bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractPhotolysis (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.
Intermediates in the Dehydrogenation of Hydroaromatic Compounds with Quinones
Authors: Müller Paul , Joly Daniel 
Published: December 2004

AbstractDehydrogenation 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

AbstractHydroboration 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 ReactionsThe 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‐Nitrocycloalkanonesα‐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’ DiacetylenesThe 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

AbstractLigand 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

AbstractReactions 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

AbstractThe 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

AbstractConduction 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

AbstractThe 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 AlkaloidsCircular 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 IonophoreThe 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

AbstractTreatment 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

AbstractThe 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

AbstractVolumes 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

AbstractMalonylmethyl 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

AbstractThis 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 GroupsThe 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 LOHERFrom 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

Abstractcis‐ 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

AbstractThe 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

AbstractOptically 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

AbstractThe 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.