bluuebunny/crossref_metadata_2025_split huggingface dataset:
Syntyhesis of 1,2,4,5‐Tetrazino[1,6‐a: 4,3‐a′]diquinoxaline
Authors: Koçak Ahmet , Berkâroǧlu ÖZer 
Published: December 2004

AbstractA new one‐step synthesis of 2 (1H)‐quinoxalinone oxime (3) from (1,2‐benzenediamine (1) and s‐trans‐chloroethanedial dioxime (2) is described. This oxime is converted into a new heterocyclic compound, 1,2,4,5,‐tetrazino)[1,6‐a: 4,3‐a′]diquinoxaline (4), by the template effect of Co(II) and Ni(II) ions.
The chemistry of drugs part IV, Configurations of antimalarials derived from qinghaosu: Dihydroqingyhaosu, artemether, and artesunic acid
Authors: Luo Xuan‐De , Yeh Herman J. C. , Brossi Arnold , Flippen‐Anderson Judith L. , Gillardi Richard 
Published: December 2004

AbstractThe structures of the antimalarials dihydroqinghaosu (2), artemether (3), and artesunic acid (7a) derived from qinghaosu were elaborated by 1H‐NMR spectroscopy, and supported with X‐ray data obtained for 2 and 3. Several new derivatives, useful for the chemical characterization of dihydroqinghaosu (2) and artesunic acid (7a), were prepared.
The synthesis and transition temperatures of ester derivatives of 2‐fluoro‐4‐hydroxy‐ and 3‐fluoro‐4‐hydroxybenzonitriles also incorporating aliphatic ring systems
Authors: Kelly Stephen M. , Schad Hanspeter 
Published: December 2004

AbstractThe synthesis and liquid‐crystal transition temperatures of forty ester derivatives of 2‐fluoro‐4‐hydroxybenzonitrile and 3‐fluoro‐4‐hydroxybenzonitrile are reported. The esters contain the trans‐1,4‐disubstituted cyclohexane or the 1,4‐disubstituted bicyclo[2.2.2]octane rings (some contain an additional phenyl ring). Many of the novel F‐substituted esters exhibit substantially higher nematic‐isotropic transition temperatures than the corresponding unsubstituted esters. The order of clearing points of these laterally substiuted esters differing only in the presence of a benzene ring and the above‐mentioned rings id established.
An Example of Head‐to‐Head Dimerization of β4.4‐Helices
Authors: Lorenzi Gian Paolo , Muri‐Valle Valentina , Bangerter Felix 
Published: December 2004

Abstract1H‐NMR and vapor‐pressure osmometry results are presented, which indicate the occurrence of a rapid equilibrium involving the head‐to‐head dimerization of β44‐helices in chloroform solutions of HCO‐L‐Ile‐(D‐AIle‐L‐Ile)4‐OMe. This equilibrium typifies the one that, in Urry's view, would be responsible for the formation and breaking down of the ion‐conducting channels formed by gramicidin A in lipid bilayers.
Further Syntheses of Optically Active Verrucarinic Acid, 43rd Communication of Verrucarins and Roridins
Authors: Grossen Peter , Herold Peter , Mohr Peter , Tamm Christoph 
Published: December 2004

AbstractTwo new syntheses of verrucarinic acid (2S, 3R‐dihydroxy‐3‐methylpentanoic acid) and its derivatives, suitably protected for the further conversion to macrocyclic trichothecenes, are described. The first one makes use of a diastereoselective alkylation of a (−)‐(S)‐malic acid ester and the regioselective reductin of one carboxyl function toa methyl group. The second approach involves a stereoselective addition of an allylsilane to a chiral glyoxylate.
Mechanismus der decarboxylativen Dimerisierung von Maleinsäureanhydrid zu Dimethylmaleinsäureanhydrid unter Einfluss von 2‐Aminopyridin
Authors: Baumann Marcus E. , Bosshard Hans , Breitenstein Werner , Rihs Grety , Winkler Tammo 
Published: December 2004

Mechanism of the Decarboxylative Dimerization of Maleic Anhydride to Dimethylmaleic Anhydride under the Influence of 2‐AminopyridineThe mechanism of the decarboxylative dimerization of maleic anhydride to dimethylmaleic anhydride was investigated. It was shwon that imidazo[1,2‐a] pyridines play an important role as intermediates in this rather unusual transformation, the key step being a Michael addition of 5 to maleic anhydride.
Novel Variant of the Tricyclooctanone Approach to Cyclopentanoid Natural Products. Synthesis of (±)‐Coriolin. Preliminary Communication
Authors: Demuth Martin , Ritterskamp Peter , Schaffner Kurt 
Published: December 2004

AbstractA total synthesis of the antitumor sesquiterpene coriolin (9; racemic) in 11 steps from 3,3,6‐trimethylbicyclo[2.2.2]oct‐7‐ene‐2,5‐dione (2a/2b) is described (yield 2a/2b→8: 28%). The sequence is unprecedentedly short and avoids difficult separation problems. The key step in the scheme is a novel facet of oxadi‐π‐methane photochemistry, i.e., the steering by subtle steric effects of the β,γ‐unsaturated ϵ‐diketone to undergo a regioselective photorearrangement involving one β,γ‐enone partial chromophore. Furthermore, the overall phototransformation, which can be carried out at unusually high concentrations (≥20% solutions), involves also a Norrish type I process equilibrating the two epimeric starting enediones 2a and 2b in favour of the desired stereoisomer.
Cyclopropylidenebis(diphenylphosphine): Note on its Synthesis, Properties and Spectral Data
Authors: Schmidbaur Hubert , Pollok Thomas 
Published: December 2004

AbstractThe title compound has been synthesized through cyclopropanation of vinylidenebis(diphenylphosphine) using dimethylsulfoxonium methylide. It is easily converted into its dioxide and disulfide. NMR data of these first geminal diphosphinocyclopropanes are presented.
Nukleophile Reaktionen an 2‐Phenylindolenin‐3‐onen
Authors: Adam Jean‐Marie , Winkler Tammo 
Published: December 2004

AbstractNucleophilic Reactions on 2‐Phenylindolenin‐3‐onesNucleophilic reagents such as 4‐nitrophenylhydrazine, malonic acid derivatives, and hydrogen peroxide react with 2‐phenylindolenin‐3‐ones giving, in the first step, addition products to the (d) NC(2) bond. This addition can be reversible, but in most cases new rearrangement products are formed. The structure of the new compounds were elucidated by 1H‐ and 13C‐NMR spectroscopy.
Light‐Induced Synthesis of Thiolanes and 2,3‐Dihydrothiophenes by Addition of (E)‐4‐Mercapto‐2‐butenoates to Alkenes or Alkynes
Authors: Anklam Elke , Margaretha Paul 
Published: December 2004

AbstractIrradiation (λ=300 mm) of methyl 4‐mercaptocrotonate (2a) in the presence of alkenes of alkynes affords methyl 3‐thiolaneacetates 7 and methyl 2,3‐dihydro‐3‐thiopheneacetates 13. The unsaturated heterocycles 13 undergo further light‐induced isomerization to methyl 2,3‐dihydro‐2‐thiopheneacetates 15. Both 13 and 15 are readily dehydrogenated to thiophenes 17 and 18, respectively.
Synthesis of Thiolanes from (E)‐4‐Mercapto‐2‐butenoates via, Consecutive Michael Additions
Authors: Anklam Elke , Margaretha Paul 
Published: December 2004

AbstractMethyl 4‐mercaptocrotonate (4) adds to α,β‐unsaturated nitriles or carbonyl compounds in the presence of Triton B, as base. Several of the primary adducts (10) cyclize to thiolanes (11) in a second (base‐catalysed) Michael addition. Dimerization of 4 under these conditions affords a mixture of the diastereomeric 14‐dithianies 7 and 8.
Deoxy‐nitrosugars. 9th communication. Chain elongation of 1‐C ‐nitroglycosyl halides by substitution with some weakly basic carbanions
Authors: Aebischer Bernrd , Meuwly Roger , Vesella Andrea 
Published: December 2004

AbstractThe 1‐C‐nitroglycosyl chloride reacted with the anions form 2‐nitropropane, nitromethane, and diethyl malonate, to give the chain‐extended products 2 (81%), 5 (72%), and 6 (83%), respectively. Treatment of the 1‐C ‐nitroglycosyl bromide 7 by the lithium salt obtained form 8 gave the dodecodiulose derivative 9 (76%). Th β‐D‐configuration of 2 and 9 was inferred form their NMR and CD spectra. Treatment of 2 and 9 with sodium sulfide gave the enol ethers 3 (96%) and 10 (92%), respectively. The (Z)‐configuration of 10 was deduced form the configuration of its hydrogenation product 11.
Planarisation of Tetracoordinate Carbon Atom. A Further Route ot (all‐cis)‐[5.5.5.5]Fenestrane
Authors: Luyten Marcel , Keese Reinhart 
Published: December 2004

AbstractThe synthesis of (all‐cis)‐[5.5.5.5]fenestrane (3) from dicyclopentadiene is reported. Key step is the Pd‐catalyzed reductive deoxygenation of an appropriately substituted cyclooctanone, which leads to transannular C,C‐bond formation.
A New Approach to 1,2,4‐Trioxanes form Cyclic Allylic Hydroperoxides
Authors: Jefford Charles W. , Jaggi Danielle , Kohmoto Shigeo , Boukouvalas John , Bernardinelli Gérald 
Published: December 2004

AbstractSummary The reaction of 4,5‐dimethyl‐4‐hydroperoxy‐1(4H)‐nephthalenone (9) with acetaldehyde, pivalaldehyde, benzaldehyde, and p‐chlorobenzaldehyde in CH2Cl2 in the presence of Amberlyst‐15 as catalyst gave the corresponding cis‐3‐methyl, t ‐butyl, phenyl and p ‐chlorophenyl derivatives of 10,10b‐dimethylnaphtono[2,1‐e][1,2,4]trioxin‐6(5)H‐one in 80‐95% yields. Acetone reacted similarly with 9 to give the 3,3′ ‐dimethyl derivative. Configurations of all trioxinones were assigned by comparison of their spectral properties with that of the p ‐chloro derivative whose structure was determined by X‐ray. 2,5‐Diphenyl‐2‐hydroperoxypyrrole was less efficient that 9, but it condensed with acetaldehyde and pivaladehyde under the same conditions giving the cis ‐ 3‐methyl and cis ‐ 3‐(t ‐butyl) derivatives of 6,7a‐diphenyl‐4a, 7a‐dihydro‐3H, 5H ‐[1,2,4]trio‐xino[3,2‐e]pyrrole in 24 and 20% yield, respectively.
Cyclic Octa‐ and Decapeptides as Ionophores for Magnesium
Authors: Behm Felix , Ammann Daniel , Simon Wilhelm , Brunfeldt Kay , Halstrøm John 
Published: December 2004

AbstractCyclic octa‐ and decapeptides have been prepared, and their ion selectivity in solvent polymeric membranes was studied. Cyclo(‐LPro‐DLeu‐)5 behaves as an ionophore which selects Mg2+ over Ca2+ by a factor of 100. Cyclo(LPro‐LLeu)5 induces selectivity in membranes for Mg2+ over Li+, Na+ and K+ by a factor of 400, 200 and 10, respectively, while selectivity of Mg2+ over Ca2+ is poor. Some evidence is presented which indicates that certain ionophores exhibit high selectivity for monovalent magnesium complexes.
Skeletal Migrations Observed during the Cob(I)alamin‐Catalyzed Reduction of 4β‐(tert‐Butyl)‐1β‐(1‐methylvinyl)cyclohexanecarbaldehyde
Authors: Ziegler Carl B. , Fischli Albert 
Published: December 2004

AbstractDuring the cob(I)alamin(1(I))‐catalyzed reduction of 3, intermediate formation of 2 and final generation of 4–10 was observed (see Scheme 1, cf. Tables 1 and 2). Identical products in similar ratios were generated starting from either 2 or 3. Accepting the intermediate formation of six interconnected cobalt complexes, i.e. A–F (cf. Scheme 2), the generation of all the products observed can be explained.
The crystal structure of racemic and meso‐diastereoisomers of aqua[2,6‐bis(3‐carboxy‐1,2‐dimethyl‐2‐azapropyl)pyridine]‐Co(III) · Hexafluorophosphate · Di‐ and monohydrate, respectively
Authors: Stoeckli‐Evans Helen , Brehm Lotte , Pousaz Philippe , Bernauer Klaus , Bürgi Hans‐Beat 
Published: December 2004

AbstractSynthesis of the pentadentate ligand 2,6‐bis(3‐carboxy‐1,2‐dimethyl‐2‐azapropyl)pyridine yields a mixture of the racemic and meso‐isomers which it was difficult to separate by column chromatography. When the cationic Co(III)‐complex of this ligand was crystallized with hexafluorophosphate as anion, two distinct crystalline forms were produced. The complex of the racemic ligand, 1, has C2 symmetry and is a dihydrate; a = 8.999(8), b = 12.047(6), c = 20.65(1) Å, orthorhombic, space group Peen,Z = 4, R = 0.074 for 1439 observed reflections. The complex of the meso‐ligand, 2, shows two independent molecules (2A and 2B) per asymmetric unit, both monohydrates with a resolved disordered H2O molecule in 2A; a = 10.109(4), b = 12.835(2), c = 16.651(3) Å, α = 89.5(1)°, β = 84.7(3)°, γ = 88.6(3)°, triclinic, space group P1, Z = 4, Rs = 0.054 for 4198 observed reflections. The coordination around the Co‐atom is distorted octahedral in both complexes, with the coordinated H2O molecule trans to the pyridine N‐atom. In the racemic form of the complex, 1, the pyridine ring is twisted about the Co‐N(1) bond with respect to the plane defined by atoms Co, N(1), O(W1), N(2) and N(2P) by 17.2(2)°. In the meso‐form of the complex, 2, the CH3 substituent C(8P) on atom C(4P), is now axial with respect to the 5‐membered chelate ring. As a result of steric hinderance between atom O(1) and CH3(8P), the pyridine ring has been displaced from the best mean‐plane formed by atoms Co, O(W1), N(2) and N(2P). The principal axis of the pyridine ring C(3)…N(1), makes an angle of 14.1(1)° (mean) with this plane. At the same time the pyridine ring is twisted about axis C(3)…N(1) with respect to this plane by 19.7(1)° (mean).
β‐Funktionalisierte Hydrazine aus N‐Phthalimidoaziridinen und ihre hydrogenolytische N,N‐Spaltung zu Aminen
Authors: Egli Markus , Hoesch Lienhard , Dreiding André S. 
Published: December 2004

β‐Functionalized Hydrazines from N‐Phthalimidoaziridines and their Hydrogenolytic N,N‐Cleavage to AminesThe three N‐phthalimido‐aziridines 1–3 were reacted with phenol, thiophenol, aniline, p‐toluenesulfonic acid, and H2O in selected combinations. These nucleophiles opened the 3‐membered ring to yield the N‐phthalimidoamines 4a–d, 5a–d, 6a–c, and 6e; all these products (except the carbinol 6e) carry an aryl‐substituted functional group on the C‐atom vicinal to the N‐substituent. Hydrazinolysis of 4, 5, 6a–c, and 6e afforded the β‐functionalized hydrazines 7, 8, 9a–c, and 9e. The reducing medium Raney‐Ni/N2H4 transformed 4, 5, 6a–c, and 6e to the β‐functionalized amines 10, 11, 12a–c, and 12e. By a study with the hydrazide 6a and the hydrazine 9a, it was shown that the N,N‐cleavage is a catalytic hydrogenolysis by H2 generated from N2H4 with Raney‐Ni and that it does not take place on the hydrazide 6, but rather on the hydrazine 9, generated as intermediate from 6 with N2H4. Spectroscopic data confirmed that the conversions of 1–3 to 4–6 occurred exclusively with inversion and that the resulting configurations remained fully intact during the transformations of 4, 5, and 6 (via 7, 8, and 9) to 10, 11, and 12, respectively.
Stereoselective glycosylation of Alcohols and Silyl Ethers Using Glycosyl Fluorides and Boron Trifluoride Etherate
Authors: Kunz Horst , Sager Wilfried 
Published: December 2004

AbstractThe stereoselective glycosylation of alcohols and their silyl ethers has been achieved using O‐alkyl‐, O‐acyl‐, and acetal‐protected glycosyl fluorides of the pyranose and furanose series and boron trifluoride etherate in CH2Cl2.
Disproof of the Overall Enzymatic Biosynthesis of Vindoline from Tryptamine and Secologanin by Cell‐Free Extracts from the Leaves of Catharanthus roseus (L.) G. DON
Authors: Stöckigt Joachim , Gundlach Heidrun , Deus‐Neumann Brigitte 
Published: December 2004

AbstractA cell‐free extract, which was isolated from the leaves of mature Catharanthus roseus plants by a previously published procedure, does not convert a mixture of secologanin and radiolabelled tryptamine to vindoline, as was recently claimed. The radioactivity in the purified alkaloid extract determined by earlier workers is certainly due to ‘impurities’ in the presumed ‘vindoline’. This was shown by extensive purification of the alkaloid extract (which contained added unlabelled vindoline as a carrier) followed by chemical conversion of vindoline to two derivatives and subsequent purification, ultimately giving unlabelled deacetylvindoline.
The Molecular Ion of 5‐Methylene‐1,3‐cyclohexadiene: Electronic Absorption Spectrum and Revised Enthalpy of Formation
Authors: Bally Thomas , Hasselmann Dieter , Loosen Klaus 
Published: December 2004

AbstractThe title compound (1) is prepared in situ from 5‐methylenebicyclo[2.2.0]hex‐2‐ene by pyrolysis and subsequent photoionization in a photoelectron spectrometer or by X‐ray irradiation in an Ar matrix where its electronic absorption spectrum is obtained. The results confirm earlier conjectures that the title cation exists as a distinct entity on the C7H8+ hypersurface and can be obtained photochemically from other isomeric ions or by a McLafferty rearrangement. The enthalpies of formation of 1, its precursor and the corresponding radical ions are compared to the most recent data available for other C7H8 isomers and their ions. It is shown that the thermodynamic stability of 1+ is closer to that of toluene cation than concluded on the basis of earlier results.
The Structures of Some Products from the Photodegradation of the Pluramycin Antibiotics Hedamycin and Kidamycin
Authors: Fredenhagen Andreas , Séquin Urs 
Published: December 2004

AbstractThe photolability of the antitumor antibiotic hedamycin (1) was investigated by irradiation in different solvents in the presence or in the absence of oxygen. The products formed were separated chromatographically and their structures determined by NMR spectroscopy. Photolysis of 1 in the presence of oxygen gave only one isolable product, photohedamycin A (3), where ring E of hedamycin had been transformed into an enol ether. The reaction in the absence of oxygen yielded the photohedamycins B, C, and D (5, 6, and 7, respectively). In these compounds, one of the epoxides of hedamycin had been opened reductively, and in photohedamycin D (7) the substituent at C(8) ‐ originally ring E of hedamycin ‐ was now acyclic. In addition to these compounds, the photolyses yielded a large number of unstable minor products, which could not be isolated.
First Optically Active Heptalenes and their Absolute Configuration
Authors: Bernhard Werner , Brügger Paul , Daly John J. , Schönholzer Peter , Weber Roland H. , Hansen Hans‐Jürgen 
Published: December 2004

AbstractIt is shown that dimethyl 7‐isopropyl‐5, 10‐dimethylheptalene‐1, 2‐dicarboxylate (1) and dimethyl 5, 6, 8, 10‐tetramethylheptalene‐1, 2‐dicarboxylate (2) can be resolved via the corresponding mono‐acids and with the aid of optically active primary or secondary amines such as 1‐phenylethylamine or ephedrine into the (−)‐(P)‐ and (+)‐(M)‐enantiomeres, respectively. Characteristic for the (P)‐chirality of the heptalene π‐skeleton with C2 or pseudo‐C2 symmetry are two (−)‐CE's at the long wavelength region (450–300 nm) followed by at least one intense (+)‐CE at wavelengths about or below 300 nm. The absolute configuration of the heptalenes was correlated with the well‐established absolute configuration of (+)‐(R)‐ and (−)‐(S)‐1‐phenylethanol.
Nucleoside und Nucleotide. Teil 22. Synthese eines Tridecanucleosiddodecaphosphats, das die unnatürliche Base 2(1H)‐Pyrimidinon enthält
Authors: Altermatt Rolf , Tamm Christoph 
Published: December 2004

Nucleosides and Nucleotides. Part 22. Synthesis of a Tridecanucleoside Dodecaphosphate Containing the Unnatural Base 2(1H)‐PyrimidinoneThe tridecanucleosid dodecaphosphate d(TpTpMpCpGpTpCpApApApApTpC incorporating the modified nucleoside 1‐(2′‐deoxy‐β‐D‐ribofuranosyl)‐2(1H)‐pyrimidione (Md,2) was synthesized using the triester method. The intermediates were the suitably protected trimer d(TpTpM) and the pentamer d(TpTpMpCpG). The latter was condensed with the protected octamer d(TpCpApApApApTpC) to yield the desired tridecanucleotide.
Spontane Öffnung des Pyrimidinringes in Pyrrolo[2,3‐d]pyrimidinen nach intramolekularer Acylierung
Authors: Rosemeyer Helmut , Kaiser Klaus , Seela Frank , Zabel Volker , Saenger Wolfram 
Published: December 2004

Spontaneous Opening of the Pyrimidine Ring of Pyrrolo[2,3‐d]pyrimidines after Intramolecular AcylationPhase‐transfer alkylation of 4‐methoxy‐2‐methylthio‐7H‐pyrrolo[2,3‐d]pyrimidine (2) with ethyl 3‐bromopropionate leads regioselectively to the ester 3a. After displacement of its methylthio group and saponification of the ester function, the acid 3e is obtained which can be transferred to the functionalized deazahypoxanthine 3f by either treatment with dry HBr/glacial AcOH or by nucleophilic displacement of the 4‐methoxide. Reaction of 3f with a H2O‐soluble carbodiimide results in an intramolecular acylation at N(1) by the activated ester; the intermediate 4 undergoes spontaneous hydroxylation and subsequent opening of the pyrimidine ring under formation of the pyrrolo[1,2‐a]pyrimidine derivative 6. Its structure was proved by X‐ray analysis. Subsequent deformylation of 6 in alkaline medium leads to the compound 7 in almost quantitative yield.
Facile Synthesis of 2′‐Deoxyribofuranosides of Allopurinol and 4‐Amino‐1H‐pyrazolo[3,4‐d]pyrimidine via Phase‐Transfer Glycosylation
Authors: Seela Frank , Steker Herbert 
Published: December 2004

AbstractPhase‐transfer glycosylation of 4‐methoxy‐1H‐pyrazolo[3,4‐d]pyrimidine with the 2‐deoxyribofuranosyl chloride 9 formed the N(1)‐β‐nucleoside 10a as main product (39%). As by‐products the α‐D‐anomer 11a (7%) and the N(2)‐isomer 12a (18%) were isolated. Assignment of these isomers was made on the basis of their 1H‐ and 13C‐NMR spectra. Removal of the sugar‐protecting groups yielded the 4‐methoxy‐nucleosides 10b, 11b, and 12b, respectively. Nucleophilic displacement of the 4‐MeO‐group gave the 2‐deoxyribofuranosides 1–4 of allopurinol and 4‐amino‐1H‐pyrazolo[3,4‐d]pyrimidine.
The Electronic Structure of Dopamine. An ab initio Electrostatic Potential Study of the Catechol Moiety
Authors: van de Waterbeemd Han , Carrupt Pierre‐Alain , Testa Bernard 
Published: December 2004

AbstractElectronic properties of dopamine were studied by the ab initio STO‐3G MO method. The molecular electrostatic potential (MEP) around the aromatic ring and the catechol group remains practically the same in 3,4‐dihydroxytoluene (a model compound) and in neutral dopamine examined in its two extended conformations, namely that found in the crystal (side‐chain and aromatic ring almost perpendicular) and the one corresponding to 2‐amino‐6,7‐dihydroxytetralin (6,7‐ADTN) (side‐chain and aromatic ring almost coplanar). In protonated dopamine and in dopamine hydrochloride, the electrostatic potential of the catechol moiety is overshadowed by the positive charge, but the main features remain discernible. The catechol moiety was examined in its two coplanar conformations containing a ‘flip‐flop H‐bond’. The electrostatic potential around the catechol moiety is quite complex, with alternating positive and negative maxima. At increasing distances above and away from the catechol moiety, only two peripheral maxima, one negative and one positive, remain perceptible. The ‘flip‐flop’ mechanism results in an approximate interchange of these two potential maxima, a fact which tends to level out the structural differences between the α‐ and β‐rotamer of dopamine. Based on these results and on the structure of rigid agonists, some pharmacophoric features of dopamine agonists are proposed.