Promoting effect of thiophenols on the ring‐opening polymerization of 1,3‐benzoxazine

Thiophenol and p‐nitrothiophenol were evaluated as promoters for the ring opening polymerization of benzoxazine. The ring‐opening polymerization of p‐cresol type monofunctional N‐phenyl benzoxazine 1a with 10 mol % of thiophenols proceeded at 150 °C, leading to the high conversion of 1a more than 95% within 5 h, whereas the polymerization of 1a without thiophenols did not proceed under the same conditions. The promotion effect of the thiophenols on curing of bisphenol‐A type N‐phenyl benzoxazine 1b was also investigated. In the differential scanning calorimetric (DSC) analysis of the polymerization of 1b at 150 °C without using any promoters, an exothermic peak attributable to the ring‐opening reaction of benzoxazine was observed after 8 h. In contrast, in the DSC analysis of the polymerization of 1b with addition 20 mol % of p‐nitrothiophenol, an exothermic peak was observed within 2 h, to clarify the significant promoting effect of p‐nitrothiophenol. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2523–2527     

Regioselective Bromination of a Thymine–Acridine Conjugate by N-Bromosuccinimide

A thymine and acridine conjugate (1), containing a benzylic carbon of thymine and an electron-rich aromatic ring (acridine) within the same molecule, was synthesized. Treatment of 1 with N-bromosuccinimide (NBS) in anhydrous chloroform in the presence of azobisisobutylnitrile produced a dibromo-substituted thymine–acridine conjugate (7) as a major product, in which the bromination was only observed on the acridine ring. Nuclear Overhauser effect (NOE) difference spectroscopy revealed that the actual bromination substitution was on C-2 and C-7 of acridine. Our results suggest that electrophilic aromatic substitution, not the expected benzylic radical reaction, takes place predominantly even when 1 is subjected to the NBS reaction condition, which favors radical processes. In addition, such selectivity is clearly solvent dependent.     

α‐Chlorination of Acetophenones Using 1,3‐Dichloro‐5,5‐Dimethylhydantoin

A novel method for the synthesis of α‐chloroacetophenones using 1,3‐dichloro‐5,5‐dimethylhydantoin (DCDMH) and p‐toluenesulfonic acid in methanol at 30–35°C is described. Substituted acetophenones at the para position or meta position of aromatic ring give α‐chloroacetophenones in high yield. However, reaction of o‐nitroacetophenone does not take place under the same condition.     

Substituent chemical shift correlations. Hammett σp+ values and shifts for exocyclic protons in para-substituted benzene derivatives

The methyl ¹H NMR shifts for series of para-substituted N,N-dimethylanilines as their conjugate acids in trifluoroacetic acid, and series of para-substituted N,N,N-trimethylphenyl-ammonium iodides in acetonitrile and in deuterium oxide, and the methylene shifts for series of para-substituted N,N-diethylanilines as their conjugate acids in deuteriosulfuric acid, are shown to be linearly related to the Hammett σ_p+ parameter. It is proposed that this dependence reflects a response of the chemical shift of the proton of the probe moiety to the electron density at the point of attachment of the probe to the aromatic ring and that this response is determined by the electric field effect of the charge at the point of attachment. Literature data are cited to indicate that Hammett σ_p+–¹H NMR shift relationships may be general for probe moieties lacking a through-resonance mechanism for interaction between the probe and the aromatic ring.     

Impact of replacement of the central benzene ring in anthracene by a heterocyclic ring on electronic excitations and reorganization energies in anthratetrathiophene molecules

The impact of changing the central benzene ring on the electronic excitations and reorganization energies (λ) of the anthratetrathiophene (ATT) molecules is studied by density functional theory (DFT) and time‐dependent DFT (TD‐DFT) quantum chemical calculations. The effect of changing the position of the sulfur atom at the periphery of anthracene on the optical and charge transfer properties is also studied. The calculated results suggest that the HOMO, LUMO, HOMO–LUMO energy gap, ionization potential (IP), electron affinity (EA), hole extraction potential (HEP), electron extraction potential (EEP), and reorganization energies (λ) are affected by replacing the central ring with different heterocyclic rings and the position of the sulfur atom. In addition, all molecules show good hole‐ and electron‐transport properties. This work may be helpful for future design and preparation of high‐performance charge‐transport materials.     

Bi(III)‐catalyzed C―S cross‐coupling reaction

A direct synthetic route for the C―S coupling of aryl halides with thiophenols is described. This method is tolerant to electron‐withdrawing and electron‐donating functional groups and also to the presence of functional groups in the ortho position of the aryl iodide or thiophenol. Aryl iodides are coupled with thiophenols without affecting the other functionalities present in the aryl ring. These reactions follow second‐order kinetics. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of solvent on the dehydrogenation of poly(1,3‐cyclohexadiene): Formation and characteristics of benzoquinone–aromatic hydrocarbon charge‐transfer complexes

The effect of solvent on the dehydrogenation of poly(1,3‐cyclohexadiene) (PCHD) with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) [or 2,3,5,6‐tetrachloro‐1,4‐(p‐)‐benzoquinone (TCQ)] was examined to improve the reactivity of benzoquinones for this dehydrogenation reaction. The dehydrogenation of PCHD with DDQ (or TCQ) was strongly affected by the type of solvent, and aromatic hydrocarbon based solvents were appropriate for this dehydrogenation reaction. A charge‐transfer complex between DDQ (or TCQ) and aromatic hydrocarbons was formed in the reaction mixture, and the reactivity of the complex was much higher than that of free DDQ (or TCQ). The formation of a DDQ–aromatic hydrocarbon complex, which has a large diamagnetic shift of the ¹³C NMR signals with respect to DDQ, was the primary factor for improvement of the reactivity of DDQ. For the TCQ–aromatic hydrocarbon complex, the existence of an electron‐withdrawing group on the aromatic hydrocarbon was the major factor for improvement of the reactivity of TCQ. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 342–350, 2010     

The unusual ability of α‐angelicalactone to form adducts: A kinetic approach

Since α‐angelicalactone (AAL) substantially inhibits the formation of tumors, here its chemical reactivity was compared with that of carcinogenic lactones. Investigation of the electrophilic potential of AAL was carried out by studying the capacity of this lactone to form adducts with NBP, 4‐(p‐nitrobenzyl)pyridine, a substrate with nucleophilic characteristics similar to DNA bases. The formation of the AAL–NBP adduct occurs about 900,000‐fold faster than with β‐propiolactone, the most effective carcinogenic lactone (ΔG^#₃₅ = 52 and 87 kJ mol^?1, respectively). A stopped‐flow technique was required for this reaction to be monitored. It was concluded that the formation of AAL–NBP adducts takes place through an entropy‐strain‐catalyzed mechanism caused by early lactone ring cleavage. The kinetic results are consistent with the AAL potential as a chemoprotective agent. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 591–594, 2007     

Gold‐Catalyzed Cyclization of Furan‐Ynes bearing a Propargyl Carbonate Group: Intramolecular Diels–Alder Reaction with In Situ Generated Allenes

Gold‐catalyzed cyclization of various furan‐ynes with a propargyl carbonate or ester moiety results in the formation of a series of polycyclic aromatic ring systems. The reactions can be rationalized through a tandem gold‐catalyzed 3,3‐rearrangement of the propargyl carboxylate moiety in furan‐yne substrates to form an allenic intermediate, which is followed by an intramolecular Diels–Alder reaction of furan and subsequent ring‐opening of the oxa‐bridged cycloadduct. It was found that the steric and electronic properties of phosphine ligands on the gold catalyst had a significant impact on the reaction outcome. In the case of 1,5‐furan‐yne, the cleavage of the oxa‐bridge in the cycloadduct with concomitant 1,2‐migration of the R¹ group occurs to furnish anthracen‐1(2H)‐ones bearing a quaternary carbon center. For 1,4‐furan‐yne, a facile aromatization of the cycloadduct takes place to give 9‐oxygenated anthracene derivatives.     

Nucleophilic Substitution Reaction of p-Dinitrobenzene by a Carbanion: Evidence for Electron Transfer Mechanism

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Preparation of thiochromans via thermal cyclization

Formation of the thiochroman ring system is achieved by a two step synthesis that involves heating 3‐thiophenyl‐1‐propanols or 4‐thiophenyl‐2‐butanols in toluene with catalytic amounts of p‐toluenesulfonic acid. The propanols are made by the addition of sulfur stabilized carbanions to styrene oxide, ethylene oxide, propylene oxide, and isobutylene oxide. The carbanions are generated by treatment of either benzyl phenyl sulfide or thioanisole with butyllithium. The effect of substitution at the 1 and 3 positions of the propanols on the reaction yields is discussed. The mechanism of the reaction apparently involves intramolecular electrophilic aromatic substitution rather than a Claisen or thio‐Claisen rearrangement.     

Photoisomerization of a Maleonitrile‐Type Salen Schiff Base and Its Application in Fine‐Tuning Infinite Coordination Polymers

Strategically designed salen ligand 2,3‐bis[4‐(di‐p‐tolylamino)‐2‐hydroxybenzylideneamino]maleonitrile ( 1 ), which has pronounced excited‐state charge‐transfer properties, shows a previously unrecognized form of photoisomerization. On electronic excitation (denoted by an asterisk), 1Z *→ 1E isomerization takes place by rotation about the C2? C3 bond, which takes on single‐bond character due to the charge‐transfer reaction. The isomerization takes place nonadiabatically from the excited‐state ( 1Z ) to the ground‐state ( 1E ) potential‐energy surface in the singlet manifold; 1Z and 1E are neither thermally inconvertible at ambient temperature (25–30 °C), nor does photoinduced reverse 1E *→ 1Z (or 1Z *) isomerization occur. Isomers 1Z and 1E show very different coordination chemistry towards a Zn^II precursor. More prominent coordination chemistry is evidenced by a derivative of 1 bearing a carboxyl group, namely, N,N′‐dicyanoethenebis(salicylideneimine)dicarboxylic acid ( 2 ). Applying 2Z and its photoinduced isomer 2E as building blocks, we then demonstrate remarkable differences in morphology (sphere‐ and needlelike nanostructure, respectively) of their infinite coordination polymers with Zn^II.     

The mechanism of thermal eliminations. Part XXVIII [1]: Thermal decomposition of benzoylformic acid

The thermal decomposition of benzoylformic acid into carbon dioxide and benzaldehyde is a unimolecular first-order reaction which takes place according to the rate equation log k = 15.3–42,500/4.575 K. At 600 K the reaction takes place 18 times faster than the corresponding decomposition of pyruvic acid into carbon dioxide and acetaldehyde. This is consistent with the 4-center process proposed previously for pyruvic acid, in which a partial negative charge develops on the carbon of the α-carbonyl group in the transition state. Benzoylformic acid is considerably less reactive towards thermal elimination than is oxalic acid, which also accords with the proposed mechanism.     

Spontaneous reactions of electron‐accepting substituted quinodimethane with substituted styrenes: Inductive and steric effects on the formation of a zwitterionic intermediate

Spontaneous reactions of an electron‐accepting substituted quinodimethane, 1‐(2,2‐dimethyl‐1,3‐dioxane‐4,6‐dione‐5‐ylidene)‐4‐(dicyanomethylene)‐2,5‐cyclohexadiene, with p‐substituted, α‐substituted, and β‐substituted styrenes were investigated. When p‐substituted styrenes were used as comonomers, no spontaneous reactions took place for styrenes with an electron‐accepting p substituent such as COOMe and CN groups, and both terpolymers and cycloadducts were formed for the other p‐substituted styrenes. When α‐substituted and β‐substituted styrenes were used as comonomers, no reactions occurred for α‐ and β‐substituted styrenes with a bulky phenyl group, and spontaneous reactions took place for those with a smaller methyl group. The reaction products were an alternating copolymer for α‐substituted styrene and both terpolymers and 5‐ethylidene‐2,5‐dimethyl‐1,3‐dioxane‐4,6‐dione for β‐substituted styrenes. The position of the methyl group in the styrenes significantly affected the product formation. This behavior in the spontaneous reactions was discussed on the basis of the ability of formation of the zwitterionic tetramethylene intermediate and its conformation, determined by polar and steric effects of the substituents in the substituted styrenes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5195–5206, 2005     

Theoretical reinvestigation of opposite electronic effects on bond lengths in thiophenols and thiophenolic radicals

Our previous study has revealed that para-substituents have opposite electronic effects on the C-S bond lengths of thiophenols and thiophenolic radicals. Although a theoretical elucidation has been given, it has not been supported by theoretically calculated atomic charges. To give an alternative explanation, we calculated the C-S bond lengths, C-S bond electron densities, and Mulliken charges on the carbon and sulfur atoms for thiophenols, thiophenolic radicals, and thiophenolic radical cations by means of the B3LYP density functional theory method using the 6-31G(d, p) basis set. It was revealed that the C-S bond length is adequately defined in terms of C-S bond electron density. The distinct electronic effects on the C-S bond lengths of thiophenols, thiophenolic radicals and thiophenolic radical cations are well elucidated by the different electronic states (electron-deficient or-rich) of the phenyl ring and SH group.     

The Adverse Effect of Benzannelation on the Aromaticity of Oxocinyl Anion: A Combined Experimental and Theoretical Study

A synthesis of 2H‐1‐benzoxocin from readily available compounds was accomplished. The potentially ‘aromatic’ π‐excessive systems 2H‐1‐benzoxocinyl and 6H‐dibenz[b,f]oxocinyl anions were generated from their corresponding conjugate acid precursors 7c and 8 , respectively. It was found that 2H‐1‐benzoxocinide 3d lacks the type of π‐frame stability associated with the parent 2H‐oxocinide 1d and that the dibenzo analog 5b is more unstable than 3d . Both 3d and 5b undergo rapid structural reorganization to form their corresponding stable isomeric anions. We were able to characterize the proton‐quenched products of these anions as the ring‐opened structures 15 and 18 , respectively. ¹H‐NMR and an ab initio calculation at the 6‐31g* level indicated that, unlike the ‘aromatic’ parent 2H‐oxocinide 1d and the aza analog 3c, 3d incorporates a non‐planar oxocinyl ring in which the negative charge is primarily localized on the pentadienyl moiety of the ring, but also partial delocalization of π‐electron density onto the benzene ring occurs.     

Quinolinium‐Based Fluorescent Probes for the Detection of Thiophenols in Environmental Samples and Living Cells

A new type of fluorescent probes for thiophenols, 6HQM‐DNP and 7HQM‐DNP, containing 6‐ or 7‐hydroxy quinonlinium as fluorophore and 2,4‐dinitrophenoxy (DNP) as nucleophilic recognition unit were constructed. As ethers, these non‐fluorescent probe molecules can release the corresponding fluorescent quinolinium (6HQM and 7HQM) through aromatic nucleophilic substitution (S_NAr) by thiolate anions from thiophenols. The sensing reaction is highly sensitive (detection limit of 8 nM for 7HQM‐DNP) and highly selective to thiophenols over aliphatic thiols and other nucleophiles under neutral conditions (pH 7.3). The probes respond rapidly to thiophenols, with second‐order rate constants k=45 M ^?1 s^?1 for 7HQM‐DNP and 24 M ^?1 s^?1 for 6HQM‐DNP. Furthermore, the selective detection of thiophenols in living cells by 7HQM‐DNP was demonstrated by confocal fluorescence imaging. In addition, these quinolinium salts show excellent chemical and thermal stability. In conclusion, this type of probes may find use in the detection of thiophenols in environmental samples and biosystems.     

Time‐dependent density functional theory study on direction‐dependent electron and hole transfer processes in molecular systems

We report on real‐time time‐dependent density functional theory calculations on direction‐dependent electron and hole transfer processes in molecular systems. As a model system, we focus on α‐sulfur. It is shown that time scale of the electron transfer process from a negatively charged S₈ molecule to a neighboring neutral monomer is comparable to that of a strong infrared‐active molecular vibrations of the dimer with one negatively charged monomer. This results in a strong coupling between the electrons and the nuclei motion which eventually leads to S₈ ring opening before the electron transfer process is completed. The open‐ring structure is found to be stable. The similar infrared‐active peak in the case of hole transfer, however, is shown to be very weak and hence no significant scattering by the nuclei is possible. The presented approach to study the charge transfer processes in sulfur has direct applications in the increasingly growing research field of charge transport in molecular systems. © 2017 Wiley Periodicals, Inc.     

Aluminium Chloride‐Catalyzed Intermolecular vs Intramolecular Friedel‐Crafts Reaction of Acrylanilides and 3‐Chloropropanamides

3‐Phenylpropionanilide ( 4a ) is obtained in a yield of 89% from acrylanilide by the treatment with AlCl₃/benzene, compared with a yield of 39% by the 1,4‐conjugate addition of phenyllithium. The formation of 4a indicated that an intermolecular Friedel‐Crafts reaction occurred, rather than the relatively more facile intramolecular ring cyclization, and provided a more efficient route than a conjugate addition of phenyllithium for the preparation of 3‐phenylpropionanilide and its derivatives. Although the methoxy group is an activator of the nucleophilic substitution, introduction of a methoxy substituent at N‐phenyl did not increase the competitive capability of the intramolecular cyclization because of AlCl₃‐catalyzed demethylation to form the ArOAlCl₂ complex which decreased the availability of the π‐electron in the N‐phenyl aromatic system.     

Fragmentation Mechanism of Trans—α—Aryl—β—enamino Esters

Electron impact-induced fragmentation mechanism of Trans-α-Aryl-β-enamino esters were investigated using mass-analyzed ion kinetic energy (MIKE) spectrometry and high resolution accurate mass data It was found that the main characteristic fragmentations of compounds studied were:an odd electron ion M^ -EtOH was formed by losing a neutral molecule of ethanol;and the skeletal rearrangements took place;and the ring opening reaction happened after losing a carbon monoxide;and the typical McLafferty rearrangement underwent in ester group.The cycliztion reation caused by losing neutral molecule of TsNH2 due to the ortho-effects of substituted group of gromatic ring was also observed.