Studies on NaI/DMSO induced retro -Michael addition (RMA) reactions on some 1,5-dicarbonyl compounds

Studies on the reaction of some 1,5-ketodiesters/1,5-diketones with NaX (X = Cl/Br/I)/DMSO have shown that under microwave/thermal conditions, facileretro-Michael addition (RMA) reaction takes place instead of formation of the expected Krapcho products. Mechanistic studies have shown that the NaI/DMSO system is a better system than NaCl/DMSO or NaBr/DMSO to promote the RMA pathway and DMSO is an essential requirement. The electrophilic halide ion could be involved in this fragmentation reaction.     

"Recapitation" of nido-Metallacarboranes as a Synthetic Tool: Preparation of Apically Substituted CoC(2)B(4) Clusters via Boron Insertion(1)

Derivatives of CpCo(2,3-Et(2)C(2)B(4)H(4)) containing substituents at the apex boron atom [B(7)], the first examples of apically functionalized small metallacarborane clusters, have been prepared in good yield via boron insertion into the nido-CpCo(2,3-Et(2)C(2)B(3)H(3))(2-) dianion. Reaction of this substrate with BX(3) (X = Cl, Br, I) or PhBCl(2) in toluene at room temperature gave the corresponding CpCo(2,3-Et(2)C(2)B(4)H(3)-7-X) derivatives (2a-c and 3 in which X = Cl, Br, I, and Ph, respectively), all of which were isolated via column chromatography as air-stable yellow solids and characterized via (1)H, (11)B, and (13)C NMR, infrared, UV-visible, and mass spectra. Treatment of the same dianion with 1,4-(Br(2)B)(2)C(6)H(4) afforded air-stable orange crystalline [CpCo(2,3-Et(2)C(2)B(4)H(3)-7)](2)C(6)H(4) (4). The structure of this compound was defined via spectroscopy and X-ray crystallography as a bis(cobaltacarborane) complex linked at the apex borons via a 1,4-phenylene bridge. Crystal data for 4: space group Pbca; a = 15.056(7) ?, b = 21.612 (8) ?, c = 11.641 (3) ?; Z = 4; R = 0.045 for 1582 independent reflections having I > 3sigma(I).     

Mechanistic considerations for the consecutive cyclization of 2,3-dibromopropylamine hydrobromide giving a strained molecule, 1-azabicyclo[1.1.0]butane

The effective formation of 1-azabicyclo[1.1.0]butane (2) by treatment of 2,3-dibromopropylamine hydrobromide (1) with n-BuLi could be understood considering a rational reaction pathway via both transition states 10 and 19 based on the intramolecular Br...Li(+) coordination. A similar cyclization pathway starting from N-benzyl-3-bromopropylamine hydrochloride (17) to afford N-benzylazetidine (18) could also be postulated on the basis of a transition state 20 involving the intramolecular Br...Li(+) coordination.     

Facile synthesis of isomerically pure fullerenols C60(OH)5Br and 1,4-C60(OH)2 from chlorofullerene C60Cl6

The chlorofullerene C₆₀Cl₆ was demonstrated as a versatile precursor for the synthesis of two isomerically pure fullerenols via tetrabutylammonium bromide promoted reactions with water. Performing the synthesis in wet chlorobenzene produced 1,4-C₆₀(OH)₂ as the only isolable product along with substantial amounts of non-functionalized C₆₀. However, the addition of DMSO as a co-solvent altered the reaction pathway, leading to the formation of C₆₀(OH)₅Br as the main product. Both isolated compounds were novel and their molecular compositions and structures were confirmed by mass spectrometry and NMR spectroscopy. The fullerenol C₆₀(OH)₅Br, which was formed in a moderate yield, represents the first isomerically pure polyhydroxylated fullerene available on a large scale.     

Synthesis of New Dibenzo-tetraaza and Dibenzo-dioxadiaza[14]annulene Derivatives Using 3-Bromo-substituted Vinamidinium Salt

Novel bromo-substituted derivatives of dibenzo-tetraaza and dibenzo-dioxadiaza[14]annulenes B–G were synthesized by a twofold condensation reaction of a symmetrical bromo-substituted vinamidinum salt A with ortho-diamino- and ortho-amino-hydroxyarenes such as 1,2-diaminobenzene, 1,2-diamino-4,5-dimethylbenzene, 2,3-diaminonaphthalene, 1,2-diamino-4-methylbenzene, 2-amino-1-hydroxybnzene, and 2-amino-1-hydroxy-5-methyl-benzene in acetonitrile/acetic acid as reaction medium. The ultraviolet/visible spectral behavior of these [14]annulenes was examined in dimethyl sulfoxide (DMSO). Elemental analysis, infrared, ¹H NMR, ¹³C NMR, and mass spectra confirm the molecular structure of the newly synthesized compounds.     

Metal binding characteristics of tetracycline derivatives in DMSO solution

A previous study of the site of metal binding in tetracycline has been extended to several derivatives of tetracycline in an effort to determine which specific functional groups are involved in binding to metal ions in DMSO solution and to explore relationships between antibacterial activity and metal binding characteristics. Proton NMR experiments using paramagnetic and diamagnetic lanthanide series ions as binding site probes indicate that the ring A tricarbonylmethane group is the binding site for tetracycline, 5-hydroxytetracycline, 4-epitetracycline and tetracyclinemethiodide in DMSO. No. NMR evidence for metal binding is found for 4-dedimethylaminotetracycline. Binding to Mg²⁺ is also investigated by NMR for several of these compounds, and a discussion of conformational preferences of tetracycline derivatives in DMSO is presented.     

Thiol–Ene “Click” Reaction Triggered by Neutral Ionic Liquid: The “Ambiphilic” Character of [hmim]Br in the Regioselective Nucleophilic Hydrothiolation

Thiol–ene “click” chemistry has emerged as a powerful strategy to construct carbon–heteroatom (C? S) bonds, which generally results in the formation of two regioisomers. To this end, the neutral ionic liquid [hmim]Br has been explored as a solvent cum catalyst for the synthesis of linear thioethers from activated and inactivated styrene derivatives or secondary benzyl alcohols and thiols without the requirement of using a metal complex, base, or free radical initiator. Furthermore, detailed mechanistic investigations using ¹H NMR spectroscopy and quadrupole time‐of‐flight electrospray ionization mass spectrometry (Q‐TOF ESI‐MS) revealed that the “ambiphilic” character of the ionic liquid promotes the nucleophilic addition of thiol to styrene through an anti‐Markovnikov pathway. The catalyst recyclability and the extension of the methodology for thiol–yne click chemistry are additional benefits. A competitive study among thiophenol, styrene, and phenyl acetylene revealed that the rate of reaction is in the order of thiol–yne>thiol–ene>dimerization of thiol in [hmim]Br.     

Synthesis and properties of cationic polyelectrolyte with regioregular polyalkylthiophene backbone and ionic‐liquid like side groups

High‐regioregular poly{3‐[6‐(1‐methylimidazolium‐3‐yl)hexyl]thiophene‐2,5‐diyl bromide}, PMHT‐Br, has been prepared by reaction of high‐regioregular (above 92%) poly[3‐(6‐bromohexyl)thiophene‐2,5‐diyl] with 1‐methylimidazole. PMHT‐Br is soluble in water and water miscible solvents such as methanol, DMSO and shows solvatochromism; λ_max (nm): 423 (H₂O); 435 (MeOH); 452 (DMSO). Increased absorption band broadening observed for aqueous solution as well as NMR spectra in D₂O suggests a micelle‐like structure of PMHT‐Br molecules in these solutions: poly(3‐hexylthiophene) core and 1‐methylimidazolium bromide shell. Despite the disturbing effect of ionic groups, the solid‐state PMHT‐Br shows absorption maximum at 520 nm, the band edge at 660 nm (ca. 1.9 eV), and fluorescence emission with maximum at 635 nm, in a good agreement with the polymer regioregularity. Fluorescence emission maxima: λ_em (nm): 598 (H₂O); 562 (MeOH); 574 (DMSO), occur in a vicinity of corresponding adsorption band edges. Plot of electrical conductivity of PMHT‐Br (measured under the dynamic vacuum conditions, 5 × 10^?5 Pa) versus 1/T shows a break at about 70 °C same as the temperature dependence of λ_max of the solid PMHT‐Br. These breaks indicate an increase in the mobility of polymer segments and ions within PMHT‐Br; however, a thermal analysis did not provide solid evidence for it. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3073–3081, 2010     

5-芳基-2-呋喃甲酰基氨基硫脲类衍生物的合成及水溶液中 阴离子识别研究

合成了一系列未见文献报道的5-芳基-2-呋喃甲酰基氨基硫脲类衍生物, 通过1H NMR, IR, 元素分析确认了其结构. 并利用紫外-可见吸收光谱考查了它们在DMSO及DMSO/H2O溶液中与F－, Cl－, Br－, I－, CH3COO－, , 等阴离子的识别作用. 结果表明: 该类受体分子能较好地识别F－, CH3COO－, 三种阴离子, 当加入这三种阴离子后, 溶液的颜色由淡黄色转变为亮黄色. 通过改变含水量可有效地调控识别作用的选择性. 1H NMR滴定实验进一步证实了受体分子与阴离子通过氢键作用形成主客体配合物.     

Ring Opening in 1- and 3-Methylpyrimidin-4-ones in the Presence of Bases

According to the data of UV and NMR spectroscopy, 1- and 3-methylpyrimidin-4-ones and their 5-fluoro-substituted analogs in water and DMSO in the presence of bases undergo ring opening with formation of -formylaminoacrylamide derivatives. The process involves attack by hydroxide ion on the C² atom, and its rate in DMSO is higher than in water by three orders of magnitude. Ring opening in 1-methylpyrimidin-4-ones occurs more readily than in the corresponding 3-methyl isomers, while the acyclic products formed from 3-methylpyrimidin-4-ones in DMSO are more stable than those derived from 1-methylpyrimidin-4-ones.     

Theoretical and experimental study of triphenylphosphonium Schiff base of 5-hydroxy-3-methyl-1-phenyl-4-formylpyrazole

The Schiff base (HLBr), containing a chelating unit and triphenylphosphonium moiety has been synthesized in the reaction of 4-aminobenzyl(triphenyl)phosphonium bromide with 5-hydroxy-3-methyl-1-phenyl-4-formylpyrazole. The composition and structure of HLBr have been determined by elemental analysis, IR, 1D and 2D NMR, electronic spectroscopy and mass spectrometry. Density functional theory (DFT) calculations (6-311G(d,p) level of theory) have been carried out to investigate tautomeric forms of HL⁺ and the reaction mechanism of its formation and spectral properties. The most stable form in the solid state and in DMSO solution is pyrazolone (keto-amine) tautomeric form.     

Oligomerization of indole derivatives with incorporation of thiols

Two molecules of indole derivative, e.g. indole-5-carboxylic acid, reacted with one molecule of thiol, e.g. 1,2-ethanedithiol, in the presence of trifluoroacetic acid to yield adducts such as 3-[2-(2-amino-5-carboxyphenyl)-1-(2-mercaptoethylthio)ethyl]-1Hindole-5-carboxylic acid. Parallel formation of dimers, such as 2,3-dihydro-1H,1'H-2,3'-biindole-5,5'-dicarboxylic acid and trimers, such as 3,3'-[2-(2-amino-5-carboxyphenyl) ethane-1,1-diyl]bis(1H-indole-5-carboxylic acid) of the indole derivatives was also observed. Reaction of a mixture of indole and indole-5-carboxylic acid with 2-phenylethanethiol proceeded in a regioselective way, affording 3-[2-(2-aminophenyl)-1-(phenethylthio)ethyl]-1H-indole-5-carboxylic acid. An additional product of this reaction was 3-[2-(2-aminophenyl)-1-(phenethylthio)ethyl]-2,3-dihydro-1H,1'H-2,3'-biindole-5'-carboxylic acid, which upon standing in DMSO-d6 solution gave 3-[2-(2-aminophenyl)-1-(phenethylthio)ethyl]-1H,1'H-2,3'-biindole-5'-carboxylic acid. Structures of all compounds were elucidated by NMR, and a mechanism for their formation was suggested.     

Pulse radiolysis studies of the reactions of bromine atoms and dimethyl sulfoxide–bromine atom complexes with alcohols

Dimethylsulfoxide (DMSO)–Br complexes were generated by pulse radiolysis of DMSO/bromomethane mixtures and the formation mechanism and spectral characteristics of the formed complexes were investigated in detail. The rate constant for the reaction of bromine atoms with DMSO and the extinction coefficient of the complex were obtained to be 4.6×10⁹ M⁻¹ s⁻¹ and 6300 M⁻¹ cm⁻¹ at the absorption maximum of 430 nm. Rate constants for the reaction of bromine atoms with a series of alcohols were determined in CBrCl₃ solutions applying a competitive kinetic method using the DMSO–Br complex as the reference system. The obtained rate constants were ∼10⁸ M⁻¹ s⁻¹, one or two orders larger than those reported for highly polar solvents. Rate constants of DMSO–Br complexes with alcohols were determined to be ∼ 10⁷ M⁻¹ s⁻¹. A comparison of the reactivities of Br atoms and DMSO–Br complexes with those of chlorine atoms and chlorine atom complexes which are ascribed to hydrogen abstracting reactants strongly indicates that hydrogen abstraction from alcohols is not the rate determining step in the case of Br atoms and DMSO–Br complexes.     

FT‐IR kinetic and product study of the Br‐initiated oxidation of dimethyl sulfide

An FT‐IR kinetic and product study of the Br‐atom‐initiated oxidation of dimethyl sulfide (DMS) has been performed in a large‐volume reaction chamber at 298 K and 1000‐mbar total pressure as a function of the bath gas composition (N₂ + O₂). In the kinetic investigations using the relative kinetic method, considerable scatter was observed between individual determinations of the rate coefficient, suggesting the possibility of interference from secondary chemistry in the reaction system involving dimethyl sulfoxide (DMSO) formation. Despite the experimental difficulties, an overall bimolecular rate coefficient for the reaction of Br atoms with DMS under atmospheric conditions at 298 K of ≤1 × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ can be deduced. The major sulfur products observed included SO₂, CH₃SBr, and DMSO. The kinetic observations in combination with the product studies under the conditions employed are consistent with rapid addition of Br atoms to DMS forming an adduct that mainly re‐forms reactants but can also decompose unimolecularly to form CH₃SBr and CH₃ radicals. The observed formation of DMSO is attributed to reactions of BrO radicals with DMS rather than reaction of the Br–DMS adduct with O₂ as has been previously speculated and is thought to be responsible for the variability of the measured rate coefficient. The reaction CH₃O₂ + Br → BrO + CH₃O is postulated as the source of BrO radicals. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 883–893, 1999     

Specific Sequestering Agents for the Actinides. 29. Stability of the Thorium(IV) Complexes of Desferrioxamine B (DFO) and Three Octadentate Catecholate or Hydroxypyridinonate DFO Derivatives: DFOMTA, DFOCAMC, and DFO-1,2-HOPO. Comparative Stability of the Plutonium(IV) DFOMTA Complex(1)

The metal complex stability constants of Th(IV) with desferrioxamine B (DFO) and three octadentate derivatives [N-(2,3-dihydroxy-4-carboxybenzoyl)desferrioxamine B (DFOCAMC), N-(1,2-dihydro-1-hydroxy-2-oxopyridin-6-yl)carbonyl)desferrioxamine B (DFO-1,2-HOPO) and N-(2,3-dihydroxy-4-(methylamido)benzoyl)desferrioxamine B (DFOMTA)] have been determined. The formation constant of the Pu(IV)/DFOMTA complex has also been determined, and the formation constants have been estimated for the other Pu(IV) complexes of octadentate DFO derivatives. The DFO derivatives form 1:1 complexes with Th(IV) in aqueous solution. The solution chemistry of the Th(IV) complexes has been studied by spectrophotometric, potentiometric and proton NMR titrations. The Th(IV) formation constants are as follows (log K(f) values and esd's): DFO, 26.6(1); DFOMTA, 38.55(5); DFOCAMC, 37.2(3); DFO-1,2-HOPO, 33.7(4). The Pu(IV)/DFOMTA formation constant, determined by competitive spectrophotometric titration is (log K(f) value) 41.7(2). The estimation of the other Pu(IV) formation constants are as follows (log K(f) values): DFOCAMC, 40.4; DFO-1,2-HOPO, 36.9. The selectivity of DFO and the three derivatives for actinide(IV) ions is discussed.     

The influence of terminal push-pull substitution on the electronic structure and optical properties of pentacenes

The synthesis of 2,3-R(2)-9,10-(OMe)(2)-substituted pentacenes (R=OMe, F, Br, CN; 1-4) from 2,3-R(2)-9,10-dimethoxy-6,13-dihydro-6,13-ethanopentacene-15,16-diones (α-diketone-bridged precursors) by photochemically induced bis-decarbonylation (Strating-Zwanenburg reaction) is described. Under matrix-isolation conditions (solid Ar, 10 K) the S(1) transitions of 1 and 2 undergo hypsochromic and those of 3 and 4 bathochromic shifts compared to parent pentacene. The S(1) transition wavelengths correlate well with the difference of substituent parameters σ(p). A computational analysis of the excited states at the CAM-B3LYP/6-311+G** level of theory provides an assignment of the electronic transitions. Photolysis in solution at room temperature yields red [R=OMe (1)], blue [R=Br (3), F (2)], and green [R=CN (4)] pentacenes. The compounds are oxygen-sensitive and have low solubility, but their formation can be monitored by UV/Vis and, in the case of R=CN, also by (1)H NMR spectroscopy. The S(1) transition in 4 does not show the typical pentacene fine structure in the electronic absorption spectrum. Photogeneration in the presence of oxygen leads to a number of photoproducts that could be identified by monitoring the reaction by (1)H NMR spectroscopy for R=OMe.     

Macrolactones built from the bis-3,4(indol-1-yl)maleimide scaffold

15, 16, and 17-Membered lactones based on the bis-3,4(indol-1-yl)maleimide framework were obtained using intramolecular esterification reaction starting from 3-(1-ω-carboxyalkyl-2,3-dihydroindol-1-yl)-4-(1-ω-hydroxyalkyl-2,3-dihydroindol-1-yl)-maleimides. 3,4-Dibromo-maleimide, ω-(2,3-dihydroindol-3-yl)alkanoic acids, and ω-(2,3-dihydroindol-3-yl)alkanoles were used as starting compounds. Substitution of Br for the substituted indolines followed by the intramolecular cyclization of O-silylated hydroxyl acids derivatives led to macrolactones that incorporated 4-(dihydroindol-1-yl)-3-(indol-1-yl)maleimide moieties. Indoline nuclei in these compounds were dehydrogenated by DDQ in refluxing toluene to give 15, 16 or 17-membered lactones 3-[(ω-3-carboxyalkylindol-1-yl)-4-(ω-hydroxyalkylindol-1-yl)maleimides. Quantum chemical calculations showed that the formation of macrolactones of smaller size (13-membered) corresponds to the higher Gibbs energy ΔG^# and correlates with the absence of the target reaction product.     

A convenient synthesis of activated enantiomerically pure 2-ethynylaziridines

2,3-cis- and 2,3-trans-N-Arylsulfonyl-2-ethynylaziridines with high enantiomeric purity have been synthesized. N-Protected amino aldehydes synthesized from natural α-amino acids were successively treated with Ph₃PC(Br)CO₂Me, DIBAL, MsCl–Et₃N, NaH in DMSO, and tert-BuOK in THF to yield 2-ethynylaziridines in good to high yields.     

Synthesis of 1,1,4,4-tetrabromo-2-butenes and related compounds via desilylation-bromination of silylated 1,3-butadiene derivatives

The combination of zirconocene-mediated coupling of silylated alkynes with a protonation-desilylation or bromination-desilylation process afforded otherwise unavailable butadiene derivatives. When (E,E)-2,3-dialkyl-1,4-bis(trimethylsilyl)-1,3-butadienes were treated with 3 equiv of Br(2) in CH(2)Cl(2), (E)-2,3-dialkyl-1,1,4,4-tetrabromo-2-butenes were obtained in excellent yields with perfect stereoselectivity.     

Preparation of phthalates via carbonylation of <Emphasis Type="Italic">o</Emphasis>-dibromobenzenes in solutions of Pd catalysts and reactivity of Ar−Br bonds

Carbonylation of o-dibromobenzene and its derivatives in the presence of palladium phosphine complexes with NaOAc or Et₃N additive leads to the formation of phthalates in high yield under mild conditions. Correlation NMR spectroscopy data and semiempirical calculations have shown that the reactivity of the C–Br bond is enhanced with the increase in the positive charge at the carbon atom, in line with the results of kinetic experiments.