bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis und thermisches Verhalten von exo‐3‐Methylidentricyclo[3.2.1.02,4]oct‐6‐en
Authors: Stämpfli Urs , Neuenschwander Markus 
Published: December 2004

Synthesis and Thermal Behaviour of exo‐3‐Methylidenetricyclo[3.2.1.02,4]oct‐6‐eneThe title compound 3 has been prepared in 16% yield starting from 8,9,10‐trinorborna‐2,5‐diene. Heating 3 at 140° for 4 h does not give triafulvene and cyclopentadiene by Diels‐Alder cycloreversion, instead the tetracyclic compound 10 has been isolated (81%), which is presumably formed via the diradical 11.
Über den Einfluss des Akzeptor‐Teilchromophors bei Dimethin‐merocyanin‐Farbstoffen auf das Aggregationsverhalten in wässriger Lösung
Authors: Kussler Manfred , Balli Heinz 
Published: December 2004

On the Influence of the Acceptor Part of the Chromophor of Dimethinemerocyanine Dyes upon the Aggregation Tendency in Aqueous SolutionA series of novel long‐chain alkyl‐dimethinemerocyanine dyes containing sulfonate groups is synthesized in good yield and their aggregation tendency in H2O and in organic solvent/H2O mixtures investigated. The merocyanine dyes 11 and 15 only exhibit an intense, red‐shifted absorption band due to J‐aggregation in H2O without addition of salt. The influence of cationic and anionic tensides and other compounds as urea, glucose, and polysaccharides upon the J‐aggregation tendency is investigated.
Locoselective [4 + 2] Cycloadditions of Vinylindoles with Inverse Electron Demand: A new access of indolyl‐substituted and annellated pyridazines
Authors: Pindur Ulf , Pfeuffer Ludwig , Kim Myung‐Hwa 
Published: December 2004

Abstract2‐Vinylindole (1a) and its donor‐ and acceptor‐substituted (E)‐derivatives 1b–e react highly locoselectively with dimethyl 1,2,4,5‐tetrazine‐3,6‐dicarboxylate (3) to form the novel (indol‐2‐yl)‐1,4‐dihydropyridazines 4a and 7 as well as the heterocyclic annellated pyridazines 4b, 5, and 6. The reactions of the structurally related 3‐vinylindoles 2a–e with 3 also gave rise to new indol‐3‐ylpyridazines 8, 9, and 10. The locoselectivities of these Diels‐Alder reactions were controlled mainly by steric effects.
Metal Complexes with Macrocyclic Ligands. Part XXIX.. Structural and kinetic studies of two isomeric Cu2+ complexes with 1,4‐dimethyl‐8‐[2‐(2‐pyridyl)ethyl]‐1,4,8,11‐tetraazacyclotetradecane
Authors: Tschudin Daniel , Riesen Andreas , Kaden Thomas A. 
Published: December 2004

AbstractThe synthesis and complexation properties of 1,4‐dimethyl‐8‐[2‐(2‐pyridyl)ethyl]‐1,4,8,11‐tetraazacyclotetra‐decane (2) are described. This ligand forms with Cu2+ two complexes, one of which has been characterized by X‐ray structure analysis. The structural, spectral, and kinetic studies indicate that the two Cu2+ complexes are isomers with the macrocycle in the trans‐III and trans‐I configuration. The rate of the interconversion of the trans‐I isomer to the thermodynamically more stable trans‐III species is proportional to [OH−]. A mechanism for this reaction is proposed.
Ein neuer Zugang zu 2,6,6‐Trimethylcyclohexa‐2,4‐dienon aus 4‐Oxoisophoron
Authors: Soukup Milan , Lukáč Teodor , Zell Reinhard , Roessler Felix , Steiner Kurt , Widmer Erich 
Published: December 2004

A New Access to 2,6,6‐Trimethylcyclohexa‐2,4‐dienone from 4‐Oxoisophorone2,6,6‐Trimethylcyclohexa‐2,4‐dienone (1), a versatile starting material for the preparation of some carotenoids and several natural products, was efficiently (73% yield) prepared from oxoisophorone 3. After conversion of 3 to the alcohol 4 or the acetate 5, H2O was eliminated (4→1) under acidic distillative conditions, whereas AcOH could be eliminated (5→l) under Pd(O) catalysis.
Structure Determination of New Isomeric Naphtho[2,3‐b]furan‐4,9‐diones from Tabebuia avellanedae by the selective‐INEPT technique
Authors: Wagner Hildebert , Kreher Bernhard , Lotter Hermann , Hamburger Matthias O. , Cordell Geoffrey A. 
Published: December 2004

AbstractBeside the known naphthoquinones, dehydro‐α‐lapachone (17) and lapachol (20), four new naphtho[2,3‐b]‐furan‐4,9‐diones, i.e. the 2‐acetyl‐5‐hydroxy. 2‐acetyl‐8‐hydroxy. (−)‐5‐hydroxy‐2‐(1′‐hydroxyethyl), and (±)‐8‐hydroxy‐2‐(1′‐hydroxyethyl) derivatives 16, 15, 12, and 13, respectively, and the new compound benzo[b]furan‐6‐carboxaldehyde (8) have been isolated from a CHCl3 extract of the inner stem bark of Tabebuia avellanedae LORENTZ ex GRISEB., together with four known naphthofurandiones, a dihydroisocoumarin derivative, (−)–6‐hydroxymellein, and five benzoic‐acid and three benzaldehyde derivatives which have not been reported previously from this plant. Structure determination of the isomeric 5‐ and 8‐hydroxynaphtho[2,3−b]furan‐4,9‐diones was carried out unambiguously by a combination of selective‐INEPT experiments and X‐ray crystallographic analysis.
Pteridines. Part XLI. Synthesis and properties of 6,7,8‐trimethyl‐4‐thiolumazine
Authors: Hübsch Walter , Pfleiderer Wolfgang 
Published: December 2004

AbstractThe first representative of the 8‐substituted 4‐thiolumazine series has been synthesized. In a sequence of reactions, 4,6‐dichloropyrimidin‐2‐(1H)‐one (1) is first converted into 4‐chloro‐6‐(methylamino)pyrimidin‐2(1H)‐one (6), then the Cl‐atom displaced by the thioxo group (→7) followed by a coupling reaction with 4‐chlorophenyldiazonium chloride to introduce the necessary N‐function into the 5‐position (→ 9; Scheme 1). Reduction of the p‐chlorophenylazo group leads to the 6‐(methlyamino)‐4‐thiouracil‐5‐amine (10) which on condensation with diacetyl gives 6,7,8‐trimethyl‐4‐thiolumazine (8). The physical properties of 8 are compared with the 2‐thio analog and 6,7,8‐trimethyllumazine indicating that 8 possesses the highest acidity and the longest UV absorption.
Diazotisation Mechanism of Heteroaromatic Amines. Diazotisation of 2‐aminothiazole as an equilibrium
Authors: Diener Heinz , Güleç Bilge , Skrabal Peter , Zollinger Heinrich 
Published: December 2004

AbstractThe rate of diazotization of 2‐aminothiazole was measured in 65 to 75% (w/w) aqueous H2SO4. The kinetic solvent isotope effect of the diazotization in 72% D2SO4/D2O was determined (kH/kD = 5.8 ± 0.2). These data are consistent with a mechanism in which the 2‐aminothiazole, protonated at the ring N‐atom, but not at the NH2 group, is attacked by the NO+ ion. The reaction does not go to completion, but to an equilibrium. The equilibrium concentration of the diazonium ion was determined in 30,50,70, and 90% (w/w) H2SO4 at three initial concentration of reagents (0.001,0.01, and 0.1m). The final concentrations of the reagents and the diazonium ion are consistent with a reversible process. This is the first diazotization for which quantitative evidence for equilibration has been found. In the very large range of acidities used (Ho = −1.73 to −9.01), it was not possible to calculate meaningful equilibrium constants that are independent of the acidity.
2,2′‐Bifurylidene‐5,5′‐diones, Coumarins, 3a, 7a‐dihydro‐1H‐inden‐1‐ones, and 5H‐furo[3,2‐b]pyran‐5‐ones from propyne and carbon monoxide
Authors: Rautenstrauch Valentin , Mégard Patrick , Gamper Betty , Bourdin Bernadette , Walther Eric , Bernardinelli Gerald 
Published: December 2004

AbstractThe [Co2 (CO)8]‐catalyzed reaction between propyne and CO in acetone at 110° and 170 bar was re‐investigated. There are five major products: (E)‐3,4′‐dimethyl‐2,2′‐bifurylidene‐5,5′‐dione (4), 3,5,8‐trimethylcoumarin (8), 3a, 7a‐dihydro‐2,4,7,7a‐tetramethyl‐1H‐inden‐1‐one (9), 2,6‐dimethyl‐5H‐furo [3,2, ‐b]‐ pyran‐5‐one (11), and 2,7‐dimethyl‐5H‐furo 3,2‐b‐pyran‐5‐one (12); of these, only one, 4. had previously been recognized. In parallel experiments were obtained 2,6‐dipentyl‐5 H‐furo[3,2‐b]pyran‐5‐one (13), 2,7‐dipentyl–5H‐furo[3,2‐b]pyran‐5‐one (14), 3a, 7a‐dihydro‐2,4,7,7a‐tetrapentyl‐1H‐inden‐1‐one (15). And 3a, 7a‐dihydro‐2,4,6,7a‐tetrapentyl‐1H‐inden‐1‐one (16) from hept‐1‐yne, and two further types of products from two atypical 1‐alkynes: 3,6,9‐tri(tert‐butyl)‐1‐oxaspiro[4.4]nona‐3,6,8‐trien‐2‐one (20) from (tert‐butyl)acetylene and the exo‐dimer 21 of 2,5‐bis(trimethylsilyl)cyclopenta‐2,4‐dien‐1‐one (22) from (trimethylsilyl)acetylene. Compounds 11,12, and 20 were identified by X‐ray analysis.
Dissimilar behaviour of 3β, 16α‐dihydroxy‐5α‐androstan‐17‐one Diacetate under Basic and Acidic Conditions
Authors: Doller Darío , Gros Eduardo G. 
Published: December 2004

AbstractThe base‐catalysed rearrangement of 3β, 16α‐dihydroxy‐5α‐androstan‐17‐one diacetate (1) in (D6)benzene/CD3OD to 3β, 17β‐dihydroxy‐5α‐androstan‐16‐one (3) is followed by 13C‐NMR spectroscopy. By the same procedure, it is determined that in (D6)benzene/CD3OD, but under acid catalysis, 1 does not rearrange to 3 but yields the intermediate product 3β, 16α‐dihydroxy‐5α ‐androstan‐17‐one 17α ‐methyl hemiacetal (5).
Metal Complexes with Macrocyclic Ligands Part XXX. Synthesis and structure of halocuprates of tetraprotonated 1,4,8,11‐tetraazacyclotetradecane and its Cu2+ complex
Authors: Studer Martin , Riesen Andreas , Kaden Thomas A. 
Published: December 2004

AbstractBy mixing acidic solutions of 1,4,8,11‐tetraazacyclotetradecane (Cy) with CuX2 (X = Cl−, Br−), either the hexahalocuprates of the tetraprotonated form of the macrocycle ([CyH4] [CuX6]) or the tetrahalocuprates of its Cu2+ complex ([CuCy] [CuX4]) are obtained. The structures of the chloro derivatives are established by X‐ray diffraction analysis. In [CyH4] [CuCl6], the Cu2+ is in a tetragonally distorted octahedral geometry with four short and two long CuCl bonds. The tetraprotonated macrocycle is centrosymmetric, and its conformation is exodentate, so that the four ammonium groups are as far as possible from each other to minimize the electrostatic repulsion. In [CuCy] [CuCl4], the Cu2+ ion complexed by the macrocycle is surrounded by four N‐atoms in a square‐planar arrangement. In addition, the axial positions are occupied by two Cl− ions of two CuCl units, which act as bridges. The macrocycle is in the trans‐III‐configuration. The other Cu2+ ion is coordinated by four Cl− ions in a distorted tetrahedral geometry. IR and VIS spectra of the chloro and bromo derivatives are used to discuss the structure of the bromo species.
Synthèse énantiospécifique de la (+)‐(R)‐éthyl‐6‐dihydro‐2,3‐méthyl‐2‐4H‐pyranone‐4, phéromone de la mite Hepialus hecta L
Authors: Deschenaux Pierre‐François , Kallimopoulos Thomas , Jacot‐Guillarmod André 
Published: December 2004

Enantiospecific Synthesis of (+)‐(R)‐6‐Ethyl‐2,3‐dihydro‐2‐methyl‐4H‐pyran‐4‐one, Sex‐pheromonal Component of the Male Swift Moth Hepialus hecta L.A new synthesis of (+)−(R)‐6‐ethyl‐2,3‐dihydro‐2‐methyl‐4H‐pyran‐4‐one ((R)‐8), sex‐pheromonal component of the male swift moth Hepialus hecta L., has been performed from (−)‐(R)‐1‐(1,3‐dithian‐2‐yl)propan‐2‐ol with an enantiomeric excess of ⩾ 97%.
Transition‐metal complexes with bidentate ligands spanning trans‐positions. Part XVIII. Crystal and molecular structure of the ligands 2,11‐bis(di‐R‐phosphinomethyl)benzo[c]phenanthrene (R = Phenyl, tert‐Butyl) and a comparison of their conformation in a variety of complexes
Authors: Bürgi Hans‐Beat , Murray‐Rust Judith , Camalli Mercedes , Caruso Francesco , Venanzi Luigi M. 
Published: December 2004

AbstractThe X‐ray crystal structures of 2,11‐bis(di‐R‐phosphinomethyl)benzo[c]phenanthrenes (R = Ph, t‐Bu) are reported. Both ligands have the same conformation and the substitution of a Ph by a t‐Bu group does not cause significant changes in the tetracyclic aromatic unit which shows the same distortions as the parent hydrocarbon. The conformations and structural features of the two ligands and 18 complexes containing these ligands as well as of one compound with a ligand with Et substituents are compared. It is pointed out that (1) the conformations of the free ligands differ significantly from those of their complexes, (2) in all the complexes characterized to date, these ligands act as chelating agents, and (3) the ligands adopt two different conformations in the complexes, one of them appearing to be more flexible than the other.
Glycosylidene Carbenes a new approach to glycoside synthesis. Part 1. Preparation of glycosylidene‐derived diaziridines and diazirines
Authors: Briner Karin , Vasella Andrea 
Published: December 2004

AbstractA new approach towards the synthesis of glycosides based upon a (formal) insertion of glycosylidene carbenes into OH bonds is presented. The synthesis and characterization of the glycosylidene‐derived diazirines 25–28, precursors of glycosylidene carbenes, are described. The diazirines were prepared by the rapid, high‐yielding oxidation of the diaziridines 20 and 22–24 with I2/Et3N. The diaziridines, the first examples of C‐ alkoxy‐diaziridines, were formed in high yields by the reaction of the [(glycosylidene)‐amino]methanesulfonates 14 and 17–19 with a saturated solution of NH3 in MeOH. The diazirines are highly reactive compounds, losing N2 at room temperature or below. The reaction of the gluco‐configurated diazirine 25 with i‐PrOH yielding a mixture of the α‐ and β‐D‐glucosides 29 and 30 illustrates the potential of glycosylidene‐derived diazirines as a new type of glycosyl donors.
Corallistin A, a second example of a free porphyrin from a living organism. Isolation from the demosponge Corallistes sp. of the coral see and inhibition of abnormal cells
Authors: D'Ambrosio Michele , Guerriero Antonio , Debitus Cécile , Ribes Olivier , Richer De Forges Bertrand , Pietra Francesco 
Published: December 2004

AbstractIt is shown that the demosponge Corallistes sp. (Tetractinomorpha, Lithistida, Corallistidae) collected in the Coral Sea, contains corallistin A (1), the second example, of a free porphyrin from a living organism. The compound proved to be active against the Kb cell line. In contrast with the geoporphyrins which do not bear any O‐atom corallistin A (1) carries two carboxylic groups.
Synthesis of hydroxy‐ and methoxy‐substituted octahydrobenzo[g]isoquinolines as potential ligands for serotonin receptors
Authors: Papageorgiou Christos , Petcher Trevor J. , Waldvogel Erwin 
Published: December 2004

AbstractIn 7 steps, 6‐ or 9‐hydroxylated or ‐methoxylated trans‐octahydrobenzo[g]isoquinolines were efficiently synthesized starling from dimethoxynaphtbalenes (Scheme), as potential new selective ligands for serotonin receptors. The 6‐substituted compounds had very little affinity to common neurotransmitter receptors, with the exception of adrenergic α2. The 9‐substituted compounds, while showing interesting affinity for 5HT1a receptors, had comparable affinities for adrenergic α1 and β2, and in one case for dopamine D2 receptors.
Synthesis of macrocyclic imides by one‐step ring enlargement
Authors: Ognyanov Vassil I. , Hesse Manfred 
Published: December 2004

AbstractBy one‐step ring‐enlargement reaction with isocyanates, 2‐cyano‐ and 2‐(ethoxycarbonyl)‐substituted cycloalkanones are converted into macrocyclic imides.
Strukturaufklärung von N6‐, 9‐ und 7‐Acyladeninen durch 1H‐und 13C‐NMR‐Spektroskopie von Festkörpern und in Lösung
Authors: Ried Walter , Woithe Heinz , Müller Arndt 
Published: December 2004

Structure Determination of N6‐, 9‐and 7‐Acyladenines by 1H‐ and 13C‐NMR Spectroscopy of Solids and in Solution.Adenine (1) reacts with carboxylic acid anhydrides or chlorides 2 to yield the acyladenine isomers 3–5. The isomeric structures were determined by 33C‐ and 1H‐NMR spectroscopy in solution and by solid‐state 13C‐NMR spectroscopy.
On the Macrolactonization of β‐Hydroxy Acids. Crystal structures of the pentolide and the hexolide from (R)‐3‐hydroxybutanoic acid. Molecular modeling studies of the tetrolide
Authors: Seebach Dieter , Brändli Urs , Müller Hans‐Martin , Dobler Max , Egli Martin , Przybylski Michael , Schneider Klaus 
Published: December 2004

AbstractThe temperature and concentration dependence of the previously reported formation of oligolides from (R)‐ or (S)‐3‐hydroxybutanoic acid under Yamaguchi's macrolactonization conditions (2,4,6‐trichlorobenzoyl chloride/base) was studied. While the content of hexolide 2 in the product mixture is almost invariably ca. 35%, the amounts of pentolide 1 and of the larger rings strongly depend upon the temperature employed (Fig.1). Cyclic oligomers (5,6) are also obtained from 3‐hydroxypentanoic acid. Enantiomerically pure β‐butyrolactone can be used for the preparation of pento‐, hexo‐, and heptolide under Shanzer's macrolactonization conditions (tetra‐oxadistannacyclodecane ‘template’). The X‐ray crystal structures of the pentolide 1 and of two modifications (space groups C 2 and P 21) of the hexolide 2 were determined (Figs. 2–6 and Tables 1 and 5). No close contacts between substituent atoms and atoms in the rings or between ring atoms are observed in these structures. The hexolide C 2 modification is ‘just a large ring’, while the crystals of the P 21 modification contain folded rings the backbones of which resemble the seam of a tennis ball. A comparison of the torsion angles in the folded hexolide ring of the P 21 modification with those in the helical poly‐(R)‐3‐hydroxybutanoate (PHB) suggests (Table 2) that the same interactions might be responsible for folding in the first and helix formation in the second case. Molecular modeling with force‐field energy minimization of the tetrolide from four homochiral β‐hydroxybutanoic acid units was undertaken, in order to find possible reasons for the fact that we failed to detect the tetrolide in the reaction mixtures. The calculated conformational energies (per monomer) for some of the tetrolide models (Figs. 7–9 and Tables 3 and 4) are not significantly higher than for the pentolide and hexolide crystal structures. We conclude that thermodynamic instability is an unlikely reason for the lack of tetrolide isolation. This result and failure to observe equilibration of pentolide 1 to a mixture of oligomers under the reaction conditions suggest that product distribution is governed by kinetic control.
Variable‐Temperature and Variable‐Pressure Kinetic and Equilibrium studies of formation and dissociation of [V(H2O)5NCS]2+
Authors: Sauvageat Pierre‐Yves , Ducommun Yves , Merbach André E. 
Published: December 2004

AbstractThe kinetics of formation and dissociation of [V(H2O)5NCS]2+ have been studied, as a function of excess metal‐ion concentration, temperature, and pressure, by the stopped‐flow technique. The thermodynamic stability of the complex was also determined spectrophotometrically. The kinetic and equilibrium data were submitted to a combined analysis. The rate constants and activation parameters for the formation (f) and dissociation (r) of the complex are: k/M−1 · S−1 = 126.4, k/s−1 = 0.82; ΔH /kJ · mol−1 = 49.1, ΔH/kJ · mol−1 = 60.6; ΔS/ J·K−1·mol−1= −39.8, ΔSJ·K−1·mol−1 = −43.4; ΔV/cm3·mol−1 = −9.4, and ΔV/cm3 · mol−1 =−17.9. The equilibrium constant for the formation of the monoisothiocynato complex is K298/M−1 = 152.9, and the enthalpy and entropy of reaction are ΔH0/kJ · mol−1 = − 11.4 and ΔS0/J. K−1mol−1 = +3.6. The reaction volume is ΔV0/cm3· mol−1 = +8.5. The activation parameters for the complex‐formation step are similar to those for the water exchange on [V(H2O)6]3+ obtained previously by NMR techniques. The activation volumes for the two processes are consistent with an associative interchange, Ia, mechanism.
Synthetic Studies Directed toward the Pseurotins. Part I. Synthesis of Related Furan‐3(2H)‐ones
Authors: Dolder Matthys , Shao Xie , Tamm Christoph 
Published: December 2004

AbstractAccording to a general concept for the total synthesis of pseurotin A (1), a secondary metabolite of Pseudeurotium ovalis STOLK, 5‐[(1S,2S,Z)‐1,2‐dihydroxyhex‐3‐enyl]‐2,2,4‐trimethylfuran‐3(2H)‐one (17) was prepared. It is a model substance for the substituted furan‐3(2H)‐one moiety of 1. The aldol condensation of the aldehyde 26, derived from D‐glucose, and the enolate of ketone 29 served as key reaction.
Intramolecular Dynamics of Tetranuclear Iridium Carbonyl Cluster Compounds. Part III. Crystallographic and dynamic evidence for the intermediate of the ‘merry‐go‐round’ process in nonacarbonyl‐μ3‐(1,3,5‐trithiane)‐tetrairidium
Authors: Suardi Gianfranco , Strawczynski Andres , Ros Renzo , Roulet Raymond , Grepioni Fabrizia , Braga Dario 
Published: December 2004

AbstractThe title complex crystallises in two C3v, isomeric forms differing in carbonyl‐ligand arrangement. In solution, the isomer 1b with three edge‐bridging carbonyls on a common face of the metal tetrahedron converts via an endothermic equilibrium into the isomer 1u with no bridging carbonyls. The latter was shown by 13C‐NMR to be the intermediate of the ‘merry‐go‐round’ process which exchanges the sites of the basal CO's.
The Bioconversion of (3RS,E)‐ and (3RS,Z)‐Nerolidol into Oxygenated Products by Streptomyces cinnamonensis. Possible Implications for the Biosynthesis of the Polyether Antibiotic Monensin A??
Authors: Holmes Duncan S. , Ashworth Doreen M. , Robinson John A. 
Published: December 2004

AbstractThe ability of the monensin‐producing organism Streptomyces cinnamonensis to bioconvert the (E)‐and (Z)‐isomers of nerolidol (= 3,7,1 1‐trimethyldodeca‐1,6,10‐trien‐3‐ol) into new oxygenated products has been investigated. When a 3H‐labelled racemic form of each sesquiterpene was added to fermentations of S. cinnamonensis, several new 3H‐labelled products could be detected. Two products were isolated from bioconversion of (E)‐nerolidol, the amide 8 and the 9 (Scheme 2), whereas four products were isolated from the bioconversion of (Z)‐nerolidol, the epoxydiol 10, triols 11 and 12, and the tetrahydrofuryl alcohol 13 (Scheme 4). Products 9–13 were obtained as a 1 : 1 mixture of diastereoisomers, and 12 was shown to arise by the overall anti addition of two OH groups to the trisubstituted (Z)‐double bond of (Z)‐nerolidol. Both isomers of nerolidol as well as the acetylene 7 are inhibitors of monensin production in shake cultures of S. cinnamonensis.
Synthese von 2‐Oxo‐2H‐pyran‐5‐Carboxylat‐Derivaten
Authors: Kvitu Vratislav 
Published: December 2004

Synthesis of 2‐Oxo‐2H‐pyran‐5‐carboxylate Derivatives3‐Substituted diethyl pent‐2‐enedioates are easily formylated by means of ethyl formate/TiCl4/4‐methylmorpholine to produce the ethoxymethylene derivatives, which are smoothly cyclized either with HCOOH or PPA to corresponding 2‐oxo‐2H‐pyran‐5‐carboxylate derivatives.
Diastereoselective Spirocyclization of C‐(Alkyloxycarbonyl)formimines of 2‐Substituted 1HIndole‐3‐ethanamines (= Tryptamines): Basic Studies. 5th Communication on Indoles, Indolenines, and Indolines
Authors: Freund Ralf , Mahboobi Siavosh , Noack Klaus , Schonhölzer Peter , Bernauer Karl 
Published: December 2004

AbstractC‐(Alkoxycarbonyl)formimines of type 15–18 were derived from the 2‐substituted tryptamines 2, 9, 10, and 11 and transformed with tosyl chloride into tricyclic 3‐spiroindoles of types 19–22 (Scheme 3). The influence of the homochiral alkoxy moieties A–D on the stereochemical outcome of this reaction was studied. Good‐to‐excellent diastereoselectivities were observed with the (−)‐8‐(phenylmenth‐3‐yl)oxy group (B) as homochiral auxiliary. The structures of the tricycles 4, (2′R,3S)‐19B, and (2′S,3R)20C were established by X‐ray analysis, the structures of the others by NOE and CD studies, and by chemical correlation. Possibilities to explain the steric course of the spirocyclizations are discussed.
Struktur der Valenciaxanthine und Valenciachrome
Authors: Märki‐Fischer Edith , Eugster Conrad Hans 
Published: December 2004

Structure of the Valenciaxanthins and ValenciachromesValenciaxanthin, a carotenoid first isolated from Californian Valencia orange juice in 1952/1954 by American scientists, was re‐isolated from fresh Spanish ‘Navelinas’ and shown, by spectroscopical and chiroptical examination, to have the unexpected (9Z)‐10′‐apo‐11′,12′‐dihydroviolaxantin‐10′‐ol structure 6. A further, very minor component represents the (all‐E)‐structure 7. Therefore, the Valenciachromes are the furanoid rearrangement products of 6 and 7 and, thus, stereoisomers of the 10′‐apo‐11′,12′‐dihydroauroxanthiiv 10′‐ols 8. Valenciaxanthin represents a modification of the common cleavage of carotenoids in higher plants according to the scheme C40 → C27 + C13, insofar as the reduction step not only includes the aldehyde function but also the subsequent conjugated double bond.