Reactions of (1‐nitroethenyl)sulfonylbenzene,a nitroethene derivative geminally substituted by a second W‐group

Nitroaldol reaction of phenylsulfonylnitromethane with formaldehyde affords a mixture of 2,4‐dinitro‐2,4‐bis(phenylsulfonyl)butan‐1‐ol and 2,4‐dinitro‐2,4‐ bis(phenylsulfonyl)pentane‐1,5‐diol. Treatment of this mixture with base followed by reacidification affords 1,1'‐[(1,3‐dinitro‐1,3‐propanediyl)bis(sulfonyl)]bis(benzene) as a mixture of (R*, R*) and (R*, S*)‐diastereomers from which the (R*, S*)‐diastereomer can be obtained pure. The intermediate in the nitroaldol reaction is (1‐nitroethenyl)sulfonylbenzene and, if dienes are present, additional products are also obtained. If either (E)‐2‐methyl‐1,3‐pentadiene or 1‐(1‐methylethenyl)cyclohexene are present, typical Diels‐Alder adducts are obtained with the major isomers explainable by assuming a transition state in which the nitro group is endo. If furan is present, its formal conjugate addition product, 2‐[2‐nitro‐2‐(phenylsulfonyl)ethyl]furan, is formed. If cyclooctatetraene is present, it first dimerizes and then affords isomeric Diels‐Alder cycloadducts of the dimer. Semiempirical calculations comparing the LUMO energies of (1‐nitroethenyl)sulfonylbenzene to the corresponding trans‐1,2 isomer are presented to explain relative reactivity of 1,1‐ and 1,2‐disubstituted dienophiles. Copyright © 2009 John Wiley & Sons, Ltd.     

Evidence from15N nuclear polarization on the mechanism of addition of nitrogen dioxide to alkenes

Nitrogen dioxide reacts with 2-ethyl-1-butene and 2-methyl-2-pentene inn-hexane as solvent to give mainly the corresponding dinitro compounds and nitro alcohols (believed to be derived from nitronitrites during the separation process). When¹⁵N-labelled nitrogen dioxide is used, the products show strong¹⁵N nuclear polarization: the signal from the first nitro group to be introduced into the alkene shows enhanced absorption and, in the dinitro compounds, the signal from the second nitro group is in emission. The results indicate that both the dinitro compounds and the nitronitrites are formed by the reaction of the alkenes with two successive nitrogen dioxide molecules. The results do not, however, exclude the possible contributions of other reaction paths.     

Regiospecific naphthyl nitration of 5,10,15,20‐tetranaphthylporphyrin

The nitration reaction of 5,10,15,20‐tetranaphthylporphyrin (TNP) was investigated in detail and the mono‐, di‐, and tri‐nitro‐TNPs were synthesized in high yield using 65% HNO₃. The ¹H‐NMR study shows that the preferred site of nitration of the naphthyl substituted porphyrin is the carbon atom of the meso‐substituents para to its bond to the porphyrin ring. The reaction leads to exquisite regioselectivity in favor of the mono, di, and tri‐nitro‐TNP. Quantum‐chemical ab initio calculations at different levels of theory were performed in order to explain the experimentally observed reactivity. Copyright © 2010 John Wiley & Sons, Ltd.     

Reactive Compatibilization of Poly(trimethylene terephthalate)/Polypropylene Blends by Polypropylene‐graft‐Maleic Anhydride. Part 1. Rheology,Morphology, Melting,and Mechanical Properties

Poly(trimethylene terephthalate)/polypropylene (PTT/PP) blends were prepared by melt blending. The rheology, morphology, melting, and mechanical properties of PTT/PP blends were investigated with and without the addition of polypropylene‐graft‐maleic anhydride (PP‐g‐MAH). The melt viscosity results showed that the fluid behavior of PTT/PP blends exhibited great disparity to that of PTT but similar to that of PP; the dispersed flexible PP phase in the blends served as a “ball bearing effect” under shear stress, which made the fluid resistance markedly reduced; by contrast, the relatively rigid PTT dispersed phase made only a small contribution to the viscosity. With 5 wt.% PP‐g‐MAH addition during melt processing, both the shear viscosity and the non‐Newtonian index of 70/30 PTT/PP blend were increased over that of the corresponding uncompatibilized one, whereas the shear viscosity of the 30/70 PTT/PP melt decreased slightly indicating that a considerable amount of PP‐g‐MAH did not act as compatibilizer but probably served as plasticizer.

With the increasing of the other component, the melting temperature of the PTT phase showed a slight decrease while the melting temperature of the PP phase showed a slight increase. 5 wt.% PP‐g‐MAH addition had little influence on the melting temperatures of the two components. When PP≤20 wt.%, the cold crystallization temperature of the PTT phase (T_cc (PTT‐phase)) showed little change with the composition; however, it shifted to higher temperature when PP≥30 wt.%. The variations of the T_cc (PTT‐phase), with and without PP‐g‐MAH, suggested that, when PTT was a minor component, the excess PP‐g‐MAH which did not act as compatibilizer might serve as a plasticizer that made the PTT's cold crystallization process to be easier. The SEM results indicated that, for the uncompatibilized blends, the interfaces from particles pulling‐out are clear and smooth, while, for compatibilized blends, the reactive products are at the interfaces. The mechanical properties suggested that PP‐g‐MAH did not result in significant improvement of the toughness of the blend, but the tensile strength increased markedly.     

β‐Elimination of an aziridine to an allylic amine: a mechanistic study

The base‐induced rearrangement of aziridines has been examined using a combination of calculations and experiment. The calculations show that the substituent on nitrogen is a critical feature that greatly affects the favorability of both α‐deprotonation, and β‐elimination to form an allylic amine. Experiments were carried out to determine whether E2‐like rearrangement to the allylic amine with lithium diisopropyl amide (LDA) is possible. N‐tosyl aziridines were found to deprotonate on the tosyl group, preventing further reaction. A variety of N‐benzenesulfonyl aziridines having both α‐ and β‐protons decomposed when treated with LDA in either tetrahydrofuran or hexamethylphosphoramide. However, when α‐protons were not present, allylic amine was formed, presumably via β‐elimination. Copyright © 2011 John Wiley & Sons, Ltd.     

The SN3–SN2 spectrum. Rate constants and product selectivities for solvolyses of benzenesulfonyl chlorides in aqueous alcohols

Rate constants for a wide range of binary aqueous mixtures and product selectivities (S) in ethanol–water (EW) and methanol–water (MW) mixtures, are reported at 25 °C for solvolyses of benzenesulfonyl chloride and the 4‐chloro‐derivative. S is defined as follows using molar concentrations: S = ([ester product]/[acid product]) × ([water solvent]/[alcohol solvent]). Additional selectivity data are reported for solvolyses of 4‐Z‐substituted sulfonyl chlorides (Z = OMe, Me, H, Cl and NO₂) in 2,2,2‐trifluoroethanol–water. To explain these results and previously published data on kinetic solvent isotope effects (KSIEs) and on other solvolyses of 4‐nitro and 4‐methoxybenzenesulfonyl chloride, a mechanistic spectrum involving a change from third order to second order is proposed. The molecularity of these reactions is discussed, along with new term ‘S_N3–S_N2 spectrum’ and its connection with the better established term ‘S_N2–S_N1 spectrum’. Copyright © 2009 John Wiley & Sons, Ltd.     

Solvent network at the transition state in the solvolysis of hindered sulfonyl compounds

Alcoholysis rates of unhindered benzenesulfonyl chlorides (X‐ArSO₂Cl, X = H‐; 4‐Br‐; 4‐Me‐) are similar in methanol; the same behavior is also observed in ethanol, whereas the reactivity order in iso‐propanol is 4 Me‐ < H‐ < 4‐Br‐. On the other hand, alcoholysis of sterically hindered arenesulfonyl chlorides (X‐ArSO₂Cl) (X = 2,4,6‐Me₃‐3‐NO₂‐; 2,6‐Me₂‐4‐tBu‐; 2,4,6‐Me₃‐; 2,3,5,6‐Me₄‐; 2,4,6‐iPr₃‐; 2,4‐Me₂‐; 2,4,6‐(OMe)₃‐) in all studied alcohols show a significant increase in reactivity, the so‐called positive steric effect. Most of the substrates showed a reaction order b ~ 2 with respect to the nucleophile in methanol and ethanol, and b ~ 3 in iso‐propanol. The correlation between reactivity and the Kirkwood function (1/ξ) gives negative sensitivity (U) for all systems. All substrates showed high sensitivity to media nucleophilicity that depends on Σσ_X. Obtained results suggest the alcoholysis of benzenesulfonyl chlorides proceeds through S_N2 mechanism where the transition state (TS) involves the participation of 2–3 alcohol molecules; such a TS can be cyclic, in the case of unbranched alcohols, or linear, for alcohols with bulkier hydrocarbon groups like iso‐propanol. To include the number of alcohol molecules playing such a role in the TS, the following terminology is proposed: cS_N2s_n for S_N2 reactions involving n solvent molecules in a cyclic (c) TS, where “s” stands for the solvent and “n” is either the closest integer or half‐integer to the reaction order relative to the solvent or, in computational studies, the proposed number of solvent molecules taking part in the TS, whereas S_N2s_n is proposed when the TS is not cyclic. Copyright © 2016 John Wiley & Sons, Ltd.     

Exploring the reaction of iodine with α‐diazo esters

In this paper we describe the unprecedented reaction between α‐diazo esters 1 and iodine. The reaction, carried out in the presence of aqueous NaHCO₃, afforded the Z‐isomer of the corresponding unsaturated‐2‐iodo ester 8 . The configuration of compounds 8 was determined using the ³J_{C? H} coupling between carbonyl carbon atom and alkene proton. Mechanistic considerations accounting for the observed phenomena and including quantum chemical calculations are proposed. Copyright © 2008 John Wiley & Sons, Ltd.     

A computational study (DFT,MP2, and GIAO‐DFT) of substituent effects on protonation regioselectivity in β,β‐disubstituted vinyldiazonium cations: formation of highly delocalized carbenium/diazonium dications

Protonation reactions were studied by quantum‐chemical theoretical methods (DFT and MP2) for a series of β,β‐disubstituted vinyldiazonium cations ( 1 ⁺ – 14 ⁺ ), bearing stabilizing electron‐releasing groups (H₃CO? , (H₃C)₂N? , H₃C? , (H₃C)₃Si? , as well as halogens F, Cl). Taking into account the various mesomeric forms that these species can represent, protonations at C_α, at the β‐substituent, and at N_β were considered. The energetically most favored pathway in all cases was C_α protonation, which formally corresponds to trapping of the mesomeric diazonium ylid. Based on the computed properties (optimized geometries, NPA‐charge densities, and multinuclear GIAO‐NMR chemical shifts), the resulting dications can best be viewed as carbenium/diazonium dications, in which the carbocation is further delocalized into the β‐substituent. For the α‐nitro derivative 15 , protonation of the nitro group was predicted to be the most favored reaction, while C_α‐ and N_β‐protonation resulted in the loss of the nitronium ion. Copyright © 2009 John Wiley & Sons, Ltd.     

Discovery of a <Emphasis Type="Italic">β</Emphasis>-glucosidase inhibitor from a chemically engineered extract prepared through sulfonylation

A semisynthetic β-glucosidase inhibitor was identified from a chemically engineered extract prepared by reaction with benzenesulfonyl chloride. The structure includes a natural histamine portion and a benzenesulfonyl portion introduced during the diversification step.     

High diastereoselectivity induced by intermolecular hydrogen bonding in [3 + 2] cycloaddition reaction: experimental and computational mechanistic approaches

A diastereoselective [3 + 2] cycloaddition of N‐aryl substituted maleimides with N,α‐diphenyl nitrone possessing 11‐hydroxyundecyloxy as a flexible substituent was performed. Experimental and comprehensive mechanistic density functional theory studies reveals that intermolecular H‐bonding and steric repulsive interaction predominate exo‐Z and exo‐E cycloaddition transition states, respectively. The reaction proceeded smoothly depending on the reactants and gave a good yield of (syn) cis‐isoxazolidine or (anti) trans‐isoxazolidine as a single diastereomer.     

Can tetra‐tert‐butylethylene be formed by ion–ion recombination or ion–molecule reaction of two di‐tert‐butylcarbene units?—a DFT study

The reaction channels of di‐tert‐butylcarbene ( 2 ), its radical anion, ( 3 ) and its radical cation ( 4 ) were investigated theoretically by using DFT/B3LYP with 6‐31+G(d) basis set and 6‐311+G(2d,p) for single point energy calculations. Conversion of the neutral carbene 2 to the charged species 3 and 4 results in significant geometric changes. In cation 4 two different types of C? (CH₃)₃ bonds are observed: one elongated sigma bond called “axial” with 1.61 Å and two normal sigma bonds with a bond length of 1.55 Å. Species 2 and 4 have an electron deficient carbon center; therefore, migration of CH₃ and H is observed from adjacent tert‐butyl groups with low activation energies in the range of 6–9 kcal/mol like similar Wagner–Meerwein rearrangements in the neopentyl‐cation system. Neutral carbene 2 shows C? H insertion to give a cyclopropane derivative with an activation energy of 6.1 kcal/mol in agreement with former calculations. Contrary to species 2 and 4 , the radical anion 3 has an electron rich carbon center which results in much higher calculated activation energies of 26.3 and 42.1 kcal/mol for H and CH₃ migrations, respectively. NBO charge distribution indicates that the hydrogen migrates as a proton. The central issue of this work is the question: how can tetra‐tert‐butylethylene ( 1 ) be prepared from reaction of either species 2 , 3 , or 4 as precursors? The ion–ion reaction between 3 and 4 to give alkene 1 with a calculated reaction enthalpy of 203.5 kcal/mol is extremely exothermic. This high energy decomposes alkene 1 after its formation into two molecules of carbene 2 spontaneously. Ion–molecule reaction of radical anion 3 with the neutral carbene 2 is a much better choice: via a proper oriented charge–transfer complex the radical anion of tetra‐tert‐butylethylene (11) is formed. The electron affinity of 1 was calculated to be negligible. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of hydroxyoligophenylenes containing electron‐donating,electron‐accepting groups,or π‐deficient aromatic ring and their solvatochromic behavior

We have reported oligo(p‐phenylene)s (OPPs) with an OH group located at one end, namely, OPP(n)‐OHs (where n is the number of benzene rings). The OPPs exhibited significant solvatochromism; the deprotonation of the OH groups of OPP(n)‐OHs , when treated with NaH, caused a bathochromic shift of absorption maxima (λ_max) that increased with the donor numbers (DNs) of the solvents. We assumed that the solvatochromism exhibited by OPP(n)‐ONa was attributed to an intramolecular charge shift from the sodium phenoxy group(s) to the adjacent rings. In this study, to investigate the assumption, hydroxyoligophenylenes ( R‐OPP(n)‐OH ) with an electron‐donating dimethylamino group (n = 3, R = NMe₂), an electron‐accepting nitro group (n = 3, R = NO₂), and a π‐deficient pyridine ring (n = 2, R = Py) were synthesized by the Suzuki coupling reaction. The deprotonation of the OH group of by treatment with NaH caused a bathochromic shift (Δλ) of λ_max of R‐OPP(m)‐ONa . The Δλ of the deprotonated species increased with the DNs of the solvents. The emission peak positions of R‐OPP(m)‐ONa depended on the DNs of the solvents; therefore, the emission color could be tuned by changing the solvent. R‐OPP(m)‐OH received an electrochemical oxidation of the OH group and OPP unit. The data related to the remarkable solvatochromic behavior of R‐OPP(n)‐ONa will be useful information for the development of new luminescent materials.     

Selectivity of nitro versus fluoro substitution in arenes in their reactions with charged O‐ and S‐nucleophiles

The relative mobility of nitro and fluoro substituents in 1,3‐dinitro‐ and 1‐fluoro‐3‐nitrobenzenes, 3,5‐dinitro‐ and 3‐fluoro‐5‐nitrobenzotrifluorides under the action of the nucleophiles (2ArYH)·K₂CO₃ and ArY^?K⁺ in solution and the nucleophiles ArYH·K₂CO₃ (Y = O, S) under heterogeneous conditions was studied by a competitive method in DMF at 40–140 °C. The unique dependences of ΔΔH^≠ on ΔΔS^≠ and ΔΔH^≠ on ΔΔG^≠ were determined for all the substrates and nucleophiles. The dependence of the mechanistic pathway on the nucleophile is discussed. Two results are relevant to the reactions studied: (i) substituent effects in the nucleophiles (2ArYH)·K₂CO₃ and ArYH·K₂CO₃ on the activation entropies suggest that the entropy favours the displacement of nitro group; (ii) the negative signs of ΔΔH^≠ and ΔΔS^≠ for the reactions of the nucleophiles ArY^?K⁺ indicate that the enthalpy determines the displacement of nitro group. It is concluded that the selectivity of the reactions with aryloxide and arylthioxide ions cannot be explained by the hard–soft acid–base principle only. Copyright © 2007 John Wiley & Sons, Ltd.     

Kinetic studies of the reaction of phenacyl bromide derivatives with sulfur nucleophiles

The reaction of the substituted phenacyl bromides 1a–e and 2a–e with thioglycolic acid 3 and thiophenol 6 in methanol underwent nucleophilic substitution S_N2 mechanism to give the corresponding 2‐sulfanylacetic acid derivatives 4a–e, 5a–e and benzenethiol derivatives 9a–e, 10a–e. The reactants and products were identified by mass spectra, infrared and nuclear magnetic resonance. We measured the kinetics of these reactions conductometrically in methanol at a range of temperatures. The rates of the reactions were found to fit the Hammett equation and correlated with σ‐Hammett values. The ρ values for thioglycolic acid were 1.22–1.21 in the case of 4‐substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.39–0.35. The ρ values for thiophenol were 0.97–0.83 in the case of 4‐substituted phenacyl bromide 1a–e, while in the case of the nitro derivatives 2a–e they were 0.79–0.74. The Brønsted‐type plot was linear with a α = ?0.41 ± 0.03. The kinetic data and structure‐reactivity relationships indicate that the reaction of 1a–e and 2a–e with thiol nucleophiles proceeds by a concerted mechanism. The plot of log k₄₅ versus log k₃₀, the plot log(k_x,3‐NO2/k_H) versus log(k_x/k_H), and the Brønsted‐type correlation indicate that the reactions of the thiol nucleophiles with the substituted phenacyl bromides 1a–e and 2a–e are attributed to the electronic nature of the substituents. Copyright © 2011 John Wiley & Sons, Ltd.     

Aromatic nitro substitution reaction between 4‐nitro‐N‐n‐butyl‐1,8‐naphthalimide and n‐heptanethiol in water–methanol binary mixtures

The second‐order rate constants of thiolysis by n‐heptanethiol on 4‐nitro‐N‐n‐butyl‐1,8‐naphthalimide (4NBN) are strongly affected by the water–methanol binary mixture composition reaching its maximum at around 50% mole fraction. In parallel solvent effects on 4NBN absorption molar extinction coefficient also shows a maximum at this composition region. From the spectroscopic study of reactant and product and the known H‐bond capacity of the mixture a rationalization that involves specific solvent H‐donor interaction with the nitro group is proposed to explain the kinetic data. Present findings also show a convenient methodology to obtain strongly fluorescent imides, valuable for peptide and analogs labeling as well as for thio‐naphthalimide derivatives preparations. Copyright © 2008 John Wiley & Sons, Ltd.     

Diastereoselectivity and kinetics of hetero diels-alder reactions under high pressure

Abstract

The Hetero Diels-Alder reaction of enamino ketones and ethyl vinyl ether to give dihydropyrans is studied in different solutions under pressure up to 7 kbar. The kinetics is measured via on-line FT IR spectroscopy. The cycloaddition shows a remarkable pressure dependent increase in diastereo-selectivity. For the difference in activation volumes referring to the reaction to the two diastereomers, values up to 5.9 ± 0.5 cm³/mol are observed. The ratio of cis and trans diastereomers can be improved by almost one order of magnitude by changing pressure and temperature from 1 bar and 90 °C to 6 kbar and 0.5 °C.     

Stereochemical Elucidation of Norbornene Derivatives Synthesized as Leukotriene D4 Receptor Antagonists

The complete ¹H and ¹³C NMR assignment and stereochemical elucidation of four norbornene derivatives (1–4) are presented. These derivatives were obtained by an asymmetric Diels–Alder reaction of a chiral dienophile, from D‐glucose, as leukotriene D4 receptor antagonists. NOE measurements of the four products between H‐7b and H‐5 readily allowed discrimination between exo‐ (2, 4) and endo‐ (1, 3) diastereomers with respect to methyl carboxylate and tetrahydrofuro[1,3]dioxolyl groups. Further discrimination and subsequent absolute configuration determination of the two endo‐ and two exo‐ products were performed by NOE peak measurements and molecular modeling calculations of relative interproton distances of the most stable conformations of each isomer.     

Synthesis and Spectroscopic Studies of Some New Polyether Ligands of the Schiff Base Type

Abstract

New polyether ligands of Schiff base type (3–13) were synthesized from the reaction of diethylene glycol bis(2‐aminophenyl)ether and triethylene glycol bis(2‐aminophenyl)ether with salicylaldehyde, 5‐methoxysalicylaldehyde, 5‐bromosalicylaldehyde, 5‐nitro salicylaldehyde, and 2‐hydroxy‐1‐naphthaldehyde. The products were characterized by elemental analysis, IR, ¹H, ¹³C NMR, and UV‐VIS techniques. The UV‐VIS spectra of those Schiff bases with an OH group in the ortho position to the imino group were studied in polar and nonpolar solvents in acidic and basic media. The compounds are in tautomeric equilibrium (enol‐imine, O–H · N?keto‐amine, O · H–N forms) in solvents, acidic chloroform, and benzene solutions and basic DMSO, chloroform, and benzene solutions. These tautomers were not observed in polar and non‐polar solvents and in basic solutions of DMSO, chloroform, and benzene for the Schiff bases 5–10. Tautomer proportions, which were obtained from ¹H NMR and UV‐VIS data in DMSO, were compared for compounds 3, 4, 11, and 12.     

The mechanism of aromatic nucleophilic substitution reaction between ethanolamine and fluoro‐nitrobenzenes: an investigation by kinetic measurements and DFT calculations

We have studied the kinetics and elucidated the mechanism by DFT calculation of the reaction between ethanolamine (EOA) and 1‐fluoro‐2,4‐dinitrobenzene (DNFB) in acetonitrile and toluene. To determine the contribution of the nitro group, the activation energy of the reaction between ethanolamine and 1‐fluoro‐2‐nitrobenzene (MNFB) vs. DNFB was determined in acetonitrile and calculated by DFT method. Kinetic measurements reveal that the reaction is faster in acetonitrile than in toluene. The reaction follows overall second‐order kinetics: first order with respect to both EOA and DNFB which is similar to the results reported for reaction between other primary amines and 1‐substituted‐2,4‐dinitrobenzenes. The calculations by using DFT methods reveal that the mechanism of the reaction involves the formation and decomposition of a Meisenheimer complex (MC). DFT calculations also reveal that the activation energy of the reaction is highest in vacuum and decreases with increasing polarity of the solvent reaching a minimum in acetonitrile. In addition, activation energies obtained by both DFT calculations and experiments show that the reactivity of MNFB is less than that of DNFB showing the effect of the 4‐nitro group. Copyright © 2010 John Wiley & Sons, Ltd.