogues has been developed from readily available enaminones, 2-arylamino-3-acetyl-5,6-dihydro4H-pyrans.

A Facile and Efficient Synthesis of Polyfunctionalized Pyridin-2(1H)-ones from β-Oxo Amides under Vilsmeier Conditions

A facile and efficient one-pot synthesis of polysubstituted pyridin-2(1H)-ones from a variety of beta-oxo amides under Vilsmeier conditions is described, and a mechanism involving sequential halogenation, formylation and intramolecular nucleophilic cyclization is proposed

Efficient and Divergent Synthesis of Fully Substituted 1H-Pyrazoles and

Efficient and divergent one-pot synthesis of fully substituted 1H-pyrazoles and isoxazoles from cyclopropyl oximes based on reaction conditions selection is reported. Under Vilsmeier conditions (POCl3/DMF), substituted 1H-pyrazoles were synthesized from 1-carbamoyl, 1-oximyl cyclopropanes via sequential ring-opening, chlorovinylation, and intramolecular aza-cyclization. In the presence of POCl3/CH2Cl2, substituted isoxazoles were obtained from the cyclopropyl oximes via ring-opening and intramolecular nucleophilic vinylic substitution (SNV) reactions

Glutathione-Mediated Release of Functional Plasmid DNA from Positively Charged Quantum Dots

DNA was efficiently bound to water-soluble positively charged CdTe quantum dots (QDs) through complementary electrostatic interaction. These QDs-DNA complexes were disrupted and DNA was released by glutathione (GSH) at intracellular concentrations. Interestingly, there was almost no detectable DNA released by extracellular concentration of GSH. The formation of QDs-DNA complexes and GSH-mediated DNA release from the complexes were confirmed by dye displacement assay, electrophoretic mobility shift assay (EMSA), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) experiments.

A general method for the rapid synthesis of hollow metallic or bimetallic nanoelectrocatalysts with urchinlike morphology

We have reported a facile and general method for the rapid synthesis of hollow nanostructures with urchinlike morphology. In-situ produced Ag nanoparticles can be used as sacrificial templates to rapidly synthesize diverse hollow urchinlike metallic or bimetallic (such as Au/Pt) nanostructures. It has been found that heating the solution at 100 degrees C during the galvanic replacement is very necessary for obtaining urchinlike nanostructures. Through changing the molar ratios of Ag to Pt, the wall thickness of hollow nanospheres can be easily controlled; through changing the diameter of Ag nanoparticles, the size of cavity of hollow nanospheres can be facilely controlled; through changing the morphologies of Ag nanostructures from nanoparticle to nanowire, hollow Pt nanotubes can be easily designed. This one-pot approach can be extended to synthesize other hollow nanospheres such as Pd, Pd/Pt, Au/Pd, and Au/Pt. The features of this technique are that it is facile, quick, economical, and versatile.