Preparation of poly(methyl methacrylate) in the presence of ferrocenyl-containing Fe(II) semi- and clathrochelates

The effect of ferrocenyl-containing semi- and clathrochelates on radical polymerization of methyl methacrylate, initiated by benzoyl peroxide, and on molecular characteristics of the polymer formed was examined.     

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.     

Assembly and packing models of [Ti6Co12] ring based on the titanium-capped cobalt clathrochelates

In this work, titanium-capped cobalt clathrochelates have been applied as secondary building units (SBUs) for the construction of supramolecular rings. Two heterometallic wheel-like [Ti₆Co₁₂] complexes based on cobalt clathrochelates, [C₆H₁₅N₄]₂[TiCo₂(μ₂-Oipr)(Oipr)₂(Dmg)₃]₆ (2, Dmg = dimethylglyoxime) and H₆[TiCo₂(μ₂-Oipr)(Oipr)₂(Dmg)₃]₆ (3), have been successfully synthesized and characterized. The supramolecular stacking modes of these wheels are largely dependent on the applied synthetic conditions, which further impact their gas adsorption properties.     

Visible-light-mediated selective thiocyanation/ipso-cyclization/oxidation cascade for the synthesis of thiocyanato-containing azaspirotrienediones

A visible-light-mediated metal-free thiocyanate radical addition/ipso-cyclization/oxidation cascade reaction for the synthesis of thiocyanato-containing azaspirotrienediones from N-phenylpropynamides is described. Cheap and readily available ammonium thiocyanate was used as a precursor to the thiocyanate free radical, which undergoes a radical addition reaction with the alkyne, followed by selective ipso-cyclization and oxidation to afford the dearomatized products. No product of ortho-cyclization was detected. The reaction completes the synthesis of C–S, C–C, and CO bonds in one pot, with abundant and renewable air oxygen as the sole sacrificial reagent and oxygen source.     

A calculation of thermal degradation initiated by random scission,unsteady radical concentration

Changes in molecular weight distribution and in sample volume were calculated for thermal degradation of a polymer. The thermal degradation scheme consists of random scission initiation, depropagation and disproportionation termination reactions. An unsteady radical concentration was considered. There are two parameters, normalized zip length z/x₀ and radical number per initial chain length z′x₀, describing the thermal degradation scheme with an unsteady radical concentration. The effects of the initial number-average molecular weight and order of the disproportionation termination reaction on changes in molecular weight, the sample volume and polydispersity are not significant as long as these two parameters have the same value for each polymer sample. Molecular weights of a degrading sample calculated from the steady state radical concentration tend to be over-estimated and sample volumes tend to be underestimated compared to those calculated with an unsteady radical concentration. The validity of approximations used in the calculation assuming a steady state radical concentration is examined by comparing with results calculated with an unsteady radical concentration for various values of the two parameters. An unrealistically large build-up of monomer radicals is found for both calculations based on the steady state and the unsteady radical concentrations. Two special treatments of monomer radicals can dissipate the build-up of monomer radicals: (1) their immediate vaporization, or (2) an enhanced rate of the termination reaction for the monomer radicals. As a guide, the model based on an unsteady radical concentration is preferred, if the value of z′x₀ exceeds 0.1.     

Reductive polymerization of Para-cyanobenzaldehyde in dimethyl sulfoxide solutions using the rotating ring-disk electrode technique

The rotating ring-disk electrode (RRDE) technique has been employed to study the reductive polymerization mechanism of para-cyanobenzaldehyde (CBA) in dimethyl sulfoxide (DMSO) solutions. The radical anion of CBA underwent polymerization through two different reaction routes. They were found to be the successive parent molecule addition to the radical anion reactions and the dimerization of the radical anion followed by parent molecule additions. Digital simulation methods were employed to simulate the mechanism and to obtain the second-order reaction rate constants of the radical anions from collection efficiency measurements. The reaction rate constants were found to be 1.45 M^?1 s^?1 for reactions of the radical anion with the parent molecules, and 28.6 M^?1 s^?1 for dimerization of the radical anion followed by trapping a parent molecule immediately after the dimeric dianion is generated.     

Zirconocene-catalyzed alkylative dimerization of 2-methylene-1,3-dithiane via a single electron transfer process to provide symmetrical vic-bis(dithiane)s

A mixture of tertiary alkyl halide and 2-methylene-1,3-dithiane was treated with butylmagnesium bromide in the presence of a catalytic amount of zirconocene dichloride. The reaction resulted in alkylative dimerization to yield the corresponding vic-bis(dithiane). The reaction would proceed as follows. A single electron transfer from low-valent zirconocene to alkyl halide would generate the corresponding alkyl radical. The radical adds to 2-methylene-1,3-dithiane to afford the corresponding radical stabilized by the two sulfur atoms. A couple of the stable radicals finally undergo dimerization.     

2,3-Diarylquinoxaline directed mono ortho-aroylation via cross-dehydrogenative coupling using aromatic aldehydes or alkylbenzenes as aroyl surrogate

2,3-Diarylquinoxaline directed mono ortho-aroylation protocol has been developed using aromatic aldehydes or alkybenzenes as aroyl surrogates. Out of the four available ortho sp² C–H bonds in the two aryl rings of 2,3-diarylquinoxaline one of the C–H bond is selectively ortho-aroylated. The reaction proceeds via the aroyl radical path in the case of aromatic aldehydes while the alkylbenzenes follow either an aroyl radical or a benzyl radical path. Varieties of functional groups present as substituents in 2,3-diarylquinoxalines, aromatic aldehydes and alkylbenzenes are tolerated under the present reaction conditions.     

Development of radical addition-cyclization-elimination reaction of oxime ether and its application to formal synthesis of (±)-martinelline

Radical addition-cyclization-elimination (RACE) reaction of oxime ether carrying unsaturated ester provides a novel method for the construction of pyrroloquinoline. Treatment of oxime ethers with Bu₃SnH and AIBN gave N-norpyrroloquinoline as a major product, which was also obtained by the radical reaction of the corresponding hydrazone and imine. The radical reaction of aldehyde and ketone carrying unsaturated ester proceeded stereoselectively to give cis-furoquinolines and cis-hydroxyesters. The RACE reactions by using each of Bu₃SnNMe₂, Bu₃SnD, and/or D₂O were also examined in order to propose a reaction pathway to N-norpyrroloquinoline. Furthermore, the synthetic utility of RACE reaction is demonstrated by preparation of a key intermediate for the synthesis of (±)-martinelline.     

Unusual spin-trap chemistry for the reaction of hydroxyl radical with the carcinogen N-nitrosodimethylamine

The reaction of the potent carcinogen N-nitrosodimethylamine (NDMA) with hydroxyl radical generated via radiolysis was studied using EPR techniques. Attempts to spin trap NDMA radical intermediates with 3,5-dibromo-4-nitrosobenzene sulfonate (DBNBS) produced only unusual DBNBS radicals. One of these radicals was shown to be generated by both reaction of DBNBS with nitric oxide, and direct oxidation of DBNBS with an inorganic oxidant (^.Br^-₂). Another DBNBS radical was identified as a sulfite spin adduct resulting from the degradation of DBNBS by a NDMA reactive intermediate. In the absence of DBNBS, hydroxyl radical reaction with NDMA gave the dimethylnitroxide radical. Unexpectedly, addition of DBNBS to a solution containing dimethylnitroxide produced an EPR spectrum nearly identical to that of NDMA solutions with DBNBS added before radiolysis. A proposed mechanism accounting for these observations is presented.     

The solvent effect on the reaction constants of tert-butyl radical addition to 2-substituted allyl chlorides

The ρ values of free radical S_H2′ reactions have been determined in various solvents. The correlation of Hammett ρ with Taft's π* gives a W value of 0.70. The W value is a measure of susceptibility of the reaction constant to change in solvent polarity. However, the W value is 2.64 in the dissociation reactions of substituted benzoic acids. The free radical reactions are less susceptible to the solvent effect than ionic reactions and this could be rationalized in terms of the partial charge formed in the transition state of free radical reaction is less than that of heterolytic reaction. The ρ values in S_H2′ reactions might not reflect truly the partial charge separation at transition state, however, it might be a measure of the susceptibility of the reaction to the electronic effect of the substituents.     

The oxidation of the alpha-carbon of amines in hydrothermal condition: an alternative synthetic route of compounds containing amide bond

Here we report experimental evidence for the simple synthesis of N,N-diethylhydroxylamine and an amide bond formation reaction from oxidation of the alpha-carbon of tertiary amines by the reaction of triethylamine and hydrogen peroxide in hydrothermal conditions. It is proved that 120 °C is a turning point: when the temperature is lower than that, the main product is N,N-diethylhydroxylamine as a result of a cope rearrangement reaction mechanism; on the contrary, the product is more complex and the main products are amides via a radical chain mechanism involving three steps: initiation, propagation, and oxidation, followed by decarbonylation and electrocyclization because the radical is easier to form under high temperature.     

Radical oxyamination of vinyl azides with N-hydroxyphthalimide under the action of [bis(trifluoroacetoxy)iodo]benzene

O,O′-Bis(phthalimido)-modified 2-(hydroxyimino)ethanols containing N–O–N fragment were synthesized in high yields via the reaction of vinyl azides with N-hydroxyphthalimide under the action of hypervalent iodine-based oxidant. The reaction proceeds under mild conditions and is compatible with a wide range of vinyl azides. Presumably, the process starts with the oxidative formation of phthalimide-N-oxyl radical, followed by its addition to vinyl azide with the subsequent trapping of the generated iminyl radical with the second phthalimide-N-oxyl radical.     

Regioselective alkylation of 3,4-dihydro-2H-pyran by xanthate-mediated free radical nonchain process

An intermolecular xanthate-mediated free radical nonchain addition reaction is introduced for the regioselective alkylation of 3,4-dihydro-2H-pyran. Additionally, we observed that the free radical nonchain reaction depends on the nature of the radical precursor.     

Photochemical and radical initiator-induced reaction of allylic indium compounds

Intramolecular cyclization of allylic radicals generated from allylindium compounds both by photolysis or by the reaction of radical initiators was examined. The photolysis of allylic indium compounds, prepared from 8-bromo- or 8-iodooct-1,6-dienes and powdered indium metal, led to the formation of the 5-exo-trig products. Benzoyl peroxide as a radical initiator was also effective for the cyclization. In contrast, the radical initiators with oxidizing nature, such as tert-butyl hypochlorite, induced iodocyclization producing iodomethylcyclopentane via an oxidation of the iodide on the indium atom.     

Alkyl radical cyclization to vinylogous carbonates for the stereoselective synthesis of unsymmetrical dioxa-cage compounds: effect of conformation on the rate of cyclization versus reduction

An efficient strategy for the stereoselective construction of unsymmetrical dioxa-cage compounds containing ether linkages employing a 6-exo-trig alkyl radical cyclization to vinylogous carbonates is developed. The radical precursors are prepared from the diols obtained from the Diels-Alder adducts via iodoetherification followed by addition of the alcohol to the ethyl propiolate. The geometrical constrains play important role in deciding the outcome of the reaction as cyclization versus simple reduction. Formation of the mono-oxa-cage compounds via a 5-exo-trig intramolecular alkyl radical cyclization to olefin is also described. The dioxa-cages could also be assembled employing a tandem oxymercuration reduction-radical cyclization to vinylogous carbonates protocol with equal efficiency and with reduced number of steps.     

Synthesis and structure of the first clathrochelate iron(II) tris-dioximates with inherent nitrile substituent(s) and new dehalogenation--reduction reaction at a quasi-aromatic macrobicyclic framework

Monoribbed-substituted mono- and dicyano-functionalized iron(II) macrobicycles were obtained for the first time by the reaction of iron(II) diiodoclathrochelate precursor with copper(I) cyanide-triphenylphosphine complex under mild conditions. The target dinitrile clathrochelate is a minor product of this reaction, whereas the major product contains only one cyano group. The clathrochelates obtained were characterized using elemental analysis, (1)H and (13)C{(1)H} NMR, IR and UV-vis spectroscopy, MALDI-TOF spectrometry and X-ray diffraction crystallography. The geometry of their FeN(6)-coordination polyhedra is intermediate between a trigonal prism (TP) and a trigonal antiprism (TAP); the distortion angles, φ, are 22.6-24.7°. In the molecule of the precursor, the Fe-N distances are close, whereas in the mononitrile macrobicycles those for their functionalized chelate fragments are substantially smaller than the corresponding distances in the α-benzyldioximate moieties. The heights, h, of the TP-TAP coordination polyhedra and the average bite angles, α, (2.33 ? and 39°, respectively) are the same for the X-rayed clathrochelates. The UV-vis spectra indicate a dramatic redistribution of the electron density in the π-conjugated clathrochelate framework caused by functionalization with inherent nitrile substituents. The proposed mechanism of the dehalogenation-reduction reaction of iron(II) diiodoclathrochelate resulting in substitution of their iodine atoms by a cyano group and hydrogen atom includes the anion-radical hydrodehalogenation of this precursor with acetonitrile as a source of hydrogen atom. Then, the monomethinemonoiodine macrobicyclic product underwent a substitution with a cyano group only. The copper(I) cyanide-triphenylphosphine-acetonitrile system is proposed as a tool for the synthesis of nitrile derivatives of electron-withdrawing heterocycles starting from their halogen-containing precursors.     

TBAB-mediated radical 6-endo-trig ortho-cyclization of N-aryl-N-(prop-2-yn-1-yl)benzenesulfonamide for the synthesis of 3-bromo-1,2-dihydroquinoline

In this work, we described a new synthetic route of 3-bromo-1,2-dihydroquinoline derivatives based on the TBAB/Oxone-mediated radical 6-endo-trig ortho-cyclization of 2-alkynylbenzamide. The reaction proceeded smoothly with moderate functional group tolerance and high reaction efficiency. It is believed that radical addition, 6-endo-dig cyclization, and oxidation are all involved in the reaction processes. Furthermore, we successfully demonstrated the usability of these derivatives in further functionalization.     

Structural chemistry of complexes with an encapsulated metal ion. α-Dioximate,oximehydrazonate, and dihydrazonate clathrochelates

The review surveys the main trends in the structural chemistry of clathrochelates: the determination of the crystal and molecular structures of various types of new complexes, their symmetry and functionality; the supramolecular organization and phase transitions of clathrochelate crystals; the structure—spectral parameter relationships and the deduction of the molecular structures; the use of X-ray diffraction data for explanation of the kinetic and thermodynamic parameters of the synthesis and decomposition of clathrochelates.Hereinafter, the papers marked with an asterisk ✾ are dedicated to Academician Yurii Nikolaevich Bubnov on the occasion of his 70th birthday.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2009–2020, October, 2004.     

Rate constants and arrhenius function for scavenging of octyl radical by an N-hydroxypyridine-2-thione ester

Rate constants for reactions of octyl radical with its N-hydroxypyridine-2-thione ester precursor were determined using the reduction of octyl radical by n-Bu₃SnH as a competition reaction.