Sealed Tube Conditions Research Articles

One‐Pot Synthesis of Sulfonylated 5‐Aroyl‐2‐Arylpyridines via Ruthenium‐Catalyzed and K2S2O8‐Mediated Domino Annulation of β‐Ketosulfones with DMF

AbstractRuthenium‐catalyzed and K2S2O8‐mediated synthesis of diverse sulfonylated 5‐aroyl‐2‐arylpyridines was developed through one‐pot stepwise annulation of two molecules of β‐ketosulfones and N,N‐dimethylformamide (DMF) under the sealed tube conditions. In the overall process, DMF acts as the synthon of one carbon and one imino moiety in the construction of pyridine skeleton via cascade formation of single (C−C/C−N) and double (C=C/C=N) bonds under refluxing DMF conditions. Plausible reaction mechanism is proposed and discussed.

One-pot synthesis of a new class of alkynyl anionic synthons: the 4-(2',2-trimethylsilylethynylphenoxymethyl)-2H-chromen-2-ones

An efficient approach for the synthesis of a new class of anionic synthons: the 4-(2',2-trimethylsilylethynylphenoxymethyl)-2H-chromen-2-ones employing a one-pot three-component reaction is reported. Reaction of trimethylsilylacetylene, o-iodophenol and nine different bromomethylcoumarins in THF solvent at 80 °C under sealed tube conditions gave nine novel 4-(2',2-trimethylsilylethynylphenoxymethyl)-2H-chromen-2-ones in greater than 90% isolated yields. All compounds were spectroscopically characterized by elemental analysis, FT-IR, MS, 1H-, and 13C-NMR techniques.

Carbon Nitride Functionalized with Sb Resulting in High Photocatalytic Activity

Composites based on Sb clusters anchored on graphitic carbon nitride (g-C3N4) are prepared via a hierarchical sealed-tube calcination method. In the first stage, thermal treatment brings the density and crystallinity of g-C3N4 to substantially increase, resulting in 4.5 times higher photocatalytic efficiency toward water splitting for hydrogen generation. After further calcination under sealed-tube conditions, Sb species are successfully anchored on the edge of the pores within the g-C3N4 matrix in the form of atomic clusters. Photocatalytic hydrogen generation from the resulting Sb@C3N4 is further enhanced 14.4 times compared with the pristine g-C3N4. Such an improvement can be ascribed to the tuning of the electronic structure in Sb@C3N4 and hastened charge transfer.

Regiospecific substitution of the β-vinylic sp2 carbon of cyclohexenones bearing the α-chloro- and β-tosylate-groups: Single crystal XRD/Hirshfeld surface/in-silico studies of three representative compounds

2-Chloro-3-tosyl-5,5-dimethyl-2-cyclohexenone was subjected to a series of regiospecific Suzuki-Miyaura cross-coupling reactions in suspensions of nine different substituted boronic acids, Pd(OAc)2, P(Ph3)3, K3PO4 and 1,4-dioxane solvent, under sealed tube conditions. The regiospecific substitution of the tosyl-group by the aryl group in preference over the chloride- group was observed. A comparison between the bromo- and tosylate group’s reactivities is highlighted. Using the methodology, the products: 2-chloro-3-aryl-5,5-dimethyl-2-cyclohexenones were isolated in greater than 85% yields. Good quality crystals of three representative compounds were obtained by slow evaporation technique and subjected to single crystal XRD studies, Hirshfeld surface analysis, 3-D energy framework, and molecular docking studies. Crystal data for compound 3; C15H17ClO4S: monoclinic, space group P21/c (no. 14), a = 8.8687(3) Å, b = 10.5537(4) Å, c = 16.6862(7) Å, β = 89.807(3)°, V = 1561.78(10) Å3, Z = 4, T = 290 K, μ(MoKα) = 0.390 mm-1, Dcalc = 1.398 g/cm3, 13623 reflections measured (6.716° ≤ 2Θ ≤ 54.962°), 3570 unique (Rint = 0.0467, Rsigma = 0.0512) which were used in all calculations. The final R1 was 0.0452 (I > 2σ(I)) and wR2 was 0.1019 (all data). Crystal data for compound 5e; C20H18O2FCl: monoclinic, space group P21/c (no. 14), a = 6.4900(5) Å, b = 18.6070(13) Å, c = 14.2146(11) Å, β = 102.324(2)°, V = 1677.0(2) Å3, Z = 4, T = 296(2) K, μ(MoKα) = 0.239 mm-1, Dcalc = 1.309 g/cm3, 25575 reflections measured (6.262° ≤ 2Θ ≤ 52.224°), 3283 unique (Rint = 0.0494, Rsigma = 0.0307) which were used in all calculations. The final R1 was 0.0875 (I > 2σ(I)) and wR2 was 0.2056 (all data). Crystal data for compound 5h; C12H13OSCl: triclinic, space group P-1 (no. 2), a = 6.7517(6) Å, b = 8.8376(9) Å, c = 12.6049(12) Å, α = 109.538(3)°, β = 98.597(3)°, γ = 90.417(3)°, V = 699.52(12) Å3, Z = 2, T = 290 K, μ(MoKα) = 0.410 mm-1, Dcalc = 1.376 g/cm3, 28754 reflections measured (6.114° ≤ 2Θ ≤ 59.288°), 3898 unique (Rint = 0.0544, Rsigma = 0.0349) which were used in all calculations. The final R1 was 0.1101 (I > 2σ(I)) and wR2 was 0.2481 (all data).

Ligand‐Free Cu‐Catalyzed Suzuki Coupling of Alkynyl Bromides with Boronic Acids in Ethanol Under Microwave Irradiation

AbstractA ligand‐free microwave assisted synthesis of internal alkynes using copper‐catalyzed Suzuki type coupling reaction of alkynyl bromides with boronic acid derivatives has been developed. This protocol uses cheap CuI, greener solvent ethanol and K3PO4 base under microwave irradiation. This strategy does not need any ligand or sealed tube conditions. This methodology provides an efficient way to synthesize 1,2‐diarylacetylenes in good to excellent yields.

Metal free synthesis of functionalized 1-aryl isoquinolines via iodine mediated oxidative dehydrogenation and ring opening of lactam in isoindoloisoquinolinones

A facile and convenient method for the synthesis of substituted 2-(isoquinolin-1-yl)benzoic acids from isoindoloisoquinolinones in the presence of molecular iodine under sealed tube condition at 100 $$^{\circ }\hbox {C}$$ has been developed. This methodology involves the oxidative dehydrogenation and ring opening of hydroxy lactam/methoxy lactam to furnish the 2-(isoquinolin-1-yl)benzoic acids. Some of these acids are successfully cyclized to furnish the azabenzanthrone derivatives, the potential precursors for the synthesis of menisporphine alkaloids and daurioxoisoaporphines. SYNOPSIS Metal-free synthesis of 1-aryl isoquinolines, which are synthetic precursors for azabenzanthrones or menisporphines, from isoindoloisoquinolinones using iodine under sealed tube conditions is reported. This methodology is successfully utilized to synthesize the 1-azabenzanthrone and analogue of menisporphine, i.e., 5-methoxy-6-hydroxy-1-azabenzanthrone.

A facile approach for the synthesis of hydroxyl-rich microporous organic networks for efficient CO2 capture and H2 storage.

A new series of porous organic networks (PONs) internally decorated with several free -OH functional groups has been synthesized through acid catalyzed condensation reaction of terephthalaldehyde and nucleophilic aromatic compounds. These materials possess high Brunauer-Emmett-Teller specific surface areas (592-865 m2 g-1) and showed maximum CO2 adsorption capacity of 4.31 mmol g-1 and H2 uptake of 8.23 mmol g-1 at 273 and 77 K, respectively, under 1 bar.

Intra- and Intermolecular Alkylation ofN,O-Acetals and π-Activated Alcohols Catalyzed by in Situ Generated Acid

Intramolecular and intermolecular alkylations of carbocation precursors of limited ionization ability, principally N,O-acetals, without the use of an exogenous reagent have been developed. The reactions are carried out in 1,1,2,2-tetrachloroethane (TCE) and take advantage of the ability of this solvent to continuously release small amounts of HCl by thermolytic elimination. A study of the reaction led to several improved protocols such as (1) preheated TCE, (2) microwave-assisted reactions, and (3) flow or sealed-tube conditions, which allow significant reaction rate enhancements and made possible some challenging reactions such as the α-amidoalkylation of ketones. Studies using flow chemistry confirmed not only that very low concentrations of HCl generated from the solvent were responsible for the reactivity but also that TCE had additional beneficial properties in comparison to other chlorinated solvents such as dichloroethane. The method can easily be extended to the alkylation using proelectrophiles such as π-activated alcohols, which are normally unreactive toward HCl catalysis. This work represents the first successful use of HCl, the simplest strong Brønsted acid, as an efficient alkylation catalyst.

Comparative Study of the Frech Catalyst with Two Conventional Catalysts in the Heck Synthesis of 2,4-Diaminopyrimidine-based Antibiotics

Comparative Study of the Frech Catalyst with Two Conventional Catalysts in the Heck Synthesis of 2,4-Diaminopyrimidine-based Antibiotics

Synthesis and biological activity of substituted 2,4-diaminopyrimidines that inhibit Bacillus anthracis

A series of substituted 2,4-diaminopyrimidines 1 has been prepared and evaluated for activity against Bacillus anthracis using previously reported (±)-3-{5-[(2,4-diamino-5-pyrimidinyl)methyl]-2,3-dimethoxyphenyl}-1-(1-propyl-2(1H)-phthalazinyl)-2-propen-1-one (1a), with a minimum inhibitory concentration (MIC) value of 1–3 μg/mL, as the standard. In the current work, the corresponding isobutenyl (1e) and phenyl (1h) derivatives displayed the most significant activity in terms of the lowest MICs with values of 0.5 μg/mL and 0.375–1.5 μg/mL, respectively. It is likely that the S isomers of 1 will bind the substrate-binding pocket of dihydrofolate reductase (DHFR) as in B. anthracis was found for (S)-1a. The final step in the convergent synthesis of target systems 1 from (±)-1-(1-substituted-2(1H)-phthalazinyl)-2-propen-1-ones 6 with 2,4-diamino-5-(5-iodo-3,4-dimethoxybenzyl)pyrimidine (13) was accomplished via a novel Heck coupling reaction under sealed-tube conditions.

Microwave-assisted Heck Synthesis of Substituted 2,4-Diaminopyrimidine-based Antibiotics

Microwave-assisted organic synthesis is an area of increasing interest for promoting clean, reproducible, high-yielding reactions under mild conditions.1,2 This is evident from the large number of papers and reviews that have appeared on this topic in the recent literature.3–8 In the current work, microwave irradiation was employed to facilitate the intermolecular formation of C–C bonds using a palladium-catalyzed Heck coupling reaction. Microwave conditions have previously been used to accelerate this type of reaction9,10 as well as other metal-catalyzed processes such as the Suzuki, Sonogashira and Negishi couplings.11,12 However, the use of microwave irradiation to induce reactions of highly functionalized molecules has not been studied in detail. We, therefore, wish to report our work on a microwave-assisted Heck reaction to prepare a series of antibacterials bearing a variety of functional groups. The goal of the current project is the synthesis 2,4-diaminopyrimidine antibiotics 3a–h, which have potential for the treatment of inhalation anthrax, a bioterror threat. The most important aspect of these drugs is that they selectively inhibit the activity of Bacillus anthracis dihydrofolate reductase (DHFR) but not human DHFR.13,14 DHFR plays a critical role in folate metabolism and is a good target for antibiotic drug candidates. Furthermore, since our compounds incorporate several structural units common to drugs that inhibit DHFR, it is less likely that bacteria exposed to these agents will readily develop a resistance to them. The synthesis involves a Heck reaction of 2,4-diamino-5-(5-iodo-3,4-dimethoxy-benzyl)pyrimidine (1) with a series of (±)-1-(1-substituted-1H-phthalazin-2-yl)prop-2-en-1-ones 2, both of which are available by known methods.13,15 Earlier syntheses of certain examples of 3 by conventional Heck procedures13,15 gave yields of 10%–37%. The products obtained by this method, however, were difficult to purify from the reaction mixture due to extensive side-product formation. We have successfully improved the synthesis by employing microwave irradiation to assist the Heck coupling process. The conventional reactions were carried out using 2.07 mmol each of 1 and 2, 2.27 mmol of N-ethylpiperidine and 0.026 mmol (1.24 mol % relative to substrates 1 and 2) of bis(triphenylphosphine)palladium(II) dichloride catalyst in 8 mL of DMF under argon at 140°C–150°C for 18 h.13,15 This procedure generally afforded the coupled product in low yield (10%–37%) with substantial side-product formation. In an effort to improve this outcome, substrate concentrations and temperatures were varied, but neither of these changes resulted in significant improvement. Attempts to adjust the catalyst loading for this transformation were also examined. An increase in catalyst loading to 2.00 mol % decreased the yield of the product and added to the impurity profile, making isolation of the product more difficult. A decrease in catalyst loading to 0.96 mol % led to incomplete reaction and recovery of starting material along with the desired product. Thus, a catalyst loading of 1.24 mol % proved optimum for the complete conversion to the product with a minimum of side reactions. Finally, the use of other catalysts (e.g. Pd(OAc)2, PdCl2, (Ph3P)4Pd, Pd/C and CuI)13 and bases (e.g. Et3N, DBU, K2CO3 and Cs2CO3)13 failed to improve the conversion to product. Reactions were also carried out on the same molar scale in sealed tubes. This resulted in slightly improved yields (42%–65%), but side-reactions were still problematic. It is conceivable that prolonged heating under conventional and sealed tube conditions caused degradation of the substrates and the catalyst, leading to a more complex product mixture. Thus, a method was sought to decrease the reaction time, which led us to the use of microwave irradiation. Microwave-assisted reactions were run on the same scale as above at 400 W and 150°C under argon for 60–80 min and gave superior conversions to products with far fewer impurities. A comparison of yields obtained using conventional, sealed tube and microwave conditions is shown in Table 1. Microwave irradiation as an alternative source of heating expedited the reaction, decreased the required catalyst loading by 20% (to 0.96 mol %) and reduced the amount of solvent needed by 25%. A series of reactions was carried out with R = propyl, isobutyl, isobutenyl, phenyl, 4-fluorophenyl, benzyl, 4-methylbenzyl and 4-trifluoromethoxybenzyl to establish the generality of the method. Products prepared in this manner were conveniently purified by placing the crude reaction mixture directly onto a silica gel column and eluting with increasing concentrations of methanol in dichloromethane. The target molecules were isolated as hydrates or solvates16 and were characterized by elemental and spectral analysis. Table 1 Yields of 3 Using Conventional, Sealed Tube and Microwave Conditions 1+2a-h→N-ethylpiperidineDMF,Δ(Ph3P)2PdCl23a-h We have successfully developed a synthesis of 2,4-diaminopyrimidine-based antibiotics that utilizes a microwave-assisted Heck reaction on highly functionalized substrates in the final step. The reaction is superior to reactions performed under conventional or sealed tube conditions, requiring less solvent and catalyst. More importantly, the use of microwave conditions reduced reaction times and provided higher coupling yields with fewer side products.

Convenient preparation of 4-aryl-2-(heteroarylamino)pyrimidines and 4-anilino-2-(heteroarylamino)pyrimidines

Abstract 4-Aryl-2-anilinopyrimidines and 2,4-dianilinopyrimidines are privileged structures found in many drug-like molecules and biologically active compounds. A method for the quick assembly of novel 4-aryl- and 4-anilino-2-(heteroarylamino)pyrimidines via Buchwald–Hartwig N-arylations at elevated temperatures under sealed tube conditions is reported. This method’s convenience and practicality is demonstrated through the preparation of several novel non-nucleoside reverse transcriptase inhibitor (NNRTI) analogues.

Thallium solubility range in Tl2 –yBa2Can– 1CunO2n+ 4 –xsuperconductors

The Tl2 –yBa2Can– 1CunO2n+ 4 –xphases corresponding to n= 1, 2 and 3 have been synthesized at 860–880 °C under sealed-tube conditions and characterized by wet chemical analysis, X-ray diffraction and magnetic susceptibility. A lower Tl solubility limit of (2 –y)= 1.25 was found for all n, but the upper limit decreased from 1.89 for n= 1 to 1.80 for n= 2 and 1.65 for n= 3. Under our controlled synthetic conditions, which allowed variation of the Tl concentration under similar temperatures and oxygen partial pressures, the equilibrium oxygen content was found to vary with the change in Tl concentration so as to keep a constant oxidation of the CuO2 sheets. Over the entire Tl solubility ranges, the superconductive onset temperatures were nearly constant: Ton= 117 ± 1 K for n= 3, Ton= 105 ± 1 K for n= 2, and Ton= 86 ± 1 K for n= 1. The superconductive properties improve sensitively with chemical homogenization, and homogenization was achieved most easily for n= 2. Processing of Tl-2212 superconductors with a controlled Tc under sealed-tube conditions appears to be feasible.

Preparation of spirocyclic cyclopropyl ketones through condensation of epoxides with .beta.-keto phosphonates

The β-keto phosphonate derivatives of several cyclic ketones have been shown to undergo condensation with epoxides upon treatment with base, affording spirocyclic cyclopropyl ketones. Moderate to resonable yields were obtained under sealed tube conditions with ethylene oxide, propylene oxide, and styrene oxide, and the substituted epoxides gave a single diastereomer in each case. The process can be viewed as an example of regiospecific geminal dialkylation, and cleavage of the cyclopropyl ring allows access to additional α,α-dialkylated ketones

Low concentration diffusion in silicon under sealed tube conditions : R. N. Ghoshtagore. Solid St. Electron.15 (1972), p. 1113

Low concentration diffusion in silicon under sealed tube conditions : R. N. Ghoshtagore. Solid St. Electron.15 (1972), p. 1113

Low concentration diffusion in silicon under sealed tube conditions

Boron and phosphorus were diffused into (111) C. Z. silicon under intrinsic vacuum sealed tube conditions. It has been observed that the low concentration migration of dopants from the vapor phase into the bulk solid is appreciably affected by a surface rate limitation process. Consequently, at four temperatures between 1100 and 1250°C extensive diffusion experiments were performed to explore the nature of the surface barrier rate constant. Diffusion profiles were processed to produce surface induced intrinsic diffusivities. Thermodynamics and kinetics of the surface barrier and thus induced diffusion processes have been analyzed for both silicon and germanium.