Preparation of ortho-aryl-benzaldehyde derivatives via free-radical ipso-substitution of an amidomethyl group

Preparation of 2-biarylcarbaldehydes using an intramolecular free-radical ispo-substitution is described. The two aryl moieties to be coupled are pre-associated using a glycolamide derivative. An unusual amidomethyl leaving group was successfully employed in this process.     

Antioxidant activity of uracil derivatives

The antiradical properties of a number of uracil derivatives are studied in initiated 1,4-dioxane oxidation as a model reaction. The antioxidant activity of the uracil derivatives as inhibitors is estimated. The antiradical activity of the compounds is quantitatively characterized in terms of the effective rate constant of inhibition, fk _In.     

Polarographic study of uracil derivatives

Eighteen uracil derivatives were studied by d.c. polarography, differential-pulse (d.p.)polarography and d.p. cathodic stripping voltammetry. In a borax buffer at ca. pH 7.6, uracil, thymine and derivatives such as 5-halouracils, 5-trifluoromethyl-,5-aza-,5-acetyl-, 5-formyl- and 5-vinyl-uracil produced well-defined peaks at potentials between 0 V and ca. 160 mV vs. silver/ silver chloride (satd. KCl). The peaks are ascribed to the formation of sparingly soluble mercury salts. For the other derivatives tested (e.g., 5-nitro- and 5-ethynyl-uracil and 6-substituted uracils), the peaks were less well-defined and in some cases the polarographic curves were very complex. 2-Thiouracil produced a single peak at ca. ?400 mV, but only at pH 12.2. The shapes, heights and potentials of the peaks depended on the kind and position of the substituent on the pyrimidine ring. Rectilinear relationships of peak current vs. concentrations were found for most compounds (10^?5-10^?4 M) by d.p. polarography; d.c.polarography was not tested quantitatively. For 5-fluorouracil and 5-vinyluracil, linear calibrations were found for concentrations of 0.5–5 × 10^?7 M by d.p. cathodic stripping voltametry. Interference studies showed that small amounts of chloride and phosphate did not interfere but 5-fluorodeoxyuridine, which did not itself produce a peak, and proteins interfered seriously.     

Reactivity of nucleophilic uracil derivatives

The reactivity of uracil derivatives bearing acidic methylene groups at N1 was investigated. On treatment with strong base, compounds with nitrile as the activating group underwent extensive dimerisation to give new tricyclic systems. Ester-activated compounds also produced dimers in the absence of an external electrophile, but their monomeric carbanions could be trapped by prompt addition of benzyl bromide to give normally alkylated products.     

New synthesis of uracil derivatives

When N,N-dialkylamide dimethylsulfate adducts are reacted with cyanoacetyl urea or carbethoxy acetyl urea, the corresponding dialkylamino alkylidene derivatives are formed which cyclize to substituted uracils in the presence of a strong base. When the adducts of cyclic amides are used, the lactam ring is opened simultaneously on cyclisation.     

Desulfurizative stannylation of uracil derivatives

Phenylthio group in the C-6 or C-5 position of uracil moiety can be removed by radical mediated stannylation with tributyltin hydride followed by protonolysis, providing a new route to 5-substituted uridines.     

Synthesis of uracil derivatives by oxidation of Fischer tungsten-carbene uracil complexes

A study on the oxidation of Fischer tungsten-carbene uracil complexes has been carried out. Several commonly used oxidants gave results strongly influenced by the presence of substituent on nitrogen atoms. In particular, usual oxidants failed in the oxidation of 3-alkyl uracil carbene complexes. Finally, we showed that t-butyl hydroperoxide is able to oxidize successfully also 3-alkyl uracil carbene complexes and can be used as a good alternative to the other methods.     

Resonance electron capture by uracil derivatives

The enol forms of uracil and its derivatives were detected in the gas phase by mass spectrometry. The [M - H]⁻ ion is produced by resonance electron capture to the lowest unoccupied molecular orbitals, the process being accompanied by the detachment of the hydrogen atom from the nitrogen atom of the diketo form (low-energy peak at 0.8 eV) and from the oxygen atom of the enol form (in the energy region of 1.4 eV). The gas phase contains ∼10⁻³% of the enol form. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1360–1362, June, 2005.     

Mass spectra of bromohydrins of uracil derivatives

The mass fragmentation of bromohydrins of uracil derivatives is discussed. Fragmentation pathways have been proposed on the basis of high-resolution data and metastable transitions. The distinct influence of substituents in position 5 of uracil on the fragmentation pathway has been observed.     

Collision-induced dissociation of uracil and its derivatives

The collision-induced dissociation of protonated uracil has been studied by tandem mass spectrometry using models extensively labeled with stable isotopes, and derivatives of the kinds found in nucleic acids. Following collisional activation at 30 eV translational energy, protonated uracil dissociates through two principal pathways which do not occur in electron ionization mass spectra: (1) elimination of NH3 almost entirely from N-3, followed by loss of CO from C-4, 0⁴; (2) loss of H2O, equally from 0² and 0⁴. Elimination of HNCO, also the principal dissociation process from odd-electron molecular ions, proceeds primarily by loss of N-3, C-Z, O² and 10% from N-l, C-Z, 0². Several secondary dissociation products are formed with quantitative site specificity of skeletal atoms: C,HO+ (4-C0, C-5, C-6); H2CN+ (N-l, C-6); C2H2+ (N-l, C-5, C-6). First-step dissociation reactions are interpreted in terms of pyrimidine ring opening at likely sites of protonation after collisional activation of MH+. Collision-induced dissociation mass spectra of uracils with structural themes common to nucleic acids (methylation, replacement of 0 by S, C-5 substitution) follow analogous reaction paths which permit assignment of sites of substitution, and exhibit ion abundance changes attributed to differences in substituent basicity and electron density.     

Pro- and antioxidant properties of uracil derivatives

Russian Chemical Bulletin - The review summarizes data on pro- and antioxidant properties of uracil derivatives comprising an important group of pharmacologically active compounds. The presence of...     

Electrophilic substitution reactions of acylated 2-aminoindole derivatives

The bromination, nitration, and acylation reactions of various acyl derivatives belonging to the 2-aminoindole series of compounds have been investigated. It has been found that substitution occurs both at the -carbon atom as well as at the 5- and 6-positions of the benzene ring. The ratio of reaction products depends upon the nature of the electrophile as well as on the degree of substitution of the 2-aminoindole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 941–945, July, 1985.     

Electrophilic substitution reactions of alkylated 2-aminoindole derivatives

Bromination, nitration, and acylation of 1-methyl-2-dimethylaminoindole under mild conditions proceed to give the 3-substituted reaction products. In acidic media, in which the parent indole exists in the form of an amidinium cation, substitution occurs in the 5-position of the benzene ring. Aminoindoles, which are capable of existing only in the iminoindoline or aminoindolenine forms, always give products derived from substitution at the para position relative to the nitrogen atom, regardless of the reaction conditions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 946–951, July, 1985.     

The aromatic carbon-carbon ipso-substitution reaction

The aim of this review is to illustrate what we have dubbed an aromatic carbon-carbon ipso-substitution reaction in which a new Ar-C bond is formed at the expense of another Ar-C bond. The potentiality of several C-based leaving groups including alkyl, carbinol, CN, COOH, and carbonyl groups in arylation reactions will be illustrated accordingly for the preparation of biphenyl-, vinyl-, alkynyl-, and alkyl-substituted aromatics.     

Electrophilic substitution in a number of N-exo-carbamoyl derivatives of sydnoneimines

Depending on the character of the substituents and the reaction conditions, the bromination of N-exo-carbamoyl derivatives of sydnoneimines may proceed in the heterocyclic ring and (or) in the phenyl ring of the exocyclic substituent. Nitration proceeds only in the phenyl rings of the substituents.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1198–1203, September, 1975.     

Polymerization of cyclic derivatives of uracil and thymine

Cyclic derivatives of uracil and thymine were synthesized from their corresponding 1-(2′-chloroethyl) derivatives by dehydrochlorination. These compounds were found to undergo a variety of reactions, giving many valuable derivatives of uracil and thymine. The cyclic derivatives, as monomers, were polymerized with a cationic initiator by a unique ring-opening process. The polymerization proceeded by ring opening with isomerization of the pyrimidine ring to give a polymer in which pyrimidine rings were connected with ethylene between N-1 and N-3 or O-4 in the pyrimidine ring. The structure of these polymers was determined by nuclear magnetic resonance (NMR), ultraviolet (UV), infrared (IR), and mass spectra. The structure was affected by polymerization temperature.