Solvation of monovalent anions in acetonitrile and N,N-dimethylformamide: Parameterization of the IEF-PCM model

The present work reports the parameterization of the polarizable continuum model for predicting the free energies of solvation for monovalent anions in acetonitrile and N,N-dimethylformamide. The parameterization of the model for acetonitrile employed the experimental free energies of solvation for a set of 12 charged solutes, containing H, C, N, O, S, F, Cl, Br, and I atoms. For the N,N-dimethylformamide solutions, experimental solvation free energies for 11 monovalent anions were used. A mean absolute error of 0.7 kcal/mol in the solvation free energies has been achieved for the 12 anions in acetonitrile, whereas the mean absolute error for the 11 anions corresponds to 0.5 kcal/mol in N,N-dimethylformamide. These results indicate that the polarizable continuum model is a suitable methodology for the study of thermodynamic effects in solutions of monovalent anions in both solvents.     

Electrochemical fluorination of N,N-dimethylperfluoroacylamides

The electrochemical fluorination (ECF) of N,N-dimethylperfluoroacylamides gives the corresponding perfluoro-N,N-dimethylacylamides in low yield. With increase of the number of carbon atoms in the perfluoroacyl radical the yield of the required perfluoro-N,N-dimethylacylamides is slightly increased.     

Metal free in situ formation of phthalimide N-oxyl radicals by light-induced homolysis of N-alkoxyphthalimides

Irradiation of N-triphenylmethyloxy- or N-diphenylmethyloxy phthalimide is reported to result in the formation of phthalimide N-oxyl radical (PINO), which is able to initiate and propagate oxidative radical chain reactions of hydrocarbons.     

ESR study of the photo-induced decomposition of polypropylene in the presence of N,N,N′,N′-tetramethyl-p-phenylenediamine

The mechanism of uv (λ > 325 nm) photodegradation of polypropylene (PP) containing N,N,N′,N′-tetramethyl-p-phenylenediamine (T₄MPD) has been investigated by means of ESR spectroscopy. The observed spectra after uv irradiation of both isotactic-PP (IPP) and stereoblock-PP (SPP) samples in vacuum at 77 K consisted principally of a broad singlet which was assigned to a T₄MPD cation radical (T₄MPD^+·). On the other hand, the spectrum observed after irradiation of an atactic polypropylene (APP) sample at 77 K in vacuum was resolved into several components which decayed almost up to ca. 263 K to give rise to the broad singlet of T₄MPD^+·. One component was a sharp quartet which was assigned to a methyl radical, ·CH₃·. The other component, a singlet, was attributed to a trapped electron, e_t^?.By comparison of the ESR spectrum of deuterated T₄MPD with that of the normal compound it was found that 60 ～ 70% of the methyl radicals arose from the added T₄MPD due to β-scission, which also formed the N,N,N′-trimethyl-p-phenylenediamine radical, T₃MPD·. The T₃MPD· radical presumably captures an electron at lower temperatures to become a carbanion, T₃MPD^?, which releases the electron to reproduce the T₃MPD· radical at elevated temperatures. This production of the radical T₃MPD· due to the liberation of an electron provides an explanation for the observed increase in intensity of the decay curve in the temperature range from ? 168 K to 185 K. The remaining fraction, 30 ～ 40%, of the total methyl radicals was produced from the PP matrix by an energy transfer from the excited T₄MPD¹ to the PP matrix. The broad singlet which appeared in the temperature range near 195 K was attributed to an acyl radical ～CH₂CH(CH₃)CH₂?O from the observed g-value. By photoillumination of this sample this broad singlet was converted reversibly into the quartet which was assigned to the radical ～CH₂CH(CH₂·)CH₂CHO.     

Photophysical properties and photoreduction of N-acetyl- and N-benzoylphthalimides

The photophysical properties and photoreduction of N-acetylphthalimide (AcP) and N-benzoylphthalimide (BzP), N-3,4,5-trimethoxybenzoylphthalimide (trimethoxyBzP) and N-4-nitrobenzoylphthalimide (nitroBzP) were studied by steady-state and transient techniques. Radicals and their precursor triplet states were detected by flash photolysis. The triplet state properties of AcP and BzP were characterized. In contrast, no triplet absorption was observed with ns-detection for trimethoxyBzP and nitroBzP. Specific products are formed upon electron transfer from triethylamine to the photoexcited acylphthalimides. In addition, H-atom transfer from 2-propanol or other alcohols to the triplet state takes place. The properties of several radical intermediates involved in photoreduction of the acylphthalimides as well as some structure-function relationships are described.     

Asymmetric radical cyclization reactions of axially chiral N-allyl-o-iodoanilides to form enantioenriched N-acyl dihydroindoles

Radical cyclizations of enantiomerically enriched N-allyl-o-iodoanilides provide N-acyl-3-alkyl-2,3-dihydroindoles in good yields and with good to excellent levels of chirality transfer from the N-Ar axis to the new stereocenter. In competitive cyclizations of N-acryloyl-N-allyl-o-iodoanilides, the addition of an o-methyl group reverses the regioselectivity of the radical cyclization from the acryloyl group to the allyl group. Approximate rate constants for representative radical cyclizations have been measured to provide insight into the origin of these observations.     

Preparation of 2-azaallyl anions and imines from N-chloroamines and their cycloaddition and allylation

Exposure of N-chloroamines to KO^tBu or LDA, in the presence of PMDETA or HMPA, provides 2-azaallyl anions capable of π4s + π2s cycloaddition reactions with a range of olefins. Good yields were achieved with stabilised systems, however, they were more modest when accessing semi-stabilised 2-azaallyl anions. By modifying the reaction conditions, one-pot dehydrochlorination/allylation can also be achieved with a range of N-chloroamines.     

Preparation of some N-substituted N-(triphenylstannyl)cyanamides

Nine N-substituted N-(triphenylstannyl)cyanamides were prepared by allowing bis(triphenylstannyl)carbodiimide to react separately with acid chlorides, trifluoroacetic anhydride, alkyl chlorocarbonates, and benzenesulfonyl chloride. The tin in these compounds was shown to have a coordination number greater than four be means of IR and Mössbauer spectroscopy.     

Convenient synthesis and anion recognition properties of N-flurobenzoyl-N′-phenylthioureas in water-containing media

Novel artificial anionic receptors N-flurobenzoyl-N′-phenylthioureas were synthesized by simple steps in good yields. The binding properties for anions of these N-flurobenzoyl-N′-phenylthioureas and 2N-benzoyl-N′-phenyl thiourea were examined by UV-vis and ¹H NMR spectroscopy. By fluorination of the benzoyl chromophore, the receptors had higher binding affinity for tested anions than the receptor 2. Especially, we studied the anion binding efficiency of the receptors 1N-(3-flurobenzoyl)-N′-phenylthiourea and 2 in dimethyl and dimethyl sulfoxide-water binary solutions in detail respectively. In pure dimethyl sulfoxide, the receptors 1 and 2 had higher binding affinity for F⁻ over AcO⁻. However, as the ratio of water to dimethyl sulfoxide increases, we found the binding properties for tested anions of 1 and 2 changed in dimethyl sulfoxide-water binary solutions. The receptor 1 showed high binding affinity and selective ability for AcO⁻ in dimethyl sulfoxide containing water with varied ratios.     

Anodic cyclization reactions: probing the chemistry of N,O-ketene acetal derived radical cations

The chemical reactivity of radical cations derived from N,O-ketene acetals has been examined and compared with the reactivity of radical cations derived from both ketene dithioacetals and enol ethers. Synthetically, the N,O-ketene acetal radical cations lead to more efficient cyclization reactions than either the ketene dithioacetal or enol ether derived radical cations. Cyclic voltammetry experiments using allylsilane trapping groups show that the efficiency of these cyclizations is not due to the N,O-ketene acetal radical cations being more reactive but rather more stable to decomposition. Finally, cyclizations using chiral oxizolidinones were examined.     

Direct conversion of epoxides into aziridines with N-arylphosphoramidates

Treatment of terminal epoxides with N-arylphosphoramidate anions leads directly to N-aryl aziridines. Existing methods for this transformation employ either multi-step syntheses or an iminophosphorane in conjunction with a Lewis acid. The described method therefore presents an advantage in terms of brevity and atom economy.     

Stereocontrol in hydride addition to ketone-derived chiral N-acylhydrazones

Chiral N-acylhydrazones derived from various aldehydes and N-amino-4-benzyl-2-oxazolidinone have previously been shown to be effective for acyclic stereocontrol of intermolecular radical and allylsilane additions. Treatment of the propionaldehyde hydrazone with tributyltin hydride in the presence of boron trifluoride etherate led to rapid chemoselective reduction of the imine bond in high yield. Preparation of similar hydrazones from ketones led to E/Z isomer mixtures, usually in ratios of 4:1 or greater. Geometry of the CN bond was assigned by steric compression shifts in ¹³C NMR spectra. Reduction with tributyltin hydride and boron trifluoride etherate afforded diastereomer mixtures in ratios very similar to the original E/Z isomer ratios. The chiral auxiliary blocked the opposite face of the CN bond relative to a related process using a chelated Lewis acid. A stereocontrol model involving monodentate interaction of the N-acylhydrazone and boron trifluoride is consistent with the observed stereochemical outcome.     

Synthesis of 1,3-bis(N,N-difluoroamino)adamantane: addition of difluoramino radicals to 1,3-dehydroadamantane

1,3-Dehydroadamantane undergoes a facile reaction with tetrafluorohydrazine to give 1,3-bis(N,N-difluoroamino)adamantane, the product of 1,3-NF₂ radical addition.     

Recent progress in controlled radical polymerization of N-vinyl monomers

This review summarizes recent advances in the controlled radical polymerization of N-vinyl monomers, such as N-vinylcarbazole, N-vinylindole derivatives, N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylformamide, N-vinylacetoamide derivatives, N-vinyl(na)phthalimides, N-vinylimidazolium salts, and N-vinyltriazoles. Recent significant progress of controlled radical polymerization of these N-vinyl monomers has allowed for the synthesis of well-defined functional polymers having various architectures, including block copolymers, branched polymers (stars, star block copolymers, miktoarm star copolymers, and graft copolymers), and hybrids. Characteristic properties, assembled structures, and three-dimensional architectures of these functional polymers derived from N-vinyl monomers are briefly introduced.     

Carbon radical addition to N-sulfonylimines mediated by triethylborane or zinc

The utility of N-sulfonylimines as radical acceptors was investigated under the different reaction conditions such as the stannyl radical-mediated addition reaction, the triethylborane-mediated tin-free radical reaction, and the zinc-mediated aqueous-medium radical reaction. The alkyl radical addition reaction of N-sulfonylimines proceeded effectively without the activation by Lewis acid. These reactions were successfully extended to one-pot reactions for preparing a wide range of amine derivatives.     

A study on the reaction between N-substituted p-phenylenediamines and ozone: experimental results and theoretical aspects in relation to their antiozonant activity

The following p-phenylenediamines (PPD): N,N,N^′,N^′-tetramethyl-p-phenylenediamine (TMPPD), N,N^′-dimethylbutyl-p-phenylenediamine (6PPD), N,N^′-diaryl-p-phenylenediamine (DPPD), tris-(N-dimethylpentyl-p-phenylenediamine)-N^′,N^′,N^′-1,3,5-triazine (6PPDTZ), have been oxidized under the action of O₃ in diluted solutions. In all cases the radical cation or semiquinone radical was the first derivative formed by monoelectronic oxidation of the substrate. The radical cation has been studied by electronic spectroscopy and the electronic spectral changes of all mentioned PPD has been followed as function of the ozonation time. The results have been discussed in the frame of the antiozonant properties of these PPD which are used as antiozonant agents in diene rubber protection. It is shown that the antiozonant activity of each PPD considered correlates with the free enthalpy of formation of the respective radical cation. The lowest is the free energy of formation of a PPD radical cation and the highest is the antiozonant activity in a diene rubber compound.     

New fused dithiabicyclic compounds from the reaction of N,N-dialkyl perfluorothioamides with allylmagnesium halides

Allylmagnesium reagents react with N,N-dialkylperfluorothioamide to give, at low temperature, an adduct stable enough to be trapped. At room temperature, this adduct can evolve by elimination of either a sulfide salt, leading to an iminium intermediate, and then an N,N-dialkyl-α,α-bis(allyl)-α-perfluoroalkylamine. This process is favoured if an excess of allyl magnesium is used. Alternatively, the adduct eliminates an aminyl moiety giving allyl(perfluoroalkyl)thioketone which is converted in situ into an unprecedented fused bis(perfluoroalkyl) bis(dihydrothiopyrane). A sequence deprotonation of the thioketone - oxidation of the resulting dienethiolate - dimerization of the dienethiyl radical is proposed to rationalize the formation of this unexpected bicyclic compound.     

Facile cyclization of amidyl radicals generated from N-acyltriazenes

N-Acyltriazenes serve as a tin-free and initiator-free source for amidyl radicals. Thermal decomposition of N,N′-diaryl-N-(4-pentenoyl)triazenes in refluxing toluene led to the formation of monocyclic and tricyclic lactams in satisfactory yields via 5-exo amidyl radical cyclization.     

Copolymerizations of N-arylmaleamic acids with styrene and butadiene

N-(3-Dimethylamino-6-methylphenyl)maleamic (I) and N-(2,4,6-trimethylphenyl)maleamic (II) acids were prepared; their radical copolymerizations with styrene and butadiene were investigated. The monomer reactivity ratios were determined and the Alfrey-Price copolymerization constants (e, Q) were calculated. The ratio of the average kinetic chain length to the number-average degree of polymerization indicates pronounced chain transfer to I and II. Inhibitors of radical polymerization stopped the copolymerizations of I and II with styrene but not those with butadiene.