An efficient one-step synthesis of fulleroisoxazolines and fulleropyrazolines mediated by (diacetoxyiodo)benzene

An efficient one-step strategy for the synthesis of fulleroisoxazolines/fulleropyrazolines from fullerene and aldoximes/hydrazones mediated by PhI(OAc)₂ has been described.     

A new look at reactions of 2-butoxy and 1-butoxy radicals in the presence of oxygen

Under atmospheric conditions, experiments show that 2-butoxy radicals in the presence of oxygen yield acetaldehyde and butanone such that the concentration ratio [acetaldehyde] [O2]/[butanone] shows a linear dependence on oxygen concentration [O2]. [Zabel et al., Phys. Chem. Chem. Phys., 2002, 4, 2579; Cox et al.Phys. Chem. Chem. Phys, 2005, 7, 3702.] A similar oxygen dependence was found by Cox et al. in the reactions of 1-butoxy radicals. These experiments imply a unimolecular rate constant that apparently depends on oxygen pressure. Previously this has been explained by postulating the presence of a small amount of excited radicals assumed to undergo 'prompt' dissociation. We propose an alternative interpretation based on the solution of the time-dependent master equation that does not require the putative presence of excited radicals. We do this by allowing the time to run until the so-called long-time steady-state, and then show that the oxygen dependence arises quite naturally if the transport matrix takes into account that in addition to the principal reaction channel (dissociation into acetaldehyde in the case of 2-butoxy and isomerization in the case of 1-butoxy), there is a small "leak" of alkoxy radicals due to the reaction with oxygen, and provided the calculation takes into account that in the cited experiments there is a continuous incoming flux of butoxy radicals.     

The reactions of C2F5 radicals with benzene in the vapor phase

C₂F₅ radicals were generated in the presence of benzene vapor by the reaction The radicals react with the benzene by addition and pseudo H abstraction The rate constant k_add for the addition reaction (7) is given by where θ = 2.303RT cal/mole and k_c is the rate constant for combination of C₂F₅ radicals. The addition becomes reversible above 110°C. The reactions of CF₃ and C₂F₅ radicals with benzene vapor are compared.     

Kinetics of gas-phase addition reactions of methyl radicals. I. Addition to ethylene,acetylene, and benzene

The reactions have been studied by a mass-balance method involving the photolysis of small amounts of biacetyl in the presence of a large excess of isobutane containing a small proportion of the unsaturated substrate. The following Arrhenius parameters have been derived:

A possible common intermediate in the motochemical reactions of benzene

The benzene nucleus is known to undergo photochemical reactions of different types. In the present report it is suggested that all these reactions may involve one common highly reactive intermediate different from the known excited singlet and triplet states. For this common intermediate a Möbius-type structure is proposed. The formation of valence tautomers is discussed employing elementary HMO.     

A novel combination of (diacetoxyiodo)benzene and tert-butylhydroperoxide for the facile oxidative dehydrogenation of 3,4-dihydropyrimidin-2(1H)-ones

A clean and efficient oxidative dehydrogenation of 3,4-dihydropyrimidin-2(1H)-ones to 1,2-dihydropyrimidines has been achieved through a novel combination of (diacetoxyiodo)benzene and tert-butylhydroperoxide in CH₂Cl₂.     

Intramolecular diels-alder reactions. XI. Modal selectivity in the syntheses of some parent cyclolignan lactones

Ph(C₂)CH₂Cl and Ph(C₂)'CO₂Na [where (C₂) = -C=C- or trans-CH=CH-, (C₂)' = -C=C- or cis-CH=CH-] reacted in refluxing dimethylformamide to yield unsaturated esters Ph(C₂)'CO₂-CH₂(C₂)Ph and/or their intramolecular Diels-Alder cyclization products (cyclolignan lactones). It was found that modal selectivity for cyclization in DMF sometimes varies from that found previously with acetic anhydride as solvent. Two new parent tetrahydrocyclolignan lactones were synthesized.     

Chemoselective oxidation and deprotection of para-methoxybenzylic position with (diacetoxyiodo)benzene in acetic-trifluoroacetic acid

(Diacetoxyiodo)benzene in the presence of acetic–trifluoroacetic acid in THF has been developed for the chemoselective para-methoxybenzylic CH bond oxidation to provide aryl carbonyl compounds at room temperature. The reaction condition is also applicable for the chemoselective deprotection of para-methoxybenzyl (PMB) ether in the presence of benzyl ether.     

Electron transfer. 123. Competitive redox reactions involving a Cobalt(I) intermediate

he hypophosphito derivative of Co^III, (NH₃)₅CoO₂PH₂ ²⁺, decomposes in basic media, yielding Co(II) quantitatively, along with a 1:1 mixture of hypophosphite and phosphite. Earlier studies point to a cobalt (I) intermediate, which rapidly reduces a second molecule of Co(III) reactant to Co(II). In the presence of an external cobalt (III) oxidant (Co³X), the latter competes with the hypophosphito complex for Co(I), lowering the yield of free hypophosphite. From the ratio of phosphorus products (P³/P¹), evaluated by proton decoupled ³¹P NMR, the relative reactivities (k_t/k_c) of the external Co(III) “traps” and the hypophosphito complex may be determined. A log-log plot comparing values of k_t/k_c with rates for reductions of the same series of Co(III) oxidants with Ru(NH₃)₆ ²⁺ (k_Ru values) is badly scattered with a slope of only 0.23, well below the value of unity stipulated by the Marcus model, indicating that an outer-sphere mechanism cannot operate for all of the Co(III)-Co(I) reactions and may not operate for any, except for that with Co(NH₃)₅(py)₃₊. Among the carboxylato-substituted oxidants, there are no rate enhancements by neighbouring pyridine, -SR,-OH, -CHO, or -SO₃H functions, in contrast to the accelerations previously observed for reductions by Cr(II), Eu(II) and Ti(III), which are attributed to intermediacy of chelate-stabilized precursor complexes. It is suggested that the Co(III)-Co(I) reactions, which determine the ratio of phosphorus products, are much more rapid than the ligand substitution at the Co(I) center which must precede chelate formation, and that the latter therefore does not intervene significantly in the redox processes.     

Photolysis of 2-mercaptobenzothiazole in the presence of surfactants

The quantum yield of the photolysis of 2-mercaptobenzothiazole (MBT) in the molecular form increases by a factor of 20 in the presence of the surfactants cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPCl) in comparison with aqueous solution. In the photolysis of the MBT ionic form, the quantum yield does not change in the presence of CTAB and decreases in the presence of CPCl. The maximums of the MBT absorption spectra shift with an increase in the surfactant concentration for both the molecular and ionic forms. Simultaneously, the MBT photolysis quantum yield increases. It has been shown that the quantum yield of MBT photolysis in water increases in the presence of compounds containing heavy atoms.     

Photochemical reactions of 1-methyl-4,6-diaryl-2(1H)-pyrimidinones in the presence of thiols

Photochemical reactions of 1-methyl-4,6-diaryl-2(1H)pyrimidinones 1a-b in the presence of thiols 2 are described. Irradiation of 1-methyl-4,6-diaryl-2(1H)-pyrimidinones 1a-b in benzene in the presence of thiols 2 gave the unexpected 2:1-adducts, 3-methyl-4,6-diaryl-5-aralkylthio-6-(1′-methyl-4′,6′-diaryldihydro-pyrimidin-2-on)yl-1,3-diazabicyclo[2.2.0]hexan-2-ones 3-6, of 1 and 2, whereas irradiation of 1a-b alone in benzene resulted in recovery of the unchanged 1a-b.     

Photolysis of ((3-(Trimethylsilyl)propoxy)phenyl)phenyliodonium salts in the presence of 1-naphthol and 1-methoxynaphthalene

Direct photolysis of ((3-trimethylsilylpropoxy)phenyl)phenyliodonium salts with different counteranions (Cl(-), SbF(6)(-), and B(C(6)F(5))(4)(-)) in methanol leads to products by both heterolytic and homolytic processes. In the presence of 1-naphthol and 1-methoxynaphthalene, products formed by a heterolytic reaction disappear, suggesting an electron-transfer process occurs between excited 1-naphthol/1-methoxynaphthalene and the iodonium salts. In the case of 1-methoxynaphthalene, three phenylated methoxynaphthalene isomers are produced. These are produced as radical coupling products from the phenyl radical and 1-methoxynaphthalene radical cation.     

Crosslinking reactions of 1,3,5-tris(2-methylaziridinyl-1-methyl)benzene (TRIMAM) with carboxyl terminated polybutadiene

Curing reactions of a new crosslinking agent, 1,3,5-tris(2-methylaziridinyl-1-methyl)benzene (TRIMAM) with carboxylterminated polybutadiene have been studied by dynamic differential thermal analysis and by IR spectroscopy. The crosslinking reactions are found to be faster for this new compound compared with the conventional tris-1-(2-methyl) axiridinyl phosphine oxide (MAPO).     

Structural effects on the beta-scission reaction of alkoxyl radicals. Direct measurement of the absolute rate constants for ring opening of benzocycloalken-1-oxyl radicals

[reaction: see text] The absolute rate constants for beta-scission of a series of benzocycloalken-1-oxyl radicals and of the 2-(4-methylphenyl)-2-butoxyl radical have been measured directly by laser flash photolysis. The benzocycloalken-1-oxyl radicals undergo ring opening with rates which parallel the ring strain of the corresponding cycloalkanes. In the 1-X-indan-1-oxyl radical series, ring opening is observed when X = H, Me, whereas exclusive C-X bond cleavage occurs when X = Et. The factors governing the fragmentation regioselectivity are discussed.     

Intramolecular rearrangement in diphenylfulvene complexes of iridium(I) and rhodium(I)

Variable temperature NMR spectra of the complexes [M(C₅H₄CPh₂)(C₈H₁₂)]X (C₅H₄CPh₂ = 6,6-diphenylfulvene; C₈H₁₂ = 1,5-cyclooctadiene; M = Ir, X = PF₆; M = Rh, X = ClO₄) provide evidence of intramolecular rearrangement involving rotation of the diphenylfulvene ligand about the metal-fulvene axis. Rearrangement is slow on the NMR time-scale for both complexes at 223 K: spectra recorded at higher temperatures indicate that the barrier to rotation of the diphenylfulvene ligand is lower for the iridium than for the rhodium complex.     

Synthesis of radicals underlain by 1,3-bis(4,5-diphenylimidazol-2-yl)benzene

A dimer of a monoradical was obtained proceeding from 1,3-bis(4,5-diphenylimidazol-2-yl)benzene and the rate constants were measured of the dissociation of dimers of 1,3-bis(4,5-diphenylimidazol-2-yl)benzene mono- and biradicals.     

Solvolysis of (1-chloro-2,2-dimethylpropyl) benzene in presence and absence of mercury(II) chloride

The kinetics of solvolysis of the title compound has been studied in water and in 10 vol. % ethanol-water in the presence and absence of mercury (II) chloride. The results confirm the earlier conclusion that mercury(II) chloride is solvated in hydroxylic solvents.

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Кинетика сольволиза заглавного соединения была исследована в воде и в смеси этанола (10 об.%) с водой в присутствии и отсутствии хлористой ртути (II). Реэультаты подтверждают более раннее заключение, согласно которому хлористая ртуть (II) сольватируется в гидроксильных растворителях.