bluuebunny/crossref_metadata_2025_split huggingface dataset:
Eigenschaften und Verwendbarkeit des 10, 11‐Dihydro‐5H‐dibenzo[a,d]cyclohepten‐5‐yl‐Rests (= 5‐Dibenzosuberyl‐Rests) als neue Schutzgruppe für Amine, Aminosäuren, Alkohole, Thiole und Carbonsäuren
Authors: Pless Janos 
Published: December 2004

Properties and suitability of the 10,11‐dihydro‐5 H‐dibenzo[a, d]cyclohepten‐5‐yl group (= 5‐dibenzosuberyl group) as a new protecting group for amines, amino‐acids, alcohols, thiols and carboxylic acids.The 10,11‐dihydro‐5H‐dibenzo[a,d]cyclohepten‐5‐yl group (5‐dibenzosuberyl group): magnified image has been found useful for protecting amines, alcohols, thiols, and carboxylic acids.Furthermore, the investigated 5‐amino compounds are extremely stable in strongly acidic media (e. g. in hydrogen bromide) and still the amino group is easily cleaved under mild conditions, such as those used for N‐trityl compounds (e.g. boiling in dilute acetic acid or catalytic hydrogenation).Hence this ring system could be a valuable and adaptable protecting group, especially in peptide chemistry.
The Electronic Structure of Vinyl Ethers and Sulfides with Interrupted Conjugation Examined by Photoelectron Spectroscopy
Authors: Batich Christopher , Heilbronner Edgar , Quinn Clayton B. , Wiseman John R. 
Published: December 2004

AbstractPhotoelectron spectroscopy has been used to examine the consequences of steric inhibition of conjugation in a distorted vinyl sulfide and vinyl ether. Based upon the degree of interaction a deviation from coplanarity of 70°–75° is calculated for 9‐oxabicyclo[3.3.1]non‐1‐ene (3) and approximately 75°–80° for the sulfur analog 6.
Umwandlung des Iboga‐Alkaloides Voacangin in das β‐Carbolin‐Derivat Voaketon. 156. Mitteilung über Alkaloide
Authors: Morita Yutaka , Hesse Manfred , Schmid Hans , Renner Ulrich 
Published: December 2004

Transformation of the Iboga alkaloid voacangine into voaketone, a derivative of β‐carboline.The reduction product voacanginol (2), obtained from the indole alkaloid (−)‐voacangine (1), gave, by treatment of its tosylate 3 with methanolic pyridine in the presence of air, the rearrangement product (−)‐5 (voaketone). Its structure was derived from spectroscopic evidence (mainly NMR. and mass spectra) and some chemical transformation reaction, especially deuterium labelling. A possible mechanism for the formation of 5 from 3 is given in Scheme 6. The absolute configuration of 5 was deduced by comparison with yohimbine derivatives.
1‐aralkylated tetrahydro‐2‐benzazepines. Part II: Synthesis from 3‐(3,4‐dimethoxyphenyl)‐propylamine
Authors: Berney Daniel , Jauner Theodor 
Published: December 2004

Abstract3‐(3,4‐Dimethoxyphenyl)‐propylamine was N‐acylated with aralkanecarboxylic acid chlorides. The resulting amides were subjected to Bischler‐Napieralski ring closure to give the corresponding 1‐aralkyl‐dihydro‐2‐benzazepines. These were reduced to the title compounds.
Asymmetric Olefins Hydroformylation. VI. Asymmetric Hydroformylation of Isomeric Butenes Using Platinum Catalysts
Authors: Consiglio Giambattista , Pino Piero 
Published: December 2004

AbstractThe asymmetric hydroformylation of the straight chain butenes with the [(−)‐DIOP]PtCl2‐SnCl2 catalytic system shows that asymmetric induction, contrary to the rhodium‐(−)‐DIOP catalytic system, takes place after the intermediate metal‐alkyl‐complex formation.
Iron Carbonyls in Organic Synthesis, I. Iron Pentacarbonyl Induced Decomposition and Transfer Hydrogenation of Aryl Azides to Substituted Ureas
Authors: Iqbal Abul F. M. 
Published: December 2004

AbstractIron pentacarbonyl catalyzes smooth decomposition of aryl azides in the presence of acetic acid to afford good (70–90°) yields of the corresponding disubstituted ureas. Possible and alternative reaction mechanism pathways are discussed.
Photochemistry of 4,4‐Dialkoxy‐2,5‐cyclohexadienones
Authors: Margaretha Paul 
Published: December 2004

AbstractIrradiation (λ > 370 nm) of 4,4‐dimethoxy‐2,5‐cyclohexadienone (1 a) in benzene affords mainly the ketene acetal 4 a, which then undergoes further rearrangement. The carbomethoxycyclopentenones 6 and 7 were isolated in modest yields (10–15°). It is conceivable that the latter results from decomposition of the unobserved bicyclohexenone 5 a, the formation of which could be expected by analogy to e.g. 1 c → 5 c. Compound 4 a is presumably formed via 1,2 hydrogen shift from the intermediate zwitterion 3 a. Under similar irradiation conditions 1,4‐dioxa‐spiro[4.5] deca‐6,9‐dien‐8‐one (1 b) gave 4 b as the only definable product. In i‐C8H18 1 a gave p‐methoxyphenol (8) as the only product, most probably via hydrogen abstraction.
3‐Alkyl‐1‐benzoxepin‐5‐on‐Derivate und 2‐Alkyl‐1, 4‐naphthochinone aus 2‐Acylaryl‐propargyläthern
Authors: Jackson‐Mülly Martha , Zsindely Janos , Schmid Hans 
Published: December 2004

3‐Alkyl‐1‐benzoxepin‐5‐one derivatives and 2‐alkyl‐1,4‐naphtoquinones from 2‐acylaryl propargyl ethers.It was found that 3‐alkyl‐1‐benzoxepin‐5(2H)‐ones of type B can be synthesized by treating 2‐acylaryl propargyl ethers of type A with sodium methylsulfinyl methide (NaMSM, dimesyl sodium) (Scheme 13). Oxepinone derivatives of type B undergo ring contraction with base (also NaMSM) to yield the quinol derivatives C which, oxidize (during work‐up), if R2 = H, to the 1,4‐naphthoquinones D (Scheme 13).The propargyl ethers used are listed in Scheme 1. The naphthalene derivatives 1 and 3 give oxepinones (E‐9 and a mixture of 14/15 respectively), whereas the expected oxepinone from 2 is transformed directly into the quinone 11 (Scheme 2, 3 and 5). Isomerizations of 2‐acetylphenyl propargyl ethers (4, 5 and 6) (Schemes 6, 7 and 8) are less successful because of side reactions. If however the acetyl group is replaced by a propionyl or substituted propionyl group (as in ethers 7 and 8) oxepinones are obtained again in good yield (Scheme 9).The mechanistic pathway for the transformation of naphthyl propargyl ethers (and phenyl derivatives) under influence of NaMSM is shown in Scheme 10. The base‐catalysed conversion of 4‐phenyl‐l‐benzoxepin‐5(2H)‐one,benzo[f]furo[2,3‐c](10 H)‐oxepin‐4‐oncsand 3‐methoxy‐G,11‐ dihydro‐dibenzo[b, e]loxepin‐11‐oneinto thc corresponding quinones has been reported [13] [20] [21].The conversion of 2‐acylaryl propargyl others via the isolable benzoxepin‐5‐one derivativcs or directly into the specifically substituted 1,4‐naphthoquinone derivatives is of synthetic interest.
Preparation of 4‐(4′‐Methyl‐2′‐oxo‐cyclohex‐3′‐en‐1′ ‐yl) ‐ pentan‐1‐ol and Derivatives of 3‐(4′‐Methyl‐2′‐oxo‐cyclohex‐3′ ‐en‐1′ ‐yl)‐ butan‐1‐ol
Authors: Leppard David G. , Raynolds Peter W. , Chapleo Christopher B. , Dreiding André S. 
Published: December 2004

Es wird über eine, bzw. zwei Methoden zur Herstellung von 4‐(4′ Methyl‐2′‐oxo‐cyclohex‐3′‐en‐1′‐yl)‐pentan‐1‐ol (Schema 1) bzw. 3‐(4′‐Methyl‐2′‐oxo‐cyclohex‐3′‐en‐1′‐yl)‐butan‐1‐olThe IUPAC‐Nomenclature of these compounds is: 6‐(4′‐hydroxy‐1′‐methyl‐butyl)‐3‐methyl‐cyclohex‐2‐en‐1‐one and 6‐(3′‐hydroxy‐1′‐methyl‐propyl)‐3‐methyl‐cyclohex‐2‐en‐1‐one.

‐Derivaten (
Schemata 2
und
3
) berichtet. Die Synthesen sind nicht spezifisch bezüglich Diastereoisomerie an den Zentren C(1′) und C(4), bzw. C(1′) und C(3). Als potentielles Terpenoid‐Synthon kommt das Produkt der Synthese nach
Schema 1
, Schritte (1) bis (3), in Frage.
A Chemical Investigation of the Volatile Constituents of East Indian Sandalwood Oil (SantalumalbumL.)
Authors: Demole Edouard , Demole Cécile , Enggist Paul 
Published: December 2004

AbstractDistillation foreruns from East Indian sandalwood oil (Santalum album L.), representing 5–8% of the oil, have been investigated using fractional distillation, preparative column chromatography, gas liquid chromatography (GLC.), and chemical treatments. This allowed the isolation and characterization by their spectral data of 46 compounds. 32 of them were newly identified sandalwood oil constituents including 4 novel substances: santalone (2), 4‐methylcyclohexa‐1,3‐dien‐1‐yl methyl ketone (4), 5,6‐dimethyl‐5‐norbornen‐exo‐2‐ol (7), and (E)‐5‐(2,3‐dimethyl‐3‐nortricyclyl)‐pent‐3‐en‐2‐one (20). The other constituents identified were 1‐furfuryl‐pyrrole (10) and 10 phenols accompanied by 17 terpene and sesquiterpene derivatives. Endo‐2,endo‐3‐dimethyl‐norbornan‐exo‐2‐ol (6), an α‐santenol (z), precursor, was present in the last group of constituents. The compounds 2, 4, 6, 7, 20 have been synthesized as well as another novel constituent, endo‐2‐mythyl‐3‐methylidene‐norbornan‐exo‐2‐ol (5).
Photoreaktionen von 3‐substituierten Cumarinen
Authors: Pfoertner Karl‐Heinz 
Published: December 2004

Photoreactions of 3‐substituted CoumarinsUV.‐irradiation of 3‐acetylcoumarin in 2‐propanol gives the dihydrodimer 2. In benzene solutions 2‐ and 4‐vinylpyridine, 1,1‐dichloro‐ethylene, 2,3‐dimethylbutadiene, vinylene carbonate and cyclohexene add to 3‐acetylcoumarin and 3‐methoxycarbonylcoumarin yielding the cyclobutanes 4 to 11.
A New Reagent for the Cleavage of NPS‐Amino Protecting Groups in Peptide Synthesis
Authors: Juillerat Marcel , Pierre Bargetzi J. 
Published: December 2004

AbstractThe value of several reagents capable of removing quantitatively the α‐amino protecting group of NPS‐aminoacyl‐ or peptidyl‐derivatives is assessed, by comparison with the reagents currently used, i.e. hydrogen chloride, RS–‐nucleophiles or alkyl thioamides, especially with regard to reaction specificity and end‐product solubility. New reagents proposed, 3‐nitro‐4‐mercapto‐benzoic acid, and its methyl ester, appear to optimize the numerous, and often competing, requirements. These were probed, under conditions suitable for both conventional and solid‐phase methods, on a series of model compounds, including diversely protected amino acids and short peptides, as well as for the actual synthesis of a triacontapeptide by the stepwise, solid‐phase approach.
Synthetical pharmaceutics. 9‐ and 10‐Oxo derivatives of 9,10‐dihydro‐4H‐benzo‐[4,5]‐cyclohepta[1,2b]thiophenes
Authors: Waldvogel Erwin , Schwarb Gustav , Bastian Jean‐Michel , Bourquin Jean‐Pierre 
Published: December 2004

AbstractVerschiedene Synthesen zur Herstellung von 9‐Oxo‐9,10‐dihydro‐4H‐benzo[4,5]cyclohepta[1,2‐b]thiophenen 17 und 10‐Oxo‐9,10‐dihydro‐4H‐benzo[4,5]cyclohepta[1,2‐b]thiophenen 18 (25), mit der 1‐Alkyl‐4‐piperidyliden‐Gruppe in 4‐Stellung, ausgehend von 9,10‐Dihydro‐4H‐benzo[4,5]cyclohepta[1,2‐b]thiophen‐4‐onen 1 bzw. Folgestufen davon, werden beschrieben. Als weitere Derivate sind die N‐Oxide 26, die 9‐ und 10‐Hydroxy‐Derivate 27 und 28, die 9‐ und 10‐Oxime 29 und 30 sowie ein 9,10‐Diketon 31 hergestellt worden.
Synthese von 4′‐Azido‐3′,5′‐ditritio‐L‐phenylalanin‐peptiden als « Photo‐affinitätsproben » für Ligand‐Rezeptor‐Wechselwirkungen. Vorläufige Mitteilung
Authors: Fischli Walter , Caviezel Mario , Eberle Alex , Escher Emanuel , Schwyzer Robert 
Published: December 2004

The Synthesis of 4′‐Azido‐3′,5′‐ditrito‐L‐phenylalanine Peptides as « Photoaffinity Probes » for Ligand‐Receptor InteractionThe synthesis of L‐p‐azido‐phenylalanine and peptides thereof containing tritium atoms in the m,m′‐positions of the phenyl ring is described. Starting materials are L‐p‐amino‐phenylalanine and L‐p‐amino‐m,m′‐diiodo‐phenylalanine. Such peptides are being used for specific photoaffinity labelling of receptor and enzyme molecules.
13C‐NMR.‐Spektren N‐acylierter Indoline. Einfluss der Orientierung der Carbonylgruppe auf die chemische Verschiebung
Authors: Fritz Hans , Winkler Tammo 
Published: December 2004

13C‐NMR. spectra of N‐acylated indolines. Effect of the orientation of the carbonyl group on the chemical shiftLarge downfield shifts are observed in the 13C‐NMR. spectra of indolines and related compounds induced by electric field effects of carbonyl and oxime groups.
Naturstoffe aus Mikroorganismen. 7. Mitteilung [1]. Synthese von racemischen Proferrorosamin und Ferrorosamin
Authors: Marcel Helbling André , Viscontini Max 
Published: December 2004

Synthesis of Racemic Proferrorosamin and Ferrorosamin A.The synthesis of proferrorosamin starting from methyl 2‐phenylacetamido‐acrylate and ethyl 3‐oxo‐3‐(2‐pyridyl)‐propionate is described. Proferrorosamin A is complexed with Fe2+ and isolated as pure ferrorosamin A.
Electronic Structure and Photophysical Properties of Isoindole and its Benzo[f]‐ and Dibenzo[e,g]‐Derivatives
Authors: Rettig Wolfgang , Wirz Jakob 
Published: December 2004

AbstractThe synthesis of N‐methyl‐benz[f]isoindole (2) and N‐methyl‐dibenz[e,g]isoindole (3) is reported. The NMR. spectra of N‐methyl‐isoindole (1) and of 2 have been analysed and the implications concerning the alternation of bond lengths are discussed. The photophysical properties of 1 to 3 have been investigated by the following methods: HeI photoelectron (PE.) spectroscopy, UV./VIS. absorption (polarization measurements by the stretched‐foil technique) and emission spectroscopy (fluorescence spectra, lifetimes and quantum yields, phosphorescence spectra), and flash spectroscopy (triplet‐triplet absorption spectra). The discussion of the results is based on HMO. and PPP SCF CI. calculations and points to the relationship between the heterocycles 1 to 3 and the corresponding benzenoid hydrocarbons obtained by replacement of the NMesubunit by CHCH. Some comments concerning the ground state properties of isoindole and related compounds are derived from the analysis of their electronic structure.
Condensed 1,2,4‐Triazines I: Behaviour of Phenanthro[9,10‐e]‐1,2,4‐triazine Derivatives Towards Alkylating and Reducing Agends, Grignard Reagents, and Amines
Authors: Sallam Mohamed Mohamed Mohamed , Ibrahim Yehia Abdu , Abdel‐Hady Sayed Abdel‐Latif 
Published: December 2004

AbstractAlkylation of 3‐hydroxy‐phenanthro[9,10‐e]1,2,4‐triazine (1a) yielded the N(2)‐alkyl derivatives 2a–2b; alkylation of the 3‐mercapto analogue 1b yielded the S‐alkyl derivatives 1f–1i.1a–1b reacted with alkyl and aralkylmagnesium halides to yield the corresponding 3‐hydroxy‐, and 3‐mercapto‐5‐alkyl‐(aralkyl)‐phenanthro[9,10‐e]2,3,4,5‐tetrahydro‐1,2,4‐triazines 5a–5f.Reduction of 1a yielded the hexahydrotriazine derivative 7. Amination of 1c yielded the 3‐amino derivatives 1j–1o after prolonged heating.
Zur Stereochemie der Geruchswahrnehmung von 1‐Dekalon‐Derivaten und ihren oxaanalogen Verbindungen
Authors: Ohloff Günther , Giersch Wolfgang , Schulte‐Elte Karl H. , Vial Christian 
Published: December 2004

Stereochemistry‐odor relationships in the 1‐decalone series and their oxa‐analogs.The olfactory relationships of (−)‐(9S,10S)‐5,5,9‐trimethyl‐trans‐1‐decalone (2a), 6 diasterioisomers in the 11‐nordriman‐9‐one series (2b‐g), and 20 racemic 2‐oxabicyclo[4.4.0]decanes are reported and correlated with the ‘Triaxial Rule of Odor Sensation’. This rule also is applied to the two internal C(13) acetals derived from (±)‐dihydro‐γ‐ionone as well as to two epimeric C(18) ethers in the labdane series. Syntheses are described for most of the compounds examined.
Stereospezifität der neuroleptischen Wirkung und Chiralität von (+)‐3‐{2‐[4‐(8‐Fluor‐2‐methyl‐10,11‐dihydrodibenzo[b,f]thiepin‐10‐yl)‐1‐piperazinyl]‐äthyl}‐2‐oxazolidinon (16). 4. Mitteilung über tricyclische Antidepressiva und Neuroleptica
Authors: Aschwanden Werner , Kyburz Emilio , Schönholzer Peter 
Published: December 2004

Stereospecifity of the neuroleptic activity and chirality of (+)‐3‐{2‐[4‐(8‐fluoro‐2‐methyl‐10, 11‐dihydrodibenzo[b,f]thiepin‐10‐yl)‐1‐piperazinyl]ethyl}‐2‐oxazolidinone (16).The synthesis and stereospecific neuroleptic action in animals of the (+)‐enantiomer of 3‐{2‐[4‐(8‐fluoro‐2‐methyl‐10,11‐dihydrodibenzo [b,f]thiepin‐10‐yl)‐1‐piperazinyl]ethyl}‐2‐oxazolidinone (16) are briefly described. The (10S)‐configuration of this compound was determined by X‐ray diffraction.
Conformations of the ten‐membered ring in 5,10‐secosteroids I. X‐ray and NMR. Analysis of (E)‐3 β‐hydroxy‐5,10‐seco‐1(10)‐cholesten‐5‐one esters
Authors: Mez Hans‐Christian , Rist Günther , Kalvoda Jaroslav , Ermer Otto , Lorenc Ljubinka , Mihailović Mihailo Lj. 
Published: December 2004

AbstractX‐ray structure determination of the p‐bromobenzoate 2b of one of the (E/Z)‐isomeric 3β‐hydroxy‐5,10‐seco‐1(10)‐cholesten‐5‐ones confirmed the (E)‐configuration proposed previously and showed the cyclodecenone ring to adopt an extended crown conformation of type A1 (Fig. 9). Analysis of the 1H‐ and 13C‐NMR. spectra of acetate 2a revealed that in solution the ten‐membered ring of this steroid exists in at least two distinct forms, the predominant (about 85%) corresponding to the solid‐state conformation of 2b (=A1), and the minor most likely to B2 (Fig. 9). From NMR. data the energy difference between the two species and the relevant activation energy were estimated. A number of conformational force field calculations using a simplified partial structural model was performed; but the computed energy differences between the various possible conformations do not reproduce the effective situation, neither in solution nor in the crystal lattice, indicating that additional effects such as the transannular interaction of the double bond with the carbonyl group may strongly influence the thermodynamic stability of the system. The conformations deduced were used to rationalize the stereochemical course of different chemical reactions of 2a.
Eine neue Methode zur Herstellung gemischter Disulfide. Vorläufige Mitteilung
Authors: Dubs Paul , Stüssi Rita 
Published: December 2004

A New Synthesis of Unsymmetrical Disulfides.A new synthesis of unsymmetrical disulfides 3a via alkylthio‐dialkyl‐sulfonium salts 6 is reported.
Reductions of Tetrahalo‐1,3,5,7‐tetramethyl‐anti‐tricyclo [5.1.0.03,5]octane‐2,6‐diones. 1,3,5,7‐Tetramethyl‐anti‐tricyclo[5.1.0.03,5]octane‐2,6‐dione
Authors: Chapleo Christopher B. , Dreiding André S. , Dyllick‐Brenzinger Rainer A. , Oth Jean F. M. 
Published: December 2004

Methoden zur Entfernung von Halogenatomen aus den leicht zugänglichen (Bis‐homo‐p‐chinon)‐Derivaten 4,4,8,8‐Tetrachlor‐ (4) und 4,4,8,8‐Tetrabrom‐1,3,5,7‐tetramethyl‐anti‐tricyclo[5.1.0.03,5]octan‐2,6‐dion (5) wurden untersucht. Mit LiAlH4 bzw. mit KFeH(CO)4, NaBH3CN oder CrCl2 entstanden Diole bzw. Diketone, in denen ohne Gerüstveränderung verschiedene Halogenatome durch Wasserstoffatome ersetzt worden waren. Die Diole wurden entweder isoliert oder zu den Diketonen aufoxydiert. Von den neun möglichen Dehalogenierungsmustern (Diketone mit unverändertem C‐Skelett) liessen sich acht beobachten, sechs davon (8 bis 13) aus 4 und sechs (14 bis 18, 6) aus 5. Nur KFeH(CO)4 entfernte alle vier Halogenatome und dies nur aus dem Tetrabrom‐dion 5, wobei das noch unbekannte anti‐Isomere von 1,3,5,7‐Tetramethyl‐tricyclo[5.1.0.03,5]octan‐2,6‐dion (6) entstand.Die Zuordnung der endo‐ oder exo‐Konfigurationen der nicht‐entfernten Halogenatome an den Cyclopropanringen erfolgte auf Grund von 1H‐NMR.‐Spektraleigenschaften. Als Basisargument diente eine H/13C‐Kopplung von 4,5 Hz zwischen exo‐HC(4) und den cis‐vicinalen Methyl‐Kohlenstoffatomen, welche im 13C‐NMR.‐Spektrum von 12 beobachtbar ist. Daraus und aus unterschiedlichen Linienbreiten der 1H‐NMR.‐Signale von endo‐ und exo‐Protonen wurde abgeleitet, dass endo‐H immer bei tieferem Feld absorbiert als exo‐H. Im Fall von 6 liess sich dies durch geeignete Vergleiche unter Anwendung eines abschirmenden Effektes der angulären Methylgruppen auf exo‐H bestätigen. Die Konfigurationen der Hydroxylgruppen in den Diolen 19 bis 22 und 24 bis 27 wurden aufgrund von Symmetrieüberlegungen bestimmt.
Zur Cyclisierung von Dehydrolinalylacetat in Gegenwart von Zinkchlorid
Authors: Strickler Hugo , Davis John B. , Ohloff Günther 
Published: December 2004

ZnCl2‐catalysed cyclisation of dehydrolinalyl acetate.Dehydrolinalyl acetate has been converted to carvenone (5), the corresponding enol acetate 2‐acetoxy‐p‐mentha‐1,3‐diene (6), and to 2‐acetoxy‐2‐carene (7). The acetate of the pyran 8 is also formed. The same intermediate is postulated in the formation of both 6 and 7.
Reinvestigation of Original Taraxanthin Samples
Authors: Buchecker Richard , Liaaen‐Jensen Synnøve , Eugster Conrad Hans 
Published: December 2004

Überprüfung einiger Originalpräparate von Taraxanthin.Das von R. Kuhn & E. Lederer 1931 entdeckte und seither in zahlreichen höheren Pflanzen nachgewiesene Taraxanthin wird anhand von Originalpräparaten aus Impatiens nolitangere L., Ranunculus acer L. sowie durch erneute Isolierung aus Taraxacum officinale L. mit modernen Methoden untersucht. Taraxanthin erweist sich als Gemisch von Xanthophyll‐epoxid (= Lutein‐epoxid; 2) oder dessen Umlagerungsprodukten und O4‐Carotinoiden bekannter Struktur. Das aus Taraxacum erhaltene Präparat setzt sich aus 2 (73%), Flavoxanthin (4, 13%) und Chrysanthemaxanthin (4 (C(8)‐Epimer), 14%) zusammen. Nicht identifizierte Carotinoide in den untersuchten Präparaten betragen weniger als 3,5%. Ein in kleiner Menge in R. acer nachgewiesenes Carotinoid ist wahrscheinlich 5,6‐Dihydroxy‐5,6‐dihydrolutein (6).Der Name Taraxanthin als Bezeichnung für ein einheitliches Carotinoid soll aufgegeben werden.
Der Einfluss von D‐Aminosäureresten auf das konformative Verhalten von Kollagenmodellpeptiden
Authors: Frey Peter , Nitschmann Hans 
Published: December 2004

The influence of D‐amino acid residues upon the conformative behaviour of collagen model peptides.(L‐Pro‐L‐Pro‐Gly)10 and (L‐Pro‐D(L)‐Pro‐Gly)10 with 10 percent D‐Prolin residues have been synthesized by the Merrifield technique. Further Poly‐(Gly‐Pro‐Pro) and Poly‐(Ala‐Gly‐Pro) with various amounts of D‐amino acid residues have been synthesized by polycondensation of the proper tripeptides. The conformational behaviour of all these polypeptides has been studied by measurements at varying temperatures of optical rotation, circular dichroism and molecular weight. The results show that limited amounts of D‐amino acid residues do not impedecollagen‐like triple helical conformations. The denaturation temperatures, however, are considerably lowered by D‐amino acid residues. The implications of these findings for the understanding of the properties of partially racemized degraded gelatins with relatively low gel melting points are discussed.
Dediazoniation of Arenediazonium Ions in Homogeneous Solution. Part IX. Spectral Evidence for a Homolytic Mechanism Involving Pyridine Complexes
Authors: Loewenschuss Hana , Wahl George H. , Zollinger Heinrich 
Published: December 2004

AbstractThe mechanism of dediazoniation of arenediazonium tetrafluoroborates in 2,2,2‐trifluoroethanol (TFE) is strongly dependent on the concentration of added pyridine. The added base complexes with the diazonium ion and diverts it to a homolytic pathway. Complex formation is indicated by the disappearance of the \documentclass{article}\pagestyle{empty}\begin{document}$\raise1pt\hbox{---} \mathop {\rm N}\limits^ \oplus \equiv {\rm N}\raise1pt\hbox{---}$\end{document} stretching vibration and appearance of a new band at about 1640–1690 cm−1 ascribed to the \documentclass{article}\pagestyle{empty}\begin{document}$\raise1pt\hbox{---} {\rm N}\raise1pt\hbox{=\kern-3.45pt=} {\rm N}\raise1pt\hbox{---} \mathop {\rm N}\limits^ \oplus {\rm C}_5 {\rm H}_5$\end{document} system. UV. and NMR. results support this conclusion.Chemically induced dynamic nuclear polarization (CIDNP) experiments clearly implicate a radical‐pair as an important intermediate in the decomposition of these complexes.
Polar Substituents in Benzobarrelene Photochemistry; The Photoreactivities of Dimethyl 10‐methoxy‐ and Dimethyl 10,11‐dimethoxy‐2,3‐benzobicyclo[2.2.2]octateraene‐5,6‐dicarboxylate
Authors: Bender Christopher Owen , Wilson John 
Published: December 2004

AbstractThe direct irradiation of the monomethoxybarrelene 8 gives cyclooctatetraene product 18 (Φ = 0.075) via the anti‐Epiotis aromatic‐vinyldiester [2π+2π] bridging route, and two semibullvalenes 16 (Φ = 0.075) and 17 (Φ = 0.075) from di‐π‐methane rearrangements initiating from vinyl‐vinyldiester bridging. Benzophenone sensitization yields 16 (Φ =0.11) and 17 (Φ = 0.11). The dimethoxybarrelene 9 gives only semibullvalene 10, this resulting from di‐π‐methane rearrangement involving the vinyl and vinyldiester bridges, upon direct (Φ = 0.009) or benzophenone sensitized irradiations (Φ = 0.38). 10 undergoes a vinylcyclopropane rearrangement to give semibullvalene 11 upon direct or acetone sensitized irradiations (Φ = 0.008).