Hydrolytic reactions of cyclic bis(3′‐5′)diadenylic acid (c‐di‐AMP)

Hydrolytic reactions of cyclic bis(3′‐5′)diadenylic acid (c‐di‐AMP) have been followed by Reversed phase high performance liquid chromatography (RP‐HPLC) over a wide pH range at 90 °C. Under neutral and basic conditions (pH ≥ 7), disappearance of the starting material (first‐order in [OH^?]) was accompanied by formation of a mixture of adenosine 2′‐monophosphate and 3′‐monophosphate (2′‐AMP and 3′‐AMP). Under very acidic conditions (from H₀ = ?0.7 to 0.2), c‐di‐AMP undergoes two parallel reactions (first‐order in [H⁺]): the starting material is cleaved to 2′‐AMP and 3′‐AMP and depurinated to adenine (i.e., cleavage of the N‐glycosidic bond), the former reaction being slightly faster than the latter one. At pH 1–3, isomerization to cyclic bis(2′‐5′)diadenylic acid competes with the depurination. Copyright © 2012 John Wiley & Sons, Ltd.     

Electroluminescence enhancement in ultraviolet organic light‐emitting diode with graded hole‐injection and ‐transporting structure

Electroluminescent intensity and external quantum efficiency (EQE) in ultraviolet organic light‐emitting diodes (UV OLEDs) have been remarkably enhanced by using a graded hole‐injection and ‐transporting (HIT) structure of MoO₃/N,N ′‐bis(naphthalen‐1‐yl)‐N,N ′‐bis(phenyl)‐benzidine/MoO₃/4,4′‐bis(carbazol‐9‐yl)biphenyl (CBP). The graded‐HIT based UV OLED shows superior short‐wavelength emis‐ sion with spectral peak of ～410 nm, maximum electroluminescent intensity of 2.2 mW/cm² at 215 mA/cm² and an EQE of 0.72% at 5.5 mA/cm². Impedance spectroscopy is employed to clarify the enhanced hole‐injection and ‐transporting capacity of the graded‐HIT structure. Our results provide a simple and effective approach for constructing efficient UV OLEDs. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

On structural and spectroscopic differences between quinoline‐2‐carboxamides and their N‐oxides in the solution and solid state

Intramolecular hydrogen bonding in the primarily and secondarily substituted quinoline‐2‐carboxamides and their N‐oxides has been studied in the solution by multinuclear NMR spectroscopy. Hydrogen bonding patterns and supramolecular arrangement in the solid state have been determined by single crystal X‐ray analysis. In quinoline‐2‐carboxamides weak, nonlinear intramolecular N? H…N hydrogen bond is present, but in the solid state the intermolecular hydrogen bonds and packing forces are the factors that decide on the properties of 3D structures. In quinoline‐2‐carboxamide N‐oxides the most important structural features are the intramolecular hydrogen bonds. Details of different weak interactions and resulting 3D arrangement of molecules are discussed. In the solution, two separate ¹H signals are observed for the primary quinoline‐2‐carboxamides in the range from ca. 5.8 to 8.1 ppm. The chemical shifts of the NH group's proton for studied R′‐quinoline‐2‐R‐carboxamides are in the range from 8.1 to 8.4 ppm. For the N‐oxide of 4‐R′‐quinoline‐2‐carboxamides (R′ = H, Me, OPh, Cl and Br), the values of the proton chemical shifts of the NH group in the range from 10.78 to 11.38 ppm (for primary amides) indicating that this group forms hydrogen bonds with the oxygen of the N‐oxide group. This bond is stronger than the N? H…N bond in quinoline‐2‐carboxamides. For the secondary amide N‐oxides, the δ(NH) values are increasing from 11.25 to 11.77 ppm in the sequence of substituents 4‐Br < 4‐Cl < 4‐H < 4‐Me < 4‐OPh. For 4‐substituted compounds these values depend also on the substituent effect. Copyright © 2009 John Wiley & Sons, Ltd.     

Lithium solvation in a PMMA membrane plasticized by a lithium‐conducting ionic liquid based on 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide

The Raman and Infrared (IR) spectra of poly(methyl methacrylate) (PMMA) membranes plasticized by ionic liquids of the (1 − x)[1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI)],xLiTFSI type, where BMI⁺ is the 1‐butyl‐3‐methylimidazolium cation and TFSI⁻ the bis(trifluoromethanesulfonyl)imide anion, are analyzed for a lithium bis(trifluoromethane sulfone)imide (LiTFSI) mole fraction x = 0.23 and PMMA contents from 0 to 50 wt%. The lithium is found to have an average coordination of about three CO groups and less than one TFSI⁻ anion. It plays the role of a cross‐linker between the ester groups of PMMA and the nonvolatile ionic liquid. Addition of PMMA to the (1 − x)(BMITFSI),xLiTFSI ionic liquid lowers the conductivity but might improve the lithium transference number by transforming the [Li(TFSI)₂]⁻ anionic clusters present in the pure ionic liquid into a mixed coordination by ester groups and TFSI⁻ anions. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrochemical reduction of 3‐phenyl‐1,2‐benzisoxazole 2‐oxide on boron‐doped diamond

The bioreduction of N‐oxide compounds is the basis for the mode of action of a number of biologically active molecules. These compounds are thought to act by forming a reactive oxygen species through an intracellular reduction and subsequent redox cycling process within the organism. With these results in mind, the preliminary investigation into the electrochemical reduction of the benzisoxazole 2‐oxide ring system was undertaken, with the thought that this class of compounds would reduce in a similar fashion to other N‐oxide heterocycles. The electrochemical reduction of 3‐phenyl‐1,2‐benzisoxazole 2‐oxide on boron‐doped diamond was studied using cyclic and square wave voltammetry as well as controlled potential electrolysis and HPLC for qualitative identification of the reaction products. It was found that the reduction proceeded with an initial quasi‐reversible one‐electron reduction followed by the very fast cleavage of either the endocyclic or exocyclic N–O bond. Subsequent electron transfer and protonation resulted in an overall two‐electron reduction and formation of the 2‐hydroxyaryl oxime and benzisoxazole. These results are analogous to those observed in the electrochemical reduction of other heterocyclic N‐oxides albeit the reduction of the benzisoxazole N‐oxides takes place at a more negative potential. However, these encouraging results warrant further investigation into the reduction potential of substituted benzisoxazole N‐oxides as well as to elucidate and characterize the nature of the intermediate species involved. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of an α‐amino nitrile and a bis α‐amino nitrile derivative of thiadiazole: reaction mechanism

The first nucleophilic addition of an inorganic nucleophile (cyanide) to the activated, rigid, α‐diazomethine groups of a 1,2,5‐thiadiazole 1,1‐dioxide is reported here. An α‐amino nitrile and a bis α‐amino nitrile derivatives were obtained in good yields (62 and 98%, respectively) and characterized by spectroscopic, analytical, and single crystal X‐ray diffraction techniques. The course of the reaction, followed by cyclic voltammetry (CV), showed that cyanide adds to only one of the two C?N double bonds of the thiadiazole, forming an anion from which an N‐methyl derivative was obtained. Adequate concentrations of cyanide and methyl iodide (MeI) produced directly the bis α‐amino nitrile derivative. Copyright © 2007 John Wiley & Sons, Ltd.     

Fast‐response organic–inorganic hybrid light‐emitting diode

We demonstrated important changes produced on the modulation frequency of hybrid organic–inorganic light‐emitting diodes to examine the applicability as a light source for visible optical communications. The fabricated device structure was 4,4′‐bis[N ‐(1‐napthyl)‐N ‐phenyl‐amino]biphenyl/4,4′‐(bis(9‐ethyl‐3‐carbazovinylene)‐1,1′‐biphenyl:4,4′‐bis[9‐dicarbazolyl]‐2,2′‐biphenyl/ZnS/LiF/MgAg. This device showed an improvement in the modulation frequency using ZnS instead of an organic material, tris(8‐hydroxyquinoline)aluminum. A maximum cutoff frequency of 20.6 MHz was achieved.

     

Kinetic study of the formation of N‐chloro compounds using N‐chlorosuccinimide

Second‐order rate constants were determined for the chlorination reaction of 2,2,2‐trifluoethylamine and benzylamine with N‐chlorosuccinimide at 25 °C and an ionic strength of 0.5 M. These reactions were found to be of first order in both reagents. According to the experimental results, a mechanism reaction was proposed in which a chlorine atom is transferred between both nitrogenous compounds. Kinetics studies demonstrate that the hydrolysis process of the chlorinating agent does not interfere in the chlorination process, under the experimental conditions used in the present work. Free‐energy relationships were established using the results obtained in the present work and others available in the literature for chlorination reactions with N‐chlorosuccinimide, being the pK_a range included between 5.7 and 11.22. Copyright © 2014 John Wiley & Sons, Ltd.     

Kinetic study of the formation reaction of N‐chloro‐2‐oxazolidinone

The chlorination reactions of 2‐oxazolidinone with hypochlorous acid (HOCl), tert‐butyl hypochlorite (^tBuOCl) and N‐chlorosuccinimide (NCS) were studied at 25 °C, constant ionic strength, and under isolation conditions. The kinetic results obtained in the formation processes of the N‐chloro‐2‐oxazolidinone are summarized in this paper. The kinetics studied showed a first order with respect to the concentration of the each reactant and a complex dependence of the pH on the rate constant. The reactivity order with respect to the chlorinating agent found is k(HOCl) > k(^tBuOCl) > k(NCS). Copyright © 2015 John Wiley & Sons, Ltd.     

Determination of N and O‐atoms and N2 (A) Metastable Molecule Densities in the Afterglows of N2‐H2, Ar‐N2‐H2 and Ar‐N2‐O2 Microwave Discharges

Early afterglows of N₂‐H₂, Ar‐N₂‐H₂ and Ar‐N₂‐O₂ flowing microwave discharges are characterized by optical emission spectroscopy. The N and O atoms and the N₂ (A) metastable molecule densities are determined by optical emission spectroscopy after calibration by NO titration for N and O‐atoms and measurements of NO and N₂ band intensities. If an uncertainty of 30% is estimated on N‐atomic density, an inaccuracy of one order of magnitude is obtained on the O and N₂ (A) densities. In N₂‐(0.05‐2.5%)H₂ and Ar‐(1‐50%)N₂‐(0.05‐2.5%) H₂ gas mixtures, the O‐atoms are coming from O₂ impurities in the discharge. Concentrations of N and O‐atoms and of N₂ (A) densities are compared to the ones obtained in Ar‐(5‐50%)N₂‐(0.2‐2.5%) O₂ gas mixtures in which a controlled amount of O₂ is added. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison of the 13C (C = N) chemical shifts of substituted N‐(phenyl‐ethylene)‐anilines and substituted N‐(benzylidene)‐anilines

Comparison of ¹³C NMR of C = N bond chemical shifts δ_C(C = N) in substituted N‐(phenyl‐ethylene)‐anilines XArC(Me) = NArY (XPEAYs) with that in substituted N‐(benzylidene)‐anilines XArCH = NArY (XBAYs) was carried out. The δ_C(C = N) of 61 samples of XPEAYs were measured, and the substituent effect on their δ_C(C = N) were investigated. The results show the factors affecting the δ_C(C = N) of XPEAYs are quite different from that of XBAYs. A penta‐parameter correlation equation was obtained for the 61 compounds, which has correlation coefficient 0.9922 and standard error 0.12 ppm. The result indicates that, in XPEAYs, the inductive effects of substituents X and Y are major factors affecting the δ_C(C = N), while the conjugative effect of them have very little effect on the δ_C(C = N) and can be ignored. The substituent‐specific cross‐interaction effects between X and Y and between Me of C = N bond and substituent Y are important factors affecting the δ_C(C = N). Also, the excited‐state substituent parameter of substitute Y has certain contribution to the δ_C(C = N). Copyright © 2015 John Wiley & Sons, Ltd.     

Thermal reaction of electron deficient 4‐oxo‐4H‐pyrazole 1,2‐dioxide with cycloheptatriene: the first examples of the formation of an endo‐[4π + 6π]‐cycloadduct and an intramolecular 1,3‐dipolar reaction leading to a heterocage

The reaction of 3,5‐bis(methoxycarbonyl)‐4‐oxo‐4H‐pyrazole 1,2‐dioxide (1a) with 1,3,5‐cycloheptatriene (2b) gave a mixture of the novel endo‐[4 + 6]‐cycloadduct (4ab), anti‐exo‐[4 + 2]‐cycloadduct (5ab), and the heterocage (6ab) derived from the intramolecular 1,3‐dipolar cycloaddition reaction of the syn‐endo‐[4 + 2]‐cycloadduct. Analogous endo‐[4 + 6] selectivity in 1,3‐dipolar cycloadditions has not been reported previously. The X‐ray analysis indicates that 6ab has a very long N_sp3–N_sp3 bond distance of 1.617(4) Å. The cycloaddition behaviour is discussed on the basis of transition‐state structures optimized at the B3LYP/6‐31G(d) level of theory, from which predictions of the peri‐, regio‐, and stereoselectivities agreed well with the experimental results. Copyright © 2012 John Wiley & Sons, Ltd.     

Use of N‐chloro‐N‐methyl‐p‐toluenesulfonamide in N‐chlorination reactions

Second‐order rate constants (k₂) were determined for the addition of ten nitrogenous organic compounds (benzylamine, 2,2,2‐trifluoethylamine chlorhidrate, methylamine chlorhidrate, glycine ethyl ester chlorhidrate, glycine, glycylglycine chlorhidrate, morpholine, pyperidine, pyperazine and dimethylamine) to the N‐chloro‐N‐methyl‐p‐toluenesulfonamide (NCNMPT) in the formation reaction of N‐chloramines in aqueous solution at 25 °C and ionic strength 0.5 M. The series of nucleophiles considered is structurally very varied and covers five pK_a units. The kinetic behaviour is similar for all compounds, being the elementary step the transfer of chlorine from the NCNMPT molecule to the nitrogen of the free amino group. These reactions were found first order in both reagents. The values of the rate constants indicate that the more basic amines produce N‐chloramines more readily. Rate constants for the nucleophilic attack are shown to correlate with literature data for some of these nitrogenous organic compounds in their reaction with N‐methyl‐N‐nitroso‐p‐toluenesulfonamide. Both reactions involve that the rate determining step is the attack of nitrogenous compounds upon electrophilic centre (Cl or else NO group). NCNMPT is a particularly interesting substrate, for which has not hitherto been published kinetic information, that allows us to assess the efficiency and the competitiveness of this reaction and compare it with other agents with a Cl⁺ atom. Copyright © 2013 John Wiley & Sons, Ltd.     

Kinetics and mechanisms of gas‐phase elimination of 2,2‐diethoxyethyl amine and 2,2‐diethoxy‐N,N‐diethylethanamine

The gas‐phase elimination kinetics of 2,2‐diethoxyethyl amine and 2,2‐diethoxy‐N,N‐diethylethanamine (320–380 °C; 40–150 Torr) in a seasoned reaction vessel are homogeneous, unimolecular and obey a first‐order rate law. These elimination processes involve two parallel reactions. The first gives ethanol and the corresponding 2‐ethoxyethenamine. The latter compound further decomposes to ethylene, CO and the corresponding amine. The second parallel reaction produce ethane and the corresponding ethyl ester of an α‐amino acid. The following Arrhenius expressions are given as: For 2,2‐diethoxyethyl amine For 2,2‐diethoxy‐N,N‐diethylethanamine Comparative kinetic and thermodynamic parameters of the overall, the parallel and the consecutive reactions lead to consider two types of mechanisms in terms of a concerted polar cyclic transition state structures. Copyright © 2008 John Wiley & Sons, Ltd.     

Adsorption of 4,4′‐thiobisbenzenethiol on silver surfaces: surface‐enhanced Raman scattering study

Adsorption of 4,4′‐thiobisbenzenethiol (4,4′‐TBBT) on a colloidal silver surface and a roughened silver electrode surface was investigated by means of surface‐enhanced Raman scattering (SERS) for the first time, which indicates that 4,4′‐TBBT is chemisorbed on the colloidal silver surface as dithiolates by losing two H‐atoms of the S H bond, while as monothiolates on the roughened silver electrode. The different orientations of the molecules on both silver surfaces indicate the different adsorption behaviors of 4,4′‐TBBT in the two systems. It is inferred from the SERS signal that the two aromatic rings in 4,4′‐TBBT molecule are parallel to the colloidal silver surface as seen from the disappearance of ν_{C H} band (3054 cm⁻¹), which is a vibrational mode to be used to determine the orientation of a molecule on metals according to the surface selection rule, while on the roughened silver electrode surface they are tilted to the surface as seen from the enhanced signal of ν_{C H}. The orientation of the C‐S bond is tilted with respect to the silver surface in both cases as inferred from the strong enhancement of the ν_{C S}. SERS spectra of 4,4′‐TBBT on the roughened silver electrode with different applied potentials reveal that the enhancement of 4,4′‐TBBT on the roughened silver electrode surface may be related to the chemical mechanism (CM). More importantly, the adsorption of 4,4′‐TBBT on the silver electrode is expected to be useful to covalently adsorb metal nanoparticles through the free S H bond to form two‐ or three‐ dimensional nanostructures. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis of novel bis(β‐cyclodextrin)s linked with aromatic diamine and their molecular recognition with model substrates

Novel β‐cyclodextrin (β‐CD) dimers with aromatic diamine linkers, 1,3‐(aminomethyl)‐benzylamine‐bridged bis(6‐amino‐6‐deoxy‐β‐CD) (2) , 4,4′‐diaminodiphenylmethano‐bridged bis(6‐amino‐6‐deoxy‐β‐CD) (3) , and 4,4′‐ ethylenedianiline‐bridged bis(6‐amino‐6‐deoxy‐β‐CD) (4) , were synthesized. The inclusion complexation behaviors of these compounds, together with 4,4′‐aminophenyl ethyl‐bridged bis(6‐amino‐6‐deoxy‐β‐CD) (5) , with substrates such as acridine red (AR), neutral red (NR), ammonium 8‐anilino‐1‐naphthalenesulfonate (ANS), sodium 2‐(p‐toluidinyl) naphthalenesulfonate (TNS), rhodamine B (RhB), and brilliant green (BG), were investigated by ultraviolet, fluorescence, circular dichroism, and 2D NMR spectroscopy. The results indicated that the two linked CD units cooperatively bound to a guest, and the molecular binding affinity toward substrates, especially curved guest ANS and linear guests such as NR and AR, was increased. The linker length between two CD units played a crucial role in the molecular recognition of the hosts with guest dyes. The binding constants of the hosts for AR, TNS, ANS, and RhB decreased with increasing linker length in hosts 2‐4 . Moreover, structurally similar hosts 3 and 5 exhibited very different binding behavior for the guests. Host 5 showed much higher Ks values toward positively charged guests and lower Ks toward negatively charged guests than host 3 . The 2D NMR spectra of hosts 3 and 5 with RhB were acquired to understand the binding difference between 3 and 5 . The molecular binding ability and selectivity of model substrates by these hosts were sufficiently investigated to reveal not only the cooperative contributions of the linker group and CD cavities upon inclusion complexation with dye guest molecules, but also the controlling factors for the molecular selective binding. Copyright © 2008 John Wiley & Sons, Ltd.     

Solvatochromism of 2‐(N,N‐dimethylamino)‐7‐nitrofluorene and the natural dye β‐carotene: application for the determination of solvent dipolarity and polarizability

The effects of solvents on chemical phenomena (rate and equilibrium constants, spectroscopic transitions, etc.) are conveniently described by solvation free‐energy relationships that take into account solvent acidity, basicity and dipolarity/polarizability. The latter can be separated into its components by manipulating the UV–vis spectra of two solvatochromic probes, 2‐(N,N‐dimethylamino)‐7‐nitrofluorene (DMANF) and a di‐(tert‐butyl)‐tetramethyl docosanonaen probe (ttbP9) whose synthesis is laborious and expensive. Recently, we have shown that the natural dye β‐carotene can be conveniently employed instead of ttbP9 for the determination of solvent polarizability (SP) of 76 molecular solvents and four ionic liquids. In the present work, we report the polarizabilities of further 24 solvents. Based on the solvatochromism of β‐carotene and DMANF, we have calculated solvent dipolarity (SD) for 103 protic and aprotic molecular solvents, and ionic liquids. The dependence of SD and SP on the number of carbon atoms in the acyl‐ or alkyl group of several homologous series (alcohols; 2‐alkoxyethanols; carboxylic acid‐ anhydrides, and esters, ionic liquids) is calculated and briefly discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Piperidine‐appended imidazolium ionic liquids as task‐specific catalysts: computational study,synthesis, and multinuclear NMR

Imidazolium ionic liquids (IMILs) with a piperidine moiety appended via variable length methylene spacers (with n = 1–4) were studied computationally to assess their potential to act as internal base for N‐heterocyclic carbene (NHC) generation. Proton transfer energies computed by B3LYP/6‐311+G(2d,p) were least endothermic for the basic‐IL with n = 3, whose optimized structure showed the shortest C₂‐H‐‐‐‐N(piperidine) distance. Inclusion of counter anion (Cl or NTf₂) caused dramatic conformational changes to enable close contact between the acidic C₂‐H and the anions. To examine the prospect for internal C₂‐H‐‐‐‐N coordination, multinuclear NMR data (¹H, ¹⁵N, and ¹³C) were computed by gauge independent atomic orbitals–density functional theory (GIAO‐DFT) in the gas phase and in several solvents by the PCM method for comparison with the experimental NMR data for the basic ILs (with n = 2–4) synthesized in the laboratory. These studies indicate that interactions with solvent and counter ion are dominant forces that could disrupt internal C₂‐H‐‐‐‐N coordination/proton transfer, making carbene generation from these basic‐ILs unlikely without an added external base. Therefore, the piperidine‐appended IMILs appear suitable for application as dual solvent/base in organic/organometallic transformations that require the use of mild base, without the necessity to alkylate at C‐2 to prevent N‐heterocyclic carbene formation. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation of N‐carbamoylamino acid nitrosation by {NO + O2} in the solid‐gas phase. Effects of NOx speciation and kinetic evidence for a multiple‐stage process

Nitrosation of N‐carbamoylamino acids (CAA) by gaseous NO + O₂, an interesting synthetic pathway to amino acid N‐carboxyanhydrides (NCA), alternative to the phosgene route, was investigated on N‐carbamoyl‐valine either in acetonitrile suspension or solventless conditions, and compared to the classical nitrosating system NaNO₂ + CF₃COOH (TFA), the latter being quite less efficient in terms of either rate, stoichiometric demand, or further tractability of the product. The rate and efficiency of the NO + O₂ reaction mainly depends on the O₂/NO ratio. Evaluation of the contribution of various nitrosating species (N₂O₃, N₂O₄, HNO₂) through stoichiometric balance showed the reaction to be effected mostly by N₂O₃ for O₂/NO ratios below 0.3, and by N₂O₄ for O₂/NO ratios above 0.4. The relative contribution of (subsequently formed) HNO₂ always remains minor. Differential scanning calorimetry (DSC) monitoring of the reaction in the solid phase by either HNO₂ (from NaNO₂ + TFA), gaseous N₂O₄ or gaseous N₂O₃, provides the associated rate constants (ca. 0.1, 2 and 10⁸ s^?1 at 25°C, respectively), showing that N₂O₃ is by far the most reactive of these nitrosating species. From the DSC measurement, the latent heat of fusion of N₂O_3, 2.74 kJ · mol^?1 at ?105 °C is also obtained for the first time. The kinetics was investigated under solventless conditions at 0°C, by either quenching experiments or less tedious, rough calorimetric techniques. Auto‐accelerated, parabolic‐shaped kinetics was observed in the first half of the reaction course, together with substantial heat release (temperature increase of ca. 20°C within 1–2 min in a 20‐mg sample), followed by pseudo‐zero‐order kinetics after a sudden, important decrease in apparent rate. This kinetic break is possibly due to the transition between the initial solid‐gas system and a solid‐liquid‐gas system resulting from water formation. Overall rate constants increased with parameters such as the specific surface of the solid, the O₂/NO ratio, or the presence of moisture (or equivalently the hydrophilicity of the involved CAA), however without precise relationship, while the last two parameters may directly correlate to the increasing acidity of the medium. Copyright © 2007 John Wiley & Sons, Ltd.     

A combined experimental and density functional study of 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes reactivity towards the allylic chlorine

Nucleophilic substitution and dehydrochlorination reactions of a number of the ring‐substituted 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes are studied both experimentally and theoretically. The developed synthetic procedures are characterized by a general rapidity, cheapness, and simplicity providing moderate to high yields of 1‐arylsulfonyl 1,3‐butadienes (48–95%), 1‐(arylsulfonyl)‐2‐R‐4‐(N,N‐dialkylamino)‐2‐butenes (31–53%), 1‐(arylsulfonyl)‐2‐R‐2‐buten‐4‐ols (37–61%), and bis[4‐(arylsulfonyl)‐3‐R‐but‐2‐enyl]sulfides (40–70%). The density functional theory B3LYP/6‐311++G(2d,2p) calculations of the intermediate allylic cations in acetone revealed their high stability occurring from a resonance stabilization and hyperconjugation by the SO₂Ar group. The reactivity parameters estimated at the bond critical points of the diene/allylic moiety display a high correlation (R² > 0.97) with the Hammett (σ_p) constants. 1‐Arylsulfonyl 1,3‐butadienes are characterized by a partly broken π conjugated system, which follows from analysis of the two‐centered delocalization (δ) and localization (λ) index values. The highest occupied molecular orbital energies of 1‐arylsulfonyl 1,3‐butadienes are lower than those of 1,3‐butadiene explaining their low reactivity towards the Diels–Alder condensation. Copyright © 2015 John Wiley & Sons, Ltd.