R. G. Gasanov

Stereoselective radical addition of carbon-centred radicals to the dehydroalanine moiety of the chiral nickel(II) complex of the Schiff′s base derived from (S)-2-[N-(N′-benzylprolyl)amino]benzophenone and dehydroalanine

A new approach to the asymmetric synthesis of β-substituted α-aminopropanoic acids by 2,2′-azoisobutyronitrile (AIBN) and Bu3SnH-initiated radical addition of Etl, PriBr, ButBr, and PhCH2Br to the dehydroalanine moiety of the NiII complex 1 of a Schiff′s base derived from (S)-o-[N-(N′-benzylprolyl)amino]benzophenone (BPB) and dehydroalanine is described. The radical addition produced a mixture of diastereoisomeric complexes 4a–d with a 40–90% excess of (S,S)diastereoisomers over the (S,R)-ones, giving the reaction products in almost quantitative yields. The diastereoselectivity of the reaction depended on the size of the entering radicals, the most effective asymmetric induction being achieved for the But radical addition. Enantiomerically pure ‘(S)-2-amino3-(tert-butyl)propanoic acid’[(S)-γ-methylleucine] and the chiral auxiliary BPB were recovered from compound 4d after its decomposition with HCl. The reactivities of the carbon–centred radicals towards the carbon-carbon double bond in the amino acid moiety of the complex 1 was quantitatively established by using ESR spectroscopy in the spin-trap technique.

Copolymers Obtained by ε-Caprolactam and Methyl Methacrylate Polymerization in the Presence of Polyimides

New copolymers have been synthesized by anionic or radical photopolymerization of ε-caprolactam or methyl methacrylate (MMA) in the presence of dissolved polyimides bearing hexafluoroisopropylidene, fluorene or other groups. Using diimides as models it was shown that the kinetics of anionic polymerization of ε-caprolactam depends on the nature of spacer between the imide cycles. The mechanical and tribological properties of copolymers, their water absorbance and the microstructure of copolymer films were studied. It was found that upon the selection of polyimide activator it was possible to gain the desirable control over the polymer properties, namely, the gel fraction content, phase composition, compression modulus, notched Izod impact strength, friction coefficient and temperature of frictional contact. The kinetics of radical polymerization of MMA in the presence of polyimide and model diimide has been studied by differential scanning photocalorimetry and infrared spectroscopy. From the results of the reaction kinetics and the study of polymer structures by Fourier transform infrared spectroscopy, nuclear magnetic resonance, size-exclusion chromatography and thermogravimetric analysis it has been established that radical photopolymerization of MMA in the presence of polyimide leads to the formation of copolymers owing to chain transfer reactions and/or chain termination by the relevant condensation polymer. It has been established that the imide cycles play a significant role in the formation of both copolymers with ε-caprolactam and MMA, respectively.

Addition of carbon-centered radicals to C60. Determination of the rate constants by the spin trap method

The rate constants of addition of the.CMe3,.CH2Me,.CH2(CH2)3Me,.CH2Ph,.CH2CH=CH2, and.CH(Me)Et radicals to fullerene C60 were determined by the method of competitive addition of free radicals to spin traps.

Homolytic Reactive Mass Spectrometry of Fullerenes: Interaction of C60 and C70 with Ketones in the Electron Impact Ion Source of a Mass Spectrometer and the Comparison of Results with Those of Photochemical Reactions of C60 with Several Ketones in Solution

Our previous investigations showed that homolytic reactions of C60 with a number of perfluoroorganic and organomercury(II) compounds occurring under electron impact (EI) in the ionization chamber (IC) of a mass spectrometer could predict the reactivity of C60 towards these compounds in solution or solid state. To expand the scope of this statement, C60 and C70 have been reacted with ketones RCOR1, where R and R1 are alkyl, aryl, benzyl, and CF3, in an IC under EI to yield products of the addition of R· and R1· radicals to the fullerenes, paramagnetic ones being stabilized by hydrogen addition and loss. Experimental evidence in support of a mechanism involving homolytic dissociation of ketone molecules via superexcited states to afford these radicals that react with the fullerenes at the IC surface has been obtained. As anticipated, the reactions between C60 and several ketones conducted in solution under UV irradiation have afforded Me-, Ph-, and CF3-derivatives of C60. However, some other products have been identified by mass spectrometry and their formation is reasonably explained. When decalin has been employed as a solvent, decalinyl derivatives of the fullerene have been found among the products and the (9-decalinyl)fullerenyl radical has been registered by EPR. Thus, incomplete but reasonable conformity of the results of the reactions of fullerenes with ketones in an IC under EI with those of the reactions of the same reagents in solution under UV irradiation has been demonstrated, and the former results can predict the latter ones to a reasonable extent.

Addition of Me2·CCN, Me2·CPh, and CCl3CH2·CHPh radicals to fullerene C60

The rate constants for addition of the Me2·CCN, Me2·CPh, and CCl3CH2·CHPh radicals to fullerene C60 at 22 °C were determined by ESR spectroscopy using spin trapping technique.

A Comparative Study of Homolytic Reactions of Fullerenes with Aldehydes in a Mass Spectrometer under Electron Impact and in Solution under UV Irradiation

C60 was reacted in the ionization chamber of a mass spectrometer under electron impact (EI) with aldehydes, RCHO (R = Ph, p-FC6H4, F5C6, p-MeOC6H4, α-thienyl, o-HOC6H4, o-BrC6H4, m-BrC6H4 and t-Bu), with the transfer of R• radicals and with Me•-transfer from i-PrCHO and t-BuCHO. Paramagnetic fullerene derivatives were stabilized by the addition of the next R• radical or a hydrogen atom, or hydrogen or bromine atom loss. A detailed study showed that the reaction between C60 and PhCHO occurred via a homolytic mechanism that matches one reported earlier for the reaction with acetone. This suggests the generality of the mechanism for the reactions of fullerenes with other species in ionization chambers under EI at ca 300°C. All aldehydes, except one, had radicals at the carbonyl group which were different from those in the ketones examined earlier in the reactions. This expanded the variety of radicals which can be transferred to fullerenes during reactions in ionization chambers under EI. Due to this and the hydrogen atom at the CO group of aldehydes, some reactions occurred that were not found for the ketones: the formation of cyclic products C60COC6H4 and C60OC6H4 for PhCHO, o-BrC6H4CHO and o-HOC6H4CHO, respectively, and HC60Ph for o- and m-BrC6H4CHO. The reaction with α-formylthiophen gives the first example of transferring an aromatic heterocyclic radical to C60 in an ionization chamber under EI. C70 reacted with PhCHO, p-FC6H4CHO and i-PrCHO similarly to C60. The results for the reactions of C60 with PhCHO and with i-PrCHO were compared with those in solution under UV irradiation. Incomplete but reasonable coincidence was found; in both modes, the addition of Ph•, PhCO• and Me• radicals to C60 occurred, whereas some other products were formed in solution and the explanation is given as to why this occurred. This conformity sup ports the hypothesis based on the results of kindred reactions with ketones and organomercurials: the results of EI-initiated homolytic reactions between fullerenes and other compounds in an ionization chamber can predict the reactivity of the fullerenes toward them in solution.

Copolymers Formation by Photopolymerization of (Meth)acrylates Containing Dissolved Polyheteroarylenes

Radical photopolymerization of (meth)acrylates in the presence of dissolved polyheteroarylenes has been investigated. The kinetics of radical polymerization of unsaturated monomers in the presence of polyheteroarylenes and model compounds has been studied by Differential Scanning Photocalorimetry and Infrared Spectroscopy. From the results of investigations into the kinetics and the polymer structures (Fourier Transform Infrared Spectroscopy, Nuclear Magnetic Resonance, Size-exclusion Chromatography, Thermogravimetric analysis), it has been established that radical photopolymerization of vinyl monomers in the presence of polyheteroarylenes leads to the formation of copolymers owing to chain transfer reactions and/or chain termination by the relevant condensation polymer. Using Electron Spin Resonance Spectroscopy the novel radicals upon the addition of model compounds for the polyheteroarylenes have been detected, and a mechanism of copolymer formation has been proposed.

Radical arylation of thiosemicarbazide and acetone thiosemicarbazone by aryldiazonium borofluorides

Conclusions1.The homolytic arylation of thiosemicarbazide and acetone thiosemicarbazone with phenyldiazonium borofluoride in the presence of CuCl2·2H2O and with p-nitrophenyldiazonium borofluoride in absence of the copper salt forms S-arylisothiosemicarbazide and its derivatives.2.The radical mechanism of arylation by p-nitrophenyldiazonium borofluoride was demonstrated by ESR.

An ESR and spin-trap study of the interaction of acyl peroxides with tetrahalomethanes in the presence of iron compounds

Conclusions1.ESR and spin-trap methods have been used to show that the interaction of Fe(CO)5 or Fe(C5H5)2 with peroxides leads to the formation of acyloxy radicals. Carried out in CCl4, these reactions lead to the formation of both acyloxy and.CC13 radicals. Initiated by the Fe(CO)5 or Fe(C5H5)2+benzoyl peroxide systems, the reaction of BrCCl3 with α-olefins lead to the formation of.CCl3 radicals and adducts of these radicals with the olefin: CCl3CH2.CHR1, where R1=C4H9, C6H13. Initiated by the iron compound + acyl peroxide system, tetrahalomethane addition to olefins proceeds through a radical chain mechanism, chain propagation being through the.CCl3 radicals.2.Spin adducts of α-phenyl-N-tert-butylnitron with acyloxy and.CCl3 radicals, and 2-methyl-2-nitrosopropane with.CCl3 and CCl3CH2CHR (R is an alkyl) radicals, have been identified.

A spin-trap ESR study of the regrouping of radicals with 1,3 or 1,5 hydrogen migration

Spin-trap (2-methyl-2-nitrosopropane) ESR methods have been used to demonstrate the formation of R1O2CĊR2CH2CH2C6H13 (R1=H, CH3 and R2=Cl, CH3) radicals during the photoinitiated reaction (λ ∼ 2537 A) of 1-octene with BrCHClCOOH and CH3CHBrCOOCH3 in the presence of tert-outyl peroxide and (C3H5)3SiH. Formation of these radicals indicates regrouping of the R1O2CCHR2CH2ĊHC6H13 radical with 1,3 H atom migraion and, possibly, regrouping of the R1O2CCHR2CH2CH(C6H13)CH2CHC6H13 radical with 1,5 H atom migration.