Conformational study of α-arylethylamides of (−)-camphanic acid

The absolute conformation and configuration of diastereomeric amides (4A,B–6A,B) of (1S,3R)-camphanic acid (lactone of 1-hydroxy-2,2,3-trimethylcyclopentan-1,3-dicarboxylic acid, (−)-camphanic acid 9) with α-arylethylamines 1–3 are deduced from ¹H NMR data and MM2 calculations. The α-arylethyl group in diastereomers A and B adopt nearly opposite absolute conformations, stabilized by hydrogen bonding in the syn-oriented O–C(1)–C(6)–N–H unit, and repulsive interaction between the 1′C–Me group and the amide CO group. The absolute configuration (1′S) is assigned to the 4A–6A diastereomers, and the (1′R)-configuration to the 4B–6B diastereomers; this assignment is confirmed by the preparation of 4A and 5A from enantiomerically pure (1′S)-α-arylethylamines 1 and 2, respectively. These results also enabled the assignment of pro-R (H_R) and pro-S (H_S) protons in the benzyl derivative 7.     

Conformational investigation of α-methylthio and α-phenylthio derivatives of acetone and cyclohexanone by molecular mechanics. An x-ray study of α-phenylthioacetone

A conformational investigation of -methylthioacetone, -methylthiocyclohexanone, -phenylthioacetone, and -phenylthiocyclohexanone was undertaken in the MM2(87) force field. In all cases theac-G rotamers with unidirectional orientation of the C=O and S-R bonds are preferred in accordance with the experimental investigations. In all cases the energy of dipole-dipole interaction makes a contribution to the stabilization of these forms. For the eclipsedsp conformers the relatively high calculated values of the energies contradict the data of the experimental investigations, which take account of their participation in the equilibrium. X-ray crystallographic analysis of -phenylthioacetone (3) showed that thesp-T structure with a planar orientation of the thioanisole fragment is realized in the solid phase.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Scientific Center, Russian Academy of Sciences, 420083 Kazan'. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1364–1371, June, 1992.     

Quantum chemical study of α-diazocarbonyl bullvalene derivatives and related heterocyclic compounds

According to the results of PBE0/cc-pVTZ quantum chemical calculations, the equilibrium mixture of α-diazocarbonyl bullvalene derivatives (C₁₀H₈N₂O) contains an impurity of the corresponding bullvaleno-[1,2,3]oxadiazoles. The carbonyl group in the major tautomer is conjugated with the three-membered ring. The concentration of other tautomers in the equilibrium mixture of two bullvaleno[1,2,3]selenadiazoles is negligible.     

Sulfoxide-mediated α-arylation of carbonyl compounds

A novel sulfoxide-mediated α-arylation of carbonyl compounds is reported. This reaction proceeds under very mild conditions at room temperature and does not require any transition-metal promoter or catalyst.     

Conformational Analysis of Acyclic α-Fluoro Sulfur Motifs

Bioactive small molecules containing α-fluoro sulfur motifs [RS(O)_nCH₂F] are appearing with increasing frequency in the pharmaceutical and agrochemical sectors. Prominent examples include the anti-asthma drug Flovent^® and the phenylpyrazole insecticide pyrafluprole. Given the popularity of these structural units in bioactive small molecule design, together with the varying oxidation states of sulfur, a conformational analysis of α-fluoro sulfides, sulfoxides, and sulfones, would be instructive in order to delineate the non-covalent interactions that manifest themselves in structure. A combined crystallographic and computational analysis demonstrates the importance of hyperconjugative donor-acceptor interactions in achieving acyclic conformational control. The conformational disparity in the syn- and anti-diastereoisomers of α-fluorosulfoxides is particularly noteworthy.     

On the stereochemical stability of α-sulfonylvinyllithium compounds

α-Lithiated vinylic sulfones have been prepared from readily available 1-alkenyl sulfones in tetrahydrofuran by treatment with methyllithium at −90°C; they appear to be configurationally unstable at −60°C.     

Alkylating potential of α,β-unsaturated compounds

Alkylation reactions of the nucleoside guanosine (Guo) by the α,β-unsaturated compounds (α,β-UC) acrylonitrile (AN), acrylamide (AM), acrylic acid (AA) and acrolein (AC), which can act as alkylating agents of DNA, were investigated kinetically. The following conclusions were drawn: i) The Guo alkylation mechanism by AC is different from those brought about the other α,β-UC; ii) for the first three, the following sequence of alkylating potential was found: AN > AM > AA; iii) A correlation between the chemical reactivity (alkylation rate constants) of AN, AM, and AA and their capacity to form adducts with biomarkers was found. iv) Guo alkylation reactions for AN and AM occur through Michael addition mechanisms, reversible in the first case, and irreversible in the second. The equilibrium constant for the formation of the Guo-AN adduct is K(eq) (37 °C) = 5 × 10(-4); v) The low energy barrier (≈10 kJ mol(-1)) to reverse the Guo alkylation by AN reflects the easy reversibility of this reaction and its possible correction by repair mechanisms; vi) No reaction was observed for AN, AM, and AA at pH < 8.0. In contrast, Guo alkylation by AC was observed under cellular pH conditions. The reaction rate constants for the formation of the α-OH-Guo adduct (the most genotoxic isomer), is 1.5-fold faster than that of γ-OH-Guo. vii) a correlation between the chemical reactivity of α,β-UC (alkylation rate constants) and mutagenicity was found.     

An electronic spectral study of the coupled effect on the tautomeric equilibria of some α-hydroxy azo compounds

The spectral behaviour of six a-hydroxy azo compounds has been investigated in solution. The bands appearing in the u.v. and visible regions are assigned to possible electronic transitions. Azo compounds containing pyrazolone and acetyl or ester moieties are found to exist mainly in the hydrazo form in solution, while those containing the naphthol moiety exist in the azo-hydrazone tautomeric equilibrium. The solvatochromic behaviour of the compounds is investigated by studying their spectra in organic solvents of different polarities. The acidity constants are determined from the spectra of the compounds in aqueous ethanolic solutions of varying pH values.     

Asymmetric synthesis of α-alkyl α-selenocarbonyl compounds catalyzed by bifunctional organocatalysts

A new organocatalytic approach for the synthesis of a variety of α-alkyl, α-phenylselenyl ketones as well as their corresponding esters and amides, by the addition of α-selenocarbonyl derivatives to nitroalkenes catalyzed by thiourea or squaramide cinchona catalysts, is presented. This catalytic system allows the preparation in high yields of enantiomerically enriched selenocarbonyl derivatives bearing two chiral centers with excellent ee's and dr's by using catalytic loadings of 3 mol%.     

Novel tocopheryl compounds. Part 16: Nitration of α-tocopheryl acetate—a mechanistic study

The reaction of α-tocopheryl acetate (vitamin E acetate, 3) with concentrated nitric acid proceeds according to a non-radical, two-step mechanism, producing 5-nitromethyl-γ-tocopheryl acetate (4) in good yields. In the first step, oxidation of 3 affords a benzylic cation intermediate (8), which in the second step adds nitrite to give 4. The acetyl group, which stabilizes intermediate 8 intramolecularly, remains bound to the tocopheryl moiety throughout the reaction.     

Addition of some α-halo ethers to unsaturated compounds

Summary The addition was carried out of 2-acetoxyethyl chloromethyl ether and of 2-chloroethyl chloromethyl ether to isobutene, to allyl chloride, to styrene, and to allyl acetate and also of 2-acetoxyethyl chloromethyl ether to butadiene and to ethyl cinnamate.     

Infrared and Raman study of alunite—jarosite compounds

Infrared and Raman spectra of alunite and jarosite compounds, AR₃(SO₄)₂(OH)₆, where R is either Fe³⁺ or Al³⁺ and A is a monovalent cation, have been obtained between 4000 and 40 cm⁻¹. The observed number and position of the i.r. and Raman bands have been analysed under the centrosymmetric D⁵_3d space group. In addition, some relationships between the crystallochemical characteristics of these compounds and their vibrational properties are presented.     

Synthesis of α-functional nitro compounds by the nitration of activated carbonyl compounds in a two-phase system

2-Nitro-1,3-dicarbonyl and -nitromonocarbonyl compounds were synthesized in the yields varying from moderate (30 %) to nearly quantitative by the nitration of -dicarbonyl compounds in a two-phase system: sulfuric/nitric acid mixture-chloroform at - 10÷10 °C. The use of phase transfer conditions made it possible to avoid the formation of furoxans as by-products and to simplify the isolation of products. This method is quite common for preparing various -functional nitro compounds including those containing a CF₃-group. Key words: nitration, -functional nitro compounds.Translated fromIzvestiya Akademn Nauk. Seriya Khimicheskaya, No. 1, pp. 76–79, January, 1994.     

Derivation of structural models for two intercalated compounds of α-zirconium phosphate

Reasonable structural models are proposed for two intercalated compounds of-Zr(HPO₄)₂·H₂O (-ZrP), one with 2,2-bipyridyl (A) and another one with 1,10-phenanthroline (B). The models are derived by considerations of the unit-cell geometry changes undergone by-ZrP upon insertion of the organic molecules and on a set of general criteria of structural analysis, already developed by us and called the comparison method. If it is assumed that the water molecules in A and B keep the positions they have in-ZrP, as fixed by their links to the phosphate-OH groups, the inserted molecules, while obeying the general conditions of optimum packing, establish interactions of the hydrogen-bonding type with the water molecules. This modeling gives for A and B a possible structural explanation to the maximum number of inserted molecules of the two species, as fixed by their stoichiometry.     

Substitution of halogen atom in α-halonitro compounds of the aliphatic series

Ethyl -halo--nitropropionate and -butyrate were prepared by alkylating ammonium salts of ethyl bromo- and chloronitroacetates. The addition of alkyl acrylates to alkyl chloronitroacetates or their salts gives dialkyl -chloro--nitroglutarates. Sodium salts of ethyl -nitro--sulfo--hydroxypropionate and -butyrate were obtained by the sulfodehalogenation of ethyl -chloro--nitro--hydroxypropionate and -butyrate with sodium dithionite. Esters of -amino acid hydrochlorides were prepared by the reduction of alkyl -chloro--nitrocarboxylates. The hydrogenation of alkyl nitrosulfoacetates leads to the corresponding disodium salts of alkyl aminodisulfoacetates and piperazine-2,5-dione.For communication 5 seeIvz. Akad. Nauk SSSR, Ser. Khim., 1990, 2012 [Bull. Acad. Sci. USSR, Div. Chem. Sci., 1990,39, 1826].Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 872–876, May, 1994.     

CpRu-catalyzed O-H insertion and condensation reactions of α-diazocarbonyl compounds

[CpRu(CH(3)CN)(3)][PF(6)] and diimine ligands catalyze together the decomposition of α-diazocarbonyl compounds leading to O-H insertion and condensation reactions. In comparison with Rh(II) and Cu(I) complexes, the CpRu catalysts produce rapid and often more selective reactions. Promising enantioselectivities are obtained in dioxole syntheses.