Verfeinerung der Kristallstruktur von 1,4-trans-Diaminocyclohexan-dihydrochlorid

The previously described structure of 1, 4-trans-diaminocyclohexane dihydrochloride has been further refined by full-matrix least-squares analysis with an improved weighting scheme.     

Photochemische Cycloadditionen von 3-phenyl-2h-azirinen mit Aldehyden. 31. Mitteilung über Photoreaktionen

Experiments concerning the photochemical condensation of 3-phenyl-2H-azirines 1 with aliphatic and aromatic aldehydes to 3-oxazolines 4 are fully described (cf. scheme 1 ). Photochemically nitrile methylides of type 2 are first formed, which then very quickly react thermally with the aldehydes in a regiospecific manner to give the 3-oxazolines 4 . Azirines monosubstituted in position 2 (l b and 1 c ) give mixtures of cis, trans-oxazoline isomers, in which the cis isomer predominates. The stereoselectivity of the cycloaddition reaction can be rationalized by a simple model (scheme 10). The stereoisomeric 3-oxazolines 4 are distinguishable in the NMR. spectra by the large homoallylic coupling constants between the H atoms on C(2) and C(5).     

Eine neue Synthese von 3,6-Dialkyl-1,2,4,5-tetrazinen

A new synthesis of 3,6-dialkyl-1,2,4,5-tetrazines (or -s-tetrazines), 4 , is described (see reaction scheme [1→2→3→4]). The 3,6-dialkyl-hexahydro-s-tetrazines, 2 , R = n-alkyl, are readily available by the reaction of fatty aldehydes and hydrazine. s-Tetrazines with branched substituents and mixed alkyl-s-tetrazines can also be prepared by the same procedure, however, in lower yields.     

Electroinitiated polymerization of vinylic monomers in polar systems. III. Polymerization of acrylates and methacrylates in alcohol solutions

Methyl, ethyl, and n-butyl acrylates and methacrylates are polymerized by electroinitiation in methanol–, ethanol–, and n-propanol–electrolyte mixtures in which the monomers are soluble whereas the polymers obtained are insoluble. The technique of changing the polarity of the electrodes described earlier was used. The relationships between molecular weights and polymer yields as function of current density, initial monomer concentration and dielectric constant of the solvent are described. A kinetic scheme for the initiation, propagation, and termination is given.     

Sulfidkontraktion via alkylative Kupplung: Eine methode zur darstellung von β-dicarbonylderivaten. Über synthetische methoden, 1. Mitteilung

The experiments described in reaction schemes 1–12 indicate that sulfide contraction via alkylative coupling (see scheme p. 729) is a potentially general method for the synthesis of secondary vinylogous amides and enolizable β-dicarbonyl compounds.     

269. Steroid total synthesis. 8. (+)-Estr-4-ene-3, 17-dione

A novel synthesis of the title compound, involving the resolution of a Mannichbase derived from racemic 11,11-o-phenylenedioxy-7-hydroxy-1-dodecen-3-one is described. In an alternate approach 2(S)-acetamido-6,6-o-phenylenedioxy-heptanoic acid was used as the optically active starting material. This scheme features the preparation of a chiral 1,2-epoxide and its regiospecific alkylation with lithio-1, 1-diethoxy-2-propyne.     

A Study on the Photochemical Transformations of <Emphasis Type="Italic">p</Emphasis>- and <Emphasis Type="Italic">m</Emphasis>-Nitrosonitrobenzenes

Photochemical oxidation of p- and m-nitrosonitrobenzenes to corresponding dinitrobenzenes was studied. The reaction was described by a scheme involving two successive steps, with the rates of photochemical decomposition of isomeric nitrosonitrobenzenes being much higher than those of dinitrobenzenes. Oligomeric azo and azoxy compounds and the products of hydroxylation of the reaction medium were found as final products of the reaction upon long-term irradiation with UV light.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 4, 2005, pp. 287–292.Original Russian Text Copyright © 2005 by Zelentsov, Logunov.     

Synthèse de deux nouveaux acides amines phénoliques comportant un cycle 1,2,4-oxadiazole

Synthesis of two phenolic amino acids containing the 1,2,4-oxadiazole ring The synthesis of α-amino-β [3-(p-hydroxyphenyl)-1,2,4, oxadiazol-5-yl]propionic acid (9) and its β-amino isomer (10) (see scheme 3) is reported. By condensation of p-benzyloxy-benzamide oxime and N-benzyloxycarbonyl asparagine the derivatives 4 and 5 (see scheme 1) are obtained leading after deprotection to 9 and 10 . The synthesis of N-carboxyanhydride of 4 (6) and its corresponding amino acid (7) and amide (8) is also described.     

Steroid total synthesis. 3. 9 , 10 -testosterone

The total synthesis of 9β, 10α-testosterone via a BCD-tricyclic intermediate is described. The latter compound – 17β-hydroxy-des-A-androst-9-en-5-one – was obtained in optically active form by our previously reported scheme, using an efficient resolution step early in the synthesis. New results regarding the asymmetric induction step are also discussed.     

Chain decomposition of 2,4,6-trinitrotoluene in hydrocarbon solvents

The rate constants for the thermal decomposition of 2,4,6-trinitrotoluene have been measured in toluene and other hydrocarbon solvents. The initial, observed rate constant (k _i) increases with dilution with toluene. The concentration dependence is described by the chain decomposition scheme with the transfer of the free valence to a solvent molecule. The activation energy and logk _i were found to linearly correlate with the dissociation energy of the C-H bond of the solvent.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1977–1980, August, 1996.     

Some aspects of curing novolac with hexamethylenetetramine

Curing novolac with hexamethylenetetramine in closed molds at T = 190°C was studied. Cured products were examined with the following experimental techniques: sol fraction determination, % N fixed in sol and gel fractions, and IR spectra. The fraction of fixed N decreased from 1 to 0.5 when the hexa mass fraction was increased from 0 to 0.3 in the mixture with novolacs. A segregation of the fixed N in the sol fraction was observed. Azomethine derivatives were present, their amounts increasing with the hexa mass fraction. Curing was described by a reaction scheme similar to the one derived from studies with model phenols. A simplified scheme was adequate for the prediction of the minimum hexa amount necessary to gel the system at full conversion.     

Kinetics of 2-Pinanol Isomerization to Linalool on the Monolith Carbon-Containing Catalyst

Isomerization of 2-pinanol into linalool is studied on a monolith carbon-containing catalyst at 733–893 and a total pressure of 2–40 torr. The rate constants of cis(trans)-2-pinanol transformation into linalool and linalool cyclization are determined. Experimental data are described by the consecutive kinetic scheme. The mechanism of linalool formation is proposed according to which pinane ring opening occurs in an intramolecular reaction. A highly selective process of linalool synthesis by the thermal isomerization of 2-pinanol is shown to be possible.     

Partitioning scheme for theab initio SCF energy

As a tool for the interpretation ofab initio SCF calculations, an energy partitioning scheme is presented. When performed within an orthogonalized basis, the scheme allows the deduction of well transferable, almost basis independent two-center terms which characterize bond strengths and non-bonded interactions. The results for a large number of molecules are given. The construction of an orthogonal minimal basis (OMBA) from arbitrary basis sets as a generalization of the symmetrical orthogonalization is described. The transferability of Fock matrix elements is discussed. The energy partitioning quantities are related to the corresponding terms obtained with the semiempirical schemes CNDO and MINDO/3.     

Structures and NMR Parameters of 1,2-Diphenylcyclobutanes

A new reaction scheme for obtaining cis and trans 1,2-diphenylcyclobutane is described. Using ¹H-NMR at 600 MHz, full spectral assignment was made for both isomers, obtaining all J coupling constants and chemical shifts. NMR results on cis and trans 1,2-diphenylcyclobutane are compared with the vicinal coupling constants obtained by the Barfield–Smith equations from the literature internal and dihedral angles of cyclobutane. In the trans isomer, in agreement with previous results on halo-cyclobutanes, the conformation with the phenyls in the pseudo-di-equatorial position is strongly preferred. On the contrary, the cis isomer fluctuates between the two equivalent conformations: phenyl pseudo-axial and pseudo-equatorial.     

A facile and novel synthesis of 1,6-naphthyridin-2(1H)-ones

A new and convenient procedure for the synthesis of 1,6-naphthyridin-2(1H)-ones and their derivatives is described. In the first scheme 5-acetyl-6-[2-(dimethylamino)ethenyl]-1,2-dihydro-2-oxo-3-pyridinecarbonitrile ( 4 ) obtained by the reaction of N,N-dimethylformamide dimethyl acetal with 5-acetyl-1,2-dihydro-6-methyl-2-oxo-3-pyridinecarbonitrile ( 3 ) was cyclized to 1,2-dihydro-5-methyl-2-oxo-1,6-naphthyridine-3-carbonitrile ( 5 ) by the action of ammonium acetate. Thermal decarboxylation of acid 7 obtained from the hydrolysis of nitrile 5 led to a mixture of 5-methyl-1,6-naphthyridin-2(1H)-one ( 8 ) and its dimer 9 . Hydrazide 11 obtained from nitrile 5 in two steps was converted to 3-amino-5-methyl-1,6-naphthyridin-2(1H)-one ( 12 ) by the Curtius rearrangement. The amino group of 12 was readily replaced by treatment with aqueous sodium hydroxide to yield 3-hydroxy-5-methyl-1,6-naphthyridin-2(1H)-one ( 13 ). In the second scheme, Michael reaction of enamines of type 20 with methyl propiolate, followed by ring closure gave 5-acyl(aroyl)-6-methyl-2(1H)-pyridinones ( 21 ) which in turn were treated with Bredereck's reagent to produce 5-acyl(aroyl)-6-[2-(dimethylamino)ethenyl]-2(1H)-pyridinones ( 22 ). Treatment of 22 with ammonium acetate led to the formation of 1,6-naphthyridin-2(1H)-ones 23 .     

Variational solution of the single-particle Dirac equation in the field of two nuclei using relativistically adapted Slater basis functions

A variational method for solving the time-independent single-particle Dirac equation in the Coulomb field of two nuclei is described. A minimax variational principle and basis functions that have the proper analytic behavior, i.e. behave like r ^γ,γ non-integer, in the neighborhood of a nucleus, are used. A momentum space integration scheme for computing the necessary two-center integrals is described. Results are given for a standard test problem on two nuclei with Z=90 with an internuclear separation of 2.0/Z. The results confirm those of a previous calculation [F.A. Parpia and A.K. Mohanty, Chem Phys Lett 238: 209 (1995)]. Received: 13 May 1998 / Accepted: 22 June 1998 / Published online: 28 August 1998     

Sequencing of cyclosporins by fast atom bombardment and linked-scan mass spectrometry

The mass spectrometric sequence determination of amino acid residues in cyclosporins using fast atom bombardment, collisionally activated dissociations in the first field-free region and linked B/E scan is described. The general fragmentation scheme was derived from the spectra of cyclosporins A, B, C, D, F, G, L and [DH-MeBmt¹]CS. The main fragmentation pathways start by primary splitting between amino acids 2–3, 1–11 and 5–6. The corresponding N-terminal b-type ions are common fragment types in the mass spectra. The 1–11 splitting can be enhanced by the introduction of a lactone group into the peptide ring by conversion of cyclosporins into isocyclosporins. The fragmentation scheme was used for amino acid sequence determination in four new natural cyclosporins, [MeLeu¹]CS, [Leu⁴]CS, [Ile⁴]CS and [Leu⁵]CS.     

The Synthesis of 2-Amino-4-(4-imidazolyl)pyridines

A general synthetic scheme for the preparation of 2-amino-4,(4-imidazolyl)pyridines, potential histamine H₂ antagonists, is described. The synthesis is based on the Neber rearrangement of l,(4-pyridyl)l-alkanone oxime 0-tosylates to the appropriate α-aminoketones or α-aminoketals, which are then converted to the corresponding imidazoles. The reaction of Grignard reagents with 2-chloroisonicotinonitrile, as well as nucleophilic displacement of chloride by amines on 2-chloroisonicotinonitrile and derivatives, are discussed in relation to the preparation of the ketone intermediates.     

New realizations of electronic configuration interaction spaces

The general properties of new models of the electronic spaces based on the notion of (p, q)‐sheaves are studied. The interrelation between simple sheaves and density operators is established. Explicit expressions for the transformed reduced Hamiltonians in terms of the standard creation‐annihilation operators are presented. The general scheme of parametrization of p‐electron states by κ‐electron means (κ = 2, 3, …) is described and studied in detail for the case of sheaves induced by κ‐electron wave functions. It is demonstrated that, under certain conditions, a p‐electron problem may be reformulated as the eigenvalue problem in κ‐electron space equipped with certain p‐electron metric. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Fragmentations Principales de Mono-, Di-, Triet Tetra-azaindolizines Sous L'Impact Electronique

The principal fragmentations of 41 azaindolizines having an imidazo[1,2-a]pyridine, imidazo[1,5-a]pyrimidine, imidazo[1,5-b]-1,2,4-triazine, triazolo[2,3-b], -[4,3-b]-, -[3,4-c]- and -[3,2-c]-1,2,4-triazine structure are described. It is shown that each structure has its own characteristic fragmentation pathways except where a Dimroth rearrangement into an isomeric product can be postulated. The degradation scheme is correlated with the number and the position of the nitrogen atoms of the azaindolizines.