Homologous SNV Reaction: Synthesis of l‐Methyl‐4‐[4′‐phenylsulfonyl‐1′,3′‐butadienyl]pyridinium Iodide and Its Reactivity with Thiol Groups Giving Rise to the Chromophoric Thioether

Thioether 4‐[(1′E,3′E)‐4′‐phenylsulfanyl‐1,3′‐butadienyl]pyridine 8 and sulfone 4‐(4′‐phenylsulfonyl‐1′,3′‐butadienyl)pyridine 14 were prepared by reaction of the carbanions derived from allylic thioether or allylic sulfone with isonicotinaldehyde. The reaction with the sulfonyl carbanion occurred at the α position and on heating the alcolate gave the dienic sulfone 14 . The corresponding pyridinium iodide 10 and 15 were prepared by reaction with methyl iodide, respectively, on pyridine derivates 8 and 14 . The dienic pyridinium thioether 10 showed a long wavelength absorption band centered at 420 nm. The reaction of dienic pyridinium sulfone 15 with thiophenol gave the dienic pyridinium thioether 10 by a nucleophilic vinylic substitution. The reaction of sulfone 15 with glutathione was of second order and the rate constant was 8.5 M^?1s^?1 at 30°C and pH 7, about 500 times smaller than the rate constant observed with (E)‐1‐methyl‐4‐(2‐methylsulfonyl‐1‐ethenyl)pyridinium iodide 1 . The dienic pyridinium thioether 10 was a negative solvatochrome.     

Selective preparation of glycosyl sulfone or glycal by treatment of phenyl thioglycoside of N-acetylneuraminic acid with m-chloroperbenzoic acid

Treatment of acetylated phenyl thioglycoside of N-acetylneuraminic acid with m-chloroperbenzoic acid (MCPBA) in CH₂Cl₂ affords quantitatively mixtures of the respective sulfone and glycal free from the sulfoxide. The outcome of the reaction does not depend on the anomeric configuration of the starting thioglycoside. The sulfone can be selectively prepared (yield 100%) by oxidation with an excess of MCPBA and NaHCO₃. In the presence of pyridine (2 equiv.) and MCPBA (2 equiv.), the major product is glycal (yields 81—88%). This version of the reaction can be regarded as a new method for the preparation of sialic acid glycals.     

Synthesis of multiblock hyperbranched‐linear poly(ether sulfone) copolymers

Hyperbranched poly(ether sulfone) was prepared in the presence of an oligomeric linear poly(ether sulfone) to generate multiblock hyperbranched‐linear (LxHB) copolymers. The LxHB copolymers were prepared in a two‐step, one‐pot synthesis by first polymerizing AB monomer to generate a linear block of a desired molecular weight followed by addition of the AB₂ monomer in a large excess (19:1, AB₂:AB) to generate the hyperbranched block. NMR integration analysis indicates that AB₂:AB ratio is independent of the reaction time. Because the molecular weight still increases with reaction time, these results suggest that polymer growth continues after consumption of monomer by condensation into a multiblock architecture. The LxHB poly(ether sulfone)s have better thermal stability (10% mass loss > 343 vs. 317 °C) and lower T_g (200 vs. > 250 °C) than the hyperbranched homopolymer, higher T_g than the linear homopolymer (<154 °C), while little difference in the solubility character was observed between the two polymers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4785–4793, 2008     

Reaction of Silica Gel with Trimethylsilyl Donors Using Conditions Useful for End-Capping HPLC Bonded Phase Packings

Abstract

Several trimethylsilyl (TMS) donors including bis-N, O-trimethylsilylacetamide (BSA), bis-N, O-trimethylsilyltrifluoro-acetamide (BSTFA), hexamethyldisilane (HMDS), trimethylchlorosilane (TMCS) with and without pyridine, 2-trimethylsiloxypent-2-en-A-one (TMSOP), trimethylsilyldimethylamine (TMSDMA), and trimethylsilylimidazole (TMSIM) were reacted with 60 Å silica. TMSIM at 60°C with reaction times of one hour or less gave coverage of silica gel equivalent to that provided by refluxing TMCS and pyridine in toluene for 67 hrs. Reactivity of the TMS donors studied may be ranked in the following order: TMSIM > TMSDMA > BSTFA > BSA > TMCS > TMSOP > HMDS. TMSIM appears to be the reagent of choice for end-capping of alkyl bonded HPLC phases.     

λ -Benzyl-L-Glutamate Graft Copolymers of Cellulose and Poly[Arylene Ether Sulfone]

Macroinitiators with primary amino substituents were synthesized by one of the following techniques: a) cyanoethylation of cellulose followed by diborane reduction to produce aminopropylcellulose, 1; b) nitration, then SnCl₂ reduction of poly(arylene ether sulfone), 5, to produce poly(2-aminoarylene ether sulfone), 2; c) phthalimidation of 5 followed by hydrazinolysis to yield poly(2-aminomethylarylene ether sulfone), 3; and d) LiAlH₄ reduction of poly(cyanophenylene arylene ether) to poly(aminomethylphenylene arylene ether), 4. Heterogeneous grafting of Λ-benzyl-L-glutamate-N-carboxyanhydride, 8, to Polymer 1 resulted in a nonrandom distribution of amino acid residues; α-helical conformations were detected at low BLG-NCA/NH₂ ratios (<5 amino acids). Using molar ratios ranging from 1 to 100 of 8, relative to the amine concentration, grafting to Polymers 3 and 4 was effected in anhydrous THF at room temperature under homogeneous conditions. If reaction times between 24 and 48 h are utilized, high grafting efficiencies (>80%) are obtained. The conformation of the polypeptide chain was evaluated by NMR and infrared spectroscopy. Polypeptides grafted to Polymers 3 and 4 appeared to adopt the expected conformation for the chain length predicted, i.e., a progression from random coil (<8 amino acids) to β-pleated sheet (8–13 amino acids) to α-helix (> 13 amino acids). The benzyl ester functions on the BLG grafts are subject to direct modification with amine nucleophiles; studies with butylamine correlate reaction conditions with extent of ester vs peptide cleavage. In the presence of 1-hydroxybenzotriazole, aminolysis of the ester is favored and conversions to Λ-amides up to 75% without peptide cleavage are achieved.     

A facile synthesis of novel 5‐substituted pyridine 2 carboxamide derivatives and their biological evaluation and 3D QSAR studies

A variety of novel 5‐substituted pyridine 2 carboxamides were designed and synthesized using both normal and solvent‐free microwave (MW) irradiation techniques. The results revealed that MW protocol proceeded smoothly under mild reaction conditions in short reaction times, thus avoiding the use of toxic organic solvents. Structural elucidation of the synthesized compounds was carried out on the basis of various spectroscopic methods, such as ¹H NMR, ¹³C NMR, LCMS, and IR. The synthesized compounds were evaluated for their in vitro antimicrobial activity (MIC) using the agar disk diffusion method. Among the various synthetic compounds, compound 3b showed higher potential activity against Escherichia coli than the other compounds. The order of activity against E. coli of the studied compounds is 3b > 3e > 3g > 3h > 3d > 3c > 3a > 3f . Additionally, 2D and 3D structural features of the synthesized derivatives were recognized by the 3D‐QSAR model. This validated model exhibited good internal (r², 0.924) and external prediction (r²pred, 0.851) correlation. The results of QSAR studies concluded that Alog P, the number of hydrogen bond acceptors, and the number of rotatable bonds were necessary features for the activity of the pyridine carboxamide derivatives.     

Ligand exchange reactions of aryl pyridyl sulfoxides with grignard reagents: Convenient preparation of 3- and 4-pyridyl grignard reagents and examination of the leaving abilities of pyridyl anions

Aryl 3- and 4-pyridyl sulfoxides undergo ligand exchange in reactions with aryl Grignard reagents to generate 3- and 4-pyridyl Grignard reagents, which, upon treatment with aldehydes or ketones, give the corresponding addition products in moderate-to-good yields. The mechanism for the exchange reaction was investigated by treating optically active 3- and 4-pyridyl p-tolyl sulfoxides with a phenyl Grignard reagent. Inversion of the configuration of the sulfur atom was the stereochemical result of the reactions. In the reactions of phenyl 2-pyridyl sulfoxide with Grignard reagents, the leaving ability of the 2-pyridyl group competes with that of the phenyl group. Both the experimental and MO calculated enthalpy values for deprotonation of α-, β-, and γ-protons of pyridine in the gas phase [1] are in accordance with the following order of the leaving abilities of aryl and pyridyl Grignard reagents: 4-PyMgBr > 3-PyMgBr » PhMgBr > p-TolMgBr > 2-PyMgBr.     

Preparation and characterization of new thermally stable and optically active poly(ester‐imide)s by direct polycondensation with thionyl chloride in pyridine

4,4′‐hexafluoroisopropylidene‐2,2‐bis‐(phthalic acid anhydride) (1) was reacted with L ‐methionine (2) in acetic acid and the resulting N,N′–(4,4′‐hexafluoroisopropylidenediphthaloyl)‐bis‐L ‐methionine (4) was obtained in high yield. The direct polycondensation reaction of this diacid with several aromatic diols such as bisphenol A (5a), phenolphthalein (5b), 1,4‐dihydroxybenzene (5c), 4,4′‐dihydroxydiphenyl sulfide (5d), 4,6‐dihydroxypyrimidine (5e), 4,4′‐dihydroxydiphenyl sulfone (5f) and 2,4′‐dihydroxyacetophenone (5g) was carried out in a system of thionyl chloride and pyridine. Expecting that the reaction with thionyl chloride in pyridine might involve alternative intermediates different from an acyl chloride, the polycondensation at a higher temperature favorable for the reaction of the expected intermediate with nucleophiles was attempted, and a highly thermally stable poly(ester‐imide) was obtained by carrying out the reaction at 80°C. All of the above polymers were fully characterized by ¹H‐NMR, ¹⁹F‐NMR FT‐IR spectroscopy, elemental analysis and specific rotation. Some structural characterization and physical properties of these optically active poly(ester‐ imide)s are reported. Copyright © 2006 John Wiley & Sons, Ltd.     

Cation,solvent, and substituent effects on the decay kinetics of alkali metal salts of diaryl disulfide radical anions in nonaqueous solutions

The transient diaryl disulfide radical anions (RSSR^?) were produced in nonaqueous solutions at room temperature by the flash photolysis of a solution of arylthiolate ion pair in the presence of the excess corresponding disulfide. The transient spectra were almost identical with those obtained from γ-radiolysis of the disulfides in 77 K 2-methyl-tetrahydrofuran (MTHF) glassy matrix. The spectra of disulfide radical anions in nonaqueous solutions were changed by cations, solvents, and para-substituents depending on the ion pair properties. The tighter ion pairs showed a shift of absorption band to the shorter wavelength. The disulfide radical anions decay by a unimolecular dissociation reaction to yield thiolate anion and thiyl radical. The decay kinetics were first-order in the initial time region. The rate constants obtained were changed by the counter cations in the order Na⁺ > K⁺ > Cs⁺ > Li⁺, and by solvents. The tighter ion pairs of the disulfide radical anions showed faster dissociation reaction. This is due to stabilization of a transition state with the counter cation.     

Sulfonic Acid Functionalized Nano Γ-Al2O3: a New,Efficient, and Reusable Catalyst for Synthesis of Thioamides

Abstract

Sulfonic acid functionalized nano γ-Al₂O₃ is easily prepared by the reaction of nano γ-Al₂O₃ with 1,3-propane sulfone. This reagent can be used as an eficient catalyst for the synthesis of thioamides. This new method consistently has the advantages of excellent yields and short reaction times. Further, the catalyst can be recovered for several times.     

Kinetic studies on the reactions of some tetrakis(arylisocyanide)cobalt(II) complexes with pyridine in 2,2,2-trifluoroethanol

The interaction of pyridine with four tetrakis(arylisocyanide)cobalt(II) complexes, [Co(CNR)₄(ClO₄)₂] R = 2,6-Me₂C₆H₃ (A), 2,4,6-Me₃C₆H₂ (B), 2,6-Et₂C₆H₃ (C) and 2,6-iPr₂C₆H₃ (D), have been studied in 2,2,2-trifluoroethanol medium. The kinetics of the reactions were investigated over the 293–318 K temperature range. The reaction profile exhibited two distinct processes, proposed to be an initial fast substitution followed by a slow reduction, for each of the reactions. The pseudo first-order rate constants for both processes increased with increasing concentration of pyridine with the reduction processes exhibiting saturation kinetics at high pyridine concentrations. Steric hindrance plays a significant role in the rates of the reactions, as the rates decrease in the order k(A) > k(B) > k(C) > k(D). The activation enthalpies, ΔH^‡, increase from A to D while the activation entropies, ΔS^‡, are relatively similar for the four reactions, indicating similar transition states and hence similar mechanisms. Complex B was first synthesized and characterized in this study.     

PHOTOCHEMISTRY OF PESTICIDES, 71. REGIOSELECTIVE PHOTODIMERIZATION OF o,o-DIETHYL-o-(3-CHLORO-4-METHYLCOUMARIN-7-YL)-THIOPHOSPHATE (COUMAPHOS)

Abstract

UV-irradiation (λ > 313 nm) of o,o-diethyl-o-(3-chloro-4-methyl-coumarin-7-yl)-thiophosphate (Coumaphos; 1) in chloroform results in an regioselective dimerization reaction to afford the head-to-tail anti-dimer 2. The structure of 2 is established by single crystal x-ray diffraction. Singlet oxygen does not affect the formation of 2.     

A New Main Group Metal Coordination Polymer: Synthesis,Structure, and Dielectric Constant Property of [Na(C6H4N5)(H2O)2]n

The reaction of NaOH with 4‐(2H‐tetrazol‐5‐yl)pyridine affords the first tetrazole‐pyridine sodium coordination polymer with chain structure, [Na(C₆H₄N₅)(H₂O)₂]_n ( 1 ). The compound could be characterized by single‐crystal X‐ray diffraction analysis. The temperature dependence of dielectric permittivity remains unchanged almost within the measured temperature range of 80 K to 270 K at 1 <SC>MH</SC>z, and the frequency dependence of the permittivity showed rapidly drops from 31.5 to 4.3 within the measured frequency range of 200 to 1 MHz at room temperature.     

A convenient synthesis and the mesomorphic properties of new chiral ferroelectric thiobenzoates

A secondary chiral (R)-(?)-2-alcohol underwent the Mitsunobu reaction with triphenylphosphine, diethyl azodicarboxylate and ethyl 4-hydroxybiphenylcarboxylate, resulting in the desired (S)-(+)-product with high enantiomeric purity (>99% ee), with the chiral branched chain attached to the biphenyl. This method is operationally simple and provides the very important chiral precursor in good yields (62% in dry THF and 72% in dry Et₂O). The condensation of the (S)-(+)-acid chloride from this material and a suitable 4-n-alkylthiophenol in toluene in the presence of pyridine or triethylamine furnishes the chiral (S)-(+)-thiobenzoate liquid crystals in good yields (80–83% in pyridine and 65–68% in Et₃N). (S)-(+)-4-(1-Methylheptyloxy)biphenyl 4-alkylthiobenzoates are abbreviated (S)-MHOBSn , where n varies from 4 to 10 and denotes the number of carbon atoms in the alkyl chain. DSC, polarizing microscopy and X-ray diffraction showed that the (S)-MHOBSn series possesses a rich phase polymorphism: two highly ordered tilted phases CrG* and SmI*, as well as the ferroelectric smectic C (SmC*) and chiral nematic (N*) phase. In this series, the seldom observed transition between the chiral phases SmI*–SmC* is seen. All the compounds possess stable enantiotropic SmC* and N* phases. The existence of weak intermolecular hydrogen-bonding in (S)-MHOBSn was confirmed by FTIR spectroscopy.     

CHLORINATION OF AROMATIC HALIDES WITH CHLOROSULFONIC ACID

Abstract

Chlorosulfonic acid–iodine mixture has been shown to chlorinate a number of aromatic halides under mild conditions. In reaction with p-dichlorobenzene, the maximum yield (82%) of hexachlorobenzene required 5 mol of chlorosulfonic acid and 2.5 mol of iodine. The yield of product increased with the amount of iodine present. A mechanism of chlorination is proposed involving iodine-catalysed homolytic decomposition of the intermediate sulfonyl chlorides followed by heterolytic chlorination by the evolved iodine monochloride.

The reaction of o-, m-, and p-dichlorobenzenes with chlorosulfonic acid has been investigated. o-Dichlorobenzene at 100° gave a good yield (85%) of 3,4,3′,4′-tetrachlorodiphenylsulfone although m and p-dichlorobenzenes gave only the expected sulfonyl chlorides. This difference arises from the lack of steric hindrance in the p-position of o-dichlorobenzene leading to facile sulfone formation.

This was confirmed by the observation that 3,4-dichlorobenzenesulfonyl chloride undergoes the Friedel–Crafts reaction with o-dichlorobenzene to give 3,4,3′,4′-tetrachlorodiphenylsulfone (60%), but m- and p-dichlorobenzenes did not give any appreciable amounts of the corresponding sulfones under identical conditions.     

Preparation and characterisation of thiol functionalised p-tert-butylcalix[4]arene-embedded polymer inclusion membranes: performance and selectivity

ABSTRACT

Here in we report the syntheses of the thiol functionalised p-tert-butylcalix[4]arene from the reaction of p-tert-butylcalix[4]arene-dialkylbromide derivative with thiourea. The structure of the thiol functionalised p-tert-butylcalix[4]arene was determined by using ¹HNMR, ¹³CNMR and elemental analysis techniques. Furthermore, the thiol functionalised p-tert-butylcalix[4]arene, cellulose triacetate (CTA) and 2-nitrophenyl octyl ether (o-NPPE) in dichloromethane were used to make a new calixarene-embedded polymer inclusion membrane (Bu^t-C@PIM). The surface and structure morphology of Bu^t-C@PIM was detected using thermogravimetric analysis, elemental analysis techniques and scanning electron microscopy. The affinity (the percentage of metal ion transferred from the source solution) of a PIM towards a range of divalent cations was found to follow the order Pb²⁺ > Zn²⁺ > Ni²⁺ > Cu²⁺ > Cd²⁺ > Co²⁺. The results also indicated that the transport efficiency of Bu^t-C@PIM was repeatable and may be beneficial in the development of a simplistic and highly influential trace metal recovery method from aqueous solution.     

Chromium(III) complexes bearing bis(benzotriazolyl)pyridine ligands: synthesis,characterization and ethylene polymerization behavior

Reaction of benzotriazole with 2,6-bis(bromomethyl)pyridine and 2,6-pyridinedicarbonyl dichloride yields the tridentate ligands 2,6-bis(benzotriazol-1-ylmethyl)pyridine (1) and 2,6-bis(benzotriazol-1-ylcarbonyl) pyridine (2). The molecular structures of the ligands were determined by single-crystal X-ray diffraction. These ligands react with CrCl₃(THF)₃ in THF to form neutral complexes, [CrCl₃{2,6-bis(benzotriazolyl)pyridine-N,N,N}] (3, 4), which are isolated in high yields as air stable green solids and characterized by mass spectra (ESI), FTIR spectroscopy, UV–Visible, thermogravimetric analysis (TGA), and magnetic measurements. After reaction with methylaluminoxane (MAO), the chromium(III) complexes are active in the polymerization of ethylene showing a bimodal molecular weight distribution. A DFT computational investigation of the polymerization reaction mechanism shows that the most likely reaction pathway originates from the mer configuration when the spacer is CH₂ (complex 3) and from the fac configuration when the spacer is CO (complex 4).     

Stereoselective Synthesis of γ-(Acyloxy)carboxylic Acids and γ-Lactones Featuring the Switch of Stereopreference of Candida antarctica Lipase B in Sodium γ-Hydroxycarboxylate Homologues

Scalable protocols of straightforward synthesis of enantiomeric γ-(acyloxy)carboxylic acids and γ-lactones are presented. The key step is lipase-catalyzed stereoselective acylation of γ-hydroxycarboxylic acid sodium salt in organic solvent followed by acidification of the product, extraction and acidic relactonization of the unreacted enantiomer. The mixture of γ-(acyloxy)carboxylic acid and γ-lactone is separated either by extraction with solution of sodium bicarbonate or by distillation. A switch of enantioinduction of Candida antarctica lipase B along homologous nucleophiles from R configuration of γ-hydroxyhexanoic acid salt to S configuration of the C7 and longer-chain homologues has been disclosed. Both enantiomers of γ-(acyloxy)pentanoic acids; γ-(acetyloxy)octanoic and -nonanoic acids with S configuration; [(1S,5R)-5-(chloroacetyloxy)cyclopent-2-en-1-yl]acetic acid and enantiomeric γ-lactones derived from them were prepared with e. r. >98.5/1.5. The rates of acylation of C5 to C9 homologous salts differ by three orders of magnitude but remain applicable for preparative synthesis by variation of the enzyme loading and reaction time.     

Microwave-Promoted Syntheses of Pyridine Carboxamides and tert-Carboximides from Novel 6-Acetylpyridine-2-carboxylic Acid

A novel 6-acetylpyridine-2-carboxylic acid (4) was obtained occasionally during the synthesis of asymmetric ethyl 6-acetylpyridine-2-carboxylate (3) from 2,6-dipiclinic acid (1). Compounds 3 and 4 could transform mutually under some specific conditions. Two reactions of distinctive types occurred when they reacted with the aromatic amines as precursors, due to different functional groups on the 2-position of pyridine in the molecules of 3 and 4: one was Schiff base condensation and the other was an amidation reaction. From the latter reaction, two series of new compounds, pyridine carboxamides (5a–d) and pyridine tert-carboximides (6a–h), resulted. The relevant reaction mechanism is discussed in detail.     

Enantio- and Diastereoselective Synthesis of Chiral Tetrasubstituted α-Amino Allenoates Bearing a Vicinal All-Carbon Quaternary Stereocenter with Dual-Copper-Catalysis

The skeletons of chiral tetrasubstituted allenes bearing a vicinal all-carbon quaternary stereocenter are of importance but still challenging to synthesize. Herein, we report enantio- and diastereoselective γ-additions of 1-alkynyl ketimines with dual-copper-catalysis under mild conditions, affording chiral tetrasubstituted α-amino allenoates bearing a vicinal all-carbon quaternary stereocenter in high yields (up to 99 % yield) with excellent enantioselectivities (up to 99 % ee) and diastereoselectivities (up to >20 : 1 dr). Importantly, the stereodivergent synthesis of the products was realized by the asymmetric γ-addition reaction and the Grignard reagent promoted epimerization. Moreover, the dual-copper-catalyzed γ-addition reactions were smoothly applied to a gram-scale reaction and adopted to introduce chiral tetrasubstituted allenyl moieties into bioactive molecules. Mechanistic experiments and density functional theory (DFT) calculations demonstrated that the asymmetric γ-addition reactions were catalyzed by double chiral copper catalysts.