Base-catalyzed Reaction Research Articles

Iodo-Bridged Transition States; New Mechanistic Pathways for Base-Catalyzed Halogen Dance

First reported by Joseph Bunnet et al., base-catalyzed halogen dance reaction has puzzled chemists for decades, to come up with new ideas regarding the mechanism of this chemical reaction. A series of deprotonation followed by fast metal-halogen exchanges are among the most recent mechanisms reported so far. Using density functional theory, DFT, computations and focused on the Bunnet type isomerization halogen dance reactions of iodobenzene derivatives, iodo-bridged transition state, TS, are proposed. The new TS is then used to lay out 8 possible isomerization and 18 possible disproportionation paths. The possible mechanistic pathways are then carefully analyzed based on TS’s energy and protonation/deprotonation steps to find the most suitable pathways. These mechanistic pathways, sketch a comprehensive pattern for base-catalyzed halogen dance. There is still a lot to study in the chemistry of poly halogenated aryls.

Selenium-Epoxy ‘Click’ Reaction and Se-Alkylation—Efficient Access to Organo-Selenium and Selenonium Compounds

This work establishes the ‘click’ nature of the base-catalyzed oxirane ring opening reaction by the selenolate nucleophile. The ‘click’-generated ß-hydroxy selenide can be alkylated to afford cationic selenium species. Hemolytic studies suggest that selenonium cations do not lyse red blood cells even at high concentrations. Overall, these results indicate the future applicability of the developed organo-selenium chemistry in the preparation of a new class of cationic materials based on the seleno-ether motif.

Porous organic polymer bearing triazine and pyrene moieties as an efficient organocatalyst

Materials with high specific surface area and bearing abundant basic sites at their pore surface are very demanding as heterogeneous catalyst for the eco-friendly base catalyzed reactions. Here we have developed a new secondary amine linked triazine and pyrene containing microporous organic polymer (TrzPyPOP) through a simple polycondensation reaction between tetramine1,4-bis(4,6-diamino-s-triazin-2-yl)-benzene (SL-1) and monoaldehyde pyrene-1-carboxaldehyde. This new porous organic polymer TrzPyPOP is very rich in N-content with high BET surface area (1016 m2 g−1). High surface area and N-rich surface basic sites have been explored in its potential as heterogeneous organocatalyst for the synthesis of dihydropyrimidones via Biginelli condensation involving three-component coupling reaction. Only a very little amount of catalyst was effective for the synthesis of dihydropyrimidones derivatives (yields = 88–99 %) together with high recycling efficiency under the optimum reaction conditions.

New Dimensions of Brønsted Base Catalyzed Carbon–Carbon Bond-Forming Reactions

Catalytic carbon–carbon bond-forming reactions of weakly acidic carbon pronucleophiles (pK a in DMSO ≥30) were developed using strong alkaline metal Brønsted bases as catalysts. Not only weakly acidic amides, esters, nitriles, sulfonamides without any activating group, and alkyl azaarenes, but also alkyl arenes such as toluene, were applicable for the reactions, which are difficult to be applied in typical Brønsted base catalyzed reactions. Expansion to enantioselective reactions was also revealed to be possible. The reactions are atom economical and require only inexpensive alkaline metals rather than precious transition metals.1 Introduction2 Catalytic Direct-Type Addition Reactions of Weakly Acidic Carbonyl and Related Pronucleophiles3 Catalytic Direct-Type Addition Reactions of Alkyl Azaarenes4 Catalytic Direct-Type Addition Reactions of Alkyl Arenes5 Conclusion

Screening of Metal Oxides to Promote CO<sub>2</sub> Adsorption Performance over Polyethyleneimine Incorporated Solid Adsorbents

Amine-modified solid sorbents have attracted extensive interests in post-combustion carbon capture for power plants. Among various amines, polyethyleneiemine (PEI) is likely to be the most effective and promising candidate. However, previous studies have mainly focused on examining various supports to increase PEI loading and then enhance CO2 adsorption capacity. In this study, one rare earth element (Ce) and 6 first-row transition metals (from V to Cu) in the oxidation states impregnated on PEI incorporated γ-Al2O3 were prepared and investigated as potential catalyst/promotor for base-catalyzed reaction. Thermodynamic analysis, including isothermal and quasi-static CO2 adsorption tests, were implemented to evaluate the performances amongst the 7 metal oxides. The results showed that MnO2, CeO2 and Fe2O3 showed a better performance in isothermal CO2 adsorption at 75°C. Upon quasi-static tests, the results also indicates that the peak adsorption temperatures (Tpeak, a) of V2O5 and Cr2O3 shifted to high temperature region, whilst opposite behavior of MnO2 was observed. In preliminary study, density functional theory (DFT) was also adopted to assist the screening of metal oxide in terms of bond length and adsorption energies.

Synthesis of 6-Alkoxy- and 1,6-Dialkoxy-4-amino-1-aryl-3-oxo-2,3-dihydro-1H-pyrrolo[3,4-c]pyridine-7-carbonitriles

Base-catalyzed reaction of 3-aroyl-6-halopyridine-3,5-dicarbonitriles with alcohols involved successive regioselective pyrrole ring fusion at the pyridine [c] side and nucleophilic substitution of chlorine. Pyrrole ring closure is the result of initial formation of furan ring with participation of the carbonyl and cyano groups, followed by iminolactone–lactam rearrangement. The reaction in anhydrous alcohol afforded 1,6-dialkoxy-4-amino-1-aryl-3-oxo-2,3-dihydro-1H-pyrrolo[3,4-c]pyridine-7-carbonitriles. If water was present in the alcohols, the products were 6-alkoxy-4-amino-1-aryl-1-hydroxy-3-oxo-2,3-dihydro-1H-pyrrolo[3,4-c]pyridine-7-carbonitriles.

FT-IR, NMR and X-ray crystallography dataset for newly synthesized alkoxy-chalcone featuring (E)-1-(4-ethylphenyl)-3-(4-(heptyloxy) phenyl)prop‑2-en-1-one

Abstract Chalcone derivative featuring (E)-1-(4-ethylphenyl)-3-(4-(heptyloxy) phenyl) prop‑2-en-1-one (4EPC) has been successfully synthesized through base-catalyzed Claisen-Schmidt condensation reaction between an aromatic aldehyde and aromatic ketones in alcoholic media under room temperature condition. The synthesized compound was characterized by FT-IR, 1D NMR, and single-crystal X-ray diffraction studies. The compound crystallized in monoclinic space group C2/c. Recently, this synthesized compound attracted considerable interest in its unique characteristic to be used in various applications such as organic light - emitting diode (OLED), organic solar cells, and molecular gas sensor.

Latent (Pro)Nucleophiles in Enantioselective Lewis Base Catalyzed Allylic Substitutions

The use of latent nucleophiles, which are molecules that are not nucleophilic but can be activated to act as a nucleophile at an opportune time during the reaction, expands the scope of Lewis base catalyzed reactions. Here, we provide an overview of the concept and show examples of applications to N- and C-centered nucleophiles in allylic substitutions. N- and C-silyl compounds are superior latent (pro)nucleophiles in Lewis base catalyzed reactions with allylic fluorides in which the formation of the strong Si–F bond serves as the driving force for the reactions. The latent (pro)nucleophiles ensure high regio­selectivity in these reactions and enable enantioselective transformations of Morita–Baylis–Hillman adducts by the use of common chiral Lewis base catalysts.1 Introduction2 Substitution of MBH Carbonates3 The Concept of Latent (Pro)Nucleophiles4 Enantioselective Allylation of N-Heterocycles5 Enantioselective Phosphonyldifluoromethylation of Allylic Fluorides6 Conclusion

Synthesis and characterization of a new class of phenothiazine molecules with 10H-substituted morpholine & piperidine derivatives: A structural insight

A series of 10H-substituted phenothiazine-based molecules were prepared by the base-catalyzed reactions. The synthesized compounds are characterized by Mass spectroscopy, NMR, and SCXRD to examine the role of different functional groups involved in the intermolecular interactions and conformational geometries. The crystal packing of the compounds is governed by O–H⋯O, C–H⋯O, and π–π interactions. A complete understanding of the intermolecular interactions is studied employing the Hirshfeld analysis, 2D Fingerprint plot. Furthermore, the density functional theory (DFT/B3LYP) method at the 6–311++G(d,p) basis set was performed to support and compare experimental & theoretical geometrical parameters of phenothiazine derivatives.

Comparative kinetic studies and pH-rate profiling of aniracetam degradation using validated stability-indicating RP-HPLC method

Aniracetam is a cognitive enhancer drug that is susceptible to chemical degradation at room temperature. A validated stability-indicating RP-HPLC has been developed and used for studying the kinetics of aniracetam degradation processes and pH-rate profiling. Chromatographic separation of aniracetam and its degradation products was achieved on a C18 column (250 × 4.6 mm) with particle size 5 μm. The stationary phase surface silanol activity and hydrophobicity was evaluated by Galushko method then the mobile phase was optimized for the separation of intact drug from degradation products. Water-acetonitrile-methanol (50:25:25 v/v/v) was used as a mobile phase in isocratic mode with flow rate 1 mL/min. Aniracetam and its degradation products were monitored at 210 nm. Determination was carried out in the concentration range of 0.4–20 µg/mL with a detection limit of 0.21 µg/mL. A new behavior of aniracetam stability was concluded based on structural elucidation of degradation products by infra-red and mass spectrometry. Degradation kinetic parameters including the order of reaction, the rate constant, and half-life have been calculated. The study of the pH-rate profile was evaluated in the range of 3–10 pH units and it was found that aniracetam is stable in uncatalyzed degradation compared to the acid or base-catalyzed reaction. Good recoveries were obtained for aniracetam capsules and the proposed method validity was assessed by standard addition technique. Moreover, the results obtained were statistically compared with those obtained by the manufacturer method and therefore the proposed RP-HPLC method could be successfully used in quality control laboratories for the determination of aniracetam and detection of degradation products.

Systematic Diffusion-Ordered Spectroscopy for the Selective Determination of Molecular Weight in Real Lignins and Fractions Arising from Base-Catalyzed Depolymerization Reaction Mixtures

The valorization of biorefinery downstream lignin fractions is a key issue in increasing the sustainability of second-generation biofuels. The development of reliable methodologies for the selective determination of the apparent masses of the poly(hydroxy)-aromatic ethers arising from lignin depolymerization reaction is crucial. Diffusion-ordered spectroscopy (DOSY) has been tested to estimate the molecular weight in downstream biorefinery lignins and base-catalyzed depolymerization reaction mixtures. Excellent correlation was found in the calibration of molecular weight and diffusion coefficients with standards. DOSY permitted the selective estimation of the apparent masses of different fractions in the lignin and in the depolymerization reaction mixtures, providing a more profound knowledge of the reaction mixture composition than that obtained with traditional size-exclusion chromatography (SEC). Excellent correlations have been achieved in the estimation of the apparent masses of poly(hydroxy)-aromatic ethers between SEC and DOSY. This permits a reliable estimation of the molecular weight of different fractions in the lignin and in the depolymerization product, which is essential for their further applications.

Michael addition curable coatings from renewable resources with enhanced adhesion performance

Novel malonate-functional polyesters from biobased and potentially biobased monomers were developed and cured through the base-catalyzed carbon-Michael addition reaction with acryloyl-functional oligomers. Both drop-in monomers, such as fully biobased diethyl malonate, and alternative raw materials, such as isosorbide and vegetable oil, were introduced. Isosorbide-based polyesters show improved performance to humidity in terms of adhesion on epoxy-amine primer, while vegetable oil-containing resins lead to improved coating appearance due to better flow and levelling. This study demonstrates that biobased malonate resins, having renewable contents up to 53%, offer attractive performance benefits in 2K RMA paints. It is anticipated that, with the development of additional fully biobased polyols, renewable contents in excess of 80% can be achieved.

Identification of rapid access to polycyclic systems via a base-catalyzed cascade cyclization reaction and their biological evaluation.

A base-mediated cascade reaction between malonate esters and acrolein was developed to access complex polycyclic systems. This novel tandem reaction enables the simultaneous generation of up to seven new bonds and at least three new stereogenic centers. Mechanistic studies indicate a series of nucleophilic 1,4 and 1,6 Michael addition reactions occur, followed by an aldol condensation reaction, culminating in the formation of three fused rings. The compounds were characterized by NMR studies and the stereochemistry was confirmed by X-ray analysis. The ability to generate multigram quantities of such complex molecular scaffolds renders the method promising for medicinal chemistry campaigns. Herein, we also demonstrate that the lead compounds display promising anti-proliferative activities against human cancer cell models.

K2CO3-Catalyzed Synthesis of 2,5-Dialkyl-4,6,7-tricyano-Decorated Indoles via Carbon-Carbon Bond Cleavage.

We describe a novel method to synthesize 2,5-dialkyl-4,6,7-tricyanoindole derivatives from a base-catalyzed reaction of 1,3-diketones with fumaronitrile. The reaction proceeds by the condensation of two molecules of fumaronitrile and one molecule of 1,3-diketone in a remarkable process that involves the cleavage of one C(sp3)-C(sp2) bond in 1,3-diketones and the formation of one carbon-nitrogen bond and four carbon-carbon bonds to construct both the aryl and pyrrole rings of the indole in one step.

Application of Dimedone Enamines as Protecting Groups for Amines and Peptides.

A simple protocol for the protection of amines was realized through a base-catalyzed one-pot reaction of dimedone, β-nitroalkene, and amine. Employing this strategy, a variety of amines/amino acids were protected in excellent yields. These acid/base stable protected amines can be deprotected by either ethylene diamine or hydrazine hydrate under mild conditions. The practical application of this orthogonal protecting group was demonstrated by the synthesis of cyclic peptide melanotan II via SPPS.

Hydrothermal Depolymerization of Biorefinery Lignin-Rich Streams: Influence of Reaction Conditions and Catalytic Additives on the Organic Monomers Yields in Biocrude and Aqueous Phase

Hydrothermal depolymerization of lignin-rich streams (LRS) from lignocellulosic ethanol was successfully carried out in a lab-scale batch reactors unit. A partial depolymerization into oligomers and monomers was achieved using subcritical water as reaction medium. The influence of temperature (300–350–370 °C) and time (5–10 minutes) was investigated to identify the optimal condition on the monomers yields in the lighter biocrude (BC1) and aqueous phase (AP) fractions, focusing on specific phenolic classes as well as carboxylic acids and alcohols. The effect of base catalyzed reactions (2–4 wt. % of KOH) was compared to the control tests as well as to acid-catalyzed reactions obtained with a biphasic medium of supercritical carbon dioxide (sCO2) and subcritical water. KOH addition resulted in enhanced overall depolymerization without showing a strong influence on the phenolic generation, whereas sCO2 demonstrated higher phenolic selectivity even though no effect was observed on the overall products mass yields. In conclusion, a comparison between two different biocrude collection procedures was carried out in order to understand how the selected chemical extraction mode influences the distribution of compounds between BC1 and AP.

Photoinduced Proton-Transfer Polymerization: A Practical Synthetic Tool for Soft Lithography Applications.

Proton-transfer photopolymerization through the thiol-epoxy "click" reaction is shown to be a versatile new method for the fabrication of micro- and nanosized polymeric patterns. In this approach, complexation of a guanidine base, diazabicycloundecene (DBU), with benzoylphenylpropionic acid (ketoprofen) generates a photolabile salt. Under illumination at a wavelength of 365 nm, the salt undergoes a photodecarboxylation reaction to release DBU as a base. The base-catalyzed ring opening reaction then creates cross-linked poly(β-hydroxyl thio-ether) patterns. The surface chemistry of these patterns can be altered through alkylation of the thio-ether linkages. For example, a reaction with bromoacetic acid produces a hitherto unknown sulfonium/carboxylate-based zwitterionic motif that endows antibiofouling capacity to the micropatterns.

Biodiesel production from refined used cooking oil using co-metal oxide catalyzed transesterification

The world is challenged with depletion of non-renewable fossil fuel and environmental pollution. Thus, this research was emphasized on converting refined used cooking oil to safer and low toxicity biodiesel by base-catalyzed transesterification reaction. Alumina supported magnesium, calcium, strontium and barium oxide-based catalysts with iron as its dopant were optimized according to various calcination temperatures and iron loadings. The optimum conditions over potential catalyst was achieved with 20 wt% of Fe loading for Fe/Ba/Al2O3 catalyst calcined at 800 °C which gave the maximum biodiesel production of 84.02%. Characterization of catalyst carried out by XRD showed that the 20Fe:80Ba/Al2O3 catalyst calcined at 800 °C had a polycrystalline structure with high BET surface area (133.59 m2/g) while FESEM analysis displayed a morphology of uniform plate-like shape grains with fine particles in the range of 55–60 nm. CO2-TPD results showed that the catalyst exhibited highest basicity of 2.5854 mmol/g, while TGA analysis proved that 800 °C was the optimum calcination temperature. The transesterification process of refined used cooking oil to produce high yield biodiesel was effectively attained using 20Fe:80Ba/Al2O3 catalyst.

Synthesis and characterization of thiol-acrylate hydrogels using a base-catalyzed Michael addition for 3D cell culture applications.

There is significant interest in developing new approaches for culturing mammalian cells in a three-dimensional (3D) environment due to the fact that it better recapitulates the in vivo environment. The goal of this work was to develop thiol-acrylate, biodegradable hydrogels that possess highly tunable properties to support in vitro 3D culture. Six different hydrogel formulations were synthesized using two readily available monomers, a trithiol (ETTMP 1300 [ethoxylated trimethylolpropane tri(3-mercaptopropionate) 1300]) and a diacrylate (PEGDA 700 [polyethylene glycol diacrylate 700]), polymerized by a base-catalyzed Michael addition reaction. The resultant hydrogels were homogeneous, hydrophilic, and biodegradable. Different mechanical properties such as gelation time, storage modulus (or the elasticity G'), swelling ratio, and rate of degradation were tuned by varying the weight percentage of polymer, the molar ratio of thiol-to-acrylate groups, and the pH of the solution. Cytocompatibility was assessed using two model breast cancer cell lines by both 2D and 3D cell culturing approaches. The hydrogel formulations with a thiol-to-acrylate molar ratio of 1.05 were found to be optimal for both 2D and 3D cultures with MDA-MB-231 cellular aggregates found to be viable after 17 days of 3D continuous culture. Finally, MCF7 cells were observed to form 3D spheroids up to 600 μm in diameter as proof of principle for the thiol-acrylate hydrogel to function as a scaffold for in vitro 3D cell culture. A comparison of the different mechanical properties of the six hydrogel formulations coupled with in vitro cell culture results and findings from previously published hydrogels conclude that the thiol-acrylate hydrogels have significant potential as a scaffold for 3D cell culture.

KOtBu-Catalyzed Michael Addition Reactions Under Mild and Solvent-Free Conditions.

Designed transition metal complexes predominantly catalyze Michael addition reactions. Inorganic and organic base-catalyzed Michael addition reactions have been reported. However, known base-catalyzed reactions suffer from the requirement of solvents, additives, high pressure and also side-reactions. Herein, we demonstrate a mild and environmentally friendly strategy of readily available KOt Bu-catalyzed Michael addition reactions. This simple inorganic base efficiently catalyzes the Michael addition of underexplored acrylonitriles, esters and amides with (oxa-, aza-, and thia-) heteroatom nucleophiles. This catalytic process proceeds under solvent-free conditions and at room temperature. Notably, this protocol offers an easy operational procedure, broad substrate scope with excellent selectivity, reaction scalability and excellent TON (>9900). Preliminary mechanistic studies revealed that the reaction follows an ionic mechanism. Formal synthesis of promazine is demonstrated using this catalytic protocol.