bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis and Diels‐Alder Reactivity of 2,3,5,6‐Tetramethylidenenorbornane
Authors: Pilet Olivier , Vogel Pierre 
Published: December 2004

AbstractPd‐catalyzed double carbomethoxylation of the Diels‐Alder adduct of cyclo‐pentadiene and maleic anhydride yielded the methyl norbornane‐2,3‐endo‐5, 6‐exo‐tetracarboxylate (4) which was transformed in three steps into 2,3,5,6‐tetramethyl‐idenenorbornane (1). The cycloaddition of tetracyanoethylene (TCNE) to 1 giving the corresponding monoadduct 7 was 364 times faster (toluene, 25°) than the addition of TCNE to 7 yielding the bis‐adduct 9. Similar reactivity trends were observed for the additions of TCNE to the less reactive 2,3,5,6‐tetramethylidene‐7‐oxanorbornane (2). The following second order rate constants (toluene, 25°) and activation parameters were obtained for: 1 + TCNE → 7: k1 = (255 + 5) 10−4 mol−1 · s−1, ΔH≠ = (12.2 ± 0.5) kcal/mol, ΔS≠ = (−24.8 ± 1.6) eu.; 7 + TCNE → 9, k2 = (0.7 ± 0.02) 10−4 mol−1 · s−1, ΔH≠ = (14.1 ± 1.0) kcal/mol, ΔS≠ = ( −30 ± 3.5) eu.; 2 + TCNE → 8: k1 = (1.5 ± 0.03) 10−4 mol−1 · s−1, ΔH≠ = (14.8 ± 0.7) kcal/mol, ΔS≠ = (−26.4 ± 2.3) eu.; 8 + TCNE → 10; k2 = (0.004 ± 0.0002) 10−4 mol−1 · s−1, ΔH≠ = (17 ± 1.5) kcal/mol, ΔS≠ = (−30 ± 4) eu. The possible origins of the relatively large rate ratios k1/k2 are discussed briefly.
Über Pterinchemie. 79. Mitteilung. 13C‐und 15N‐NMR.‐spektroskopische Untersuchungen an der (6RS)‐5, 10‐Methylen‐5, 6, 7, 8‐tetrahydro‐L‐folsäure; eindeutiger Beweis ihrer Struktur
Authors: Kalbermatten Roger , Städeli Werner , Bieri Jost H. , Viscontini Max 
Published: December 2004

13C‐ and 15N‐NMR.‐Spectroscopic Studies on (6RS)‐5, 10‐Methylene‐5, 6, 7, 8‐tetrahydro‐L‐folic Acid; Unequivocal Proof of thier StructureThe existence of a 5, 10‐methylene bridge in the title compound has been established with the help of 15N‐NMR, and 13C‐NMR. spectroscopy. The simultaneous coupling of 13C(11) with 15N(5) and 15N(10) proves that C(11) must be bound as a methylene bridge to both N‐atoms. Some other aspects of the NMR. spectra of the compound are discussed. Synthesis of the title product with the label 15N is described.
Synthese von (−)‐(5R,6S)‐5,6‐Epoxy‐5,6‐dihydro‐β‐ionon
Authors: Acemoglu Murat , Eschenmoser Walter , Eugster Conrad Hans 
Published: December 2004

Synthesis of (−)‐(5R,6S)‐5,6‐epoxy‐5,6‐dihydro‐β‐iononeOptically active 5,6‐epoxy‐5,6‐dihydro‐β‐ionones have been prepared for the first time and their absolute configurations were determined by correlation with (−)‐(S)‐α‐ionone. Acid catalyzed hydrolysis of the epoxide proceeds with retention of the configuration at C(6) and with inversion at C(5).
Dediazoniation of Arenediazonium Ions. Part XIX. Effect of thiocyanate ion in the reactions of 2,4,6‐trimethylbenzenediazonium tetrafluoroborate in 2,2,2‐trifluoroethanol
Authors: Szele Ivanka , Zollinger Heinrich , Deshpande Ashok D. 
Published: December 2004

AbstractThe dediazoniation of 2,4,6‐trimethylbenzenediazonium tetrafluoroborate (1) in 2,2,2‐trifluoroethanol (TFE) was studied in the presence of potassium thiocyanate. The effect of added salt on the dediazoniation rate, the Nα‐Nβ rearrangement (Eqn. 2), the exchange of the 15N‐labelled diazo group with molecular nitrogen (Eqn. 3), and the reaction products was determined. With 0.3M KSCN a dediazoniation‐rate increase of 16.5% was achieved, and the amounts of rearranged and exchanged product were reduced to 88% and 70%, respectively, of the values found in pure TFE. The dediazoniation products formed are ArF (3), ArOCH2CF3 (4), ArSCN (5), ArNCS (6) and traces of 5, 7‐dimethylindazole (7). All the data are in agreement with, and support the previously proposed mechanism (Equ. 1) of heterolytic dediazoniation of arenediazonium salts.
The Radicals and Radical Dianions of Bridged [11]‐ and [15]Annulenyls as Compared with Those of Benzotropyl and 2,3‐Naphthotropyl
Authors: Gerson Fabian , Huber Walter , Müllen Klaus 
Published: December 2004

AbstractThe 1,6‐methano[11]annulenyl (1·), 1,6:8, 14‐propane‐1,3‐diylidene[15]annulenyl (2·), benzotropyl (3·) and 2,3‐naphthotropyl (4·) radicals have been characterized by their ESR. spectra. The corresponding radical dianions, , , and , have also been studied both by ESR. and ENDOR. spectroscopy. Assignment of the coupling constants aHμ to protons in the individual positions μ of these radicals and radical dianions is to a large extent based on investigations of specifically deuteriated derivatives. The radicals 1·, 2·, 3· and 4· exist in temperature‐dependent equilibria with (1)2, (2)2, (3)2 and (4)2, respectively, where (1)2 to (4)2 denote mixtures of dimers of 1· to 4·. The dissociation enthalpies, ΔH°, of (1)2 (102 kJ/mol) and (2)2 (88 kJ/mol) are considerably smaller than those of (3)2 and (4)2 which do not significantly differ from the ΔH° value of bitropyl (139 ± 6 kJ/mol). This finding indicates that the gain in π‐electron delocalization energies, Δ(DE)π, upon dissociation markedly increases on going from bitropyl, (3)2 and (4)2 to (1)2 and (2)2, and thus points to an additional ‘resonance stabilization’ of 1· and 2·, as compared with 3· and 4·. A more pronounced π‐spin localization on the 7‐membered ring is observed in 3·, 4·, and relative to the corresponding species, 1·, 2·, and . It can be interpreted in terms of simple π‐perimeter models without explicitly invoking substantial homoconjugative interactions between the bridged centres in 1·, 2·, and . However, the shortcomings of these crude models do not allow one to make a clear‐cut statement about the contributions of the homotropyl structures to the π‐systems of these paramagnetic species. The radical dianions and exhibit considerable hyperfine splittings from one 23Na or 39K nucleus of the counter‐ion, whereas for and such splittings stem from two equivalent alkali metal nuclei. This finding is readily rationalized by different geometries of the bridged annulenyls and their benzo‐ and naphthotropyl analogues. Hyperfine data are also given for the radical anions of 7 H‐benzocycloheptene, (3‐H)\documentclass{article}\pagestyle{empty}\begin{document}$2^{\ominus \atop \dot{}}$\end{document}, and 6 H‐(2,3‐naphtho)cycloheptene, (4‐H)\documentclass{article}\pagestyle{empty}\begin{document}$2^{\ominus \atop \dot{}}$\end{document}, as well as for the radical dianion of 1,6:8,14‐bismethano[15]annulenyl,5\documentclass{article}\pagestyle{empty}\begin{document}$2^{\ominus \atop \dot{}}$\end{document}.
Relationship between Molecular Properties and Conformation of Chiral Alkanes
Authors: Azzena Ugo , Luisi Pier Luigi , Suter Ulrich W. , Gladiali Serafino 
Published: December 2004

AbstractMixtures of the diastereomers of 2,2,3,5,6‐pentamethylheptane were prepared in two ways, either starting with compounds of (3R)‐configuration, or from compounds of (5R)‐configuration. Comparison of the GC. and optical rotatory power of the fractions of these two mixtures permitted the unambiguous assignment of the absolute configuration and molar rotatory power to the various diastereomers ([M] = + 119.1° for the (3R, 5R)‐ and [M] = + 79.8° for the (3R, 5S)‐diastereomer). The very high molar rotatory power which was expected on the basis of the conformational analysis carried out with a rotational‐isomeric‐3‐states model is interpreted as arising from the molecular ‘conformational rigidity’, i.e. from the presence of only few conformers. Conformational properties of these compounds were computed using a new approach, which scans the whole space of each bond (2 π) in 5° steps and calculates the conformational energy based upon semiempirical potential functions. The conformational flexibility of each bond of the two diastereomers is evaluated in terms of the a priori probability density function of that bond. This allows us to analyze in detail how configurational differences affect conformational properties. The molar rotatory power of the two diastereomers as calculated with a new method recently developed in our group is in excellent agreement with experimental data. The molar rotatory power is analyzed in terms of the contribution of the single bonds.
Transition metal ions and amides. VIII. Discrimination between different models for the complexation of Cu2+ with N, N′‐diglycyl 1, 2‐ethanediamine, N, N′‐diglycyl‐1, 3‐propanediamine and glycine ethylamide by potentiometric or by spectrophotometric titration
Authors: Briellmann Markus , Zuberbühler Andreas D. 
Published: December 2004

AbstractThe complexation of Cue2+ with 1, 8‐diamino‐3, 6‐diaza‐2, 7‐octanedione (N, N′‐diglycyl‐1, 2‐ethanediamine, DED) and with 1, 9‐diamino‐3, 7‐diaza‐2, 8nonanedione (N, N′‐diglycyl‐1, 3‐propanediamine, DPD) has been studied by potentiometric and by spectrophotometric titration. With both ligands L the complexation to Cue2+ leads to relatively complicated equilibria with CuLH3+, CuL2+, CuLH−2, and dimeric Cu2L complexes. With DED, another dimeric species, Cu2L2H, is formed in addition. Independent numerical treatment of spectrophotometric and poteritiometric titrations was used to obtain a satisfactory model for the complexation and to test the relative discriminatory power of the two methods. Titrations of glycine ethylamide (GEA) were used as an additional test and as a model for DED and DPD. It was shown that in each case spectrophotometric titrations give results of similar reproducibility and have a discriminatory power equal to or better than potentiometric titrations, provided that optimum mathematical algorithms are used in the numerical treatment.
Mechanisms of Diazo Coupling Reactions. Part XXXII. The Diazoamino Rearrangement in 20% Acetonitrile/Aqueous Buffers
Authors: Kelly Richard P. , Penton John R. , Zollinger Heinrich 
Published: December 2004

AbstractThe rearrangements of 4′‐methoxy‐N‐methyl‐ and N‐methyl‐4′‐nitro‐diatzoaminobenzene have been studied in 20% acetonitrile/aqueous buffers. The reactions are specifically acid catalyzed and involve pre‐equilibrium formation of amine and diazonium salt followed by rate‐limiting attack of the diazonium ion at a C‐atom (C‐coupling) to give the corresponding aminoazo compounds. There is no evidence to suggest that, under the present conditions, mechanisms other than the established Friswell‐Green mechanism occur. The traditional two‐stage synthesis of aminoazo compounds via isolated diazoamino compounds can therefore be replaced by a one stage process for amines which undergo initial attack at a N‐atom by diazonium ion (N‐coupling).
Physico‐chemical properties of deuteriated compounds. 6th Communication. The H/D exchange in mixtures between hydrogen and heptane, methylcyclohexane or cycloheptane over Ni‐catalyst
Authors: Dessauges GÉRald , Gäumann Tino 
Published: December 2004

AbstractThe isotopic exchange between hydrogen and saturated hydrocarbons over Nicatalysts has been studied as a function of temperature and degree of deuteriation. The experimental results can be explained by a model containing four parameters. Two different adsorbed species are assumed: in the ‘alkyl’‐species one H‐atom is exchanged in a single adsorption step; the ‘olefin’‐species exchanges at least two H‐atoms at the same time. Both species can undergo multiple exchange per adsorption step.
Vinylketenes as Synthons for Bicyclo[4.2.1]nonadienones
Authors: Huston Rima , Rey Max , Dreiding André S. 
Published: December 2004

AbstractSechs Vinylketene (9a–9f), wovon fünf Chlor‐vinylketene (9a–e) (s. Schema 2), in situ durch 1,4‐Eliminierung von HCI aus den entsprechenden α, β‐ungesättigten Säurechloriden hergestellt, wurden mit Cyclopentadien (2) bzw. 6,6‐Dimethylfulven (3) umgesetzt. Durch [2 + 2]‐Cycloaddition entstanden fünf 7‐vinylsubstituierte Bicyclo[3.2.0]‐2‐hepten‐6‐one (10/11) bzw. drei 4‐Isopropylidenbicyclo [3.2.0]‐2‐hepten‐6‐one (12/13), wobei das Stereoisomerenverhältnis 10:11 bzw. 12:13 von der Grösse der Ketensubstituenten beeinflusst wurde. Die Vinylketen‐Cycloaddukte 10/11 und 12/13 enthalten ein Cope‐System, das entweder in einer syn‐(10 und 12) oder in einer anti‐Konfiguration (11 und 13) vorliegt. Beim Erwärmen auf 140–190° ergaben 10/11 bzw, 12/13 durch Cope‐Umlagerung die entsprechend substituierten Bicyclo[4.2.1]‐3,7‐nonadien‐2‐one (14) bzw. 9‐Isopropylidenbicyclo[4.2.1]‐3,7‐nonadien‐2‐one (15). Mittels der beschriebenen Reaktionen werden die Ringsysteme von 14 und 15 in einer zweistufigen Synthese leicht zugänglich.
Malzoxazin, eine tricyclische Verbindung aus Gerstenmalz
Authors: Tressl Roland , Helak Bernd , Rewicki Dieter 
Published: December 2004

Maltoxazine, a Tricyclic Compound from MaltA new tricyclic compound, named maltoxazine, has been isolated from malt as well as from the reaction products formed in a model reaction of maltose with proline. The structure of maltoxazine (1) has been established by 1H‐ and 13C‐NMR. spectroscopy. The formation of 1 in several model reactions is strongly correlated with the formation of maltol and 5‐hydroxy‐5,6‐dihydromaltol.
(Perhalogenmethylthio)heterocyclen. XII. Herstellung von Perfluoroalkylsulfonylharnstoff‐Derivaten sowie CCl3−nFnX‐substituierten Heterocyclen und deren biologische Wirkung
Authors: Gerstenberger Michael R. C. , Haas Alois , Pauling Horst 
Published: December 2004

(Perhalomethylthio)heterocycles XII. Preparation of Perfluoroalkylsulfonylurea Derivatives as well as CCl3−nFnX‐Substituted Heterocycles and Their Biological ActivityXI, Mitt., s.[1]
In the presence of CF3SO3H (chlorodifluoromethylthio)thiophene 1 reacts with CClF2SCl to give the 2,5‐disubstituted thiophene 2a which on oxidation with 30% H2O2‐solution yields the corresponding sulfonyl compound 2b · R1SO2NCO adds amines to give R1SO2NHC(O)NHR 3a–g. Some biological properties of these compounds were investigated.
Selektive Reaktionen an Cytochalasin D
Authors: Chappuis Georges , Tamm Christoph 
Published: December 2004

AbstractIn connection with the total synthesis of cytochalasans the cleavage of the macrocyclic system of cytochalasin D (3) was studied in order to gain useful relay compounds. Selective scission of the double bond in 19‐position was achieved by controlled ozonolysis leading to compound 7 (Scheme 1). Treatment of 3 with OsO4 and subsequent acetylation gave the tetraacetoxy‐ and diacetoxy derivatives 8 and 9, respectively. Sharpless epoxidation of 3 yielded the mono‐, di‐ and the two epimeric triepoxides 10, 11, 12, and 13, respectively.Further studies concerned the isomerization of the 6(12)‐double bond to 6(7)‐double bond by an allylic rearrangement. Treatment of 3 with mesylchloride and triethylamine led to 12‐hydroxy‐, 12‐mesyloxy‐ and 12‐chlorozygosporin (14, 16, and 17, resp.) (see Scheme 2). Epoxidation of 14 gave a mixture of the two epimeric 6,7‐epoxides 21 and 23. Zn‐reduction of 18 (the corresponding bromide of 17) led to zygosporin G (20).In order to convert a carbocyclic cytochalasan into a macrocyclic derivative, 3 was converted to 32 (Scheme 2). Treatment of 32 with H2O2 in acetic acid/chloroform or with phenylselenylperacid/H2O2 yielded the enollactone 33.Finally, 17,18‐secocytochalasin D derivatives were prepared for the synthesis of unnatural analogs of macrolidic cytochalasans. The diol 26 was converted into the ketoaldehydes 38 and 40 and to the corresponding keto‐acids 43 and 44 (Scheme 3), which were reduced to the ω‐hydroxycarboxylic acids 45–48. Treatment of 47 with 2,2/‐dipyridyldisulfide/triphenylphosphine/xylene gave probably the lactone 50.
Lipophilic Diamides as Ionophores for Alkali and Alkaline Earth Metal Cations
Authors: Erne Daniel , Ammann Daniel , Zhukov Alex F. , Behm Felix , Pretsch Ernö , Simon Wilthelm 
Published: December 2004

AbstractA series of lipophilic N, N, N′,N′‐tetrasubstituted diamides were prepared and their selectivity in solvent polymeric membranes was studied, cis‐N, N, N′, N′‐Tetraisobutylcyclohexane‐1,2‐dicarboxamide induces a selectivity in membranes for Li+over alkaline earth metal cations and other alkali metal cations by a factor of about 1000 and 100 respectively. The ionophore N, N′‐diheptyl‐N,N′‐dimethylethylmalonamide is an attractive candidate for the use in microelectrodes for the determination of intracellular Mg2+‐activities.
Zur Synthese sulfonierter Derivate von 4‐Fluoranilin
Authors: Courtin Alfred 
Published: December 2004

Syntheses of Sulfonated Derivatives of 4‐FluoroanilineSynthesis of 2‐amino‐5‐fluorobenzenesulfonic acid (2) was achieved by baking the hydrogen sulfate of 4‐fluoroaniline (1). Sulfonation of p‐fluoroacetanilide (4) with oleum followed by hydrolysis gave 5‐amino‐2‐fluorobenzenesulfonic acid (3). The same reaction with 1 yielded 3 in an impure state. The structures of 2 and 3 were confirmed by converting the diazonium chlorides derived from 5‐fluoro‐2‐nitroaniline (5) and from 2‐fluofo‐5‐nitroaniline (8) to 5‐fluoro‐2‐nitrobenzene‐sulfonyl chloride (6) and 2‐fluoro‐5‐nitrobenzenesulfonyl chloride (9), respectively, followed by hydrolysis of 6 to 5‐fluoro‐2‐nitrobenzenesulfonic acid (7), and of 9 to 2‐fluoro‐5‐nitrobenzenesulfonic acid (10), and by final reduction. Compound 10 was also obtained by sulfonation of 1‐fluoro‐4‐nitrobenzene (11) with oleum.
Photochemical Synthesis of 9‐Methyl‐tetracyclo[5.3.04,9.08,10]‐decane‐2,6‐dione
Authors: Margaretha Paul , Grohmann Klaus 
Published: December 2004

AbstractIrradiation (λ > 340 nm) cis‐8a‐methyl‐1,2,4a,7,8,8a‐hexahydronaphthalene‐2.7‐dione (1) in benzene affords the title compound 2 via an intramolecular [2 + 2]‐cycloaddition.
The Photoelectron Spectrum of [18]Annulene
Authors: Baumann Harold , Bünzli Jean‐Claude , Oth Jean Françcois Michael 
Published: December 2004

AbstractThe PE. spectrum of [18]annulene has been measured and correlated with MO‐calculations. The experimental ionization energies can only be explained by computing the electronic states of the cation, that is by taking into account the electron correlation and reorganization in the ionic states. The results allow a discussion of the structure of the neutral molecule; they are consistent with a D6hpoint group of symmetry.
Photochemical Reactions. 126th Communication. Photochemistry of an α, β: δ, ε‐unsaturated ketone: 4‐(2′, 7′, 7′‐Trimethylbicyclo [3.2.0]hept‐2′‐en‐1′‐yl)‐3‐buten‐2‐one
Authors: Ishii Keitaro , Lyle Terry A. , Schweizer W. Bernd , Frei Bruno 
Published: December 2004

AbstractOn 1n,π*‐excitation, the title compound 2 undergoes a photoinduced intramolecular [4 + 2]‐cycloaddition affording the tetracyclic enol ether 3 as the only product in 79% yield. The assigned structure of 3 was confirmed by its conversion to the p‐nitrobenzoate 6 whose structure was determined by X‐ray analysis.
Das Pyrrocorphin‐Ligandsystem: Synthese des 2,2,7,7,12,12,17‐Heptamethyl‐2,3,7,8,12,13‐hexahydroporphyrins. Kurzmitteilung
Authors: Sehwesinger Reinhard , Waditschatka Rudolf , Rigby James , Nordmann René , Schweizer Wolfhard B. , Zass Engelbert , Eschenmoser Albert 
Published: December 2004

The Pyrrocorphin Ligand System: Synthesis of 2,2,7,7,12,12,17‐Heptamethyl‐2,3,7,8,12,13‐hexahydroporphyrinReaction Schemes 4 and 6 summarize the synthesis of the title compound, a representative of a recently described novel type of hexahydroporphinoid ligand system (‘pyrrocorphin’). Pyrrocorphins incorporate structural elements of both corrins and porphyrins and are chemically closely related to the tautomeric non‐pyrrolic corphins (Scheme 1).The synthesis exemplifies a methodology for constructing pyrrolic hydro‐porphinoids with the methods of corrin instead of porphyrin synthesis. An X‐ray analysis of 2‐(cyanomethyl)‐2‐methyl‐3‐oxobutanamide has been carried out.
Technische Verfahren zur Synthese von Carotinoiden und verwandten Verbindungen aus 6‐Oxo‐isophoron. V. Synthese von Astacin
Authors: Widmer Erich , Lukáč Teodor , Zell Reinhard , Bernhard Kurt 
Published: December 2004

Technical Procedure for the synthesis of Carotenoids and Related Compounds from 6‐Oxo‐isophoroneTeil 4 dieser Reihe: [1].

. V. Synthesis of Astacene
Starting from optically inactive astaxanthin intermediates, the highly oxygenated carotenoid astacene was synthesized in seven steps (55% overall yield from 6‐oxo‐isophorone). Key features of the new approach are base‐ and acid‐catalyzed rearrangements of acetylenic intermediates such as those described in Schemes 2, 7 and 8.
Unexpected Configurational and Conformational Preference in Bicyclo [3.2.0]heptane Systems
Authors: Rey Max , Roberts Stanley M. , Dreiding André S. , Roussel Albert , Vanlierde Huguette , Toppet Suzanne , Ghosez Léon 
Published: December 2004

AbstractEinige 7endo‐monosubstituierte Bicyclo[3.2.0]hept‐2‐en‐6‐one and Bicyclo‐[3.2.0]heptan‐6‐one zeigen eine unerwartete thermodynamische Stabilität gegenüber den entsprechenden 7exo‐Isomeren. Die basenkatalysierte Epimerisierung (NaOH oder N(CH2CH3)3) verschiedener 7‐monosubstituierter Bicyclo[3.2.0]‐hept‐2‐en‐6‐one (1‐7) und Bicyclo[3.2.0]heptan‐6‐one (8–10) führt je nach Substituent (R) zu folgenden endo/exo‐Gleichgewichtsgemischen: (a) Bicyclo[3.2.0]‐hept‐2‐en‐6‐one: R = F: 89/11, R = C1: 87/13, R = CH3: 76/24, R = CH2CH3: 65/35, R = CH (CH3)2: 57/43, R= C (CH3)3: 10/90, R= C6H5: 66/34; (b) Bicyclo[3.2.0]‐heptan‐6‐one: R = C1: 85/15, R = CH3: 45/55, R= C (CH3)3: 0,4/99,6. In jedem Fall wurde das gleiche Epimerengemisch erhalten, ausgehend sowohl vom endo‐ wie auch vom exo‐Isomeren.Die bemerkenswerte endo‐Stabilität wird einer Bevorzugung der Konformation 11 des Cyclobutanonringes zugeschrieben, verursacht durch geringere Pitzer‐Spannung. So kann ein endo‐Substituent an C(7) eine pseudoäquatoriale Lage am Cyclobutanonring einnehmen. Bei sehr sperrigen Substituenten mit zunehmender Raumerfüllung nimmt eine 1,2‐abstossende Wechselwirkung langsam überhand, bis im Falle des t‐Butylsubstituenten die exo‐Konfiguration die stabilere wird.Die Dehalogenierung von 7‐Halo‐substituierten Bicyclo [3.2.0]hept‐2‐en‐6‐onen (15 bis 21) mit Zink und Eisessig und mit Tributylzinnhydrid führte zu den folgenden endo/exo‐Epimerengemischen der entsprechenden 7‐monosubstituierten Bicyclo [3.2.0]hept‐2‐en‐6‐one (2 bis 7): R = C1: 92/8, R = CH3: 93/7, R = CH2CH3: 93/7, R = CH(CH3)2: 92/8, R = C(CH3)3: 93/7, R = C6H5: 93/7. In allen Fällen, also unabhängig vom Substituenten R, war das endo‐isomere stark bevorzugt. Es muss sich also um eine kinetische Kontrolle im isomerenbestimmenden Schritt handeln: Die Reduktion verläft über das Enolat, bzw. über eine Radikalspezies mit trigonal‐planarer Anordnung am C(7), so dass die (irreversible) Wasserstoff‐Anlagerung von der weniger behinderten Site, der exo‐Seite her erfolgt.
Sterisch gehinderte Pyrrolidine. Umsetzung von 2,5,5‐Trimethyl‐1‐pyrrolin‐1‐oxid mit α‐Chloracrylnitril
Authors: Schneider Hermann 
Published: December 2004

AbstractReaction of the nitrone 1 with α‐chloroacrylonitrile (4) as ketene equivalent yields the 5‐isoxazolidinone 2a and the α‐chloroimine 5. The mechanism of the reaction is discussed. The compound 2a is useful for the synthesis of hindered pyrrolidines 3.
Die spontane Spaltung von 3,3‐Diäthyl‐5‐methylpiperidin‐2,4‐dion(Methyprylon) in die optischen Isomeren. Eine Rötgenstrukturanalyse eines isodimorphen Systems von Mischkristallen
Authors: Oberhänsli Willi E. 
Published: December 2004

The Spontaneous Resolution of the 3,3‐Diethyl‐5‐methylpiperidine‐2,4‐dione (Methyprylon) into its Optical Isomers. An X‐Ray Structure Analysis of an Isodimoophous System of Mixed CrystalsRepeated recrystallizations from acetone of a racemic mixture of the title compound successively result in a spontaneous resolution into optical isomers [1]. In this process batches of mixed crystals of increased optical purity are formed [2]. This phenomena was investigated on a molecular basis using X‐ray diffraction methods. The mixed crystals belong to the space group P212121 and their diffraction patterns give no indication of major disorders. There is a linear relationship between the changes in unit cell parameters a and b and the optical rotation of the sample. The structures of the mixed crystals from four fractions belonging to two different crystalline modifications have been determined. The molecular shape is such that most of the atomic positions of the two enantiomers superimpose almost perfectly. Occupation factors determined for the asymmetric C‐ sites agree well with the optical activity of the crystals fraction.