bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactivity of Carbenes and Related Compounds towards Molecular Nitrogen
Authors: Grieve Duncan M. A. , Lewis Graham E. , Ravenscroft Michael D. , Skrabal Peter , Sonoda Takaaki , Szele Ivanka , Zollinger Heinrich
Published: December 2004

The thermal N2 exchange of a number of 15N‐labelled diazo compounds was studied in solution. The compounds involved were 3‐diazo‐1‐methylindolin‐2‐one (1), 9‐diazofluorene (2), 5‐diazo‐1,3‐cyclopentadiene‐1,2,3,4‐tetracarbonitrile (3), 2‐diazo‐2H‐imidazole‐4,5‐dicarbonitrile (4), 4‐diazocyclohexa‐2,5‐dienone (5), and the conjugate acids of 4 and 5, namely 4,5‐dicyano‐1H‐imidazole‐2‐diazonium ion (6) and 4‐hydroxybenzenediazonium ion (7). Only 1, 4, 6, and 7 exchange their diazo group with ‘external’ molecular N2. The results are explained on the hypothesis that only organic species which have an empty σ orbital and which are effective in π electron back‐donation are able to react with N2. Thus, reaction with carbenes is likely to occur only if the carbene is in the 1A2 singlet state and if its electrophilicity is high.
HPLC von Carotinen mit ψ‐Endgruppen und (Z)‐Konfiguration an terminalen konjugierten Doppelbindungen; Isolierung von (5Z)‐Lycopin aus Tomaten
Authors: Zumbrunn Albrecht , Uebelhart Peter , Eugster Conrad Hans
Published: December 2004

HPLC of Carotenes with ψ‐End Groups and (Z)‐Configuration at Terminal Conjugated Double Bonds; Isolation of (5Z)‐Lycopene from Tomatoes

Five carotenes bearing (5Z)‐ψ‐end groups were synthesized and carefully characterized: (5Z)‐lycopene (6), (5Z5′Z)‐lycopene (7), (5′Z)‐neurosporene (8), (5′Z)‐β,ψ‐carotene (12), and (5′Z)‐ε,ψ‐carotene (14). Lycopene 6 was isolated from tomatoes and its structure proven by 1H‐NMR spectroscopy.
Über den Einfluss der pK‐Werte von Anilinen auf die Bildung und Folgereaktionen von substituierten Butadienen aus Cumalinsäure‐methylester
Authors: Kvita Vratislav , Sauter Hanspeter , Rihs Grete
Published: December 2004

The Influence of Aniline pK Values on the Formation and Reactivity of Substituted Butadienes from Methyl Coumalate

The product of the reaction between 2 equiv. of methyl coumalate (1) and 1 equiv. of a substituted aromatic amine depends on the pK value of the latter. Aromatic amines with pK values between 1.05 and 2.8 produce bicyclic lactones 4, whereas those with higher pK values also give 2‐azabicyclo[3.3.1]nona‐3,7‐diene‐9‐carboxylic acids 9. The latter, products of the intramolecular Diels‐Alder reaction 8 → 9, may in certain cases even prevail.
Hetero‐Cope‐Umlagerungen. 4. Mitteilung. Regiokontrollierte Indolsynthesen
Authors: Blechert Siegfried
Published: December 2004

Hetero‐Cope‐Rearrangements, Regio‐Controlled Synthesis of Indoles

The reaction of O‐deprotonated N‐phenylhydroxylamines 1 with various electron‐deficient allenes 2, 14, 16 gives, via Michael addition and Cope‐rearrangement, substituted anilines 5, which are easily convertible into indoles 6. In this manner, sulfoxides 17, serve as equivalents of 2‐vinylindoles. Diels‐Alder reaction with this 2‐vinylindole equivalent followed by indolisation affords isoquinuclidine derivative 21 which may be a useful precursor for the preparation of Iboga alkaloids.
Tritiation of Peptides to High Specific Radioactivity. Part 1. Synthesis and Biological Properties of [13‐(3H4)Norvaline]‐α‐MSH and of [2,23‐Bis((3H2)tyrosine)]ACTH(1–24)
Authors: Eberle Alex N. , Zeller Albert
Published: December 2004

α‐MSH and ACTH(1–24) were tritiated to high specific radioactivity (> 100 Ci/mmol) using a new tritiation apparatus with which the tritiation reaction can be performed at slightly elevated pressure. This allows short reaction times with the least possible damage to the molecule. The starting compounds for the tritiation were [13‐propargylglycine]α‐MSH and [2,23‐Bis(3′,5′‐diiodotyrosine)]ACTH(1–24). Both tritiations were quantitative and yielded products of high purity, full biological activity, and with a specific radioactivity of 115 Ci/mmol and 100 Ci/mmol, respectively.
Studies on the Carbon Zip Reaction of 2‐Oxocycloalkane‐1‐carbonitriles
Authors: Süsse Manfred , Hájíček Josef , Hesse Manfred
Published: December 2004

As a part of continuing interest in the zip reaction, we present the results on a carbon ring‐enlargement reaction of activated ketones with a CN group as a charge stabilizer. Two series of (1‐cyano‐2‐oxocy‐cloalkyl)alkanoates were prepared from 8‐ and 12‐membered cyano‐ketones 1 and 2, respectively, namely the propanoates 3 and 4, the butanoates 6, 8 and 9 as well as the pentanoates 12 and 15. While treatment with t‐BuOK of the former two homologous esters resulted in both ring enlargement and competitive transesterification, the pentanoates 12 and 15 afforded mostly the diastereoisomeric mixtures of bicyclic alcohols 20a–c and 31a,b, respectively, which remained intact on further exposure to base. It was shown that – apart from the base used (t‐BuOK) vs. Li(i‐Pr)2N – the distribution of products was greatly influenced by the ring size of substrates. This is further illustrated by treatment of ketones 34 and 35 with t‐BuOK. While the former rearranged smoothly to diketone 36, no reaction at all took place with the latter. The behavior of the substrates is discussed in terms of steric and energetic reasons.
Synthesen und chemische Reaktionen von ω,ω‐Bis(alkylthio)chinonmethiden des 1,6‐Methano[10]annulens
Authors: Neidlein Richard , Hartz Georg
Published: December 2004

Syntheses and Chemical Reactions of ω,ω‐Bis(alkylthio)quinonemethides of 1.6‐Methano[10]annulenes

The syntheses of the donor‐acceptor‐substituted compounds 3–5, 9 starting from 2, 7, or 8, furthermore, the syntheses of 12, 15–21 are described. The detailed results of 1H‐ and 13C‐NMR‐spectroscopic measurements are reported.
X‐Ray Diffraction Study of 2‐Aminopropenenitrile at 97 K
Authors: Seiler Paul , Dunitz Jack D.
Published: December 2004

2‐Aminopropenenitrile crystallizes in the space group P212121 with two molecules in the asymmetric unit. Both molecules show appreciable pyramidalization at the amino group. The crystal structure is built from approximately centrosymmetric dimers stabilized by hydrogen bonding between the amino group of each molecule and the nitrile group of its partner. The dimers are linked into chains by further hydrogen bonds in which the amino group of one molecule acts as donor, the amino group of the other as acceptor. The two types of molecule thus play different roles in the crystal structure. Electron density difference maps for the two independent molecules show characteristic bonding density features. The molecular structure as obtained by the low‐temperature X‐ray analysis is closely similar to that derived from ab initio molecular orbital calculations and leads to rotational constants close to those obtained from a microwave spectroscopic study.
Asymmetric Diels‐Alder Reactions of Neopentyl‐Ether‐Shielded Acrylates and Allenic Esters: Syntheses of (−)‐Norbornenone and (−)‐β‐Santalene
Authors: Oppolzer Wolfgang , Chapuis Christian , Dupuis Dominique , Guo Maodao
Published: December 2004

Starting from (+)‐ or (−)‐camphor, the antipodal alcohols 14 and 18, respectively, have been prepared; the corresponding acrylates 15 and 19 underwent TiCl2(i‐PrO)2‐mediated Diels‐Alder additions to cyclopentadiene to give adducts 20a and 22a respectively, with 95 % endo‐ and 99.2% πpH‐face selectivities. Adduct 22a was converted to enantiomerically pure norbornenone 26. Addition of 1,3‐butadiene to acrylate 15 in the presence of TiCl4 afforded 3‐cyclohexenyl carboxylate 29 with > 95.6 % stereodifferentiation. The TiCl2(i‐PrO)2‐promoted [4 + 2] cycloaddition of cyclopentadiene to allenic ester 43 proceeding with 99 % face differentiation served as the key step for an efficient enantioselective synthesis of (−)‐β‐santalene ((−)‐41) with concomitant recovery of the chiral control alcohol 14.
Synthese von 15‐Hydroxy[9]metacyclophan
Authors: Lorenzi‐Riatsch Annalaura , Wälchli Rudolf , Hesse Manfred
Published: December 2004

Synthesis of 15‐Hydroxy[9]metacyclophane

3‐(1‐Nitro‐2‐oxocyclododecyl)propanal (1) was converted to 15‐hydroxy[9]metacyclophane (3) on two different routes. In the first case the internal aldol reaction product of 1 was treated with K2CO3/THF to give 3 in 29 % yield with regard to cyclododecanone. Alternatively, the aldehyde 1 reacted with a primary amine to form e.g. 4 which gave 3 in the presence of CH3I/K2CO3 in 48 % yield.
1H‐NMR Spectra of Cyclohexa‐1,4‐dienes and Cyclohexenes Annellated to Bicyclo[2.2.1]hept‐2‐enes. The Inter‐Ring Homoallylic H,H Coupling Constants as Stereochemical Probes
Authors: Mahaim Cyril , Carrupt Pierre‐Alain , Vogel Pierre
Published: December 2004

The 360‐MHz‐1H‐NMR spectra of cyclohexa‐1,4‐dienes and cyclohexenes annellated to bicyclo[2.2.1]hept‐2‐enes and 7‐oxabicyclo[2.2.1]hept‐2‐enes show inter‐ring homoallylic coupling constants between the bridgehead protons of the bicyclo[2.2.1]heptenes and the exo‐protons of the allylic methylene groups (0.8 ± 0.15 Hz for bicyclo[2.2.1]hept‐2‐enes; 0.8–1.4 Hz for 7‐oxabicyclo[2.2.1]hept‐2‐enes). Contrastingly, the corresponding coupling between the bridgehead protons and the endo‐protons is absent. The observed values are compared with those calculated by the INDO and CNDO/2 methods and discussed in the light of the bicyclo[2.2.1]hept‐2‐ene bond π‐anisotropy. Vicinal as well as intra‐ring homoallylic coupling constants are consistent with a small puckering of the cyclohexa‐1,4‐diene rings toward the endo‐face. The allylic exo‐methylene protons are more deshielded than the endo‐protons independent of the nature of the substituents, the nature of the bridges, and the degree of unsaturation of the annellated systems. These results constitute a probe for the configuration of cyclohexa‐1,4‐dienes and cyclohexenes annellated to these bicyclic skeletons.
Formale Totalsynthese von (±)‐Isocomen durch Anwendung der α‐Alkinon‐Cyclisierung
Authors: Manzardo Giuseppe G. G. , Karpf Martin , Dreiding André S.
Published: December 2004

Formal Total Synthesis of (±)‐Isocomen by Application of the α‐Alkinon Cyclization

A total synthesis of the racemic form of the sesquiterpene isocomene (A) was accomplished by application of the cyclopentenone anellation B→D (Scheme 1) which includes the α‐alkynone cyclization C→D, a gas‐phase flow thermolytic process. Starting with the known product 2 (Scheme 3) of the anellation B→D, the elaboration of ring C of A proceeded in 9 steps to the α‐alkynone 16 (Scheme 5) which was cyclized at 540° selectively to give the angularly fused triquinane 4 (77%). A two‐step procedure then led to 5 (Scheme 6), a last but one intermediate in a known total synthesis of (±)‐A. The conversion of 16 to 4 also demonstrated the compatibility of an acetoxy function with the anellation sequence B→D.
Pteridine. Teil LXXX. Synthese, Reaktionen und Photochemie von Pteridinthionen
Authors: Heekel Armin , Pfleiderer Wolfgang
Published: December 2004

Synthesis, Reactions, and Photochemistry of Pteridinethiones

The pteridine‐6(5H)‐thione 1 and various pteridine‐7(8H)‐thiones (13, 22, 26) have been synthesized, and their photochemical reactivity has been investigated under aerobic conditions. The formation of different photooxidation products is pH‐dependent. In acidic to neutral media, disulfides (2, 15, 23, 29) are formed, whereas neutral to alkaline solutions favour the formation of pteridinesulfinic (3, 17) and ‐sulfonic acids (6, 16, 24, 30). Prolonged irradiation of the disulfides 2 and 15 led to the intensively yellow fluorescing bis(thio)dilumazines 19 and 20, respectively.
Deoxy‐nitrosugars 12th communication Synthesis of isosteric mono‐phosphonate analogues of β‐and α‐D‐fructose 2,6‐bisphosphate
Authors: Meuwly Roger , Vasella Andrea
Published: December 2004

A synthesis of the isosteric mono‐phosphonate analogues 2a and 19 of the β‐and α‐D‐fructose 2,6‐bisphosphate, respectively, is described. Chain elongation of the 1‐deoxy‐1‐nitro‐D‐arabinose 3 (Scheme 1) by a Henry reaction with paraformaldehyde followed by protection of the resulting alcohol (methoxymethyl ether) and a radical‐chain substitution by nitromethane anion gave the key intermediates, the gluco‐anhydroalditol 6 and the manno‐anhydroalditol 7. These products equilibrated under basic conditions. Conversion of 7 to the aldehyde 9, Abramov reaction of 9 with diphenyl phosphite followed by deoxygenation according to Barton gave the phosphonate 11 (Scheme 2). Selective hydrogenolysis of 11, phosphorylation and deprotection gave 2 which was converted to the tetrasodium salt 2a. Similarly, 6 was transformed into the isosteric phosphonate analogue 19 of the α‐D‐fructose 2,6‐bisphosphate (Scheme 3).
Umsetzungen von 1,3‐Thiazol‐5(4H)‐thionen mit Grignard‐ und Organolithium‐Verbindungen: Carbophile und Thiophile Additionen
Authors: Jenny Christjohannes , Heimgartner Heinz
Published: December 2004

Reactions of 1,3‐Thiazole‐5(4H)‐thiones with Grignard‐ and Organolithium Compounds: Carbophilic and Thiophilic Additions

Organolithium compounds and 1,3‐thiazole‐5(4H)‐thiones 9 reacted via thiophilic addition on the exocyclic S‐atom. The intermediate anion E has been trapped by protonation to give 12 and by alkylation to yield 16, respectively (Schemes 5 and 6). In competition with protonation of E, a fragmentation to benzonitrile and a dithioester 14 was observed (Scheme 5). In some cases, the alkylation of E led to the formation of dithioacetals 17 instead of 16 (Scheme 6). Methyl, ethyl, and isopropyl Grignard reagents and 9 in THF underwent again a thiophilic addition yielding 4,5‐dihydro‐1,3‐thiazoles of type 12 (Scheme 3). In contrast to this result, MeMgI reacted with 9a in Et2O via carbophilic addition to 11. Again a carbophilic attack at C(5) of 9 was observed with allylmagnesium and 2‐propynylmagnesium bromide, respectively, in Et2O.
Synthese von Triafulven‐Vorstufen für Retro‐Diels‐Alder‐Reaktionen
Authors: Krebs Jürg , Guggisberg Dominik , Stämpfli Urs , Neuenschwander Markus
Published: December 2004

Synthesis of Triafulvene Precursors for Retro‐Diels‐Alder Reactions

Triafulvene precursors exo−15 and endo−15 have been prepared by addition of dibromocarbene to benzobarrelene 12 followed by a lithium‐halogen exchange, methylation, and elimination of HBr (12→13→14→15), (Scheme 2). Gas‐phase pyrolysis of exo/endo‐mixtures of 15 above 400° gave minor amounts of naphthalene (16), traces of a hydrocarbon C4H4 identified by MS (presumably triafulvene 1) and predominantly (36%) the isomerization product 17 (Scheme 3). In a second synthetic approach the well‐known cycloheptatriene‐norcaradiene equilibrium of type 26⇆27 has been utilised to prepare various endo‐trans‐3‐(X‐methyl) tricyclo[3.2.2.02,4]nona‐6,8‐dienes 31 (Scheme 5). However, numerous elimination experiments 31→9 failed so far. The structure of two rearrangement products 33 and 34 (Scheme 6) has been elucidated.
Perimeter‐Type Structures in Charged [4n + 2] Annuleno [4n + 2] annulenes. The Importance of the Frontier‐Orbitals
Authors: Huber Walter , Müllen Klaus , Schnieders Christoph , Iyoda Masahiko , Nakagawa Masazumi
Published: December 2004

The tetra(tert‐butyl)[14]annuleno[14]annulene 1 is transformed, via alkali metal reduction, into its radical monoanion, dianion, radical trianion, and tetraanion. The paramagnetic species are characterized by ESR and ENDOR spectroscopy and the diamagnetic species by 1H‐ and 13C‐NMR spectroscopy. Well‐resolved ESR and NMR spectra can only be obtained, if the reduction is carefully monitored. For the interpretation of the data, the ions derived from the structurally related [14]‐ and [22]annulenes 3 and 5 as well from the tetra(tert‐butyl)[14]annuleno[18]annulene 2 serve as suitable model compounds. While the behavior of the neutral annulenoannulene 1 is governed by that of the [14]annulene‐subunit, the corresponding ionic systems can best be described as macrocyclic perimeters. This outcome can be rationalized by the nodal properties of the frontier MO's.
Insight into the Behaviour of a Lithium Enolate in Solution
Authors: Strazewski Peter , Tamm Christoph
Published: December 2004

(2S,4S)‐2‐(tert‐Butyl)‐5‐oxo‐1,3‐dioxolan‐4‐acetic acid (1) was dilithiated to the enolate 2 in toluene and THF with lithium diisopropylamide (LiN(i‐Pr)2) under various conditions. Deuteration experiments with 2 showed that two different stable forms of the enolate could be produced, depending on whether the deprotonation of 1 had been carried out in toluene or THF. The generated (i‐Pr)2NH was coordinated to the enolate and, hence, served as a strong lipophilic solvating agent. LiN(i‐Pr)2 could substitute the amine ligands of the two species to a different extent. THF was partially able to displace (i‐Pr)2NH that solvated the species produced in toluene, but the coordination of the amine to the one produced in THF was quantitive. Correlations with given explanations are made.
Cyclometallated Rhodium(III) Complexes with Diimine Ligands
Authors: Mäder Urs , Von Zelewsky Alex , Jenny Titus
Published: December 2004

The synthesis of a mononuclear Rh(III) complex, as a representative example of a series of related species, containing two cyclometallating ligands ppy (2‐phenylpyridine) and one diimine bpy (2,2′‐bipyridine) from a binuclear Cl‐bridged compound is described. The absorption spectrum shows a maximum at 364 nm (ε = 7000), with a very weak shoulder (ε = 10) at 454 nm. This band is tentatively assigned to a metal‐to‐ligand charge‐transfer transition. A reversible, one‐electron reduction appears in the cyclic voltammogram at E1/2 = −1.41 V (vs. NHE) and a irreversible oxydation at Ep = + 1.1 V. A detailed NMR analysis including 13C‐NMR, NOE, SFORD as well as deuteration of the bpy ligand indicates the formation of only one isomer, having a C2 axis, bisecting the bpy ligand, with the two carbon ligands in cis‐position. 103Rh, 13C and 103Rh,H couplings are observed.
Are ionic solids really built of ions? New evidence from x‐ray diffraction
Authors: Seiler Paul , Dunitz Jack D.
Published: December 2004

A new, accurate, low‐temperature X‐ray analysis of lithium tetrafluoroberyllate, Li2BeF4, reveals that the charge density in this crystal is better represented as a superposition of spherical neutral‐atom charge distributions than as a superposition of ionic charges. The two distributions are so similar that they are hardly distinguishable by examination of the total charge density in real space. However, the two models are clearly differentiated by analysis of the weak low‐order reflections; the measured intensities are reproduced better by calculations based on neutral‐atom scattering curves. This result may appear to run counter to the current conventional wisdom concerning ionic solids, but it is unlikely to have any important practical consequences.
Cation‐Response Mechanism of Neutral Carrier Based Ion‐Selective Electrode Membranes
Authors: Morf Werner E. , Simon Wilhelm
Published: December 2004

Results of voltammetric, potentiometric, chronoamperometric, ion transport, and extraction studies on neutral carrier based, plasticized poly(vinyl chloride) membranes are summarized. They unambiguously confirm that such bulk membranes dispose of immobile anionic sites. These fixed sites lead to a Donnan exclusion of other anions from the membrane and thus to a permselectivity for cations. The results are in perfect agreement with the predictions of earlier membrane models. A rigorous Poisson‐Boltzmann analysis of macroscopic liquid membranes clearly indicates that space‐charge at the membrane/solution interfaces does not influence the electrochemical properties and the ion‐selectivity behavior at steady state.
Diastereoselectivity and Reactivity in the Diels‐Alder Reactions of α‐Chloronitroso Ethers
Authors: Felber Helena , Kresze Günther , Prewo Roland , Vasella Andrea
Published: December 2004

The structure of the α‐chloronitroso ether 1, obtained from the hydroximolactone 2 and tert‐butyl hypochlorite (89%), was established by X‐ray crystallographic analysis. The [4 + 2] cycloadditions of 1 with the dienes 3 and 8–11 led to the N‐unsubstituted 3,6‐dihydro‐2H‐1,2‐oxazines 6 and 12–16 in high enantiomeric excess (Table 1). Due to the additional α‐alkoxy group, the reactivity of 2 is much superior to the one of known α‐chloronitrosoalkanes. The reactive conformation of 1 was deduced from the X‐ray analysis as well as the high diastereoselectivity of the cycloadditions. The importance of the α‐alkoxy group was evidenced from the similar reactivity of the racemic α‐chloronitroso ethers 25–27 which were prepared from the hydroximo ethers 28–30 and tert‐butyl hypochlorite.
Regioselektive Funktionalisierung von N,N‐Diethyl‐1,6‐methano[10]annulen‐2‐carbonsäureamiden
Authors: Neidlein Richard , Wirth Wolfgang
Published: December 2004

Regioselective Functionalisation of N,N‐Diethyl‐1,6‐methano[10]annulene‐2‐carboxamides

Lithiation of N,N‐diethyl‐1,6‐methano[10]annulene‐2‐carboxamide with BuLi followed by quenching with different electrophiles yields 2,10‐disubstituted‐1,6‐methano[10]annulenes.
NMR Studies of Alkaloids. Assignment of the Configuration at C(20) in Tubotaiwine (Dihydrocondylocarpine)
Authors: Lounasmaa Mauri , Koskinen Ari , O'Connell John
Published: December 2004

Two‐dimensional, high‐field NMR methods are employed in confirming the relative configuration at the C(20) ethyl side‐chain junction as S* in the natural alkaloid tubotaiwine (dihydrocondylocarpine).
Neue Heterocyclen: Über Tetrazinodi(heteroarene). Synthese und Struktur
Authors: Eichenberger Thomas , Balli Heinz
Published: December 2004

Novel Heterocycles: Tetrazinodi(heteroarenes), Synthesis and Structure

A series of 7 new symmetric tetrazinodi(heteroarenes) is obtained in a two‐step synthesis by N‐aminating heterocyclic compounds substituted with a leaving group and by treating the latter with an organic or inorganic base. The new compounds are characterized, and the postulated structures are confirmed by X‐ray analysis of a representative example.
Synthesen und Ringerweiterungsreaktionen von 2‐(4‐Hydroxyalkyl)‐2‐nitrocycloalkanonen
Authors: Stach Hans , Hesse Manfred
Published: December 2004

Syntheses and Ring‐Enlargement Reactions of 2‐(4‐Hydroxyalkyl)‐2‐nitrocycloalkanones

Syntheses of the title compounds were achieved by [Pd{P(C6H5)3}4]‐catalyzed reaction of 2‐nitrocycloalkanones 3 with vinyloxirane followed by catalytic hydrogenation. By another route, the known methyl 4‐(1‐nitro‐2‐oxocycloalkyl)butanoates 6 were reduced to the corresponding aldehydes 7 which by NaBH4 reduction or methylation with (CH3)2Ti(i‐Pr)2 were transformed to the alcohols 5 and 8, respectively (Saheme 1). Treatment of 5 and/or 8 with KH/THF under reflux gave, via a 7‐membered intermediate, the nitrolactones 12 and oxolactones 13 (Scheme 3). Compared with similar reactions running via 5‐ or 6‐membered intermediates (see 1 and 2), the yields are distinctly lower. The natural occurring 12‐tridecanolid (14) was synthesized.
Eine einheitlich verlaufende aliphatische Benzilsäure‐Typ‐Umlagerung
Authors: Schaltegger Alexander , Bigler Peter
Published: December 2004

An Uniformly Occurring Aliphatic Benzil‐Benzilic‐Acid‐Type Rearrangement

Treatment of 6‐bromo‐2,2,5,5‐tetramethylcyclohex‐3‐enone (2) with aqueous alkaline and air affords 1‐hydroxy‐2,2,5,5‐tetramethylcyclopent‐3‐enecarboxylic acid (8) as the major product of a benzil‐benzilic‐acid‐type rearrangement. The key compound is 2,2,5,5‐tetramethylcyclohex‐3‐ene‐1,2‐dione (11). The by‐product of the reaction is (E)‐2,2,5,5‐tetramethylhex‐3‐enedioic acid (9) as the result of an oxidative cleavage of the 6‐membered ring and the isomerization of the double bond.
Asymmetric and ‘anti’‐Selective Aldolisations of Acetates and Propionates. Preliminary Communication
Authors: Oppolzer Wolfgang , Marco‐Contelles José
Published: December 2004

Starting from acetates 1 and propionates 6, TiCl4‐mediated addition of their silyketene acetals 2 and 7 to aldehydes gave aldols 4 and 9, respectively, with high π‐face and ‘anti’ differentiation (Schemes, and Tables 1 and 2). Alternation of the (E/Z)‐enolate geometry led to reversed α‐ and β‐inductions (7 → 9b, 8 → 10b). Non‐destructive removal of the auxiliary yielded enantiomerically pure β ‐hydroxycarboxylic acids 13.
Enantiomerenreine Pyrrolidin‐Derivate aus trans‐4‐Hydroxy‐L‐prolin durch elektrochemische oxidative Decarboxylierung und Titantetrachlorid‐vermittelte Umsetzung mit Nukleophilen
Authors: Renaud Philippe , Seebach Dieter
Published: December 2004

Enantiomerically Pure Pyrrolidine Derivatives from trans‐4‐Hydroxy‐L‐proline by Electrochemical Oxidative Decarboxylation and Titanium‐Tetrachloride‐Mediated Reaction with Nucleophiles

Preparative electrolysis of N‐methoxycarbonyl‐O‐[(t‐butyl)dimethylsilyl]hydroxyproline 4 in MeOH leads to substitution of the COOH by a MeO group (oxidative decarboxylation). The mixture 5 of the two diastereoisomers (ca 1:1) thus obtained was reacted in CH2Cl2 with nucleophilic silylated compounds (such as allylsilane, silyl cyanide and 1‐phenyl‐1‐silyloxyethane) or with trimethyl phosphite in the presence of TiCl4 to give 2‐allyl‐, 2‐cyano‐, 2‐(2‐oxo‐2‐phenylethyl)‐ and 2‐phosphono‐substituted hydroxypyrrolidines, respectively, with high diastereoselectivities (≥ 90%, products 6‐12). The configuration of two of the products (6/7 and 8/9) was shown to be cis.
Synthetic applications of electrochemically produced α‐methoxyamides. Part 2. Oxidation of hydroxyproline derivatives
Authors: Thaning Mikkel , Wistrand Lars‐G.
Published: December 2004

The electrochemical methoxylation of N‐acetyl‐4‐hydroxyproline esters has been investigated. Both the free alcohol 3 and the corresponding 4‐acetoxy derivative 4 as well as the cis‐4‐acetoxyproline 17 are methoxylated anodically preferentially at C(5), giving a mixture of stereoisomeric methoxy compounds. These mixtures can be used for further substitution as exemplified by the allylation of the methoxylated 4‐acetoxy derivatives, giving substitution products preferentially trans to the acetoxy group although with low selectivity. The low selectivity is discussed in terms of kinetic vs. thermodynamic control.
New Synthetic Routes to β‐Olefinic Trialkoxyphosphonium Salts and Phosphonates: Organometallic Variants of the Michaelis‐Arbuzov Reaction
Authors: Hafner Andreas , Von Philipsborn Wolfgang , Salzer Albrecht
Published: December 2004

The low‐temperature addition of tertiary phosphites to [(allyl)Fe (CO)4]+X− complexes proceeds regio‐ and stereospecifically and produces metal‐coordinated β‐olefinic trialkoxyphosphonium ions. These can be converted by various routes into the uncomplexed phosphonium salts or phosphonates. Similar reactions of acyclic [(dienyl)Fe(CO)3]+X− compounds give metal‐coordinated (2,4‐dien‐1‐yl)trialkoxyphosphonium salts or dialkyl (2,4‐dien‐1‐yl)phosphonates. The mechanisms and their relationship to the classical Michaelis‐Arbuzov reaction are discussed. The new compounds are characterized, if possible, by 1H‐, 13C‐, and 31P‐NMR spectra. The new phosphonium salts and phosphonates, potentially useful for Wittig‐Horner reactions, are difficult to obtain by conventional routes.
3,7‐Dioxaazelaamides as Ionophores for Lithium Ion Selective Liquid Membrane Electrodes
Authors: Metzger Erich , Aeschimann Roland , Egli Martin , Suter Gaby , Dohner René , Ammann Daniel , Dobler Max , Simon Wilhelm
Published: December 2004

Lipophilic neutral carriers were synthesized which show Li+/Na+ selectivities of up to ca. 80 in highly lipophilic liquid membranes. The sensor membranes exhibit improved response times and increased lifetimes as compared to systems described earlier. They allow reliable measurements of Li+ in blood serum within the clinical concentration range. A 1:1 Li+/ionophore complex of one representative (N,N,N′,N′‐tetracyclohexyl‐5,5‐dimethyl‐3,7‐dioxaazelaamide) has been prepared, and its structure was elucidated by X‐ray analysis.
Carbophile Additionen von Organocupraten mit 1,3‐Thiazol‐5(4H)‐thionen
Authors: Jenny Christjohannes , Wipf Peter , Heimgartner Heinz
Published: December 2004

Carbophilic Additions of Organocuprates and 1,3‐Thiazole‐5(4H)‐thiones

Organocuprates and 1,3‐thiazole‐5(4H)‐thiones 1 react in THF at 0° via carbophilic addition onto the CS bond to give 4,5‐dihydro‐1,3‐thiazole‐5‐thiols 3 (Scheme 3). This observation is in marked contrast to the previously described reaction of organolithium compounds and 1, which undergo a thiophilic addition onto the exocyclic S‐atom. As an exception, treatment of the 1,3‐thiazole‐5(4H)‐thione 1a with tert‐butyl cuprate leads to 7a (Scheme 3).
Chiral Diaminodiamide Copper(II) Complexes for the Enantioselective Recognition of Amino Acids: Synthesis of the Ligands and Formation Constants
Authors: Armani Elisabetta , Marchelli Rosangela , Dossena Arnaldo , Casnati Giuseppe , Dallavalle Francesco
Published: December 2004

(S,S)‐N,N′ ‐Bis(aminoacyl)ethane‐ and (S,S)‐N,N′ ‐bis(aminoacyl)propanediamines (AA‐NN‐2 and AA‐NN‐3, respectively, AA = alanine, phenylalanine, valine) were synthesized as the dihydrochlorides, and their complexes with Cu(II) studied potentiometrically. Since these ligands in the presence of Cu(II) are able to perform chiral resolution of D,L‐dansylamino acids in HPLC (reversed phase), in a certain pH range (6.5–8.5), it is important to know the equilibria existing between ligands and copper in aqueous solution. For AA‐NN‐2, four species, CuLH3+, CuL2+, Cu2L2H, and CuLH−2, were detected, whereas for AA‐NN‐3, only CuLH3+, CuL2+, and CuLH−2 were found. The aim is to find out which complexes may be involved in the recognition process.
Stereochemical Analysis of an Aromatic Triplet Di‐π‐methane Rearrangement
Authors: Scholl Bernhard , Hansen Hans‐JÜRgen
Published: December 2004

It is shown that (−)‐(S)‐N,N‐dimethyl‐2‐(1′‐methylallyl)aniline ((−)‐(S)‐4), on direct irradiation in MeCN at 20°, undergoes in its lowest‐lying triplet state an aromatic di‐π‐methane (ADPM) rearrangement to yield (−)‐(1′R,2′R)‐ and (+)‐(1′R,2′S)‐N,N‐dimethyl‐2‐(2‐methylcyclopropyl)aniline ((−)‐trans‐ and (+)‐cis‐7) in an initial trans/cis ratio of 4.71 ± 0.14 and in optical yields of 28.8 ± 5.2% and 15 ± 5%, respectively. The ADPM rearrangement of (−)‐(S)‐4 to the trans‐ and cis‐configurated products occurs with a preponderance of the path leading to retention of configuration at the pivot atom (C(1′) in the reactant and C(2′) in the products) for (−)‐trans‐7 and to inversion of configuration for (+)‐cis‐7, respectively. The results can be rationalized by assuming reaction paths which involve the occurrence of discrete 1,4‐ and 1,3‐diradicals (cf. Schemes 10, 12, and 13). A general analysis of such ADPM rearrangements which allows the classification of these photochemical reactions in terms of borderline cases is presented (Scheme 14). It is found that the optical yields in these ‘step‐by‐step’ rearrangements are determined by the first step, i.e. by the disrotatory bond formation between C(2) of the aromatic moiety and C(2′) of the allylic side chain leading to the generation of the 1,4‐diradicals. Moderation of the optical yields can occur in the ring closure of the 1,3‐diradicals to the final products, which may take place with different trans/cis‐ratios for the individual 1,3‐diradicals. Compounds (−)‐trans‐7 as well as (+)‐cis‐7 easily undergo the well‐known photochemical trans/cis‐isomerization. It mainly leads to racemization. However, a small part of the molecules shows trans/cis‐isomerization with inversion of configuration at C(1′), which is best explained by a photochemical cleavage of the C(1′)–C(3′) bond.
Metal complexes of macrocyclic ligands. Part XXIII. Synthesis, properties, and structures of mononuclear complexes with 12‐ and 14‐membered tetraazamacrocycle‐N,N′,N″,N‴‐tetraacetic Acids
Authors: Riesen Andreas , Zehnder Margareta , Kaden Thomas A.
Published: December 2004

The two tetraazamacrocycle‐N,N′,N″,N‴‐tetraacetic acids H4dota and H4teta form with Ni2+, Cu2+, and Zn2+ (M2+) mononuclear complexes MLH2 and M′[ML], M′ being an alkaline earth ion. The structures of Ni(H2dota) and Cu(H2dota) have been solved by X‐ray structure analysis. The metal ions are in a distorted octahedral geometry coordinated by four amino N‐atoms and two carboxylates. In the case of Cu2+, the distortions are more pronounced than for Ni2+ indicating that the Jahn‐Teller effect is operating. Starting from these two structures, the coordination geometry of the other complexes is discussed using VIS and IR spectra.
Neue Cyclosporine aus Tolypocladium inflatum. Die Cyclosporine K–Z
Authors: Traber René , Hofmann Hans , Loosli Hans‐Rudolf , Ponelle Monique , von Wartburg Albert
Published: December 2004

Novel Cyclosporins from Tolypocladium inflatum. The Cyclosporins K–Z

The fungus T. inflatum produces a plethora of oligopeptides, the cyclosporins, which exhibit remarkable biological activities. Cyclosporin A, the main metabolite, represents a potent immunosuppressant which opened new ways in the immunotherapy of bone marrow and organ transplantations. In addition to the already described cyclosporins A–I, we report now the isolation of the cyclosporins K–Z. The structural assignments of these novel congeners are based on chemical degradation, correlation reactions, mass spectra, and extensive analysis of 1H‐ and 13C‐NMR spectra. All cyclosporins are cyclic undecapeptides differing from each other by minor variations in the amino‐acid sequence. Comparison of the immunosuppressive and antifungal effects furnished new information concerning structure‐activity relationships.
Addition of Chiral Glycine, Methionine, and Vinylglycine Enolate Derivatives to Aldehydes and Ketones in the Preparation of Enantiomerically Pure α‐Amino‐β‐Hydroxy Acids
Authors: Seebach Dieter , Juaristi Eusebio , Miller David D. , Schickli Christof , Weber Theodor
Published: December 2004

Chiral enolates of imidazolidinones and oxazolidinones from the title amino acids react with carbonyl compounds to afford the corresponding alcohols in excellent yields (see Scheme 5). Furthermore, the addition to aldehydes proceeds with high diastereoselectivity to give, after acid hydrolysis, threo‐α‐amino‐β‐hydroxy acids of high enantiomeric purity. Some of the threo‐α‐amino‐β‐hydroxy acids prepared in this work are the proteinogenic (S)‐threonine (26), the naturally occurring (S)‐3‐phenylserine (28), and (S)‐3‐hydroxyleucine (27) as well as the unnatural (S)‐4,4,4‐trifluorothreonine (30) and (S)‐3‐(4‐pyridyl)serine (31). The N‐methylamide of (2S,3R,4R,6E)‐3‐hydroxy‐4‐methyl‐2‐(methylamino)‐6‐octenoic acid (32), the unique amino acid in the immunosuppressive cyclosporine, was prepared by the new method. This report presents also information suggesting that both steric and stereoelectronic effects are responsible for the good stereoselectivities observed.
Revised Structure of the Fungal Germination Self‐Inhibitor Gloeosporone
Authors: Meyer Walter L. , Schweizer W. Bernd , Beck Albert K. , Scheifele Werner , Seebach Dieter , Schreiber Stuart L. , Kelly Sarah E.
Published: December 2004

Gloeosporone, the germination self‐inhibitor from the fungus Colletotrichum gloeosporioides f.sp. jussiaea, is shown by spectroscopic data and X‐ray analysis to have the constitution and relative configuration as shown in Formula 2 (either (1S,6R,12R)‐1‐hydroxy‐6‐pentyl‐5,15‐dioxabicyclo[10.2.1]pentadecan‐4,13‐dione or its enantiomer), rather than the previously assigned constitution 1.
A Liquid‐Crystal Study of Heptalene
Authors: Gottarelli Giovanni , Hansen Hans‐Jürgen , Spada Gian Piero , Weber Roland H.
Published: December 2004

The chiral structure of heptalene is characterised, for a given configuration, by helicities, which are opposite in the direction (x) of the central C(5a)‐C(10a) bond and in the direction (y) of a line perpendicular to it, passing through the C(3)‐and C(8)‐atoms. These two helicities can be experimentally established and differentiated by the handedness of the cholesteric mesophases induced in a biphenyl‐type liquid crystal (LC) by chiral heptalenes with substituents favouring the x or y orientation along the nematic director of the LC.
Nucleoside und Nucleotide Teil 27 Festphasensynthese eines Tridecanucleosid‐dodecaphosphats, das die unnatürliche Base 4‐Amino‐2(1H)‐pyridinon enthält, und eines Octanucleosid‐heptaphosphats zur Untersuchung der DNA‐Polymerase‐Spezifität
Authors: Charczuk Roland , Tamm Christoph
Published: December 2004

Nucleosides and Nucleotides. Solid Phase Synthesis of a Tridecanucleoside Dodecaphosphate Containing the Unnatural Base 4‐Amino‐2(1H)‐pyridinone and of a Octanucleoside Heptaphosphate for the Determination of the DNA‐Polymerase Specificity

The tridecanucleoside dodecaphosphate d (T‐T‐Z‐C‐G‐T‐C‐A‐A‐A‐A‐T‐C) incorporating the modified nucleoside 4‐amino‐1‐(2′‐deoxy‐β‐D‐ribofuranosyl)‐2(1H)‐pyridinone (Zd, 1) and the octanucleoside heptaphosphate d (G‐A‐T‐T‐T‐T‐G‐A) were synthesized by the solid‐phase method using the triester method. The carrier material was a copolymer consisting of styrene with 1% divinylbenzene.
Synthese und NMR‐Spektren von Nonafulven sowie Vergleich mit 10‐Phenylnonafulven
Authors: Furrer Jürg , Bönzli Peter , Frey Alfred , Neuenschwander Markus , Engel Peter
Published: December 2004

Synthesis and NMR Spectra of Nonafulvene and Comparison with 10‐Phenylnonafulvene

Experimental procedures for the reaction of cis,cis,cis,trans‐cyclononatetraenide (ccct‐CNT−; see 4) with bromomethyl acetate (1a, R = H, X = Br) to give (cyclononatetraenyl)methyl acetate (5a; 84% yield) as well as for the base‐induced elimination of HOAc from 5a to give nonafulvene (6a; 44% yield) are described. Spectroscopic as well as chemical evidence for 6a and 6b is presented. An approximate high‐field‐NMR analysis of 6a and 6b has been completed. The results are in favour of a fast interconversion of the type 6A⇄6B (Scheme 4), and supported by the MNDO‐optimised geometry of 6a. The first X‐ray analysis of a cyclononatetraene (i.e. of 5b) has been accomplished: 5b is a polyolefinic molecule with largely alternating bond lengths and with a nine‐membered ring deviating strongly from planarity.
Structures and Electrical Properties of Some New Organic Conductors Derived from the Donor Molecule TMET (S,S,S,S,‐Bis(dimethylethylenedithio) tetrathiafulvalene)
Authors: Karrer Andreas , Wallis John D. , Dunitz Jack D. , Hilti Bruno , Mayer Carl W. , Bürkle Markus , Pfeiffer Jürgen
Published: December 2004

Crystal structures and electrical properties of radical‐cation salts of the chiral organic donor TMET (S,S,S,S,‐bis‐(dimethylethylenedithio)tetrathiafulvalene) are described. Two structural types, 2:1 with octahedral anions Pf, AsF, SbF, I (incommensurate), and 3:2 with tetrahedral anions BF−4, CIO−4, ReO−4 are observed. Resistivity measurements between 2 and 298 K indicate that the 3:2 types are organic metals, while the other compounds are semiconductors. (TMET)3(CIO4)2 is metallic down to about 120 K at ambient pressure and remains metallic down to 2 K at 8 kbar.
Isolation and Structure Elucidation of Some Components of the Antitumor Antibiotic Mixture ‘Rubiflavin’
Authors: Nadig Heinz , Sèquin Urs
Published: December 2004

The antitumor antibiotic ‘rubiflavin’ was investivated. It was shown to be a mixture of several compounds, nine of which ‐ after isolation by HPLC ‐ could be identified by 1H‐NMR spectroscopy. The rubiflavins A (4), B (5), C‐1(6), C‐2(7), D(8), and E(9) are pluramycin antibiotics differing only in their side chains at C(2). Rubiflavin B(5) was found to be identical with kidamycin, rubiflavin F(10) with isokidamycin. Two unpolar compounds isolated which lack the two sugar rings typical for pluramycin antibiotics were called rubiflavinone C‐1 (2) and C‐2 (3); they are the ‘aglycones’ of the corresponding rubiflavins.
Binding of AMP, ADP, and ATP Nucleotides by Polyammonium Macrocycles
Authors: Hosseini Mir Wais , Lehn Jean‐Marie
Published: December 2004

The macrocyclic polyamines 4–6, when protonated, bind strongly and selectively nucleotides (AMP, ADP, ATP) and pyrophosphate in aqueous solution. The stoichiometry of the complexes formed was determined by titration experiments followed by 31P‐NMR spectroscopy. Compounds 4 and 5 form 1:1 complexes with ATP, ADP, and pyrophosphate, whereas 6 forms complexes with ATP and ADP involving 2 nucleotides and 1 receptor molecule. The stability constants of these complexes have been determined by pH‐metric measurements. At pH 7, both 5 and 6 give complexes of mainly the fully protonated species 5.6H+ and 6.8H+, whereas 4 yields predominantly complexes of 4.5H+ and 4.4H+.
Morphological and Thermal Investigations of the ‘Active’ Dimer Hydroxide of Chromium(III)
Authors: Spiccia Leone , Marty Werner , Giovanoli Rudolf
Published: December 2004

The ‘active’ dimer hydroxide, [Cr2(μ‐OH)2(OH)4(OH2)4]·2 H2O, has been characterised by means of IR spectroscopy, thermal analysis, X‐ray powder diffraction, and electron microscopy. Thermogravimetric measurements and the Cr content of the hydroxide are in agreement with this composition. The IR spectrum supports the notion that this hydroxide is composed of unaltered dimer fragments linked through hydrogen bonds of ca. 2.8 Å. The compound is microcrystalline in nature with an X‐ray powder diffraction pattern distinctly different from that of the isomeric ‘active’ monomer hydroxide. Electron micrographs of the ‘active’ dimer hydroxide indicate that this material consists of platelets the sie of which is dependent on the pH of precipitation.
2,3‐Bis(diphenylphosphino)‐1,3‐butadien
Authors: Schmidbaur Hubert , Dziwok Klaus , Reber Gabriele , Müller Gerhard
Published: December 2004

2,3‐Bis(diphenylphosphino)‐1,3‐butadiene

A method for synthesis of the title compound is described, using the readily available 2,3‐bis(diphenylphosphinoyl)‐1,3‐butadiene (1) as the starting material. For the protection of the diene system, 1 is first converted into the 1,4‐dibromo‐ and 1,4‐dichloro derivatives 2a and b, respectively, by addition of Br2 or Cl2, respectively. The structure of 2b has been determined by single‐crystal X‐ray diffraction. The molecule has a centrosymmetrical (E)‐configuration. Reduction of the phosphinoyl groups by HSiCl3(to give the bis(diphenylphosphino)compound 3), followed by removal of the Cl‐atoms using Zn powder, affords the bis(diphenylphosphino)butadiene 4. Compounds 3 and 4 give quaternary phosphonium salts 5 and 6, respectively, on addition of CH3OSO2F or CH3I. The sulfur analogue of 1 is formed on treatment of 4 with elemental sulfur.
Synthesis of (±)‐trans‐2,5‐Dialkylpyrrolidines from the Lukes‐Šorm Dilactam: Efficient Preparation of (±)‐trans‐2‐Butyl‐5‐heptylpyrrolidine and Analogs Present in Ant Venoms
Authors: Gessner Wieslaw , Takahashi Kimio , Brossi Arnold , Kowalski Marek , Kaliner Michael A.
Published: December 2004

A 7‐step synthesis of (±)‐trans‐2‐butyl‐5‐heptylpyrrolidine (14) from the Lukes‐Šorm dilactam 1 was accomplished in 6% overall yield without counting for a reconversion of cis‐isomer 13 into trans‐isomer 14 which was also accomplished. Reduction of pyrroline 12, the precursor of 14, with NaBH4 afforded a 1:1 mixture of cis‐isomer 13 and trans‐isomer 14 separated by chromatography. Reductive N‐methylation of 14 afforded the N‐methyl analog 15, another ant alkaloid. The synthetic route to 14 was extended to a similar synthesis of analogs 23–25 and is representative for the synthesis of trans‐2,5‐diakyl‐substituted pyrrolidines. Results on the screening of a few compounds for the effect on vascular permeability are reported.
Spectroscopic, Electrochemical, and Kinetic Characterization of New Ruthenium(II) Tris‐chelates Containing Five‐Membered Heterocyclic Moieties
Authors: Orellana Guillermo , Quiroga María L. , Braun André M.
Published: December 2004

Synthesis, redox, photophysical, and photochemical properties of Ru(NN) complexes NN = 2‐((2′‐pyridyl)thiazole (pyth), 2‐(2′‐pyrazyl)thiazole (pzth), 2,2′‐bithiazole (bth), 5‐(2′‐pyridyl)‐1,2,4‐thiadiazole (pytda), 2‐(2′‐pyridyl)imidazole (pyim), 1‐methyl‐2‐(2′‐pyridyl)imidazole (Mepyim), and 2‐(2′‐pyridyl)oxazole (pyox)) are described. Oxidation potentials for the Ru3+/2+ couples in MeCN varied from about 0.80 V to 1.60 V vs. NHE. Three reduction waves were observed in all the cases except for Ru(pyim) and Ru(Mepyim) complexes and asigned to the one‐electron reduction of each bidentate ligand. Absorption spectra contained bands in the UV (280–325 nm) and VIS (437–481 nm) regions which have been assigned to ligand‐centered π‐π* and metal‐to‐ligand charge‐transfer dπ‐π* transitions, respectively. Emission spectra at 77 K were determined for all the complexes presenting maxima in the 580–650‐nm region, with vibrational progression in some of them. Only pyth, pzth, bth, and pytda tris‐chelates showed luminescence at room temperature in aqueous solution, with quantum yields ranging from 0.0013 to 0.0095 and excited‐state lifetimes from 55 to 390 ns, as determined from pulsed laser techniques. Their E0–0 spetroscopic energies have been estimated from emission wavelength maxima at 77 K which, in turn, have allowed calculation of excited‐state redox potentials. A plot of E0–0 vs. ΔE1/2, where ΔE1/2 = E1/2(3+/2+) − E1/2(2+/+), was linear with a slope of ca. 1.1 and a correlation coefficient of 0.999, demonstrating an identical nature of the orbital involved in spectroscopic and electrochemical processes. Photochemical properties of Ru(NN) complexes have been tested using methyl viologen (MV2+) in Ar‐purged aqueous solution at pH 5. Stern‐Volmer treatment has led to the determination of bimolecular quenching constants (0.5 to 2 × 109m−1·s−1) which parallel electron‐transfer free‐energy changes. Homogeneous back‐reaction of primarily produced MV+· and Ru(NN) has been measured resulting to be slightly higher than diffusion control and independent of ligand nature. Rate constants for the scavenging of Ru(NN) by added edta have been also determined (1.7 to 8.2 × 108M−1 · S−1). Under such conditions, net production of MV+· is attained with quantum yields varying from 0.003 to 0.038 (single‐shot laser results).
Die stereoisomeren Sinensiaxanthine und Sinensiachrome: Trennung und Bestimmung ihrer absoluten Konfiguration. 7. Mitteilung über Rosenfarbstoffe
Authors: Märki‐Fischer Edith , Eugster Conrad Hans
Published: December 2004

Stereoisomeric Sinensiaxanthins and Sinensiachromes: Separation and Absolute Configuration

The so‐called sinensiaxanthins and sinensiachromes, important apocarotenols from various fruits, have been separated into 2 and 4 stereoisomers, respectively, and their absolute configurations have been determined: (3S,5R,6S)‐5,6‐epoxy‐5,6‐dihydro‐10′‐apo‐β‐carotene‐3,10′‐diol (2), its (9Z)‐stereoisomer 7, the (8R)‐ and (8S)‐epimers of (3S, 5R)‐5,8‐epoxy‐5,8‐dihydro‐ 10′ ‐apo‐β‐carotene‐3, 10′‐diol (4 and 5), and their (9Z)‐stereoisomers 3 and probably 6. Thus, sinensiaxanthins are cleavage products from (Z/E)‐isomeric antheraxanthins or violaxanthins (scission at C(9′)–C(10′)) and sinensiachromes analogously from mutatoxanthins or auroxanthins.
17O‐NMR Spectra of Mesoionic Compounds: The polarized carbonyl group
Authors: Dahn Hans , Ung‐Truong My‐Ngoc
Published: December 2004

The 17O‐NMR spectra of 5 mesoionic compounds have been measured; in two cases, the peak attribution between endo‐ and exocyclic O‐atoms has been made unambiguous by synthesizing specifically O‐labelled samples. The signal of the exocyclic O‐atom appears at particularly high field, closer to the values of enolate than of carbonyl O‐atoms. The cyclic O‐atom resonates close to values of furans (or isoxazol, if bound to N). The exocyclic O‐atom is much more susceptible to structure and substituent variations than the endocyclic, an observation which is in favour of a chain‐conjugated (non‐aromatic) structure 1E.