bluuebunny/crossref_metadata_2025_split huggingface dataset:
Approaches to the Synthesis of Cytochalasans. Part 3. Synthesis of a substituted tetrahydroisoindolinone moiety possessing the same relative configuration as proxiphomin
Authors: Schmidlin Tibur , Züurcher Werner , Tamm Christoph 
Published: December 2004

AbstractThe total synthesis of the tetrahydroisoindolinone moiety corresponding to proxiphomin (1) is described, bearing functional groups for the attachment of the macrocyclic ring. Knoevenagel‐Cope condensation of racemic 2‐(benzyloxycarbonyl‐amino)‐3‐phenylpropanal (2) with methyl (4‐methyl‐2,4‐hexadienyl) malonate (3) yielded a mixture of the (E)‐ and (Z)‐olefins 4a and 4b, which upon heating underwent intramolecular Diels‐Alder cyclization (cf. Scheme 1). From the resulting products the tetrahydroisoindoline derivative 6 was isolated. X‐ray analysis of 6[5] revealed the same relative configurations at C(3), C(4), C(5) and C(8) as in 1, but not at C(9). Hydrolysis of 6 with KOH was accompanied by a change in configuration at C(9) yielding the hydroxy acid 14 which was converted into the hydroxy ester 11 (cf. Scheme 4). The presence of a cis‐anellated lactam ring in 11 has been confirmed by X‐ray analysis of its O‐acetyl derivative 16 [5]. Ring closure of the hydroxy acid 14 gave the lactone 17, corresponding to the natural product 1 as to the configuration. The presence of the N‐benzyloxycarbonyl group in lactone 6 has been shown to be essential for the above‐mentioned ‘inversion’ at C(9), because no configurational change occurred with the N‐unprotected lactone 8 when treated under the same conditions. The only product obtained was the hydroxy ester 10 possessing the same configuration at C(9) as 8. Along with stereochemical considerations, mechanistic aspects of the reactions are discussed.
Selectivities in the Reactions of Alkyl‐, Aryl‐ and Heterosubstituted Organotitanium Compounds Preliminary Communication
Authors: Weidmann Beat , Widler Leo , Olivero Alan G. , Maycock Christopher D. , Seebach Dieter 
Published: December 2004

AbstractSolutions of the title compounds R‐Ti(OR′)3 (1) are generally available from organolithium (or magnesium) derivatives according to equation 1. It is shown (Table 1) that some heterosubstituted organotitanium compounds are more stable thermally than their lithium counterparts. The reagents 1 are highly selective carbonylophiles (Tables 1 and 2), their reactivity can be modified by variation of the R′O‐group (Table 3) and with the chiral (S)‐2‐methyl‐l‐butoxy group an enantioselective addition can be achieved [equ. 2].
Dediazoniations of Arenediazonium Ions in Homogeneous Solution. Part XIV. 15N‐CIDNP. Investigation of the reactions of diazonium ions in weakly alkaline aqueous solutions
Authors: Dreher Eberhard‐Ludwig , Niederer Paul , Ricker Anton , Schwarz Wolfgang , Zollinger Heinrich 
Published: December 2004

Abstract15N‐CIDNP. spectra recorded during the reaction of diazonium cations with OH− in weakly alkaline aqueous solutions show that the dediazoniation is at least partially homolytic. The polarizations observed for the diazonium and trans‐diazotate ions can be explained by reaction proceeding via a cage involving diazenyl and diazotate radicals using Kaptein's rules and simple intensity considerations.
Preferential Solvation of the Sodium Cation in Binary Mixtures of Tetrahydrofuran with Unidentate Nitrogen Ligands
Authors: Delville Alfred , Detellier Christian , Gerstmans André , Laszlo Pierre 
Published: December 2004

Abstract23Na‐chemical shifts for the NaClO4solute depend markedly upon the composition of binary solvent mixtures of THF with amines (pyridine, piperidine, pyrrolidine, aniline, propylamine, and isopropylamine). These changes, analyzed in a novel application of theHillformalism, show equality of the intrinsic equilibrium constant K for the successive steps, upon displacement of THF from sodium coordination by one of these amines. The results, which are entirely consistent with tetracoordination of the sodium cation by these solvents, also indicate proportionality of the K values to the amine chemical shifts.
Dérivés de désoxy‐hydroxylamino‐sucres et radicaux libres diglycosylnitroxydes correspondants. Communication préliminaire
Authors: Tronchet Jean M. J. , Winter‐Mihaly Eva , Habashi Ford , Schwarzenbach Dominique , Likić Ubavka , Geoffroy Michel 
Published: December 2004

Deoxy‐hydroxylamino‐sugar Derivatives and Corresponding Diglycosylnitroxides RadicalsA number of sugar aldonitrones, including C,N‐diglycosylnitrones, and ketonitrones have been treated with Grignard reagents or cyanide anion leading to the corresponding deoxy‐hydroxylamino‐sugars. On oxidation (air, H5IO6 or PbO2), these compounds gave the corresponding nitroxide radicals whose ESR. spectra are reported. Analogues of disaccharides, in which the interglycosidic O‐bridge is replaced by a hydroxyimino group, have been obtained by reacting a partially blocked sugar bearing a free hemiacetal group either with a deoxy‐hydroxylaminosugar or with hydroxylamine, followed by reaction with an aldehydosugar and a reducing agent (NaBH4). These reactions represents the key synthetic steps for the oligosaccharide‐type synthesis of deoxy‐hydroxyimino‐oligosaccharides. Their oxidation yielded the corresponding nitroxide radicals whose ESR. spectra gave information on the conformation about the ‘interglycosidic’ bridge. This type of compounds should constitute useful spin markers for biological studies.
Anil‐Synthese. 24. Mitteilung. über die Herstellung von Styryl‐ und Stilbenyl‐Derivaten des 1H‐Benzotriazols
Authors: Siegrist Adolf Emil 
Published: December 2004

Preparation of Styryl and Stilbenyl Derivatives of 1H‐Benzotriazoles1‐(p‐Tolyl)‐substituted 1H‐benzotriazoles react with anils of aromatic aldehydes in the presence of dimethylformamide and potassium hydroxide to yield the corresponding 1‐(styr‐4′‐yl)‐1H‐benzotriazoles and 1‐(stilben‐4′‐yl)‐1H‐benzotriazoles, respectively (‘anil synthesis’). Further, under the same reaction conditions, the Schiff's bases derived from p‐chloroaniline and 4‐(1′H‐benzotriazol‐1′‐yl)benzaldehydes give, with p‐tolyl‐substituted heterocycles, the corresponding heterocyclic substituted stilbenyl derivatives.
Conformations of the Ten‐membered Ring in 5, 10‐Secosteroids. III: (Z)‐3β‐ and (Z)‐3α‐Hydroxy‐5, 10‐seco‐1 (10)‐cholesten‐5‐one Esters and (Z)‐5, 10‐seco‐1 (10)‐Cholestene‐3, 5‐dione
Authors: Fuhrer Hermann , Lorenc Ljubinka , Pavlović Vladimir , Rihs Grety , Rist Günther , Kalvoda Jaroslav , Mihailović Mihailo Lj. 
Published: December 2004

Abstract(Z)‐3β‐Acetoxy‐ and (Z)‐3 α‐acetoxy‐5, 10‐seco‐1 (10)‐cholesten‐5‐one (6a) and (7a) were synthesized by fragmentation of 3β‐acetoxy‐5α‐cholestan‐5‐ol (1) and 3α‐acetoxy‐5β‐cholestan‐5‐ol (2), respectively, using in both cases the hypoiodite reaction (the lead tetraacetate/iodine version). The 3β‐acetate 6a was further transformed, via the 3β‐alcohol 6d to the corresponding (Z)‐3β‐p‐bromobenzoate ester 6b and to (Z)‐5, 10‐seco‐1 (10)‐cholestene‐3, 5‐dione (8) (also obtainable from the 3α‐acetate 7a). The 1H‐and 13C‐NMR. spectra showed that the (Z)‐unsaturated 10‐membered ring in all three compounds (6a, 7a and 8) exists in toluene, in only one conformation of type C1, the same as that of the (Z)‐3β‐p‐bromobenzoate 6b in the solid state found by X‐ray analysis. The unfavourable relative spatial factors (interdistance and mutual orientation) of the active centres in conformations of type C1 are responsible for the absence of intramolecular cyclizations in the (Z)‐ketoesters 6 and 7 (a and c).
Über den Anteil sigmatroper 1, 5‐Wanderung von Kohlenwasserstoffgruppen bei der thermolytischen Skelettisomerisierung 5,5‐disubstituierter 1, 3‐Cyclohexadiene
Authors: Schiess Peter , Dinkel Rolf 
Published: December 2004

On the Extent of Sigmatropic 1, 5‐Migration of Hydrocarbon Groups in the Thermolytic Skeletal Rearrangement of 5,5‐Disubstituted 1,3‐CyclohexadienesThe uncatalyzed skeletal isomerization of 5, 5‐disubstituted 1, 3‐cyclohexadienes was investigated with the aim to establish the extent to which sigmatropic 1,5‐shifts of hydrocarbon groups are participating in these reactions.Gas phase pyrolysis of 5,5‐diethyl‐1,3‐cyclohexadiene (7) at 460° followed by chloranil aromatization yields only 4% of 1,3‐diethylbenzene resulting from 7 through a 1, 5‐ethyl migration in the primary reaction step. 2, 3‐Dimethylethylbenzene (56%) and 1, 4‐diethylbenzene (4%) are obtained as other C10‐compounds. This shows that isomerization proceeds mainly through a sequence of electrocyclic and 1, 7‐shift reactions. Ethylbenzene (24%) and other aromatic C8‐ and C9‐hydrocarbons are formed to a considerable extent, indicating that C, C‐bond cleavage is a major competing process and that the 1, 3‐diethylbenzene found is the result of a radical recombination reaction and not of a concerted sigmatropic shift of the ethyl group.5‐Methyl‐5‐phenyl‐1, 3‐cyclohexadiene (12) yields 3‐methylbiphenyl (14) and biphenyl upon thermolysis and aromatization. Through 13C‐substitution of the methyl group in 12 it is shown that in solution at 300° skeletal isomerization proceeds through electrocyclic and 1, 7‐H‐shift reactions exclusively. In the gas phase at 500° 4% of the isomerization product is formed by a 1, 5‐shift of a substitutent, presumably of the methyl group, through a dissociative mechanism.Thermolysis of 5, 5‐diphenyl‐1, 3‐cyclohexadiene (22) at 560° in the gas phase leads to 1, 1‐diphenyl‐1, 3, 5‐hexatriene (23) and 1‐vinyl‐4‐phenyl‐1, 2‐dihydronaphthalene (24) through electrocyclic reaction steps. In addition a small amount of m‐terphenyl is obtained at high conversion of 22. This indicates that sigmatropic 1,5‐phenyl migration can participate in product formation only at high temperature and in the absence of other irreversible pathways to stable products.
Electrochemical Properties of Hydroxyphenazine‐Coated Electrodes
Authors: Haas Otto , Zumbrunnen Hans‐Rudolf 
Published: December 2004

AbstractGlassy carbon and gold electrodes were coated with 1‐hydroxyphenazine, and the electrochemical properties of these electrodes were tested using them as a rotating disc electrode to reduce Ru (bipy)33+, Fe3+, quinoxaline, O2, and to oxidize Eu2+. The fixed redox couple can be reversibly reduced and oxidized, and acts as an intermediate medium for the electron transfer. For example the Ru(bipy)33+ (E1/2= 1010 mV vs. SCE. (saturated calomel electrode) on a glassy carbon electrode in 1M H2SO4) is only reduced at 50 mV, whereas the oxidation of Eu2+ (E1/2= −460 mV vs. SCE. on a Hg‐electrode in 1M HCl) takes place at − 100 mV. The heterogeneous rate constant depends on the second order reaction between the attached coating and the redox couple in solution. Depending on this rate constant, selectivity of the electrode is observed.
Zur Konfiguration des Vitamin‐D3‐Metaboliten 25, 26‐Dihydroxycholecalciferol: Synthese von (25S,26)‐ und (25R,26)‐Dihydroxycholecalciferol
Authors: Barner Richard , Hübscher Josef , Daly John J. , Schönholzer Peter 
Published: December 2004

Configuration of the Vitamin‐D3‐Metabolite 25,26‐Dihydroxycholecalciferol: Synthesis of (25S,26)‐ and (25R,26)‐DihydroxycholecalciferolFor selective synthesis of the title compounds, (25S)‐1b and (25R)‐1b (Scheme 1), the protected cholesterol precursors (25S)‐6 and (25R)‐6 were prepared from stigmasterol‐derived steroid‐units 4a‐d and C5‐side chain building blocks 5a–d by Grignard‐ or Wittig‐coupling (Scheme 2), the configuration at C(25) of the target compounds being already present in the C5‐units. Conversion of the cholesterol intermediates to the corresponding vitamin‐D3 derivatives was carried out via the 7,8‐didehydrocholesterol compounds (25S)‐2b and (25R)‐2b (Scheme 1), using the established photochemical‐thermal transformation of the 5,7‐diene system to the seco‐triene system of cholecalciferol. The configuration at C(25) of the cholesterol precursors as assigned on basis of the known configuration of the C5‐units used, was found to be in agreement with the result of a single crystal X‐ray analysis on compound 11. The configuration at C(25) remained untouched on conversion of the cholesterol ring system to the seco‐triene system of vitamin D3 as evident from comparison of the lanthanide‐induced CD. Cotton effects observed for (25S)‐3b and (25S)1b. 25,26‐Dihydroxycholecalciferol observed as a natural vitamin‐D3 metabolite has (25S)‐configuration.
Wittig‐Reaktionen von sulfonierten Phosphoniomethylstrylaromaten mit aromatischen und heteroaromatischen Aldehyden
Authors: Märky Michael 
Published: December 2004

Wittig Reactions of Phosphoniomethylaryl Compounds with Sulfonated Aromatic and Heteroaromatic AldehydesBis (triphenylphosphoniomethyl)aryl dichloride derivatives react with aromatic or heteroaromatic aldehydes which have a sulfonic or carboxylic group attached to the ring system, to yield stilbene compounds of a betaine‐type structure. These betaines are reacted further with various aromatic or heteroaromatic aldehydes yielding asymmetrically substituted derivatives in excellent yields. This new method is widely applicable to the preparation of water‐soluble, fluorescent whitening agents of the bis‐stilbene type.
A Note on Stereochemical Observations of the Deprotonation of Ethyl 2‐Alkenoates
Authors: Krebs Ernst‐Peter 
Published: December 2004

AbstractDeprotonation of ethyl (E)‐2‐alkenoates 1, 3 and 4 yields after protonation the double bond migrated (3 Z)‐isomers 5, 7 and 9 as major products. In contrast, deprotonation and reprotonation of ethyl (Z)‐2‐pentenoate (2) gives the (3 E)‐isomer 6 exclusively. These findings are explained by reaction paths starting from different ester conformations.
Synthesis of Reactive Intermediates for Natural Cyclopentane Derivatives from (−)‐Quinic Acid: Preparation of 11α‐hydroxy‐13‐oxaprostanoic acid
Authors: Barrière Jean‐Claude , Chiaroni Angèle , Cléophax Jeanine , Géro Stephan D. , Riche Claude , Vuilhorgne Mare 
Published: December 2004

AbstractWe describe a flexible, stereocontrolled synthesis of enantiomerically pure substituted cyclopentenes and cyclopentanes ‐ including 11α‐hydroxy‐13‐oxaprostanoic acid 20 ‐ (−)‐quinic acid via an acyclic precursor 6 by an intramolecular aldolisation‐dehydration reaction.
Chiral 1, 4‐Benzodiazepin‐2‐one, template for enantioselective synthesis of α‐amino acids and their α‐deuterio congeners. Preliminary communication
Authors: Decorte Enio , Toso Roberto , Sega Alessandro , Šunjié Vitomir , Ružić‐Toroš Živa , Kojić‐Prodić Biserka , Bresciani‐Pahor Nevenka , Nardin Giorgio , Randaccio Lucio 
Published: December 2004

AbstractAbsolute conformation of 7‐chloro‐5‐phenyl‐1‐[(S)‐α‐phenylethyl]‐1, 3‐dihydro‐2H‐1, 4‐benzodiazepin‐2‐one (1c) in crystal, and its inversion rate in solution were determined, enabling prognosis of direction of asymmetric induction during C(3)‐alkylation.
Total Synthesis of All Eight Stereoisomers of α‐Tocopheryl Acetate. Determination of their diastereoisomeric and enantiomeric purity by gas chromatography
Authors: Cohen Noal , Scott Clifford G. , Neukom Christian , Lopresti Rocco J. , Weber Giuseppe , Saucy Gabriel 
Published: December 2004

AbstractAll eight stereoisomers of α‐tocopheryl acetate have been synthesized in a state of high chemical and stereoisomeric purity. Key chiral side‐chain intermediates were prepared from (+)‐(S)‐3‐hydroxy‐2‐methylpropanoic acid. New routes to (2R, 4′ RS, 8′ RS)‐α‐tocopheryl acetate, a mixture of four diastereoisomers, were also developed. A sensitive gas chromatographic method was developed to determine the diastereoisomeric and enantiomeric purity of α‐tocopherol samples as the methyl ethers. It was established for the first time that naturally occurring α‐tocopherol is essentially a single enantiomer (2 R, 4′ R, 8′ R), synthetic all‐rac‐α‐tocopherol an equimolar mixture of four racemates, and that natural (E)‐(7 R, 11 R)‐phytol is diastereoisomerically and enantiomerically homogeneous.
2‐Oxocephems and 2‐Acetylpenems ‐ Selective Formation in an Intramolecular Wittig Reaction
Authors: Ernest Ivan , Main Alan J. , Woodward Robert B. 
Published: December 2004

AbstractSelective formation ‐ in intramolecular Wittig condensations ‐ of the 2‐oxocephem‐4‐carboxylate 8a and of the 2‐acetylpenem‐3‐carboxylate 9, respectively, was observed as a consequence of different carbonyl reactivities in two homologous α‐oxoacylthio groupings. Free, racemic and 7‐unsubstituted 2‐oxocephem‐4‐carboxylic acid (10) was prepared from 8a for biological testing. Attempts to prepare the free 2‐acetylpenem‐3‐carboxylic acid from 9 failed, probably due to the high lability of the β‐lactam system.
Röntgenstrukturanalyse eines neuartigen spirocyclischen Diglycosides, eines Abbauproduktes der Antibiotika Papulacandin A, B and C
Authors: Rihs Greti , Traxler Peter 
Published: December 2004

X‐Ray Analysis of a Novel Spirocyclic Diglycoside, a Degradation Product of the Antibiotics Papulacandin A, B and CStructure 4 has been established for a novel spirocyclic diglycoside which is a degradation product of the antibiotics papulacandin A, B and C. By X‐ray analysis the diglycoside was shown to consist of a galactose moiety connected by a β‐1, 4‐linkage to a glucose. This diglycoside is further connected by a spiro union to a oxaindan‐diol moiety.
Nucleotide. XIV. Substituierte β‐Phenyläthyl‐Gruppen. Neue Schutzgruppen für Oligonucleotid‐Synthesen nach dem Phosphorsäuretriester‐Verfahren
Authors: Uhlmann Eugen , Pfleiderer Wolfgang 
Published: December 2004

XIV. Substituted β‐Phenyl‐ethyl Groups. New Blocking Groups for Oligonucleotide Syntheses by the Phosphotriester ApproachVarious o‐ and p‐substituted β‐phenylethanols (2–10) have been synthesized and investigated as blocking groups in the phosphotriester approach. A large number of 5′‐O‐tritylated thymidine‐3′‐phosphotriesters (13–36) with two different phosphate protecting groups have been prepared, characterized, and studied according to their chemical stability and usefullness for oligonucleotide syntheses. The combination of a 5′‐O‐monomethoxytrityl‐ and a 3′‐(2,5‐dichlorophenyl, p‐nitrophenylethyl)‐phosphate function as in 18 turned out to possess optimal properties as a monomeric nucleotide building block due to the fact that these blocking groups can be quantitatively and selectively be removed without harming each other by trifluoroacetic acid in chloroform to 41, by oximate to 42, and by DBU to 43. The base‐catalyzed removal of the monosubstituted phenylethyl groups by DBU or DBN respectively as well as the disubstituted phenylethyl groups by triethylamine in aprotic solvents is a β‐elimination process leading to phosphodiesters without attack on the P‐center.
Nucleophilic Aromatic Substitutions. Part XIV.. Investigation of the mechanism of hydroxy‐denitration of 4,2‐and 2,4‐chloronitrobenzenediazonium ions as a function of pH
Authors: Pikulik Ivan I. , Weber Rudolf U. , Zollinger Heinrich 
Published: December 2004

Abstract4,2‐Chloronitrobenzenediazonium ions in aqueous buffer solutions between pH 2.9 and 7.9 do not hydrolyze by dediazoniation as previous authors have assumed, but by denitration. The isomeric 2,4‐compound reacts by denitration (ca. 70%) and dechlorination (ca. 30%). The reactions are general base catalyzed. The products and kinetics are consistent with an SNAr‐mechanism in which the general base‐catalyzed addition of a hydroxyl group at the reacting C‐atom is rate‐limiting. The rate maxima at or near the pH‐values corresponding to (pK1 + pK2)/2 of the diazonium ⇄ cis‐diazotate equilibria can be rationalized on the assumption that the diazonium ion is the only equilibrium form of the diazo compound which enters the substitution proper, and the superposition of the rate term kB[B] of all nucleophiles involved (H2O, OH− and buffer bases).
Laser Flash Photolysis of Phthalocyanines in Solution and Microemulsion
Authors: Jacques Patrice , Braun André M. 
Published: December 2004

AbstractTriplet state formation (Φisc) and properties (εT‐T, τT) of phthalocyanine (HPC) and zinc phthalocyanine (ZnPC) have been characterized in homogeneous solutions (1‐chloronaphthalene, 1‐propanol) and in microemulsion by investigating the variation of the transient optical density as a function of the intensity of the exciting laser. Experimental results follow the theoretically predicted dependence only for very low intensities of the exciting pulse. At higher intensities, a more complicated scheme of primary reactions has to be taken into account, implicating qualitative restrictions in the application of saturation experiments. The observed transients at high‐intensity excitation are interpreted as being perturbed by aggregational phenomena.
The structure of covalent hydrates of alloxazines. A reinvestigation
Authors: Koziol Jacek , Tyrakowska Bozena , Müller Franz 
Published: December 2004

AbstractIt is shown by 13C‐NMR. and synthesis of 6,7‐dimethyl‐3‐ethoxycarbonylamino‐quinoxaline‐2‐carboxamide (5) and methyl 6,7‐dimethyl‐3‐(N′‐methylureido)‐quinoxaline‐2‐carboxylate (6) that hydrolysis of lumichrome (1, R = H) must yield 6,7‐dimethyl‐3‐ureidoquinoxaline‐2‐carboxylic acid (2, R = H) and not 6,7‐dimethyl‐2‐oxo‐1,2,9,9a‐tetrahydrooxazolo[4,5‐b]quinoxaline‐9a‐carboxamide (2a, R = H), as previously proposed.
Kettenverlängerung funktionalisierter Alkanone durch Umlagerung
Authors: Lorenzi‐Riatsch Annalaura , Nakashita Yoshihiko , Hesse Manfred 
Published: December 2004

Chain Expansion of Functionalized Alkanones by Rearrangement ReactionsIn analogy to the transamidation reactions which were published earlier a method is described to prolong aliphatic C‐chains by two or four C‐atoms. 1,3‐Diketones or 2‐nitro alkanones which are monosubstituted at C(2) are condensed with e.g. methyl vinyl ketone. The reaction product is transformed to its chain‐prolonged isomer in the presence of strong base via a 4‐ or 6‐membered intermediate. The most effective reagent for the Michael reaction is methyl 3‐oxo‐4‐pentenoate (20). In this case it was possible to convert 3‐nitro‐2‐butanone (21) to methyl 2‐acetyl‐6‐nitro‐3‐oxoheptanoate (26) in 82% yield.
PCILO and CD. Conformational study of sulpiride, a dopamine antagonist
Authors: van de Waterbeemd Han , Testa Bernard 
Published: December 2004

AbstractThe conformational behaviour of sulpiride has been investigated by the quantum mechanical PCILO method and by CD. measurements. The results indicate the predominance of a folded, intramolecularly H‐bonded conformer, with extended conformers being only slightly less stable. The pharmacological relevance of these results is briefly discussed.