bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Cyclophan‐Metall)‐Komplexe: Synthese und Kristallstruktur von ([3.3]Paracyclophan)gallium(I)‐tetrabromgallat(III)
Authors: Schmidbaur Hubert , Bublak Wolfgang , Huber Brigitte , Müller Gerhard 
Published: December 2004

Cyclophane‐Metal Complexes: Synthesis and Crystal Structure of ([3.3]Paracyclophane)gallium(I) Tetrabromogallate(III)[3.3]Paracyclophane forms 1:1 complexes 2a and 2b with both Ga[GaCl4] and Ga[GaBr4]. The crystalline products obtained from toluene solution at room temperature are much less sensitive to air and moisture than most other arene complexes of Ga(I). Solubilities in standard organic solvents are very low, suggesting coordination polymers. The X‐ray diffraction analysis of 2b confirms the presence of a two‐dimensional network. Both aromatic rings of each cyclophane molecule are η6‐coordinated from the outer side to Ga(I)‐atoms. The position of these metal cations is 2.75 Å above the ring centres. The arene rings are parallel within each cyclophane, but tilted by 48.5° with respect to those of the neighbouring cyclophane. The coordination sphere of the Ga(I) centres is completed by two Br‐atoms of two GaBr anions, which link the Ga(I) cations to give … Ga[GaBr4] Ga[GaBr4]Ga … strands. The double interconnection of the Ga(I)‐atoms gives rise to a two‐dimensional sheet structure, which is thus different from the structure of the previously described Ga[GaBr4] complex of [2.2]paracyclophane, where a three‐dimensional network was observed.
The Formation of Bridged Bicyclic 1,2,4‐Trioxanes by Intramolecular Capture of β‐Hydroperoxy Cations
Authors: Jefford Charles W. , Favarger France , Ferro Serenella , Chambaz Daniel , Bringhen Alain , Bernardinelli Gerald , Boukouvalas John 
Published: December 2004

AbstractThe 1,4‐endoperoxide, prepared from 3‐(4‐methylnaphth‐1‐yl)propanal by photo‐oxygenation in CH2Cl2, gave on treatment with Amberlyst‐15®, 3,10b‐epidioxy‐2,3,4a,10b‐tetrahydro‐6‐methyl‐1H‐naphtho[2,1‐b] pyran in 85% yield. Its structure was determined by X‐ray crystal structure analysis. The 1,2,4‐trioxane moiety is locked in a twist‐boat conformation with trans fusion to the parent six‐membered ring. The 1,4‐endoperoxides of the methyl, butyl, and phenyl ketone analogues of the aforementioned aldehyde underwent similar acid‐catalyzed rearrangement to the corresponding bridged bicyclic trioxanes in 94, 47, and 48% yields, respectively.
Enantioselective Synthesis of β‐Necrodol and of 1‐Epi‐β‐necrodol via Asymmetric 1,4‐Addition and Magnesium‐Ene Cyclization. Preliminary Communication
Authors: Oppolzer Wolfgang , Schneider Philippe 
Published: December 2004

AbstractEnantiomerically pure β‐necrodol (1) and its 1‐epimer 16 have been synthesized starting from aldehyde 5. The two key steps are an asymmetric conjugate addtion/Mannich reaction tandem (10→12) and a type‐II‐magnesiumene cyclization/oxidation sequence (14→1 + 16).
Conformationally Restricted Analogs of Platelet‐Activating Factor (PAF)
Authors: Hadváry Paul , Weller Thomas 
Published: December 2004

AbstractThe synthesis of the five‐membered cyclic phosphorodiamidic‐acid derivatives 10 and 11 as well as the preparation of the six‐membered cyclic phosphates 18, 19, 22–25, and phosphoramidates 27–32 is described. The effects of these conformationally restricted platelet‐activating factor analogs on rabbit platelet aggregation are briefly discussed. The 2‐oxo‐1,3,2‐dioxaphosphorinanes 19, 25, and 30 were found to be equally potent platelet‐activating factor antagonists as the known thiazolium salt 33.
4‐Methylumbelliferyl 5‐Acetamido‐3,4,5‐trideoxy‐α‐D‐manno‐2‐nonulopyranosidonic Acid: Synthesis and Resistance to Bacterial Sialidases
Authors: Baumberger Franz , Vasella Andrea , Schauer Roland 
Published: December 2004

AbstractThe synthesis of 4‐methylumbelliferyl α‐D‐glycoside 13 of N‐acetyl‐4‐deoxyneuraminic acid and its behaviour towards bacterial sialidases is described. N‐Acetyl‐4‐deoxyneuraminic acid (1) was transformed into its methyl ester 2 and then acetylated to give the anomeric pentaacetates 3 and 4 of methyl 4‐deoxyneuraminate and the enolacetate 5 (Scheme). A mixture 3/4 was treated with HCl/AcCl to give the glycosyl chloride, which was directly converted into the 4‐methylumbelliferyl α‐D‐glycoside 9 of methyl 7‐O,8‐O,9‐O,N‐tetraacetylneuraminate and into the 2,3‐dehydrosialic acid 11. The ketoside 9 was de‐O‐acetylated to 12 with NaOMe in MeOH. Saponification (NaOH) of the methyl ester 12 followed by acidification gave the free 13, which was also converted into the sodium salt 14 by passage through Dowex 50 (Na+). The 4‐deoxy α‐D‐glycoside 13 is not hydrolyzed at significant rates by Vibrio cholerae and Arthrobacter ureafaciens sialidase. Neither the free N‐acetyl‐4‐deoxyneuraminic acid (1), nor the α‐D‐glycoside 13 inhibit the activity of these sialidases.
Nucleosides and nucleotides. Part 25.. Synthesis of a protected 1‐(2′‐deoxy‐β‐D‐ribofuranosyl)‐1 H‐benzimidazole 3′‐phosphate
Authors: Papageorgiou Christos , Tamm Christoph 
Published: December 2004

Abstract1‐(2′‐Deoxy‐5′‐O‐dimethoxytrityl‐′‐D‐ribofuranosyl)‐1 H‐benzimidazole 3′‐[(p‐chlorophenyl)(2‐cyanoethyl) phosphate] (6) has been synthesized from 1‐(β‐D‐ribofuranosyl)‐1H‐benzimidazole (3b) using regiospecific 2′‐deoxygenation. The latter compound was obtained by glycosylation of benzimidazole with the D‐ribose derivative 2 leading exclusively of the β‐D‐anomer.
A Simple and Effective Chemical Phosphorylation Procedure for Biomolecules
Authors: Bannwarth Willi , Trzeciak Arnold 
Published: December 2004

AbstractA general chemical phosphorylation method based on P(III) chemistry has been developed. The system is demonstrated for the phosphorylation of oligonucleotides, directly after their synthesis on a solid support, and for the O‐phosphorylation of serine, threonine, and tyrosine as well as for a serine‐containing peptide.
Syntheses of Tetrahydrolipstatin and Absolute Configuration of Tetrahydrolipstatin and Lipstatin
Authors: Barbier Pierre , Schneider Fernand 
Published: December 2004

AbstractLipstatin (1), a natural product, and tetrahydrolipstatin (2) are pancreatic lipase inhibitors. Non‐stereoselective and partially stereoselective syntheses of 2 are used to establish the absolute configuration of tetrahydrolipstatin and lipstatin.
Photoionization of Naphthalene and Anthracene in Acetonitrile
Authors: Vauthey Eric , Haselbach Edwin , Suppan Paul 
Published: December 2004

AbstractNaphthalene and anthracene undergo a monophotonic ionization process in MeCN to produce the radical cations in low quantum yields (around 0.06 for anthracene). This reaction originates from the relaxed singlet excited state S1, and it is not due to traces of H2O in the solvent.
Triaziridine 8. Mitteilung. Zur Acylierung Von Dialkyl‐triaziridinen
Authors: Hilpert Hans , Hoesch Lienhard , Dreiding André S. 
Published: December 2004

On the Acylation of Dialkyl‐triaziridines(2,3‐trans)‐Diisopropyl‐ (1) and (2,3‐cis)‐1,3‐cyclopentylenetriaziridine (2) were reacted with ClCOOCH3. In the case of 1, with or without pyridine, an expected acylation at N(1) resulted in the methoxycarbonyl derivative 3. In the case of 2, the reaction in pyridine led to the γ‐ and α‐dihydropyridyl derivatives 5 and 6, respectively, where the acylpyridinium moiety had become attached by a ring C‐atom to N(1); without pyridine, it afforded the N‐cyclopentenylcarbamates 13 and 14by opening of the triaziridine ring and loss of N2. The mechanisms proposed for these reactions involve the initial attack of an electrophile at N(1) of 1 but at N(2) (or N(3)) of 2. This difference is rationalized with steric factors, inasmuch as the hindrance to an attack at N(2) (or (3)) is greater in i than in 2, whereas this hindrance at N(1) is smaller in 1 than in 2. The greater resistance to opening of the saturated N3‐homocycle during acylation of the monocyclic triaziridine 1, as compared to that of the tricyclic one 2, is attributed to greater strain in the latter system.
Copper and Silver Atoms in the β‐Cage of a Zeolite: Model Calculations
Authors: Calzaferri Gion , Forss Lars 
Published: December 2004

AbstractThe electronic structures of the 4‐4 SBU, the β‐cage, and the β‐cage with two 4‐4 SBU's attached to it have been studied by means of EH‐MO calculations. No indication of the formation of a band structure has been found. The HOMO region consists of many closely spaced, localized states, 98.6% of them concentrated on the O‐atoms. Reversible color changes of Cu+1 and Ag+1 zeolites observed upon hydration‐dehydration experiments can be understood as charge‐transfer transitions from the HOMO concentrated on the zeolite O‐atoms to the metal cations. As soon as the Cu+1 or Ag+1 are partially hydrated, the ns* and np* states are shifted to higher energies. The luminescence observed with dehydrated Cu+1‐zeolites X is caused by a 4p*←HOMO absorption, followed by spontaneous 4s*←4p* emission. After a detailed study of a Cu+1 in the 6‐6 SBU, we discuss the electronic structure of a β‐cage filled with 1,2,4,8, and 9 Cu+1. In each case, the β‐cage is found to be too small to allow the formation of a band structure. The levels caused by the added copper are distinctly quantized. Calculations on [Ag3(H2O)3]3+ in a β‐cage are reported. The direct interaction between the Ag‐atoms is significant. As a consequence, the states formed by Ag 5s and 5p atomic orbitals are delocalized over the three Ag‐centers. In both the Cu+1 and the Ag+1 zeolites, the ligand‐field picture is found to be insufficient to explain the electronic structure, when the metal is coordinated to the zeolite oxygen framework.
Chemical Degradation of Sarverogenin, Proof for the Presence of the Steroid Carbon Skeleton. Glycosides and Aglycones, 335th Communication
Authors: Lardon André , Reichsten Tadeus 
Published: December 2004

AbstractChemical degradation of sarverogenin (1) to several bile‐acid derivatives of known structures is described. This is a proof that 1 contains the normal tetracyclic steroid skeleton, and that the structure suggested for 1 by Fuhrer et al. [3] on the basis of spectral data is correct.
Drüsefarbstoffe aus Labiaten: Identifizierung von 17 Abietanoiden aus Plectranthus sanguineus BRITTEN
Authors: Matloubi‐Moghadam Firouz , Rüedi Peter , Eugster Conrad Hans 
Published: December 2004

Pigments from Leaf‐Glands from Labiatae: 17 Quinonoid Abietanoids from Plectranthus sanguineus BRITTENFrom the glandular trichomes of the title plant from Nyasaland, Malawi, 17 abietanoid quinones and hydroquinones were isolated and identified, the most interesting amongst them being the novel tricyclic, sevenmembered anhydride 8. A detailed HPLC separation of the compounds is presented.
Octacarbonyldicoblat‐Inauced (1,3) H Shits in 1‐Methylallenecarboxylates and Allenic Lactones
Authors: Trifonov Latchezar S. , Orahovats Alaxander S. , Heimgartner Heinz 
Published: December 2004

AbstractThe allenecarboxylates 1a,b and allenic lactones 4a,b undergo thermally induced (1,3) H Shifts in the presence of Co2(CO)8. The non‐isolated 1,3‐dienes 2a,b react further affording the Diels‐Alder Adducts 3a,b Scheme 1 in high yields. These adducts were not formed in the case of the 2‐vinybutenolides 5a,b. On irradiationin the presence of Co2(CO)8 or Mn2(Co)10, the studied allenes reacted in a different manner, yielding either cyclization products 7 and 8 (Scheme 3) or products 9 and 10, formed via H abstracton and solvent addition (Schemes 4 and 5).
Chemie der α‐Aminonitrile 1. Mitteilung Einleitung und Wege zu Uroporphyrinogen‐octanitrilen
Authors: Ksander Gary , Bold Guido , Lattmann René , Lehmann Christian , Früh Thomas , Xiang Yi‐Bin , Inomata Katsuhiko , Buser Hans‐Peter , Schreiber Jakob , Zass Engelbert , Eschenmoser Albert 
Published: December 2004

Chemistry of α‐Aminonitriles I: Introduction and Pathways to Uroporphyrinogen‐octanitriles.An introduction to experimental studies on the chemistry of α‐aminonitriles potentially relevant to the problems of prebiotic chemistry is presented. The framework of conditions wherein the investigation is chosen to be carried out implies both molecular oxygen and ‐ whenever feasible ‐ water to be excluded from reaction conditions. This study focusses on 2‐amino‐2‐propenenitrile (3) (Scheme 6) as central starting material of reaction sequences which aim at the nitrile forms of proteinogenic amino acids as well as at the aza forms of building blocks of biological cofactor molecules as their targets (Scheme 5). Schemes 13,16,23 as well as 25 and 26 summarize reaction sequences by which 3 is transformed within the defined framework of conditions into the thermodynamic (statistically controlled) mixture of the four isomeric uroperphyrinogen‐octanitriles 57–60. HPLC's of such mixtures document the dominance of the least symmetrical isomer whose constitutional pattern of peripheral substituents happens to be the one percent in all biological porphinoids. Preparative procedures for the synthesis of 3(Scheme 9), the β,β‐disubstituted pyrrol‐nitriles 30,53 and 54 (Scheme 19) as well as the porphyrinogenoctakis(propionitrile) and‐octakis(acetonitrile) 65 and 66, respectively (Scheme 24) are given.
Enzyme‐Catalyzed Hydrolysis of Some Functionalized Dimethyl Malonates
Authors: Luyten Marcel , Müller Susanna , Herzog Beat , Keese Reinhart 
Published: December 2004

AbstractA method is described for the preparation of (+)‐(R)‐methyl hydrogen 2‐(tert‐butoxymethyl)‐2‐methyl‐malonate (5e) in synthetically useful amounts from readily available starting material.
Synthesis of 12‐Methyl‐13‐tridecanolide
Authors: Stanchev Stephan , Hesse Manfred 
Published: December 2004

AbstractThe title compound was prepared from 2‐nitrocyclodecanone (2). Compound 2 was treated with 2‐methylpro‐penal to give the Michael‐addition product 3 which was reduced to the alcohol 5 and the latter ring‐enlarged with Bu4NF to 12‐methyl‐10‐nitro‐13‐tridecanolide (6) followed by reductive elimination of the NO2 group by Bu3SnH.
Synthesis of 2‐Cycloalkenones (Parts of 1,4‐Diacyl‐1,3‐butadiene Systems) and of a Heterocyclic Analogue by Metal‐Catalyzed Decomposition of 2‐Diazoacylfurans
Authors: Wenkert Ernest , Guo Ming , Pizzo Ferdinando , Ramachandran Kishore 
Published: December 2004

AbstractFurans with side‐chains at C(2) of various lengths terminating in diazomethyl keto groups are shown to undergo Rh2(OAc)4‐catalyzed furan unravelling with the production of 2‐cyclopentenone, 2‐cyclohexenone, and 2‐cycloheptenone to each of whose olefinic C(β) is attached an acrylaldehyde unit. Interposition of a cyclohexane or a methylaminomethylene moiety between the furan and diazoketo functions leads to the formation of a hydroindenone and pyrrolone, respectively. Replacement of the diazomethylketo terminus by an α‐diazoethylketo system or a α‐diazo‐β‐keto‐ester function produces 2‐substituted 2‐cycloalkenones. A furan with a C4, diazo‐methylketo‐terminating side‐chain at C(3) is described to be transformed into a 4‐formylmethylidene‐2‐cyclohe‐xenone.
Preparation and C‐Alkylation of Enantiomerically Pure S‐Phenyl Aziridinecarbothioates. On the Structure of Small‐Ring Ester Lithium Enolates
Authors: Häner Robert , Olano Bernardo , Seebach Dieter 
Published: December 2004

AbstractRacemic and enantiomerically pure methyl N‐(tert‐butyl)‐N‐benzyl‐ and N‐1‐(phenylethyl)aziridinecarboxylates are prepared by known methods and converted to phenyl thioesters (1, 2, 15, 16; Schemes 2 and 3). These are deprotonated with lithium diisopropylamide (LDA) and BuLi (for removal of diisopropylamine) in THF at dry‐ice temperature. The resulting lithiated species are surprisingly stable and are deuterated, alkylated (CH3, C2H5, allyl, benzyl), and added to aldehydes and nitroolefins in good yields (50–80 %, 18 examples; Schemes 1 and 4–6). The configurational stability of the lithiated species is studied, and conclusions about their structures are drawn. Thus, a C(α)‐lithiated ester (see L, Scheme 9) or an O‐lithiated ‘enolate’ (see M) with pyramidalized C(β)‐atom is proposed for the species from levorotatory S‐phenyl N‐benzylaziridinecarbothioate which does not undergo racemization after 1 h at −60° (THF solution).
New Antifungal Chromenyl Ketones and their Pentacyclic Dimers from Hypericum revolutum VAHL
Authors: Décostered Laurent A. , Hostettmann Kurt , Stoeckli‐Evans Helen , Msonthi Jerome D. 
Published: December 2004

AbstractTwo new 2H‐1‐benzopyranyl ketones 1 and 2 and three new pyrano[3,2‐c: 4,5,6‐d′ e′]di[1]benzopyrandiyl diketones 3, 4a/4b, and 5 have been isolated from the leaves and twigs of Hypericum revolutum VAHL (Guttiferae). The structure of 3 (hyperevoline) was established by X‐ray analysis as 1,1′‐[1,13,13a,13b‐tetrahydro‐5,8,10‐trihydroxy‐2,2,6,9,13,13‐hexamethyl‐2H, 7aH‐pyrano[3,2‐c:4,5,6‐d′e′]di[1]benzopyran‐4, 11‐diyl]bis[2‐methyl‐1‐propanone]. The structures of the isolated compounds were established by spectroscopic (UV, IR, EI‐MS, 1H‐ and 13C‐NMR) and chemical (acetylation and acidic dimerization) methods.
Acid‐Catalyzed Rearrangements of 5,6‐exo‐Epoxy‐7‐oxabicyclo[2.2.1]hept‐2‐yl Derivatives. Migratory Aptitudes of Acyl vs. Alkyl Groups in Wagner‐Meerwein Transpositions
Authors: Le Drian Claude , Vogel Pierre 
Published: December 2004

AbstractIn the presence of HSO3F/Ac2O in CH2CL2, 2‐exo‐ and 2‐endo‐cyano‐5,6‐exo‐epoxy‐7‐oxabicyclo[2.2.1]hept‐2‐yl acetates (6a, b) gave products derived from the epoxide‐ring opening and a 1,2‐shift of the unsubstituted alkyl group (σ bond C(3)–C(4)). In contrast, under similar conditions, the 5,6‐exo‐epoxy‐7‐oxabicyclo[2.2.1]heptan‐2‐one (6c) gave 5‐oxo‐2‐oxabicyclo[2.2.1]heptane‐3,7‐diyl diacetates 20 and 21 arising from the 1,2‐shift of the acyl group. Acid treatment of 5,6‐exo‐epoxy‐2,2‐dimethoxy‐7‐oxabicyclo[2.2.1]heptane (6d) and of 5,6‐exo‐epoxy‐2,2‐bis(benzyloxy)‐7‐oxabicyclo[2.2.1]heptane (6e) gave minor products arising from epoxide‐ring opening and the 1,2‐shift of σ bond C(3)–C(4) and major products (25, 29) arising from the 1,3‐shift of a methoxy and benzyloxy group, respectively. Under similar conditions, 5,6‐exo‐epoxy‐2,2‐ethylenedioxy‐7‐oxabicyclo[2.2.1]heptane (6f) gave 1,1‐(ethylenedioxy)‐2‐(2‐furyl)ethyl acetate (32, major) and a minor product 33, arising from the 1,2‐shift of σ bond C(3)–C(4). The following order of migratory aptitudes for 1,2‐shifts toward electron‐deficient centers has been established: acyl > alkyl > alkyl α‐substituted with inductive electron‐withdrawing groups. This order is valid for competitive Wagner‐Meerwein rearrangements involving equilibria between carbocation intermediates with similar exothermicities.
Mammalian Alkaloids: Configurations of Optically Active Salsoline‐ and 3′,4′‐Dideoxynorlaudanosoline‐1‐carboxylic Acids
Authors: Chrzanowska Maria , Schönenberger Bernhard , Brossi Arnold , Flippen‐Anderson Judith L. 
Published: December 2004

AbstractSynthesis of the optical isomers of (±)‐methyl 6,7‐dimethyl‐3′,4′‐dideoxynorlaudanosoline‐1‐carboxylate ((±)‐2) was accomplished by reaction of (±)‐2 with (+)‐(R)‐1‐phenylethyl isocyanate, separation of the urea diastereoisomers (−)‐4A and (+)‐4B, and alcoholysis of the ureas in refluxing BuOH. Optically active isoquinoline‐carboxylates 2A,B and hydantoins 8A,B isolated were characterized. The absolute configuration of the reaction products was established by X‐ray analysis of the optically active hydantoin (+)‐8A. Hydrolysis of the methyl isoquinolinecarboxylates 2A,B with 48% HBr soln. at reflux afforded the desired optically active 3′,4′‐dideoxynorlaudanosoline‐1‐carboxylic acids 1A,B required for enzyme‐inhibition studies. Details of the X‐ray diffraction analysis of (+)‐methyl salsoline‐1‐carboxylate hydrobromide ((+)‐11A·HBr) prepared earlier are included. CD spectra of (+)‐(S)‐methyl 6,7‐dimethyl‐3′,4′‐dideoxynorlaudanosoline‐1‐carboxylate hydrobromide ((+)‐2A. HBr) and (−)‐(R)‐methyl salsoline‐1‐carboxylate hydrochloride ((−)‐11B·HCl) confirmed the assignment of their (S)‐ and (R)‐configurations, respectively.
Synthesis of 1,2‐five‐ring‐annellated barrelenes via the intramolecular Diels‐Alder reaction of acetylenic derivatives
Authors: Trifonov Latchezar S. , Orahovats Alexander S. 
Published: December 2004

AbstractThe intramolecular Diels‐Alder reaction conducted with acetylenic acylureas, obtained from carbodiimides, and the acetylenic acid 5 and its derivatives 13 gave the 1,2‐annellated barrelene 14 (from 13a) and the benzobarrelenes 8 (from 5) and 15 (from 13b); in the case of 3‐butynoic acid (1),[1,3]‐H shift were observed. The formation of the azabarrelenes 16 (from 13c) as an intermediate is postulated which looses HCN to afford the indolinone 17. The acylureas 6 and 9 underwent isocyanate cleavage instead of [4+2] cyclization.
General Synthesis of Ketones from Carboxylic Esters and Carboxamides by Use of Mixed Organolithium‐Magnesium Reagents: Syntheses of Artemisia Ketone
Authors: Fehr Charles , Galindo José , Perret Roland 
Published: December 2004

AbstractThe novel reagents formed by combination of Grignard reagents (RMgX) with lithium diisopropylamide (LDA) convert non‐enolizable or slowly enolizable carboxylic esters or caboxamides into ketones which are protected from further reaction by their in situ conversion into enolates. These enolates can be trapped with electrophiles such as Me3SiCl and allyl bromide. The scope of this Grignard mono‐addition is illustrated by two direct syntheses of artemisia ketone (14).
The Eu(III) Ion as Luminescent Probe: Investigation of the Metal‐Ion Sites in a Dicyclohexyl‐18‐crown‐6 Complex
Authors: Plancherel Dominique , Jin Linpei , Massara Romano , Bünzli Jean‐Claude G. 
Published: December 2004

AbstractThe metal ion sites of the 3:2 complex between europium nitrate and the A‐isomer of dicyclohexyl‐18‐crown‐6, [Eu(NO3)2(DC18C6)]2[Eu(NO3)5], have been probed by high‐resolution excitation and emission spectra at 296 and 77 K. The [Eu(NO3)5]2− anion gives rise to a luminescent spectrum dominated by the 5D0→7F2 transition. The crystal‐field splitting of the 7Fj levels is close to that observed for (Phe4As)2[Eu(NO3)5], pointing to a structurally similar pentakis(nitrato) species. The 5D0←7F0 excitation spectrum of the two crystallographically independent complex cations displays five maxima. A detailed analysis of the corresponding and selectively excited emission spectra leads to the following conclusions. Well differentiated spectra are assigned to different conformations of the complex cation, in which half of the ligand atoms, including O‐atoms, Present large thermal motions. The other spectra are very similar and arise from slightly unequivalent [Eu(NO3)2(DC18C6)]+ moieties differing in the conformation of their ethylene bridges. This dimonstrates the sensitivity of the Eu(III) ion as conformational probe in the solid state.
‘Face‐to‐Face’‐Benzo‐anellierte homologe Hypostrophene. Synthesen, Röntgenstrukturanalysen und PE‐Spektren
Authors: Fessner Wolf‐Dieter , Sedelmeier Gottfried , Knothe Lothar , Prinzbach Horst , Rihs Grety , Yang Zhong‐Zhi , Kovač Branka , Heilbronner Edgar 
Published: December 2004

‘Face‐to‐Face’ Benzo‐anellated Homologous Hypostrophenes. Syntheses, X‐Ray‐Structure Analyses and PE Spectra‘Face‐to‐face’ Benzo‐anellated homologous hypostrophenes (series M), of interest as substrates for [6 + 6]‐photocycloaddition reactions, have been synthesized. From X‐ray structural analyses of 13b and 13c shortest CC distances of 2.80(2.76)/2.71 Å and interorbital angles (ω) of 129° (128°)/130° between the benzene rings have been determined. The PE spectra are discussed in the context of transannular π,π interactions.