bluuebunny/crossref_metadata_2025 huggingface dataset:
Indolalkaloide aus Kopsia dasyrachis Ridl. 185.Mitteilung über organische Naturstoffe
Authors: Homberger Katharina , Hesse Manfred
Published: December 2004

Indole Alkaloids of Kopsia dasyrachis Ridl.

From the leaves of Kopsia dasyrachis Ridl. three new indole alkaloids, kopsidasine‐N‐oxide (1), kopsidasine (2) and kopsidasinine (3) have been isolated. Reduction of 1 with SO2 afforded 2; treatment of 2 with m‐chloroperbenzoic acid gave 1. The structure elucidation of 1 and 2, and the deternmination of their relative configurations are based mainly on the correlation of derivative 6 with the known ring skeleton of pleiocarpine (9) (Scheme 1). The structure of 3 has been established via its Hofmann degradation product 13 also prepared by treatment of 2 with CH3I (Scheme 3).
Synthese von heterocyclen. V. 1, 3, 4‐thiadiazol‐2 (3 H)‐one
Authors: Kristinsson Haukur , Winkler Tammo
Published: December 2004

A new and highly versatile method for the synthesis of 1, 3, 4‐thiadiazol‐2 (3 H)ones 1 is described. Methoxy‐1,3,4‐thiadiazoles‐ 5, which are readily available by condensation of O‐methyl thiocarbazate (2) with acid derivatives 3, undergo an efficient cleavage to 1 and methyl chloride with hydrochloric acid in an anhydrous medium. Many new 5‐substituted thiadiazolones, unavailable by earlier routes, were synthesized. Preparative as well as mechanistic aspects are discussed. With the aid of 13C‐NMR. spectroscopy, the tautomerism of 1 was studied, and the tautomeric equilibria was shown to be dependent on the nature of the substituent in the 5‐position. The thiadiazolones 1 exist predominantly in the oxo form. The percentage of the hydroxy form, however, increases with strongly electron withdrawing substituents in the 5‐position. A good correlation with pKa− and σ‐values was observed.
Synthesen der enantiomeren Aleuriaxanthine. Nachweis eines vorherrschenden (Z)‐Aleuriaxanthins in Aleuria
Authors: Eschenmoser Walter , Uebelhart Peter , Eugster Conrad Hans
Published: December 2004

Syntheses of the Enantiomeric Aleuriaxanthins. Detection of a Predominant (Z)‐Aleuriaxanthin in Aleuria

The enantiomeric C10‐building blocks 9 ((+)‐(2 E, 6 R)‐6, 7‐dihydroxy‐3, 7‐di methyl‐2‐octen‐l‐yl acetate) and ent‐9, and 11 ((+)‐(2 E, 6 R)‐3, 7‐dimethyl‐2, 7‐octadien‐l, 6‐diyl diacetate) and ent‐11, prepared from the optically active epoxy‐geraniols 7 and ent‐7, respectively, have been used for the syntheses of (2′ R)‐aleuriaxanthin (1) and (2′ S)‐aleuriaxanthin (ent‐1).

At room temperature aleuriaxanthin exhibits no significant CD. nor ORD. However, at −180° a very distinct CD. was observed, which in the UV. range showed a surprising resemblance to that of (3 R, 3′ R)‐zeaxanthin. By direct comparison of 1 with aleuriaxanthin isolated from Aleuria aurantia [2], the (2′ R)‐chirality assigned to the latter by Liaaen‐Jensen et al. [5] is confirmed.

HPLC. separation of the mixture of carotenoids from Aleuria shows the presence of a predominant (Z)‐aleuriaxanthin of yet undetermined structure.
Basicity, Lipophilicity, and Lack of Receptor Interaction of N‐Aminoalkylbenzamides and N‐Aminoalkyl‐o‐anisamides as Model Compounds of Dopamine Antagonists
Authors: Anker Lucien , Testa Bernard , Van De Waterbeemd Han , Bornand‐Crausaz Anne , Theodorou Andreas , Jenner Peter , Marsden C. David
Published: December 2004

N‐Aminoalkylbenzamides and N‐aminoalkyl‐o‐methoxybenzamides have been prepared and examined for their pKa, log P and dopamine receptor affinity. The pKa values range from ca. 7.5 for the derivatives having a one‐C‐atom side‐chain, to ca. 10.3 for the N‐aminobutyl derivatives. These variations with chain length are satisfactoryly explained by a field model. The variations in (log P)‐values as a function of chain length and substitution at the N‐atom indicate the involvement of proximity and conformational effects. The complete inability of the compounds to displace 3H‐spiperone and 3H‐sulpiride from their specific rat striatal binding sites demonstrates the critical role of adequate aromatic substitution at positions 4 and 5.
The He(Iα) Photoelectron Spectra of Substituted 1,2‐Dithietes
Authors: Jian‐qi Wang , Mohraz Manijeh , Heilbronner Edgar , Krebs Adolf , Schütz Karin , Voss Jürgen , Köpke Brigitte
Published: December 2004

The He(Iα) photoelectron (PE.) spectra of a series of substituted 1,2‐dithietes have been recorded and assigned with respect to the orbital sequence derived from an STO‐3G model calculation and by correlation with the PE. spectra of related compounds. The results provide additional support for the presence of a closed, four‐membered ring moiety in all the 1,2‐dithietes investigated. In all cases the two highest occupied molecular orbitals are b2(π)= HOMO, a2(π), with exception of 3,4‐bis(trifluoromethyl)‐1,2‐dithiete where the sequence b2(π), a2(π) or a2(π), b2(π) is uncertain.
Metal complexes with macrocyclic ligands, XVII. Synthesis of two key intermediates for the preparation of mono‐N‐functionalized tetraazamacrocycles and their metal complexes
Authors: Hediger Markus , Kaden Thomas A.
Published: December 2004

With a modification of the cyclization procedure of Richman & Atkins [8] the two macrocycles 1,4,7‐tritosyl‐11‐benzyl‐1,4,7,11‐tetraazacyclotetradecane (8) and 1,7,11‐tritosyl‐4‐trityl‐1,4,7,11‐tetraazacyclotetradecane (15) were prepared. After selective cleavage of the benzyl and trityl group, respectively, one obtains the two key products 1,4,7‐tritosyl‐11‐benzyl‐1,4,7,11‐tetraazacyclotetradecane (9) and 1,7,11‐tritosyl‐4‐trityl‐1,4,7,11‐tetraazacyclotetradecane (16) which have three N‐atoms protected by tosyl groups and one accessible for further reactions.

To test some of the possibilities we have alkylated 9 and 16 with iodoacetamide, 1‐tosyl‐aziridine and acrylonitrile. After detosylation with HBr in glacial acetic acid in the presence of phenol mono‐N‐functionalized tetraazamacrocycles were thus obtained. The advantage of this synthesis is that the cyclization which is the most difficult step of the whole procedure, has to be done only once, regardless of the nature of the pendant arm. In addition a large number of derivatives can be prepared by varying the alkylation component.

With Ni2+, Cu2+ and Zn2+ metal complexes of these new ligands were prepared and their IR. and VIS. spectra studied. In the case of the carbamoyl derivatives 12, 14 and 18 the Cu2+‐complexes exist in two forms. Whereas at low pH the carboxamide group of the pendant arm is probably not bound to the metal ion, at high pH after deprotonation it coordinates in one of the axial positions.
Versuche zur Herstellung eines «Bis(triasterans)» und Synthese des heterocyclischen (Tricyclo[4.4.1.01,6]undeca‐3,8‐dien‐11,11‐dimethyl)sulfits
Authors: Neidlein Richard , Wesch Karl Friedrich
Published: December 2004

Tentative Synthesis of ‘Bis(triasterane)’ and Synthesis of the Heterocyclic (Tricyclo[4.4.1.01,6]undeca‐3,8‐diene‐11,11‐dimethyl)sulfite

The synthesis of the bis(triasterane) (1) has been tried; the reaction of ‘isotetraline’ (1,4,5,8‐Tetrahydronaphthalene; 2) with diazomalonate yielded the tricyclic systems 5 and 6, and not 4. Hydrolysis of 5 gave the monocarboxylic acid 7, and not the dicarboxylic acid 9. The latter could be obtained from the dibromoderivative 8, but 9 couldn't be converted to the acyl chloride 10. The reduction of 9 with LiAlH4 yielded the crystalline diol 11, which was cyclized with SOCl2 to the heterocycle 12. The spectral data of the new compounds 5, 6, 7, 11 and 12 are reported and discussed.
Nichtplanare Doppelbindung in einem kristallinen Derivat von anti‐Sesquinorbornen (anti‐Tetracyclo[6.2.1.13,6.02,7]dodec‐2(7)‐en)
Authors: Ermer Otto , Bödecker Claus‐Dieter
Published: December 2004

Non‐Planar Double Bond in a Crystalline Derivative of anti‐Sesquinorbornene (anti‐Tetracyclo[6.2.1.13,6.02,7]dodec‐2(7)‐ene)

The olefinic double bond of the title compound 2 has been observed by X‐ray techniques to deviate from planarity by 13.2 (0.3)° (symmetric out‐of‐plane bending). Empirical force field calculations for the parent hydrocarbon 1 (anti‐sesquinorbornene) give a much larger corresponding deviation of 35.6°. The calculated nonplanar double bond deformations in anti‐sesquinorbornene 1 as well as in the syn‐isomer 4 and other related olefins are a consequence of substantial widenings of the exocyclic C(sp3)–C(sp2–Csp3) angles when keeping the double bond planar. The considerable computational exaggeration of this novel out‐of‐plane bending mechanism is attributed to various possible force field deficiencies.
Photochemical Reactions. 128th Communication. Isolation of a Thermally Labile 2,8‐Dioxabicyclo[3.2.1]oct‐3‐ene Intermediate on Photolysis of 3,4: 5,6‐Diepoxy‐5,6‐dihydro‐β‐ionone
Authors: Bischofberger Norbert , Frei Bruno , Jeger Oskar
Published: December 2004

Photolysis (λ = 254 mm, THF) of the diepoxyenone (E)‐1 at −78° leads to the 2,8‐dioxabicyclo[3.2.1]oct‐3‐ene intermediate 3 (51%). At ambient temperature 3 undergoes an unexpectedly rapid electrocyclic opening to the triketone 2 in quantitative yield. Compound 3 seems likely to be the intermediate in the acid‐catalyzed rearrangement of (E)‐1 → 18 also.
Substitution électrophile aromatique dans l'anhydride sulfureux liquide. Etude cinétique de la réaction de bromation d'anisoles monosubstitués. Transmission des effets électroniques et caractéristiques de l'état de transition
Authors: Castellonèse Paul , Villa Pierre
Published: December 2004

Reactivity‐structure correlations for anisole and eleven of its substituted derivatives established from bromination rate constants in liquid SO2, unlike observations in water, show the reaction to be highly sensitive to substituent effects, (ρ = −7.1; ρ = −10.51). This result is ascribed to the solvation of the methoxy group which decreases the conjugation of para‐substituted (ρ = −9.70) compared to that of ortho‐substituted derivatives (ρ = −8.86). The highly solvated transition state lies far from reactants on the reaction coordinate and the positive charge developed in this state is nearly unity.
Intermediates in the Dehydrogenation of Hydroaromatic Compounds with Quinones
Authors: Müller Paul , Joly Daniel
Published: December 2004

Dehydrogenation of hydroaromatic compounds with quinones was reinvestigated in the light of recent criticism of the reaction mechanism. Kinetic and spectroscopic evidence shows that disappearance of substrate proceeds at the same rate as the product‐forming step. A mechanism consisting in fast formation followed by slow decomposition of an intermediate can be ruled out. The order of reactivities of 1,4‐cyclohexadiene (1), 1,4‐dihydronaphthalene (8) and 9,10‐dihydroanthracene (11) changes in going from benzoquinone to chloranil or 2,3‐dichloro‐5,6‐dicyanobenzoquinone. It is suggested that this behaviour could be due to contribution of CT‐complexes or HOMO‐LUMO interactions for determining the reactivity of the substrates.
Synthesis and Diels‐Alder Reactivity of 5,6,7,8‐Tetramethylidene‐2‐bicyclo[2.2.2]octanol and ‐octanone. Selective Oxidations of the Corresponding Bis(irontricarbonyl) Complexes
Authors: Gabioud Raphy , Vogel Pierre
Published: December 2004

Hydroboration of the syn, anti‐[Fe(CO)3]2 double complex 24 of the readily available 5,6,7,8‐tetramethylidene‐2‐bicyclo[2.2.2]octene (22) gave the corresponding doubly complexed 2‐bicyclo[2.2.2]octanol 25. CrO3‐oxidation furnished ketone 27. The syn‐Fe(CO)3‐groups in 25 and 27 were oxidized selectively with trimethyl‐amine oxide and yielded the corresponding anti‐Fe(CO3)‐monocomplexed tetraenes 26 and 28. The anti‐Fe(CO)3‐group in 28 could be removed, and 5,6,7,8‐tetramethylidene‐2‐bicyclo[2.2.2]octanone (11) was obtained. NaBH4‐reduction of 11 afforded tetraenol 10. TCE‐cycloadditions to 10 and 11 (k1) were at least 10 times as fast as those (k2) to the corresponding monoadducts 35/36 and 34, respectively. This Diels‐Alder reactivity difference vanishes (k1 ≈ k2) with methyl propynoate. The latter dienophile added to the anti‐Fe(CO)3‐monocomplexed tetraenone 28 with ‘para’‐regioselectivity.
Additionsreaktionen von 2‐Amino‐1‐azetinen mit Cyclopropenonen; Bildung von Azepinderivaten durch Ringerweiterung. Vorläufige Mitteilung
Authors: Stierli Friedrich , Prewo Roland , Bieri Jost H. , Heimgartner Heinz
Published: December 2004

Addition Reactions of 2‐Amino‐1‐azetines with Cyclopropenones; Formation of Azepine Derivatives by Ring Expansion Reactions

The reaction of 2‐amino‐1‐azetines of type 6 with 2,3‐diphenylcyclopropenone (1a) in acetonitrile leads to azetol[1,2‐α]pyrroles (cf. 7 and 9, Schemes 3 and 4) in good yield. It is remarkable that in the reaction of 6a with 1a only endo‐7 is formed. With silicagel in ether endo‐7 isomerizes to the thermodynamically more stable exo‐7 (Schemes 3 and 6). The crystal structure of the latter compound has been established by X‐ray crystallography. The reaction of 6a and 2‐isopropyl‐3‐phenyl‐cyclopropenone (1b) yields only one product, which isomerizes with silicagel in ether to exo‐10 (Scheme 4). The structure of exo‐10 has been determined by NMR‐spectroscopy. It seems reasonable that this structure results from a nucleophilic attack of the four‐membered amidine to the phenyl‐substituted C‐atom of 1b.
Synthesen von ω‐substituierten ω‐Nitrocarbonsäureestern aus α‐Nitrocycloalkanonen
Authors: Huggenberg Walter , Hesse Manfred
Published: December 2004

Synthesis of ω‐Nitroalkanoates Substituted in ω‐Position from α‐Nitrocycloalkanones

α‐Nitrocycloalkanones substituted in α‐position by a functionalized alkyl residue underwent ring opening to the corresponding chain derivatives by intermolecular nucleophilic attack; ω‐nitroalkanoates substituted in ω‐position were obtained (Scheme 1). The so formed methyl 6‐nitro‐9‐oxodecanoate (3) was used to prepare methyl 8‐(2‐methyl‐1,3‐dioxolan‐2‐yl)octanoate (15), an intermediate in the synthesis of the sex phermone of the honey bee.
Synthese von ‘Push‐Pull’‐Diacetylenen
Authors: Stämpfli Urs , Galli Roberto , Neuenschwander Markus
Published: December 2004

Synthesis of ‘Push‐Pull’ Diacetylenes

The first synthesis of push‐pull diacetylenes of type 1 is described. Reaction of perchlorobutenyne (8) with two equivalents of dialkylamine, followed by dechlorination using two equivalents of butyllithium gives lithio‐dialkylamino‐diynes 7. Final acylation of these intermediates leads to push‐pull diacetylenes 1b–1e in good yields. The method allows the introduction of both push and pull substituents in a simple one‐pot‐procedure. In addition, 1a is prepared by hydroxymethylation of lithio‐morpholino‐diyne 7c, followed by oxidation with manganese dioxide in acetone.
Transition Metal Complexes with Bidentate Ligands Spanning trans‐Positions. XII. Steric effects in the kinetics and mechanism of substitutions at hydride and methyl bisphosphine platinum (II) complexes
Authors: Elding Lars I. , Kellenberger Bruno , Venanzi Luigi M.
Published: December 2004

Ligand substitution reactions on square‐planar platinum (II) complexes of the types trans‐[PtRXL2], trans‐[PtR(4‐PADA)L2][BF4], trans‐[PtRX(magnified image) and trans‐[PtR(4‐PADA)(magnified image)][BF4] R=H, Me; X=Cl−, I−; L=PEt3, bis(3‐trifluoromethyl‐phenyl)benzylphosphine (4), magnified image=the trans‐spanning 2,11‐bis[bis(3‐trifluoro‐methylphenyl)phosphinomethyl]benzo [c]phenanthrene (3); 4‐PADA (=pyridine‐4‐azo‐4′‐(N, N‐dimethyl)aniline have been studied at 30° using stopped‐flow and conventional spectrophotometry, methanol as solvent, and 2.5 × 10−2 M ionic strength (LiClO4 as supporting electrolyte). 4‐PADA was used as indicator ligand, as its absorption spectrum differs from those spectra where it is complexed.

The expected steric effects of the bulky ligands, especially of 3, on the rates and mechanisms of all the reactions studied are small. All reactions take place by the usual two‐term rate law. Noteworthy, for the complexes with the bulky ligands 3 and 4, the direct reaction path with the entering nucleophile is predominant. There is no preference for a solvent or dissociative path. The reactivity order for the hydride complexes is trans‐[PtHX (PEt3)2]<trans‐[PtHX(4)2]<trans‐[PtHX (3)]. However, for the corresponding methyl complexes, there is some retardation by ligand 3, probably due to an interaction between the methyl group and the hydrocarbon moiety of 3, which inhibits the fluxional behavior of this ligand. The results have some relevance for the understanding of olefin‐insertion reactions of hydride complexes containing these phosphine ligands.
Reactions of Alkenediazonium Salts. Part 1. 2,2‐Diethoxyethene‐diazonium hexachloroantimonate: A diazonium, a carbenium or an oxonium salt?
Authors: Szele Ivanka , Tencer Michal , Zollinger Heinrich
Published: December 2004

Reactions of the title compound 1 with various nucleophiles have been studied. The salt behaves like an alkylating agent towards ethers, alcohols and water forming ethyl diazoacetate (2), which reacts further with excess of the nucleophile. A solvent cage mechanism accounting for the observed products is proposed. Thermal decomposition in inert solvents leads to the alkylation of the counter‐ion, i.e. formation of chloroethane, and in anisole, alkylation and chlorination of the solvent are also observed.

With a standard coupling component, 2‐naphtholate ion, no azo coupling reaction of 1 is observed, but instead 14‐methyl‐14 H‐dibenzo[a,j]xanthene (17) is formed. The products of the reaction with diethylamine are diethylcyanoformamide (18) and ethyl diethylcarbamate (19). None of the chemistry of salt 1 is explained by the intervention of vinyl cations expected to be formed in a heteroytic dediazoniation. The predominant pathways seem to involve reactions of an oxonium salt (alkylating properties) or, in the case of diethylamine, a carbenium salt (primary nucleophilic attack on the β‐C‐atom of 1).

The free energy barrier to CC rotation in 1 is estimated to be 75 to 77 kJ/mol (18.0 to 18.5 kcal/mol), a value which falls between those expected for a double and a single bond.
Reactions of Alkenediazonium Salts. Part 2. Methanolysis of 2,2(2′,2″‐biphenylylene)ethene‐1‐diazonium hexachloroantimonate. A rearrangement to 9‐methoxyphenanthrene
Authors: Szele Ivanka , Tencer Michal , Zollinger Heinrich
Published: December 2004

The title compound (1) reacts with excess methanol forming a rearranged product, 9‐methoxyphenanthrene (2). 9‐(Methoxymethylidene)fluorene (4) does not rearrange to give 2 under the same conditions. In deuterated methanol no labelled product is obtained, showing that the possible mechanism involves either the formation of a primary vinyl cation 5 rearranging to an aryl cation 6 or the formation of a β‐alkoxycarbene (12), which rearranges to an arene. The results obtained are compared with previously reported reactions, which were postulated to proceed via a 2,2(2′,2″‐biphenylylene)ethene‐1‐diazonium ion (23).
Photoreduction of Thiosulfate in Semiconductor Dispersions
Authors: Borgarello Enrico , Desilvestro Jean , Grätzel Michael , Pelizzetti Ezio
Published: December 2004

Conduction band electrons produced by band gap excitation of TiO2‐particles reduce efficiently thiosulfate to sulfide and sulfite.
\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm 2e}_{{\rm cb}}^ - ({\rm TiO}_{\rm 2}) + {\rm S}_{\rm 2} {\rm O}_3^{2 - } \longrightarrow {\rm S}^{2 - } + {\rm SO}_3^{2 - } $\end{document}

This reaction is confirmed by electrochemical investigations with polycrystalline TiO2‐electrodes. The valence band process in alkaline TiO2‐dispersions involves oxidation of S2O to tetrathionate which quantitatively dismutates into sulfite and thiosulfate, the net reaction being:
\documentclass{article}\pagestyle{empty}\begin{document}$ 2{\rm h}^{\rm + } ({\rm TiO}_{\rm 2}) + 0.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } + 1.5{\rm H}_{\rm 2} {\rm O} \longrightarrow {\rm SO}_3^{2 - } + 3{\rm H}^{\rm + } $\end{document}

This photodriven disproportionation of thiosulfate into sulfide and sulfite: \documentclass{article}\pagestyle{empty}\begin{document}$ 1.5{\rm H}_{\rm 2} {\rm O } + 1.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } \mathop \to \limits^{h\nu} 2{\rm SO}_3^{2 - } + {\rm S}^{{\rm 2} - } + 3{\rm H}^{\rm + } $\end{document} should be of great interest for systems that photochemically split hydrogen sulfide into hydrogen and sulfur.
Synthesis of Unique Spin‐Labeled Nucleic Acids by Combined Enzymatic and Chemical Approaches
Authors: Toppin Charles R. , Thomas Ingrid E. , Bobst Albert M.
Published: December 2004

The synthesis of uridine‐5′‐diphosphate analogs, spin‐labeled either at C(4) or C(5) is reported as well as their enzymatic incorporation into ribonucleic acids, some of which had previously been shown to be potent interferon inducers upon annealing with poly (inosinic acid). Also, the synthesis of spin‐labeled poly (cytidylic acid) obtained by chemical acylation is presented.
Dischroïsme circulaire des alcaloïdes du groupe de l'hétéroyohimbane
Authors: Seguin Elisabeth , Koch Michel , Ahond Alain , Gulhem Jean , Poupat Christiane , Potier Pierre
Published: December 2004

Circular Dischroism of Heteroyohimbane‐Type Alkaloids

Circular dichroism cannot be used directly to determine the C (3)‐configuration of heteroyohimbines. A preliminary chemical transformation is necessary.
NMR‐Spektroskopische Untersuchungen der kinetischen Limitierung der Kationenselektivität eines cadmiumselektiven Ionophors
Authors: Hofstetter Peter , Pretsch Ernö , Simon Wilhelm
Published: December 2004

NMR Studies of the Kinetic Limitation of Cation Selectivity of a Cadmium‐Selective Ionophore

The Cd2+‐selective ionophore N,N,N′,N′‐tetrabutyl‐3, 6‐dioxaoctanedithioamide (1) looses its capability to induce cation selectivity in solvent polymeric membranes if these are contacted with Cu2+, Pd2+, Pt2+, Ag+ and Hg2+. For systems with a free energy of activation of the ligand exchange reaction of more than about 65 kJ mol−1 (in acetonitrile) the cation complexes of the ionophore act as anion exchangers (Pt2+, Pd2+). Below about 45 kJ mol−1 cation permselectivity is observed (Zn2+, Cd2+). Ag+ and Hg2+ induce a decomposition of the ionophore.
Preparation and Diels‐Alder Reactivity of Tricarbonyliron Complexes of [2.2.2]Hericene
Authors: Hänisch Ulrich , Tagliaferri Enrico , Roulet Raymond , Vogel Pierre
Published: December 2004

Treatment of [2.2.2]hericene 10 with Fe2(CO)9 in hexane gave a mixture of monometallic complex 14, two isomeric dimetallic complexes 15 and 16, and a trimetallic complex 19 in which all the three diene moieties of 10, are coordinated. The rate constants of the Diels‐Alder additions of tetracyanoethylene (TCE) and dimethyl acetylenedicarboxylate (DMAD) to the uncomplexed diene moieties of 14–16 have been evaluated and compared with those measured for the uncomplexed 10 and its monoadducts 11A, 11B and bis‐adducts 12A, 12B. The tricarbonyldieneiron function retards the cycloaddition of an homoconjugated, exocyclic s‐cis‐butadiene. The effect is significantly larger for TCE‐ than for DMAD‐additions. The origin of this effect is discussed briefly in terms of the valence‐bond model which is usually assumed to describe the properties of a tricarbonyldieneiron complex, and in terms of the inductive and steric factors of the Fe(CO)3‐group.
Synthesis of Reversible Inhibitors of Acetylcholinesterase (EC 3.1.1.7)
Authors: Thanei‐Wyss Peter , Waser Peter G.
Published: December 2004

The synthesis and characterization of some reversible acetylcholinesterase inhibitors are described in detail. They are structurally related to the natural substrate acetylcholine. All of them bear a trimethylammonium moiety as ‘cationic head’. Instead of an electrophilic ester group, the title compounds include a variety of functionalities, such as halide, ether, thioether, epoxide, amide, ketone and a double bond. The substances are thus suited as probes for the investigation of the esteratic subsite of the acetylcholinesterase active center.

Most of the synthesized compounds inhibit the enzyme in a competitive manner with inhibition constants in the range of 10−5 M to 10−3 M. With respect to acetylcholine (KD ≤ 10−5 M and Km = (1.6±0.5) 10−4 M) their affinity to acetylcholinesterase is in the same order of magnitude.
High‐Pressure Stopped‐Flow Study of the Kinetics of Base Hydrolysis of the Dichromate Ion by Hydroxide Ion, Ammonia, Water, and 2,6‐Lutidine in Aqueous Solution
Authors: Moore Peter , Ducommun Yves , Nichols Peter J. , Merbach André E.
Published: December 2004

Volumes of activation for the base hydrolysis of the dichromate anion have been measured at 298.2 K, using high‐pressure stopped‐flow spectrophotometry. The values of ΔV* (cm3 · mol−1), − 17.9 ± 0.6, − 19.2 ± 0.9, − 24.9 ± 0.9 and − 26.0 ± 0.7 for OH−, NH3, H2O and 2,6‐lutidine, respectively, are consistent with an interchange mechanism with associative activation mode (Ia).
Structure and Chemistry of Malonylmethyl‐ and Succinyl‐Radicals. The search for homolytic 1,2‐rearrangements
Authors: Aeberhard Urs , Keese Reinhart , Stamm Erich , Vögeli Ulrich‐Christian , Lau Willy , Kochi Jay Kazuo
Published: December 2004

Malonylmethyl radical I [· CH2CH(COOEt)2] and its thioester analogue II [· CH2CH(COOEt) (COSEt)] were generated by standard photolytic and thermolytic methods from perester and bromo precursors. The structures of I and II were examined by ESR spectroscopy and found to exist in preferred conformations. However, no indication for their rearrangement by 1,2‐shift of either an ethoxycarboxyl or (ethylthio)carbonyl group to the corresponding succinyl radicals III and IV, respectively, was found at temperatures below − 40°C. At higher temperatures of up to 140°C, the search for malonylmethyl → succinyl rearrangement was examined by thorough‐product analysis of the perester decomposition. There is evidence for the rearrangement of the radical I to III by photolysis and of the radical II to IV by thermolysis at 130°C in chlorobenzene to only a small extent.
Alkyl Shifts between Transition Metals and Coordinated Main Group Atoms
Authors: Ortiz J. V. , Havlas Zdenêk , Hoffmann Roald
Published: December 2004

This work considers the theoretical aspects of the shift of an alkyl(or aryl) group from a coordinated phosphine to the 16‐electron d8 transition metal to which it is coordinated. This rearrangement at first seems to resemble an anionic [1,2]‐sigmatropic shift. But a detailed analysis of the relatively low barrier calculated for the reaction shows how all traces of the forbiddeness of the reaction have vanished. Phenyl migration should eb still more facile. We also analyze in some detail the possible pathways of alkyl halide addition to a phenyl‐Pt complex. An alkyl migration, now from metal to coordinated C‐atom, could possibly intervene in this process.
C45‐ und C50‐Carotinoide. 2. Mitteilung. Synthese von optisch aktiven acyclischen C15‐Endgruppen
Authors: Kramer Andreas , Pfander Hanspeter
Published: December 2004

C45‐ and C50‐Carotenoids. Synthesis of Optically Active Acyclic C15‐End Groups

The optically active C15‐end groups (S)‐12, (S)‐13 and (R)‐14 were prepared from the C12‐synthon (S)‐11 in good chemical and optical yield. These C15‐end groups are suitable compounds for the synthesis of optically active C45‐ and C50‐carotenoids.
Die Herzglykoside des Pfeilgiftes von Lophopetalum toxicum LOHER. 13. Mitteilung über Celastraceen‐Inhaltsstoffe
Authors: Wagner Hildebert , Habermeier Helmut , Schulten Hans‐Rolf
Published: December 2004

The Heart Glycosides of the Arrow Poison of Lophopetalum toxicum LOHER

From the cytotoxic and positive inotropic acting bark extract of the Philippinan Lophopetalum toxicum eight heart glycosides have been isolated and their structures have been elucidated mainly by field‐desorption‐MS‐ and 1‐ and 13C‐NMR spectroscopy. Besides the known k‐Strophanthidin (1), Antiarigenin (6) and β‐Antiarin (Antiarigenin‐3‐β‐O‐α‐L‐rhamnoside, 10) the following mono‐ and diglycosides could be identified: strophanthidin‐3‐β‐O‐α‐6‐desoxy‐D‐allopyranoside (strophalloside, 2), strophanthidin‐3‐β‐O‐β‐6‐desoxy‐D‐glucopyranoside (= Strophanthidin chinovoside, 3), strophanthidin‐3‐β‐O[‐4Oβ‐D‐allopyranosyl‐β‐6‐desoxy‐D‐allopyranoside] (4), strophanthidin‐3‐β‐O‐[3‐O‐β‐D‐glucopyranosyl‐β‐6‐desoxy‐D‐talopyranoside] (5), antiarigenin‐3‐β‐O‐[3‐O‐β‐D‐gulopyranosyl‐β‐6‐desoxy‐D‐talopyranoside] (7), antiarigenin‐3‐β‐O‐[4O‐β‐D‐allopyranosyl‐β‐6‐desoxy‐D‐allopyranoside] (8), and antiarigenin‐3‐β‐O‐β‐6‐desoxy‐D‐allopyranoside (antiallosid) (9). The structure of strophanthidinchinovoside (3) could be confirmed by synthesis.
Stereochemistry of Dehydrogenation of 1,4,‐Cyclohexadiene with 2,3‐Dichloro‐5,6‐dicyano‐p‐benzoquinone
Authors: Müller Paul , Joly Daniel , Mermoud François
Published: December 2004

cis‐ and trans‐(3,6‐D2)‐1,4‐cyclohexadienes 1a and 1b have been synthesized from cis‐3,4‐dichlorocyclobutene (5). Aromatization to benzene with DDQ is cis‐stereospecific with an uncertainty of 5%. This result is discussed in relation to concerted or stepwise mechanisms for aromatization of 1,4‐dihydroaromatics with 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ).
Approaches to the synthesis of cytochalasans. Part 6. Synthesis of the C(14)–C(23) subunit of cytochalasins A, B. F and desoxaphomin
Authors: Ackermann Jean , Waespe‐Šarčevic̀ Nada , Tamm Christoph
Published: December 2004

The synthesis of methyl (4R, 8R,)‐10‐bromo‐8‐methyl‐4‐(1,3,6‐trioxaheptane)‐2‐deceneoate (5), a synthon for the construction of the macrocyclic moieties of the cytochalasins A (1), B. (2) F (3) and desoxaphomin (4) is described. (S)‐Glutamic acid (6) was transformed to the C5‐epoxide 10 and 3‐methylglutaric acid (11) to the C5‐bromide 15. Coupling of both 10 and 15 by a CuI‐catalyzed Grignard reaction gave the decanol 16 in very high yield. The latter was transformed by several steps to synthon 5.
Stereoselectivity in reactions of metal complexes VIII. Asymmetric synthesis of some amino acids by stereoselective transamination of aliphatic keto acids in mixed ligand copper(II)‐Schiff‐base complexes
Authors: Deschenaux Robert , Bernauer Klaus
Published: December 2004

Optically active alanine, valine and leucine were obtained by a transamination reaction between pyridoxamine and the corresponding α‐keto acid in the presence of a Cu2+‐complex with the tridentate ligand 2,6‐bis[(3S)‐3‐phenykl‐2‐azabutyl]pyridine. In each case the amino acid with (R)‐configuration was formed preferentially, and the maximum enantiomeric excesses were 54% (alanine), 48% (leucine) and 29% (valine). The stereoselectivity of the reaction is discussed in terms of the possible structure and the stability of the intermediate Cu2+‐ketimine‐ligand complex.
Photoelectron‐Spectroscopic Characterization of 3,4‐Dimethyl‐2,4‐hexadienes
Authors: Honegger Evi , Zhong‐zhi Yang , Heilbronner Edgar , Doering William V. E. , Schmidhauser John C,
Published: December 2004

The He(Ia) photoelectron (PE) spectra of the (E,E)‐, (E,Z)‐ and (Z,Z)‐isomers of the title compound have been recorded to obtain information about their conformation in the gas phase. For a valid correlation with the PE data of other dienes it is necessary to take the potentials V(φ) for internal rotation and the corresponding conformer population densities P (φ) into account, as well as the rather complicated way wy in which the π−1 ionization energy gap ΔI(φ) depends on the direct π‐orbital interaction and the long‐range ‘through‐space’ interaction between the semi‐localized methyl‐group orbitals and the π‐orbitals. These factors being taken into account, the mean twist angles, φ, compatible with the PE‐spectroscopic results are φ (E,E) ≈︁ O° ± 30°, φ (E,Z) ≈︁ 80° or 110° within ± 15°, and φ (Z,Z) ≈︁ 85° to 105°. These results are in rough agreement with electron diffraction data by Traetteberg [15], other spectroscopic results and, for the (E, E)‐ and (Z,Z)‐isomers, internal rotation potentials V(φ) previously calculated by Roth [17]. On the other hand the potential V (φ) proposed for the (E,Z)‐isomer does not seem to be compatible with our findings.
Cob(I)alamin Differentiating Alkenes During Saturation
Authors: Schönholzer Peter , Süss Daniel , Wan Terence S. , Fischli Albert
Published: December 2004

The olefins 2, 7, 11, and 19, have been reduced using catalytic amounts of cob(I)alamin(I(I)). During a slow saturation, the catalyst is able to differentiate the two diastereotopic faces of the endocyclic double bonds in 11 (t1/2 4 h,. cf. Scheme 3) are reduced much faster. A rationalization of the data can be obtained formulating tertiary alkylcobalamins as intermediates. Of the oxime 6 (cf. Scheme 2) and the p‐ bromobenzoate 23 (cf. Scheme 5) the structures have been determined by X‐ray analysis.
Absolute Configuration of Gilmaniellin
Authors: Snatzke GÜNther , Tamm Christoph
Published: December 2004

The absolute configuration of dechlorogilmaniellin (2) could be determined from its chiroptical data by applying coupled‐oscillator theory to the CD couplet around 272 nm and from the sign of its n →π* Cotton effect. Gilmaniellin (1) has the same absolute configuration.
Oxygenation of Dimethylsulfoxide and Copper‐Catalyzed Autoxidation of Substituted Benzoins
Authors: Gampp Harald , Haspra Doris , Spieler Walter , Zuberbühler Andress D.
Published: December 2004

The catalytic activity of autoxidized copper (I) in the oxidation of para‐disubstituted benzoins in dimethylsulfoxide by O2 was studied both kinetically and by product analysis. Stoichiometry (1), accounts for more than 80% of the reaction. The catlytic oxydation was followed by monitering th consumption of O2 manometrically by a fully automatic apparatus.
equation image
(X = H, CH3, OCH3, C6H5 CI)

A redox shuttle mechanism is proposed, where the rate‐determining step is the autoxidation of Cu(I) followed by a rapid oxidation of the substrate by an oxocupric species. The redox stiochiometry (I) corresponds to that found for external monooxy‐genases (or mixed‐function oxidases), and the significance of our results with respect to analogous catalytic systems is discussed.
Ein neuer Zugang zu Bicyclo[4.1.0]heptan‐Derivaten
Authors: Spreitzer Helmut , Buchbauer Gerhard
Published: December 2004

A New Approach to Bicyclo[4.1.0]heptane Derivatives

The reaction of the dienone 1 with ethyl α‐bromoacetate does not furnish the expected glycidic acid ester 2 but leads to the bicyclo[4.1.0]heptenone derivative 3. The structure of this new compound has been proved by means of spectroscopic methods (1R, 1H‐NMR, 13C‐NMR, MS). The elucidation of the configuration at C(7) could be realized by measuring a NOE effect. Other α‐alkylated α‐bromoacetates react with 1 in the same manner.
8α,9α‐Epoxy‐7‐oxoroyleanon, ein Diterpen‐Epoxychinon aus einer abessinischen Plectranthus‐Art (Labiatae)
Authors: Rüedi Peter
Published: December 2004

8α,9α‐Epoxy‐7‐oxoroleyanone, a Diterpenoid Epoxyquinone from an Abyssinian Plectranthus Species (Labiatae)

Reexamination of the title plant, in additon to the previously identified abietanoid hydroxy‐1,4‐benzoquinones 1a, 1b, 1c, 1e, 1f, 1g, and 1h, yielded the known 7α‐acetoxyroleanone ( = 7‐O‐acetylhorminone; 1d) and the novel 8α, 9α‐epoxy‐7‐oxoroyleanone (2a). Spectroscopic methods, partial synthesis by epoxidation of 7‐oxoroyleanone (1h), and chiroptical correlation establish the structure 2a. Royleanone 2a is the first diterpenoid epoxyquinone isolated so far. Moreover, a detailed 13C‐NMR analysis of the royleanones 1b, 1c, 1e, 1g, and 1h lead to the complete assignment of their spectra.
3‐Lithiopyrroles by Halogen‐Metal Interchange of 3‐Bromo‐1‐(triissopropylsilyl)pyrroles. Synthesis of Verucarin E and Other 3‐Substituted Pyrroles. Preliminary Communication
Authors: Muchowski Joseph M. , Naef Reto
Published: December 2004

3‐Lithio‐1‐(trimethylsilyl)pyrrole (7, Schem 2), obtained by halogen‐metal interchange from the 3‐bromo compound 2, reacted with various electrophilic reagents to provide products, which on fluoride ion desilylation, gave 3‐substituted pyrroles in good overall yields. One such pyrrole 13 (Schem 3), was converted into 2‐formyl‐3‐octadeclpyrrole (14), reputed to be a metabolite of the marine sponge Oscarella lobularis.

3,4‐Dibromo‐1‐(triisopropylsityl)pyrrole (5) was efficiently transformed, by a process involving two consecutive bromine‐lithium exchange reactions (Scheme 4), into the antibiotic verrucarin E 17.
New Carbonyl Compounds in the High‐Boiling Fraction of Lavender Oil. 3rd Communication
Authors: Kaiser Roman , Lamparsky Dietmar
Published: December 2004

The occurrence of a series of new constituents which can be considered as Diels‐Alder adducts of methyl vinyl ketone and ocimene (→1–4), myrcene (→9, 10) or β‐far‐nesene ( →11, 12), respectively, was reported. Furthermore, the structures of four isomeric cyclohexene derivatives could be established as adducts 21–24 of (E, Z)‐ and (E, E)‐1,3,5‐undecatrience and methyl vinyl ketone. Another series of constituents having the norbornane skeleton represents adducts 25–32, and 33–40 of methyl cyclopentadiene and 1‐octen‐3‐one or methyl vinyl ketone, respectively. In accordance with Alder's endo‐rule the endo‐isomers are preponderant in the natural as well as in the synthetic mixtures. Most of these constituents could also be identified in a lavender absolute as well as in a freshly prepared hexane extract of lavender flowers (Lavandula officinalis CHAIX).
Stoffwechselprodukte von Mikroorganismen 227. Mitteilung. Isolierung und Strukturaufklärung von Rutamycin B
Authors: Wuthier Damian , Keller‐Schierlein Walter , Wahl Barbara
Published: December 2004

Isolation and Structure of Rutamycin B

Botrycidin was found to be identical with rutamycin. From the cultures of the actinomycete producing botrycidin and the venturicidines. A and B, a fourth antifungal antibiotic, rutamycin B, was isolated. Through a series of degradation products its structure could be correlated to that of rutamycin, which had been determined before by an X‐ray structural analysis. Rutamycin B has been identified as 12‐deocy‐rutamycin.
Model Compounds for Rhodospin and Bacteriorhodopsin: Synthesis, and 1H‐ and 13C‐NMR Study
Authors: Rabiller Claude , Danho Doubou
Published: December 2004

The reaction of all‐trans‐retinal and 5‐(2,6,6‐trimethylcyclohexeyl)‐3‐methyl‐2,4‐pentadienal with amino acids, amino esters and their salts was studied. The structure of the polyenic imines and iminium salts thus prepared was elucidated with the aid of 1H‐and 13C‐NMR spectroscopy. The condensation results in an equilibrium between the imine and its zwitterionic form as shown by variable‐temperature 13C‐NM measurements. Addition of an inorganic salt (LiClO4) favours the zwitterionic form. Comparison of the 13C chemical shifts of these species with those obtained from the protonation of the corresponding imino‐ester gave the percentage of the two forms. The species prepared from the amino acids constitute model compounds, and rhodopsin and bacteriorhodopsin are believed to exhibit similar behaviour.
Eine thermische, intramolekulare [2 + 2]‐Cycloaddition eines Allenyl‐benzols; Synthese von Allenylbenzolen durch säurekatalysierte Dienol‐Benzol‐Umlagerung
Authors: Summematter Walter , Heimgartner Heinz
Published: December 2004

A thermal Intermolecular [2 + 2]‐Cycloaddition of an Allenyl‐Allyl‐Benzene; Synthesis of Allenylbenzenes via Acid‐Catalyzed Dienol‐Benzene Rearrangement

A few years ago, it has been shown that the acid‐catalyzed dienol‐benzene rearrangement of 2‐propinyl‐substituted cyclohexadienols is a convenient synthesis for allenyl‐substituted benzene derivatives. The cyclohexadienols 20 and 21 were prepared via C‐alkylation of the corresponding phenols with 2‐propinylbromide (Scheme 3), followed by reduction of the cyclohexadienone 13 and 17 with LiAlH4. Treatment of 20 and 21 with p‐toluenesulfonic acid in ether at −15°) yielded the desired allenyl benzenes 8 and 9, respectively, via [3,4]‐sigmatropic rearrangements (Scheme 4). The 2‐propinylbenzenes 22–24, formed via [1,2]‐sigmatropic shift of the 2‐propinylgroup, were found as by‐products. Thermolysis of allenyl benzene 8 in decane yielded two bicyclic (25 and 26) and two tricyclic products (27 and 28; Scheme 5). For the formation of 25 and 26, a pericyclic reaction mechanism (Scheme 6) as well as a mechanism via biradical intermediates (Scheme 7) is discussed. A [2 + 2]‐cycloaddition of the α,β‐allenic and the allylic C,C‐double bound of 8 led to the tricyclic products 27 and 28 (Scheme 9). All attempts to realize a [1,7]‐sigmatropic H‐shift in the allene 9 failed so far, and the starting material underwent a rapid polymerisation.
Improved Synthesis of Oligodeoxyribonucleotides by Solid‐Phase Phosphotriester Method Utilizing O6‐[2‐(p‐Nitrophenyl)ethyl]‐2′‐deoxyguanosine Derivatives
Authors: Chollet André , Ayala Edgar , Kawashima Eric H.
Published: December 2004

The synthesis of oligodeoxyribonucleotides on a cross‐linked polystyrene solid support utilizing stable mono‐ and dinucleotide phosphotriester building blocks is presented. The use of O6[2‐(p‐nitrophenyl)ethyl]‐2′‐deoxyguanosine derivatives yields cleaner DNA fragments by suppressing side reactions. Modifications improving the phosphotriester methodology are presented. The purification methods and analysis of synthetic oligodeoxyribonucleotides are described.
Water‐Exchange Mechanism of Tetraaquapalladium(II). A Variable‐Pressure and Variable‐Temperature Oxygen‐17 NMR Study
Authors: Helm Lothar , Elding Lars I. , Merbach André E.
Published: December 2004

Water exchange of square‐planar Pd(H2O)24+ has been studied as a function of temperature (240 to 345 K) and pressure (0.1 to 260 MPa, at 324 K) by measuring the 17/O‐FT‐NMR line‐widths of the resonance from coordinated water at 27.11 and 48.78 MHz. The following exchange parameters were obtained: k298ex = (560 ± 40) s−1, ΔH* = (49.5 ± 1.9) kJ mol−1, ΔS* = – (26 ± 6) J K−1 mol−1 and ΔV* = – (2.2 ± 0.2) cm3 mol−1. The values refere to an aqueous perchlorate medium with an ionic strength between 2.0 and 2.6 m and a perchloric‐acid concentration between 0.8 and 1.7 m, and are interpreted in terms of an associative (a) activation for the exchange. The exchange rate for Pd(H2O)24+ is 1.4 × 106 times faster than for Pt(H2O)24+ at 298 K. A comparison with reactions between other nucleophiles and Pd(H2O)24+ is also made.
Etudes sur les composés organométalliques partie XX Sélectivité de l'addition 1,4 de composés benzyliques du titane IV avec la benzylidéneacétone
Authors: Roulet Daniel , Capéros José , Jacot‐Guillarmod André
Published: December 2004

Studies of Organometallic Compounds, XX. Selectivity of 1,4‐Addition of Benzyltitanium Compounds with Benzylildenacetone

Tetrabenzyltitanium and dialkoxydibenzyltitanium compounds give essentially 1,4‐ addition with trans‐4‐phenyl‐3‐buten‐2‐one.
Drüsenfarbstoffe aus tropischen Labiaten: Parviflorone aus Plectranthus strigosus BENTH.
Authors: Alder Aldredo Carlos , Rüdi Peter , Eugster Conrad Hans
Published: December 2004

Red‐Coloured Abietanoids from Leaf‐Glands of Plectranthus strigosus BENTH.

Chromatographic examination of the red‐coloured diterpenoids from the South‐African title plant yielded the following compounds: parviflorone A(1), parviflorone B (2), parviflorone C(3), parviflorone E (4) parviflorone D (5), parviflorone F (6), parviflorone G (7), and parviflorone H (8). Compounds 7 and 8 represent new variants of these quinone methides.
Synthese von neuen Morphin‐Teilstrukturen des Typs 15,16‐Secomorphinan
Authors: Révész László
Published: December 2004

Synthesis of New Morphine Partial Structure 15,16‐Secomorphinan

The synthesis of a new morphine partial structure, 15,16‐secomorphinan, is described. One of the series, (±)‐15, 16‐secocyclorphan (5), has the analgesic potency of morphine and exhibits good binding to the opiate receptor.
Monoolefin and Diene Cycloaddition Induced by Transition‐Metal Carbonyls. Cyclodimerization of 5,6‐Dimethylidene‐7‐oxabicyclo[2.21]hept‐2‐ene Catalyzed by Dodecacarbonyltriosmium
Authors: Vioget Philippe , Bonivento Massimiliano , Roulet Raymond , Vogel Pirre
Published: December 2004

The products generated by heating 5,6‐dimethylidene‐7‐oxabicyclo[2.2.1]hept‐2‐ene (1) with Fe2(CO)9, Ru3(CO)12, Os3(CO)12, Cr(CO)3(MeCN)3, (or W(CO)5(MeCN) or by treatment with Fe‐atoms have been characterized by spectroscopic methods. Apart from the expected η2‐ and η4‐complexes of the triene 1, condensation products are formed which arise from the formal [4 + 2]‐cyclodimerization of 1 involving the endocyclic double bond of one molecule and the diene moiety of a second. The [4 + 2]‐cyclodimerization is catalyzed by Os3(CO)12 in MeOH and gives 1,4‐epoxy‐7‐methoxy‐2,3‐dimethylidene‐1,2,3,4,4a,9,9a,10‐octahydroanthracene (15)). Fe‐Atoms induce a stereoselective [2 + 2]‐cyclodimerization pf 1 which involves its endocyclic double bond and produces the dimer 8.
Photochemical reactions. 139th Communication. Photochemistry of acylsilanes: 1. Siloxcarbene formation versus γ‐H‐abstraction
Authors: Scheller Markus E. , Frei Bruno
Published: December 2004

The Syntheses and the photolyses of the acylsilane 1 and the corresponding methyl ketone 2 are described. On n,π*‐excitation, the silyl ketone 1 as well as the methyl ketone 2 undergo a Norrish type II reaction involving γ‐H‐abstraction and fragmentation to the diene 12, and acetone (20) or the acylsilane 26, respectively. The methyl ketone 2, but not the acylsilane 1, isomerizes to cyclobutanols (21A‐D). Additionally, compound 1 shows photochemical behavior typical of acylsilanes undergoing rearrangement to the siloxycarbene intermediate c. Insertion of c into the OH‐ond of the enol 28 leads to compound 13. Initial trapping of the siloxycarbene c by H2O, however, gives rise to the formation of compounds 16–18. As minor photolysis products of 1, compounds 14 and (Z)‐15 were formed; however, on vapor phase thermolysis (520°) of 1, compounds 14 and (E/Z)‐15 were obtained in 92% combined yield. To a small extent the acylsilane 1 also undergoes Norrish type I cleavage leading to the acid 19.
(all‐E)‐1,3,5,7‐Octatetraene: Electron‐Energy‐Loss and Electron‐Transmission Spectra
Authors: Allan Michael , Neuhaus Louis , Haselbach Edwin
Published: December 2004

Electron‐energy‐loss and electron‐transmission spectra of (all‐E)‐1,3,5,7‐octatetraene were recorded with a trochoidal electron spectrometer. The energy‐loss spectra reveal two triplet states at 1.73 and 3.25 eV (0,0‐transitions), the UV‐active 11Bu state at 4.40 eV, and a higher‐lying singlet state at 6.04 eV. The 21Ag state recently reported to be the lowest excited singlet state in this polyene, could not be observed. This failure is probably de to a small excitation cross section under the scattering conditions used and the presence of the second triplet sate in the pertinent energy region. The electron‐transmission spectrum revealed three resonances (i.e. short‐lived anion states) at 1.5, 2.5, and 4.15 eV.
Bonding Capabilities of the Biochemical Buffer TRIS toward Copper(II) Ion. Structure and Magnetic Properties of Binuclear and Tetranuclear Systems
Authors: Masi Dante , Mealli Carloo , Sabat Michal , Sabatini Antonio , Vacca Alberto , Zanobini Fabrizio
Published: December 2004

Following X‐ray crystal structure studies, the products of the reaction between Cu(II) halides and tris(hydroxymethyl)methylamine (TRIS) can be formulated as [Cu(TRISH−1)(TRIS)]2X2 and [Cu(TRISH−1)X]4 (X  Cl, Br). TRISH−1 is the deprotonated ligand. Initial metal‐ligand stoichiometric ratios of 1:2 and 1:1 are required to obtain the former and the latter species, respectively. Relevant crystal data for the dimeric compound with X  Br are: monoclinic, a = 11.39(2), b = 10.049(2), c = 12.149(2) Å, β = 95.83(2)°, space group P21/c, Z = 2. The tetramer with X  Cl crystallizes in teh triclinic space group P 1 with a 9.182(1), b = 9.120(2), c = 8.817(1) Å, α = 88.95(1), β = 87.01(1), γ = 84.13(1), Z = 1. In the dimer, two square planar Cu(II)‐units are held together by two H‐bonds of the type OH …︁ O, which involve the O‐atoms coordinated to the metals. The formation of an eight‐membered cycle containing two metal ons ensues. The tetramer contains two dinuclear units formed by two metal centers, square planar in first approximation, which share one edge; the arrangement is significantly puckered at this vector. One of these bridging O‐atoms has μ3 character as it serves as a weak apical donor for a Cu‐atom of another binuclear unit. Thus a step‐like geometry of the central core is obtained. Both compounds have constant magnetic moments at least down to the liquid N2 temperature. In this respect, they differ from other complexes of Cu(II) having comparable geometries, but temperature‐dependent magnetic moments.