bluuebunny/crossref_metadata_2025_split huggingface dataset:
Halogenierte Pyridine V. Fluorierte und bromierte Pyridinverbindungen
Authors: Mutterer Francis , Weis Claus D. 
Published: December 2004

Halogenated pyridines V.Fluorinated and brominated pyridine compounds.Ring chlorinated 3‐chloromethyl‐pyridines provide a source of new halogenopyridines the fluorination of which is described. Variously substituted 2, 6‐dibromopyridines are prepared from the corresponding dichloro compounds by halogen displacement with hydrogen bromide in acetic acid at elevated temperatures.
Ermittlung von Bildungskurven nach J. Bjerrum mittels differenzieller Dampfdruckosmometrie
Authors: Kirsch Norbert N. L. , Simon Wilhelm 
Published: December 2004

Determination of Bjerrum Formation Curves by Differential Vapour Pressure Osmometry.A differential vapour pressure osmometry method for the determination of Bjerrum formation curves is described. This technique allows the determination of formation constants in nonaqueous solvent systems.
Über Pterinchemie. 54. Mitteilung [1]. Eine allgemeine Methode zur Synthese von Folsäure, Folsäurekonjugaten und Folsäureanalogen
Authors: Khalifa Esam , Sengupta Pradip K. , Bieri Jost H. , Viscontini Max 
Published: December 2004

A general method for synthesis of folic acid, its conjugates and analogues.A new and general method for the synthesis of folic acid, folic acid conjugates and folic acid analogues is described. The key step, i.e. the condensation of N(2′)‐acetyl‐6‐formyl‐pterine (I: R1  COCH3) with aminoaryl derivatives II, is achieved by refluxing in absolute ethanol to afford the azomethines III. NaBH4‐reduction followed by basic hydrolysis gives pure V products in high yield, free from 7‐isomers.
Organic Phosphorus Compounds 68. The direct synthesis of tri(alkyl‐ and arylseleno)phosphites and of tris(p‐anisyltelluro)phosphite [1]
Authors: Maier Ludwig 
Published: December 2004

AbstractWhite phosphorus reacts with organic diselenides in a dipolar aprotic solvent in the presence of a base with the formation of tri(alkyl‐ or aryl‐seleno)phosphites in good yield.

Tri(methylseleno)phosphitc shows a 31P‐chemical shift = −107 ppni (JP, 77Se = 233 Hz). It is readily oxidizcd in air to the corresponding selenophosphate, (CH3Se)3 PO, 31P‐chemical shift = −16 ppm.Tri(phenylseleno)phosphite reacts readily with mercury oxide to give the tri(phenylseleno)phosphate, a yellow solid of m.p. 105–110°. It also reacts with sulfur in refluxing benzene solution to give tri(phenylseleno)thiophosphate, also a yellow solid of m.p. 55–58°. However, an attempt to prepare tri(phenylseleno)selenophosphate failed. Under the same conditions as given above, white phosphorus also reacts with di‐p‐anisyl ditelluride to give tris(p‐anisyltelluro)phosphite, shiny, rusty brown crystals which decompose rapidly at room temperature, but are stable for several months when kept in acetonc solution at −20°.
A New and Convenient Synthesis of Substituted Acylthioacylureas. Reaction of aryl and alkyl thioamides with acyl isocyanates
Authors: Cohen Victor Israel 
Published: December 2004

AbstractThe addition of acyl isocyanates to a solution of aryl and alkyl thioamides affords substituted acylthioacylureas. The IR. spectra of substituted acylthioacylureas is described.
Planare Pt(II)‐ und Pd(II)‐Komplexe aus dreizähnigen Azo‐ und Azomethinliganden: Ein Beitrag zur Frage der Nα/Nβ‐Isomerie
Authors: Steiner Eginhard , Mayer Carl , Schetty Guido 
Published: December 2004

Planar Pt(II)‐ and Pd(II)‐Complexes with Terdentate Azo‐ and Azomethine Ligands: A Contribution to the Question of Nα/Nβ‐Isomerism.The preparation and properties of novel Pt(II)‐ and Pd(II)‐complexes with terdentate azo‐ and azomethine ligands and with an amine in the fourth coordination position of the metals are described. In certain cases the formation of isomeric complexes is observed, which are interpretated as Nα/Nβ‐isomers according to their 1H‐NMR.‐signals.The postulated isomerism will be proved by 15N‐NMR.‐spectroscopy – in the following publication [5] using 15N‐enriched compounds whose syntheses are described in this publication.
Concerning the Conformation of Isolated Benzylideneaniline
Authors: Bally Thomas , Haselbach Edwin , Lanyiova Suzana , Rossi Michel , Marschner Freimuth 
Published: December 2004

AbstractFrom PE.‐spectroscopical studies the torsional angle φ of the N‐phenyl ring in isolated benzylideneaniline 1 has been found to be definitely smaller than φ= 90°. An approximate valueφ= 36°has been estimated which is even smaller than the one observed in the crystal (φ= 55°) and suggested to prevail also in solutions of 1. A reevaluation of the gas phase optical spectrum of isolated 1 supports a torsional angle similar to that found in the other phases.Calculations of the most stable conformation of 1 as well as of stilbene and azobenzene by the MINDO/3‐technique lead to torsional angles φ= 90° for both phenyl rings in all cases. These results are at variance with the experimental results and suggest that MINDO/3‐like its less advanced precursor MINDO/2 or like CNDO/2–is unreliable for low energy processes involving rotation of π‐systems connected by essential single bonds.It is concluded that the π‐energy of benzylideneaniline, like that of stilbene or azobenzene, would favor a planar conformation. The increased torsional angle in 1 as compared to the other two iso‐conjugate systems arises from a larger steric interaction between phenyl‐ and bridgeprotons.
Radiolabelled Peptide Ergot Alkaloids. 83. Mitteilung über Mutterkornalkaloide
Authors: Schreier Emil 
Published: December 2004

AbstractPaspalic acid (11), labelled at different positions with 3H or 14C and at specific activities up to 1 Ci/mmol (3H) and 2mCi/mmol (14C), has been prepared biosynthetically in a scale of 2–5 mmol in submerged cultures of a selected strain of Claviceps paspali by incorporation of DL‐[5‐3H]‐tryptophan, DL‐[6‐3H]‐tryptophan, DL‐[alanine‐2,3‐3H]‐tryptophan, or DL‐[alanine‐3‐14C]‐tryptophan. Radioactive lysergic acid (12) was obtained from paspalic acid by base catalysed rearrangement.The procedures for labelling the precursors at high specific activity arc described.The ergolene carboxylic acids 11 and 12 were used as key intermediates for tlie chemical synthesis of radiolabelled peptide ergot alkaloids 14 required for pharinacokinetic and metabolic studies. Linking of the aminocyclols 13 (peptide parts) of the ergotarnine (R1 = methyl), ergoxine (R1 = ethyl) and ergotoxine (R1 =isopropyl) series with a reactive derivative of either lysergic acid or its mixture with paspalic acid was accomplished by standard procedures. l‐Mctliyl‐[13‐3H]‐ergotarnine (MY 25) (16) and 2‐brotno‐α‐ergocryptine (bromocriptine, C73 154) (17), labelled with 3H at position 12 and with 14C in position 4, were obtained by alkylating 3H‐ergolamine and by ljrominating appropriately labelled α‐ergocryptines.Radioactive peptide ergot alltaloitls labelled by tlic present nietliotl proved suitable for the use in biological tracer studies.
Über die Konstitution von Loroglossin. Vorläufige Mitteilung
Authors: Gray Robert W. , Guggisberg Armin , Segebarth Klaus Peter , Hesse Manfred , Schmid Hans 
Published: December 2004

The Constitution of Loroglossine.Loroglossine, a characteristic constituent of orchids, is shown to be bis‐[4‐(β‐D‐glucopyranosyloxy)‐benzyl]‐(2 R, 3 S)‐2‐isobutyl‐tartrate (1). Hydrolysis and esterification gave 1 mol‐equiv. of dimethyl (+)‐2‐isobutyl‐erythro‐tartrate ((+)‐3) and 2 mol.‐equiv. of a glucoside which, after acetylation, gave 4, identical with a synthetic sample. The erythro configuration of (+)‐3 by oxidation of isobutyl‐maleic acid with osmium tetroxide and subsequent esterification. The absolute configuration of (+)‐3 was based on Horeau experiments and NMR. data of the diastereomeric mixture of its esters 7 and 8 with S (+)‐ and R (−)‐α‐phenylbutyric acid respectively.
Note on the Preparation of Alkyl‐ and Oxaälkyl‐dimethylsilanols
Authors: Boksányi László , Liardon Olivier , Kováts Ervin sz. 
Published: December 2004

AbstractThe preparation of a series of alkyl‐ and (mono‐, di‐ and poly‐) oxaälkyl‐dimethylsilanols is described. The stability of these compounds on storage is considerably increased by previous filtration through a silica gel column.
One‐Step Purification of Bovine Adrenal Glucose‐6‐phosphate Dehydrogenase by Affinity Chromatography
Authors: Bürgisser Ernst , Fauchère Jean‐Luc 
Published: December 2004

AbstractDas konventionelle Reinigungsverfahren von Glucose‐6‐phosphat‐dehydrogenase (G6PDH) (E.C. 1.1.1.49) aus Rinder‐Nebennierenrinde wird durch eine einzige affinitätschromatographische Trennungsstufe ersetzt. Die Anwendung einer mit Nicotinamid‐Adenin‐Dinukleotid‐Phosphat (NADP) substituierten Sepharose ergibt aus dem Rohextrakt eine Protein‐Fraktion, aus welcher nach Einengen die G6PDH unmittelbar kristallisiert. Die Reinheit des Enzyms wird durch analytische Gel‐Elektrophorese sowie durch Vergleich mit schon bestehenden. Literaturdaten geprüft. Vier weitere NADP‐abhängige Dehydrogenasen werden im Eluat identifiziert und partiell gereinigt.
A Convenient Alkyl, Cycloalkyl and Aralkyl Disulfides Synthesis from Aliphatic and Aromatic Aldehydes, Aliphatic Ketones and Cycloketones
Authors: Israel Cohen Victor 
Published: December 2004

AbstractThe reaction of aliphatic and aromatic aldehydes, aliphatic ketones, and cycloketones with hydrogen sulfide in anhydrous pyridine tiethylamine medium, provides a satisfactory method for preparation of alkyl, cycloalkyl, and aralkyl disulfides.
Electron Spin Resonance of Oxiranyl Radicals in Solution: Configurational Stabilities and Rearrangement Reactions
Authors: Itzel Hanshelmut , Fischer Hanns 
Published: December 2004

AbstractSeveral alkyl substituted oxiranyl radicals derived by hydrogen abstraction from oxiranes are observed in solution by ESR.‐spectroscopy. The ESR.‐spectra demonstrate that oxiranyl radicals have pyramidal configurations at the radical carbon atom and undergo inversion. Alkyl substituted oxiranyls rearrange by ring opening to α‐keto alkyl radicals. The rates of inversion decrease and the rates of rearrangement increase with alkyl substitution. The activation parameters of these processes are given for several cases and are related to radical structure. Line broadening effects caused by inversion allow the determination of relative signs of γ‐CH3‐coupling constants.
Enaminosucres et sucres halogénoacétyléniques. Communication préliminaire
Authors: Tronchet Jean M. J. , Baehler Bruno , Bonenfant Alain 
Published: December 2004

Enamino‐ and Halogenoacetylenic sugarsTraitment of an aldehydosugar (1) with secondary amines gave in an essentially quantitative yield the expected enamines (4–6). Chloro‐ and bromo‐acetylenic sugars (11–14) were obtained in good yields by reacting with lithium methylphenylamide the corresponding gem‐dihalo‐olefinic sugars (7–10), whereas a Z‐gem‐fluoro‐enamine (17) was formed when the difluoro‐olefinic sugar 15 was submitted to the same reaction. The fluoro‐enamine 17 is a useful synthetic intermediate allowing the preparation of several kinds of C‐glycosylic compounds bearing heterocycles like isoxazole, chromone or coumarin.
The Clemmensen Reduction of α, β‐Unsaturated Ketones
Authors: Jefford Charles W. , Boschung André F. 
Published: December 2004

AbstractEleven structurally different α, β‐unsaturated ketones were subjected to the Clemmensen reduction under anhydrous conditions using amalgamated zinc, hydrogen chloride in a solution of ethyl ether, and acetic anhydride. In all cases but one the formation of cyclopropyl acetates was observed. 4‐Methyl‐3‐penten‐2‐one, methyl vinyl ketone, 2‐isopropylidene‐1‐cyclopentanone, and 2‐cyclohepten‐1‐one led to substituted cyclopropyl acetates. Stereospecific reactions were found with 2‐ethylidene‐1‐cyclopentanone, 2‐benzylidene‐1‐cyclohexanone, and methyl 1‐cyclohexenyl ketone, whereas 3‐penten‐2‐one, 3‐methyl‐3‐buten‐2‐one, and 2‐methyl‐2‐cyclohexen‐1‐one afforded mixtures of the isomeric cyclopropyl acetates.These results are interpreted in terms of the intital formation of an allylic anion which undergoes electrocyclic closure. A stereospecific course is followed when geometric constraints permitted. Exceptions are discussed.
Synthesen der diastereoisomeren Caparrapioxide
Authors: Lombardi Paolo , Cookson Richard C. , Weber Hans Peter , Renold Walter , Hauser Arnold , Schulte‐Elte Karl H. , Willhalm Bruno , Thommen Walter , Ohloff Günther 
Published: December 2004

Syntheses of Diastereoisomeric Caparrapi oxides.Two pathways have been developed for the synthesis of caparrapi oxide from the dihydroionones. The four diastereoisomeric racemates and their dehydro‐ and dihydro‐derivatives are described. NMR. spectra indicate that the sesquiterpene ethers having cis‐fused rings exist in two different conformations.
Stereoselective Syntheses of Benz[f]isoindoline‐Derivatives by Intramolecular Cycloadditions of Styrenes to Olefins
Authors: Oppolzer Wolfgang , Achini Roland , Pfenninger Emil , Weber Hans Peter 
Published: December 2004

AbstractThe N‐allyl‐N‐cinnamyl amide 10 undergoes thermal cyclization to a 2:1‐mixture of the trans‐ and cis‐benz(f)isoindolines 11a and 12a. By comparison, the thermolysis of the corresponding bis‐cinnamylamide 14 proceeds in a highly stereoselective manner to give the cis‐fused[4+2]‐adduct 16a. Similarly, the trans‐fused stereoisomeric adducts 30a and 31a were obtained with high stereochemical control on heating the N‐allyl‐N‐diphenylallyl amide 28. The thermal transformations 4 → 5+6a and 17 → 18a+20a show the competitive formation of [2+2]‐adducts. An alternative approach to (substituted) benz[f]isoindolines 16 via the all‐cis‐isomer 24a has been developed. The described structures have been assigned on the basis of spectral evidence, chemical correlations and by X‐ray‐diffraction study of the isomer 16b. These results illustrate the utility of substituent interactions in order to direct intramolecular cyclo‐additions at will towards either endo‐ or exo‐products.
Photochemische Reaktionen. 90. Mitteilung. Die UV.‐Bestrahlung von (E)‐5‐Isopropyl‐6‐methyl‐5,6‐epoxy‐hept‐3‐en‐2‐on
Authors: Eichenberger Herbert , Wolf Hans Richard , Jeger Oskar 
Published: December 2004

Photolysis of (E)‐5‐Isopropyl‐6‐methyl‐5,6‐epoxy‐hept‐3‐en‐2‐on.This paper continues the series of investigations of the photochemistry of α, β‐unsaturated γ, δ‐epoxy‐ketones, by examinating the photochemical behaviour of the aliphatic vinylogous epoxy‐ketone 1, the chromophore of which is structurally similar to that of γ, δ‐epoxy‐(E),β‐ionone (44).On π, π*‐excitation (λ = 254 nm) 1 isomerizes mainly to the enol‐ether 2 and gives as minor products the isomeric dihydrofurane 3, the 1,5‐diketones 4 and 5 and the 1,3‐diketone 6. To a smaller extent, 1 also undergoes photofragmentation to the furane 7, the allenyl‐ketone 8 and the cyclopropenyl‐ketone 9. On n,π*‐excitation (λ ≥ = 347 nm) 1 yields the photoisomers 3, 4, 5 and in traces the hydroxyallenyl‐ketone 14, but no fragmentation products. It is shown that on irradiation at λ ≥ = 254 nm the 1,5‐diketone 4 isomerizes to 5, 6 and 15 and photodecarbonylates to the β, γ‐unsaturated ketone 16.The isomers 3, 4 and 5, obtained both from n, π*‐ and π,π*‐excitation, represent products of cleavage of the C(γ)O‐bond in 1. The enolether 2, on the other hand, formed only by π,π*‐excitation, results from cleavage of the C(γ)C(δ)‐bond.Finally, the fragmentation products 7, 8 and 9, which could be detected only on π,π*‐excitation, may arise from a common intermediate g ↔ h.
Contribution à la phytochimie du genre Gentiana. XIV: Identification de nouveaux dérivés de l'isoorientine extraits des feuilles de Gentiana burseri LAPEYR (2e communication)
Authors: Luong Minh Duc , Hostettmann Kurt , Jacot‐Guillarmod André 
Published: December 2004

Phytochemistry of genus Gentiana XIV: Identification of new derivatives of iso‐orientin in the leaves of Gentiana burseri LAPEYR. 2nd Communication.Two new derivatives of iso‐orientin have been isolated and identified. The structures of the new compounds were established as: trans‐feruloyl‐2″‐iso‐orientin (1) and trans‐feruloyl‐2″‐iso‐orientin‐4′‐O‐β‐D‐glucoside (2).
Coordinating Abilities Towards Sodium of Oxygenated Solvents
Authors: Detellier Christian , Laszlo Pierre 
Published: December 2004

AbstractTetracoordination of the sodium cation is indicated by the 23Na‐NMR. chemical shifts for NaClO4 in binary mixtures of ether and alcohol solvents. Solvent exchange occurs by a sequential process, and involves one or several intermediates. In competition with tetrahydrofurfuryl alcohol, whereas glyme corresponds to monocyclic intermediates, diglyme and triglymeFor abbreviations see Table 1.
favor formation of bicyclic intermediates. The relevant conformational factors are analysed, and also serve to explain the better coordinating abilities of diglyme and triglyme, as compared to glyme. The mechanism for solvent exchange is discussed.
Methyl Substitution as a Probe for π‐Spin Distribution in the Radical Anion of 1,6‐Methano[10]annulene
Authors: Gerson Fabian , Müllen Klaus , Wydler Christoph 
Published: December 2004

AbstractESR. and ENDOR. spectra are reported for the radical anion of the 2‐methyl derivative (III) of 1,6‐methano[10]annulene (I). Comparison of the hyperfine data for I·⊖ and III·⊖ with those for the radical anions of naphthalene (II) and its 1‐methyl derivative (IV), respectively, confirms the suggestion that – despite the vastly different α‐proton coupling constants – the π‐spin distributions should be similar in the two series. This result provides further support for the view that the π‐spin distribution, in particular, and the cyclic π‐delocalisation, in general, are not seriously perturbed by moderate deviations of the π‐perimeter from planarity.
Dérivés C‐Glycosyliques XXXII. Synthèse de dérivés spiro‐C‐glycosylidéniques par cyclisation nucléophile. Communication préliminaire
Authors: Tronchet Jean M. J. , Gentile Bernard 
Published: December 2004

C‐Glycosylic derivatives XXXII. Synthesis of spiro‐C‐glycosylidenic derivatives via nucleophilic cyclization.On treatment with compounds bearing two nucleophilic groups as ethylenediamine, o‐phenylenediamine or their monooxa or monothia analogues, 1,2:5, 6‐di‐O‐isopropylidene‐α‐D‐ribo‐hexofuranos‐3‐ulose gave with excellent yields the corresponding spiro‐C‐glycosylidenic derivative; for example, when using o‐phenylenediamine, a spirobenzimidazoline (5) was obtained. The latter compound underwent, on oxidation, a ring expansion to a morpholinobenzimidazole (8). Spirobenzodiazepines, spirobenzooxazepines and spirobenzothiazepines were formed when applying the same type of cyclization reaction to 3‐C‐acetylmethylene‐3‐deoxy‐1,2:5,6‐di‐O‐isopropylidene‐α‐D‐ribo‐ and α‐D‐xylo‐hexofuranoses.
Photochemical reactions. VI. Photo‐Beckmann rearrangement with vinyl migration. Preliminary communication
Authors: Armengol Miguel , Coll Esperanza , Reixach María , Ribalta José M. , Repollés José , Bonet Juan‐Julio 
Published: December 2004

AbstractThe carefully controlled UV. irradiation of 3‐hydroxyimino‐Δ4‐ and 3‐hydroxyimino‐Δ4, Δ6‐steroids yield as a result of vinyl and alkyl migration, lactams besides products expected.
Medium Ring Compounds. XXIX. Cyclooctane‐1,5‐dione‐dioxime
Authors: Winkler Fritz K. , Seiler Paul , Chesick John P. , Dunitz Jack D. 
Published: December 2004

AbstractThe crystal structure of the title compound (orthorhombic a = 26.724, b = 10.899, c = 9.483 Å, space group Pna21, Z = 12) has been determined by X‐ray analysis. The structural units consist of hydrogen‐bonded trimers with approximate C3h symmetry. The results are discussed in relation to the Beckmann rearrangement of the title compound, which yields exclusively the mirror‐symmetric diamide.
The Electronic Structure of Azuleno[1,2,3‐cd]phenalene and Azuleno[5,6,7‐cd]phenalene, a Comparison
Authors: Gleiter Rolf , Spanget‐Larsen Jens , Thulstrup Erik W. , Murata Ichiro , Nakasuji Kazuhiro , Jutz Christian 
Published: December 2004

AbstractThe photoelectron (PE.) spectra of azuleno[l, 2, 3‐cd]phenalene (1) and azuleno‐ [5,6,7‐cd]phenalene(2) have been recorded. The first five bands of both compounds could be assigned to transitions corresponding to removal of electrons from 4a2, 6b1, 5b1, 3a2 and 4bl orbitals. This assignment is based mainly on a comparison between the observed ionization potentials and orbital energies calculated in a HMO and a PPP model.The UV./VIS. polarized absorption spectrum of 1 in the region 10000–45000 cm−1 has been measured by means of the stretched film technique. The measurements were performed in polyethylene sheets at 77°K. Several bands could be assigned to π* ← π transitions calculated by a PPP‐CI method.A comparison between the electronic structures of 1 and2 is made by means of a simple HMO diagram.
Komplexone XLVII. The Stability of Palladium(II) Complexes with Aminopolycarboxylate Anions
Authors: Anderegg Giorgio , Malik Subhash C. 
Published: December 2004

AbstractThe formation of Pd(II) complexes with aminopolycarboxylate anions has been investigated using pH and UV.‐spectrophotometric measurements at ionic strength 1 M and 20°. In some cases bromide or thiocyanate ions have been used as auxiliary ligands. Pd2+ forms the strongest complexes of the hitherto investigated divalent metal ions. The stability constants are discussed in relation to the particular stereochemistry of Pd(II) complexes.
Zum Mechanismus der photochemischen Umwandlung von 2‐Alkyl‐indazolen in 1‐Alkyl‐benzimidazole. I. Struktur und Reaktivität eines Zwischenproduktes
Authors: Heinzelmann Willy , Märky Michael , Gilgen Paul 
Published: December 2004

Mechanistic studies on the photoisomerization of 2‐alkyl‐indazoles into 1‐alkyl‐benzimidazoles. I. Structure and reactivity of an intermediate.2‐Alkyl‐indazoles (1) undergo photochemical isomerization to 1‐alkyl‐benzimidazole via previously unknown intermediates 3 (Scheme 1). In the present paper the structure and reactivity of these intermediates are discussed. Low‐temperature irradiation (−60°) of 1 b with 300 nm light gives 3 b in quantitative yield. 3 b is transformed during warm‐up to 1 b and 2 b (UV.‐evidence). The formations of 1 and 2 show the same temperature dependence but their ratio is found to be temperature‐independent. In contrast to the above behaviour, low‐temperature irradiation with 250 nm light of 3 b yields 1 b only (no 2 b). These findings are consistent with the proposed reaction mechanism 2 c in Scheme 2.On the basis of spectroscopic properties and the described reaction pathways, it appears that the most suitable structure for intermediate 3 is a 7,8‐diaza‐tricyclo[4.3.0.07,9]nona‐2,4,6(10)‐trien (9). In Scheme 4 the reaction pathway for the iudazole‐benzimidazole‐rearrangement is summarized.
Contribution to the Problem of Nucleophilic Substitution Reactions at Small‐Ring Carbon Atoms Occurring with Retention of Configuration
Authors: Gray Robert W. , Chapleo Christopher B. , Vergnani Tiziana , Dreiding André S. , Liesner Michael , Seebach Dieter 
Published: December 2004

Beitrag zum Problem der nucleophilen Substitutionsreaktionen am Kohlenstoffatom kleinerer Ringe mit Retention der Konfiguration.Mit Natriumiodid und mit Tetraäthylammoniumacetat in Aceton findet auch unter energischen Bedingungen keine nukleophile Substitution des Bromatoms in 4‐endo‐Brom‐1,3,5,7‐tetramethyl‐anti‐tricyclo[5.1.0.03,5]octane‐2,6‐dion (10) statt, obschon bei 10 – nach neueren Anschauungen – gute Voraussetzungen für eine solche Reaktion vorhanden sein sollten. Dies bestätigt die bekannte Trägheit von Dreiring‐Kohlenstoffatomen gegenüber SN2‐Reaktionen und erhöht die Wahrscheinlichkeit, dass trotz der verwendeten Bedingungen die relativ schnellen Substitutionen der Bromatome in den Ketonen 6 und 7 durch Acetat unter Retention der Konfiguration nicht SN2‐Reaktionen sind. Ein Alternativmechanismus mit vorübergehender Öffnung des Dreirings wird für diese Umwandlungen in Betracht gezogen, und zwar 6 → 11 → 8 und 7 → 12 → 9.