Addition Of DBU Research Articles

Synthesis of Nonisocyanate Poly(hydroxy)urethanes from Bis(cyclic carbonates) and Polyamines.

Nonisocyanate polyurethane materials with pending alcohol groups in the polymeric chain were synthesized by polyaddition reaction of bis(cyclic carbonates) onto diamines. For the platform molecule, 1,4-butanediol bis(glycidyl ether carbonate) (BGBC, 1) was used. The polyaddition reaction of 1 onto a wide range of diamines with different electronic and physical properties was explored. All PHUs were obtained quantitatively after 16 h at 80 °C temperature in MeCN as solvent. The low nucleophilicity of L-lysine has proven unable to ring-open the cyclic carbonate and, thus, no reaction occurred. The addition of DBU or TBD as the catalyst was tested and allows the obtention of the desired PHU. However, the presence of strong bases also led to the formation of polyurea fragments in the new PHU. The different poly(hydroxyurethane) materials were characterized using a wide range of spectroscopic techniques such as NMR, IR, MALDI-ToF, and using GPC studies. The thermal properties of the NIPUs were investigated by DSC and TGA analyses. Moreover, reactions employing different monomer ratios were performed, obtaining novel hydroxycarbamate compounds. Finally, sequential and one-pot experiments were also carried out to synthesize the PHUs polymers in one-step reaction.

Nucleophilic Acylation with Aromatic Aldehydes to 2 Bromoacetonitrile: An Umpolung Strategy for the Synthesis of Active Methylene Compounds.

A novel one-pot N-heterocyclic carbene (NHC)-catalysed acylation of 2- bromoacetonitrile with aromatic aldehydes is reported. The protocol involves carbonyl umpolung reactivity of aldehydes in which the carbonyl carbon attacks nucleophilically (as d1 nucleophile) on the electrophilic terminal of 2-bromoacetonitrile to afford 3-aryl-3-oxopropanenitrile. The salient features of this procedure are short reaction time, operational simplicity, ambient temperature, no by-product formation and high yields. A flame-dried round bottom flask was charged with Imidazolium salts (3a) (0.20 mmol). Aldehyde 1a (1.0 mmol), 2-bromoacetonitrile 2 (1.0 mmol), and THF / t-BuOH 5 mL; 10:1) were added at positive nitrogen pressure followed by the addition of DBU (0.15 mmol) through stirring. The resulting yellow- orange solution was stirred at room temperature for 5-6 h. After completion of the reaction (TLC monitored), the reaction mixture was concentrated under reduced pressure. The product was purified using hexane / EtOAc (10:1) as an eluent to provide analytically pure compound 4a. Physical data of representative compounds and the NMR spectroscopic data are in agreement with the literature value. The salient features of this procedure are short reaction time, operational simplicity, ambient temperature, no by-product formation and high yields. To sum up, we have developed a convenient, efficient and one-pot route for 3-oxo-3- phenylpropanenitrile synthesis from NHC promoted direct nucleophilic acylation of aromatic aldehydes using 2- bromoacetonitrile. This method provided a wide range of products and good yields. To best of our knowledge, this is the new report for the synthesis of 3-oxo-3-phenylpropanenitrile through NHC promoted nucleophilic acylation of aromatic aldehyde.

Advancing the Synthesis of Isocyanate-Free Poly(oxazolidones)s: Scope and Limitations

Poly(oxazolidone) is an emerging class of polyurethanes (PUs) that is easily accessible by an isocyanate-free pathway via the step-growth copolymerization of CO₂-based monomers (bis(α-alkylidene cyclic carbonate)s) with primary diamines at room temperature. Here, we explore the scope and limitation of this process by investigating the influence of the diamine and the reaction conditions on the structure and macromolecular parameters of the polymer. Less hindered diamines (aliphatic and benzylic) provide selectively poly(hydroxyoxazolidone)s, whereas the bulkier ones (cycloaliphatic) furnish polymer chains bearing two types of linkages, oxo-urethane and hydroxyoxazolidone ones. The increase of the reaction temperature or the addition of DBU as a catalyst enables to accelerate the polymerizations. The quantitative polymer dehydration is also achieved by refluxing in acetic acid, providing a new class of unsaturated poly(oxazolidone)s composed of α-alkylidene oxazolidone linkages (for hindered polymers) or a mixture of α- and β-alkylidene oxazolidone linkages (for the less hindered ones). These unsaturated poly(oxazolidone)s present a high glass transition temperature (90 °C ≤ Tg ≤ 130 °C) and a remarkable thermal stability (Td > 360 °C), rendering these polymers attractive for applications requiring high temperatures. This work is therefore opening an avenue to novel functional isocyanate-free PUs, with the pendant hydroxyl or olefin groups that are expected to be easily derivatized.

Formal Bimolecular [2 + 2 + 2] Cycloaddition Strategy for the Synthesis of Pyridines: Intramolecular Propargylic Ene Reaction/Aza Diels-Alder Reaction Cascades.

Two methods for the synthesis of multisubstituted pyridines are described. In each strategy, a highly reactive vinylallene is generated via an intramolecular propargylic ene reaction in the presence of an azadienophile. Reactions employing ethyl N-(tosyl)iminoacetate furnish an intermediate that undergoes elimination and isomerization upon the addition of DBU. The reaction of the intermediate vinylallene with TsCN leads to the isolation of a 2-sulfonylpyridine that serves as a versatile intermediate undergoing substitution reactions with oxygen and carbon nucleophiles.

Copper-catalyzed highly selective synthesis of 2-benzyl- and 2-benzylidene-substituted benzo[b]thiazinones from 2-iodophenylcinnamamides and potassium sulfide.

An efficient and practical procedure for the synthesis of 2-benzyl- and 2-benzylidene-substituted benzo[b]thiazinones from easily available 2-iodophenylcinnamamides and potassium sulfide has been developed. In the presence of DBU, the reaction proceeds via electrophilic addition, followed by dehydrogenation and reduction to give 2-benzyl benzo[b]thiazinones. Furthermore, 2-benzylidenebenzo[b]thiazinones were obtained in moderate to good yields without the addition of DBU.

Ligand and base additive effects on the reversibility of nucleophilic addition in palladium-catalyzed allylic aminations monitored by nucleophile crossover

A nucleophile crossover experiment was used to monitor the reversibility of nucleophilic addition of benzylamine to π-allylpalladium complexes. Dppe, dppp, dppb, and PHOX showed more crossover than PPh3 and dppm in both DMF and dichloromethane. Crossover was inhibited by the addition of DBU or Cs2CO3, but much less elimination to diene side products was observed with Cs2CO3. Analysis of percent crossover vs. percent reaction completion using the PHOX ligand revealed that with added DBU or Cs2CO3 crossover only began occurring after 100% completion had been reached.

A Facile Anti-selective Synthesis of 3-Nitropyridin-2-ones Using Morita- Baylis Hillman Adduct of Nitroalkene

Background: Amide functionality is an important in many areas of chemistry, including peptide, polymer, and complex molecule synthesis. Furthermore, Morita-Baylis-Hillman (MBH) reaction is well known efficient and economical carbon-carbon bond forming reaction which affords densely functionalized scaffolds. δ-Lactams are important constituents of natural products and have widespread applications from pharmaceuticals to synthetic organic chemistry. To the best of our knowledge, MBH adducts of nitro alkenes and their further oxidized products have not been utilized to construct the target molecule of present investigation. With aim to incorporate nitro group in pyridin-2-ones, we wished to prepare MBH adduct of nitroalkenes, which would be a novel scaffold that can be utilized for synthesis of diverse molecules. Methods: A flame-dried round bottom flask was charged with benzimidazolium salt, α- nitrocinnamaldehyde, phenacyl bromide, and amine in THF/ButOH under positive pressure of nitrogen followed by addition of DBU. The resulting pale yellow solution was stirred for 12-14 h at room temperature and finally after work-up we isolated the desired amide. Then, a mixture of prepared amide and molecular iodine in dichloromethane was stirred at room temperature for 4.5-6 h yields the target lactams. Results: [E]-α-Nitrocinnamaldehydes, prepared from Morita-Baylis-Hillman adduct of nitoalkenes, were converted into functionalized amides (81-95%) under the catalysis of N-heterocyclic carbenes. The reaction proceeds via d3 nucleophile of homoenolate and involves three components coupling strategy. A probe to utilized the prepared amide scaffold for construction of pyridin-2-one was also performed and the reactions gave excellent yields (82-93%) of pure products with highly diastereoselective (>92%) in favor of trans isomer. Conclusion: We have documented an original NHC-catalyzed direct synthesis of α-nitro amides with diverse functionalities, which opens up a new aspect for the utility of MBH adducts of nitroalkenes in organic synthesis. We have also disclosed a new anti-selective synthesis of 3-nitropyridin-2-ones from the prepared amide scaffold. Thus, the envisaged atom-economic strategy for the synthetically important functionalized amides and pharmaceutically important 2-pyridones would be a practical alternative to the existing procedures for their preparations. Keywords: Nitroalkene, Baylis-Hillman adduct, N-heterocyclic carbene, pyridin-2-one, stereoselectivity.

Kinetics of multifunctional thiol-epoxy click reactions studied by differential scanning calorimetry: Effects of catalysis and functionality

Isothermal reaction kinetics of thiol-epoxy (multifunctional thiol-difunctional epoxy) reactions with and without external catalyst 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) were studied using differential scanning calorimetry (DSC). Autocatalytic behavior is observed both without DBU and with DBU, which is attributed to autocatalysis effects of hydroxyl products of the reaction. The isothermal curing kinetics are well described by the Kamal autocatalytic model, which is expressed as dα/dt=(k1 + k2αm)(1 − α)n (α: fractional conversion; dα/dt: apparent rate of reaction). Parameters of the reaction, including reaction orders m and n, apparent rate parameters k1 and k2, and activation energies are determined by fitting the experimental data to the Kamal model. For the thiol-epoxy reaction without DBU, the overall reaction order (m + n) is approximately 3 (with m ≈ 2 and n ≈ 1) but decreases to 2 (with m ≈ 1 and n ≈ 1) upon addition of DBU. Based on the most commonly described mechanism for nucleophilic thiol-epoxy reactions in the literature, new reaction schemes are proposed by incorporating the hydroxyl autocatalysis effect as well as the effect of external catalyst DBU on apparent reaction order. The proposed reaction schemes allow for excellent fits to reaction kinetics for thiol-epoxy reactions with and without DBU. In contrast to the strong effect of external DBU catalyst on reaction kinetics, changing the thiol monomer functionality leads to relatively small changes in apparent rate parameters and no change in the order of reaction or reaction mechanism.

Synthesis and photo-property of 2-cyano boron-dipyrromethene and the application for detecting fluoride ion

Three 2-cyano boron-dipyrromethene (BODIPY) based derivatives (CB1–CB3) have been synthesized and characterized. The photophysical properties of these compounds are investigated by means of UV/Vis absorption and fluorescence spectroscopy. CB1–CB3 exhibit small Stokes shift and high fluorescence quantum yield. Noticeably, CB2 with styrene moieties at 5-position of BODIPY displays absorption alternation with maximum of 120 nm red-shift upon addition of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) as a base, giving remarkable color change which can be detected by naked eye. Meanwhile, the compound CB3 shows high selectivity toward fluoride ion via fluorescence quenching mechanism by release of the masked phenolate form of CB2 through fluoride ion induced deprotection reaction. It also exhibits fast signal response time (30 s) and excellent selectivity over other competing analytes, making it a good candidate as colorimetric sensor for fluoride sensing.

1,8-Diazabicycloundecene-mediated Separation of Singly Bonded Fullerene Dimer and Application to Facile Preparation of C61H2

We investigated the complexation of a singly bonded fullerene dimer [C60(CH2SiMe2OiPr)]2 and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in order to develop facile separation of a fullerene derivative from the mixture of fullerene and its derivatives without the use of time consuming and expensive chromatographic techniques. Addition of DBU to a 1,2,4-trimethylbenzene (TMB) solution of C60 and [C60(CH2SiMe2OiPr)]2 afforded complexation only with [C60(CH2SiMe2OiPr)]2, leading to precipitation of the [C60(CH2SiMe2OiPr)]2-DBU complex. Decomplexation with 1,2-dichlorobenzene gave [C60(CH2SiMe2OiPr)]2 in 56% recovery. In addition, the [C60(CH2SiMe2OiPr)]2-DBU complex could be used for the synthesis of dihydromethano[60]fullerene C61H2.

Fluorescence Modulation in Tribranched Switchable [4]Rotaxanes

Two novel tribranched [4]rotaxanes with a 1,3,5-triphenylene core and three rotaxane arms have been designed, synthesized, and characterized by (1)H and (13)C NMR spectroscopies and HR-ESI mass spectrometry. [4]Rotaxanes 1 and 2 each possess the same three-armed skeleton. Each arm incorporates two distinguishable binding sites for a dibenzo[24]crown-8 ring, namely a dibenzylammonium site and an N-methyltriazolium site, and is terminated by a 4-morpholino-naphthalimide fluorophore as a stopper. [4]Rotaxane 1 has three di-ferrocene-functionalized dibenzo[24]crown-8 rings whereas 2 has three simple dibenzo[24]crown-8 rings interlocked with the thread component. Uniform shuttling motions of the three macrocycles in both 1 and 2 can be driven by external acid-base stimuli, which were confirmed by (1)H NMR spectroscopy. However, [4]rotaxanes 1 and 2 show distinct modes of fluorescence modulation in response to external acid-base stimuli. [4]Rotaxane 1 exhibits a remarkable fluorescence decrease in response to the addition of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a base, which can displace the ferrocene-functionalized macrocycle from the dibenzylammonium station to the N-methyltriazolium station. In contrast, the fluorescence intensity of [4]rotaxane 2 showed an enhancement with the addition of DBU. Time-resolved fluorescence measurements have been performed. The different photoinduced electron-transfer processes responsible for the fluorescence changes in the two molecular systems are discussed. Topological structures of this kind have significant potential for the design and construction of large and complex assemblies with controllable functions.

Synthesis and biological activity of novel 3-heteroaryl-2H-pyrido[4,3-e][1,2,4]thiadiazine and 3-heteroaryl-2H-benzo[e][1,2,4]thiadiazine 1,1-dioxides.

A series of novel 1,2,4-thiadiazine 1,1-dioxides were synthesized by condensation of 2-chlorobenzenesulfonamide and 4-chloropyridine-3-sulfonamide with heterocyclic methyl carbimidates obtained from heterocyclic carbonitriles and used at the time of their creation. Substituted amidines were isolated as the intermediates in the reaction with 2-chlorobenzenesulfonamide. Those intermediates were successfully cyclized to corresponding 1,2,4-thiadiazine 1,1-dioxides in pyridine with the addition of DBU. The newly synthesized compounds were evaluated for their tuberculostatic and anticancer activities. Eight compounds were able to inhibit the growth of some renal and non-small cell lung cancer cell lines.Graphical

Studies on two different diastereoselective reaction pathways from a serinol derivative to 4-hydroxymethyl-2-oxazolidinones using 2-chloroethyl chloroformate and N,N′-disuccinimidyl carbonate

Two reaction pathways and their diastereoselectivity-determining steps of the asymmetric desymmetrization of (R)-2-(α-methylbenzyl)amino-1,3-propanediol 1 with 2-chloroethyl chloroformate (CCF) and with N,N′-disuccinimidyl carbonate giving (4S,αR)-4-hydroxymethyl-3-α-methylbenzyl-2-oxazolidinones (4S)-3 and its (4R,αR)-diastereomer (4R)-3 were investigated. The reaction of serinol 1 and CCF to give the corresponding carbonates was not a diastereoselectivity-determining step. The carbonates gave (R)-5-(α-methylbenzyl)amino-1,3-dioxan-2-one 4 after addition of DBU, and an intramolecular acyl transfer of 4 was found to be a diastereoselectivity-determining step to give (4S)-3. Conversely, the reaction of serinol 1 and N,N′-disuccinimidyl carbonate afforded directly the opposite diastereomer (4R)-3 but not via the intermediate 4. Thus, their diastereoselectivities depended on the acylating reagent.

Synthesis, structure, and chemical property of the first fluorine-containing porphycene.

[structure: see text] A pyrrolic macrocycle, beta-tetrakis(trifluoromethyl)porphycene, is the first example of a fluorine-containing porphycene. Four electron-withdrawing CF(3) substituents provide a highly distorted structure and an attractive electron-deficient nature for the porphycene framework. From the electrochemical study, it is found that the LUMO energy level for the beta-trifluoromethylporphycene is 1.24 V more stabilized compared to that for etioporphyrin. Moreover, the deprotonation of the inner N[bond]H proton in the porphycene was observed upon the addition of DBU.

Anodic oxidation of carboxamides. IV. Anodic dimerization of 4- and 4'-substituted benzanilides in the presence of a strong base.

Anodic oxidation of several 4-and 4'-substituted benzanilides in the presence of a strong base, 1, 8-diazabicyclo [5. 4. 0] undecene-7 (DBU), was investigated by cyclic voltammetry and controlled potential electrolysis at a glassy carbon electrode in acetonitrile. The original voltammetric peak of the anilides shifted to less positive potentials on addition of DBU. The magnitude of the cathodic shift was linearly correlated with the Hammett σ values of the 4'-substituents, and the oxidation process could be explained in terms of a one-electron abstraction from the anilide which exists as a hydrogen-bonded complex with the base. Controlled potential electrolysis of the anilides under basic conditions gave three different types of dimers depending on the nature of the 4'-substituent, X. When X=alkyl group, the 4- (N-benzoyl-N-phenyl) amino-2, 5-cyclohexadienone derivative (2) was obtained. Diphenylamine derivatives (3) and (4) produced through N-2' and N-4' dimerization were the main products when X=hetero atom and X=H, respectively. A sandwich-type approach of the radicals formed by the initial one-electron transfer can account for these results.