N-h insertion reactions of Boc-amino acid amides: solution- and solid-phase synthesis of pyrazinones and pyrazines

A series of alpha-diazo-beta-ketoesters were reacted with Boc amino acid amides in the presence of rhodium octanoate catalyst. The resulting N-H insertion products were treated with acid, providing the 1,4-azine intermediates, which were oxidized by air to form the corresponding pyrazine-6-one products. The pyrazine-6-ones were further derivatized by N-alkylation or by conversion to the arylpyrazines using sequential bromination and Suzuki coupling reactions. [reaction: see text]     

Beiträge zur frage der existenz eines tautomerengleichgewichtes in lösungen von dithizon in organischen solvenzien—I: Die korrelation zwischen den lösungsmittelabhängigen reaktionsunterschieden in den systemen palladium/dithizon und kupfer/dithizon und den lösungsmittelabhängigen unterschieden der spektren der dithizonlösungen

Significant differences have been observed in the reactions of substoichiometric amounts of reagent for the extraction of palladium dithizonate and of copper dithizonate. These differences depend on both the organic solvent and the composition of the aqueous phase, and suggest that dithizone can react with metals in two ways, and can exist as a mixture of tautomeric forms in organic solvents. Moreover the differences in the reactions show a clear correlation with the differences in the visible absorption spectra of dithizone in various organic solvents. A mathematical analysis of these spectra has allowed calculation of the spectra of the individual thione and thiol forms of dithizone, and also estimation of the position of the tautomeric equilibrium in the different solvents.     

Polymerization photoinitiated by carbonyl compounds. IV. α-diketones and α-substituted alkanones

The photoinitiation efficiency of the free-radical polymerization of methyl methacrylate and styrene by several carbonly compounds has been determined. The compounds considered were α-substituted ketones and α-dicarbonyl compounds. For the ketones, the initiation efficiency employing methyl methacrylate depends on the α substitution; the values obtained change from less than 10^?3 (acetone) to 0.65 (3-hydroxy-3-methyl-2-butanone). All ketones are more efficient towards methyl methacrylate than styrene. This result can be explained in terms of triplet quenching by the last monomer. The results obtained employing α-dicarbonyl compounds do not conform to a simple pattern. In particular, benzil shows a considerably larger efficiency towards styrene than for methyl methacrylate. Since benzil is efficiently quenched by styrene, the initiation must involve the interaction of an excited benzil molecule and the monomer.     

An electrode for the coulometric generation of hydrogen ion

The anodic generation of hydrogen ion on bright platinum in 1.0M sodium perchlorate is not quantitative owing to the formation of a chemical species With oxidizińg properties, presumably a peroxydiperchlorate, but 100% current efficiency can be obtained in the anodic generation of hydrogen in 0.25M sodium hydrazinium sulphate, Na(N(2)H(5))SO(4). Five hydrogen ions are formed for each four electrons passed. The efficiency of this "hydrazine-platinum anode" has been demonstrated by the high-precision coulometric titration of tris(hydroxymethyl)aminomethane.     

Determination of the absolute specific conductance of primary standard KCl solutions

A determination of the absolute specific conductance of KCl solutions is demonstrated. The measurement is based on the conductance cell with a well defined geometry, having a difference in the removable center tube of accurately measured dimensions. The specific conductance of the solution is obtained from the measured resistances of the cell with and without the center tube and the measured l/A ratio of the center tube. Specific conductances obtained using the cell agree with the previously accepted standards for 0.1 demal and 0.01 demal solutions within 0.02%. Results are also presented for solutions based on molality. The temperature control, bridge, and detector technology used to obtain results of this accuracy are described.     

Untersuchungen zur anwendung ternärer komplexe in der photometrie—I Die bestimmung des Titan(IV) mit Tiron in gegenwart von äthylendiamintetraessigsäure

Two model systems and three analytical procedures based on them have been investigated analytically and characterized statistically with the aim of evaluating the application of ternary complexes in photometry. From measurements on the systems Ti(IV), Tiron (TiR^8?₃, procedure I), Ti(IV), Tiron, EDTA (TiR^8?₃, procedure II), Ti(IV), Tiron, EDTA [TiO(HY)R^5?, procedure III], the molar absorptivities, standard deviations, coefficients of variation, calibration data, limits of detection and determination have been calculated, and the possible interferences of 45 ions have been examined. Procedure III is shown to be the least sensitive of the three, but to offer a higher selectivity towards titanium in the presence of Cr(III), Cu(II), Fe(III), Mn(II), Mo(VI), Ni(II), U(VI) and W(VI). The reasons for this are discussed, and some suggestions are offered concerning the intended application of ternary complexes.     

Über alkylierte Amide bicyclischer Dicarbonsäuren, 4. Mitt.:

It has been found that nitrogen-containing functional derivatives of fumaric acid can act under certain conditions as dienophiles in Diels-Alder reactions. A decisive influence of the solvent has been established. The adducts of cyclopentadiene and cyclohexadiene with fumaric acid amide and several N-substituted fumaric acid diamides are described. Some of the adducts have been hydrogenated to the saturated compounds.     

Mechanical Properties of Organic-Inorganic Hybrid Materials Determined by Indentation Techniques

Summary. The mechanical properties of hybrid materials consisting of polystyrene (PS), which was cross-linked with different proportions of the multifunctional cluster Zr₆O₄(OH)₄(methacrylate)₁₂ (Zr6) were investigated. With the help of (micro)indentation and scratch testing, the influence of the Zr6 clusters on mechanical properties, such as hardness, stiffness, creep, craze initiation, and scratch resistance was shown. There was only a slight increase in hardness and in indentation modulus with higher cluster loadings. While this observation was in agreement with the compression behaviour of the materials, the tensile properties showed a much stronger dependence on the Zr6 content. With increasing cluster loading, an increase of craze initiation stress, as determined by ball indentation experiments, was found. Performing scratch testing with constant load, a reduction of pile-up and a stronger recovery were observed for the hybrid materials compared to the neat PS. Scratch tests with a constant increase of load showed an increase of the critical load for crack opening during scratching.     

Untersuchungen an reagenzien für niob und tantal—I

On examination of a wide range of hydroxylic organic compounds it has been found that two hydroxyl groups in the ortho position to each other in an aromatic system act as a functional analytical group for niobium and tantalum. peri-Dihydroxynaphthalene derivatives react similarly. After a systematic examination, tribromopyrogallol is proposed as a new selective and sensitive reagent for niobium.

Résumé

Au cours de l'étude d'un grand nombre de composés organiques oxhydrilés, il a été constaté qu'en présence d'acide tartrique, les composés possédant deux groupements oxhydriles en ortho sur un noyau aromatique présentaient des propriétés analytiques spécifiques pour le niobium et le tantale. Les dérivés du péri-dihydroxynaphtalène réagissent d'une manière analogue. Après une étude systématique, le tribromopyrogallol est proposé comme un nouveau réactif spécifique et sensible du niobium.     

New Results on the Stereoselective Alkylations of Malic Acid Derivatives Supported by Molecular Modeling

The stereoselectivity of the alkylation of dialkyl malates is dependent on steric hindrance of both ester alkyl groups. It was found that the two alkyl groups have opposite effects on diastereoselectivity. Increased steric hindrance at the C(1) carboxy group increases the anti‐selectivity, whereas increased steric hindrance at the C(4) carboxy group decreases it. The results are explained by comparing the structures of the enolates, which were obtained by molecular modeling. Alkylation at C(4′) of dioxolanones, derived from benzyl‐substituted malic acids, with an additional stereogenic center on the side chain is dependent on the stereogenic centers of the ring acetal and of the side chain. Alkylation at low temperatures occurs only with cis‐dioxolanones having an (R)‐configured side‐chain stereogenic center. The corresponding trans‐dioxolanone and the cis‐dioxolanone with a (S)‐configured side‐chain stereogenic center were recovered unchanged. A rationale is presented with models of monolithiated dioxolanones obtained by ab initio calculations.