bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simple Conversion of Colchicine into Demecolcine
Authors: Capraro Hans‐Georg , Brossi Arnold 
Published: December 2004

AbstractN‐Deacetylcolchiceine (7), readily available from colchicine (1), was converted into N‐trifluoroacetyl‐deacetylcolchiceine (8). Methylation of 8 with methyl iodide in the presence of potassium carbonate afforded a mixture of N‐trifluoroacetyl‐demecolcine (10) and its isomer 11. The mixture of 10 and 11 was detrifluoroacetylated and separated by chromatography to afford demecolcine (2) and isodemecolcine (12). A more practical route to 2 started with 8, and gave N‐trifluoroacetyl‐deacetylcolchicine (13) and its isomer 14 after O‐methylation with diazomethane. N‐Methylation of 13 and 14 with methyl iodide and potassium carbonate afforded 10 and 11. The overall yield in the conversion of colchicine (1) into demecolcine (2) via 7, 8 and 13 was 55%.
New Olefinic Cyclizations by Oxymetallation. Conversion of (−)‐elemol to (−)‐selina‐4α, 11‐diol (cryptomeridiol) and (−)‐guai‐1 (10)‐ene‐4α, 11‐diol
Authors: Renold Walter , Ohloff Günther , Norin Torbjörn 
Published: December 2004

AbstractAcetoxythallation of (−)‐elemol acetate (1b) yields a diacetate 2b which after treatment with lithium aluminium hydride gives (−)‐guai‐1 (10)‐ene‐4α, 11‐diol (2a). (−)‐Elemol (1a) is converted to (−)‐selina‐4α, 11‐diol (9, cryptomeridiol) by hydroxymercuration followed by reductive demercuration. (+)‐γg‐Elemene (5) similarly yields (+)‐selin‐7(11)‐en‐4α‐ol (11, juniper camphor). The stereochemistry and mechanism of these metal salt‐induced olefinic cyclization and their biogenetic implication are discussed.
Crystal Structures of the (−)‐DIOP Complexes of Nickel, Palladium and Platinum Dichloride
Authors: Gramlich Volker , Consiglio Giambattista 
Published: December 2004

AbstractThe crystal structures of PdCl2[(−)‐DIOP], PtCl2[(−)‐DIOP] and of NiCl2‐[(−)‐DIOP] have been determined by X‐ray analysis and refined by least‐squares methods [(−)‐DIOP=(−)‐2,2‐dimethyl‐4,5‐bis(diphenylphosphinomethyl)‐1,3‐dioxolane]. The coordination around the nickel atom is tetrahedral, the coordination around palladium and platinum is square planar. The unit cell of the palladium complex contains two non‐equivalent molecules with different conformations of the seven‐membered chelate ring involving the metal and the two phosphorus atoms. PtCl2[(−)‐DIOP] is isostructural with the corresponding palladium complex.
Charge‐Transfer‐Übergänge im Pentacyano‐benzonitril‐ferrat (II)
Authors: Calzaferri Gion , Grüniger Hans‐Rudolf 
Published: December 2004

Charge Transfer Transitions of Pentacyano‐Benzonitrile‐Ferrate(II)Pentacyano‐benzontrile‐ferrate(II) shows two charge transfer transitions, which are interpreted as central atom to benzonitrile transitions d‐1π* and d‐2π*. Selective excitation to the d‐1π* state leads to a completely reversible photoreaction. An isosbestic point is observed at 398 nm in aqueous solution.
Intramolekulare Inversionssubstitution am Dreiring von 77exo‐Brombicyclo[4.1.0]heptan‐3endo‐ol unter Bildung eines Tetrahydrofuranringes
Authors: Seebach Dieter , Neumann Helmut , Dammann Reinhard 
Published: December 2004

Intramolecular Substitution under Inversion at the Threemembered Ring of 7exo‐Bromobicyclo[4.1.0]heptan‐3endo‐ol yielding a Tetrahydrofuran RingThe reaction 1a → 2a involving substitution at a cyclopropane carbon atom can be observed only with the bromophilic alkyllithium reagents but not with the bases lithium diisopropyl amide (LDA) (Table 1) or potassium t‐butoxide (KTB). The mechanism must be an insertion as outlined in Scheme 1. ‐ The monobromides 1b, 1c and 1d are prepared stereoselectively from the acetal 3a. Again, cyclization of 1b takes only place with LDA in the presence of alkyllithium (Table 2, entries 1‐‐4) suggesting an insertion mechanism (route (a) or (b) in Scheme 2). In contrast, KTB effects the substitution in high yield with no loss (from 1c) or incorporation of deuterium at the cyclopropane substitution center (Table 2, entries 5‐‐7); the possibility is discussed that this process is an SN2‐type reaction.
Intramolecular de Mayo Reactions of 3‐Acetoxy‐2‐alkenyl‐2‐cyclohexenones. Preliminary communication
Authors: Oppolzer Wolfgang , Bird T. Geoffrey C. 
Published: December 2004

AbstractThe photoaddition, hydrolysis, retro‐aldol sequences 1 → 2 → 3 and 4 → 5 + 6 → 7 proceeded in high yield and in a regiospecific manner. However, the enol acetate 8 on irradiation furnished the tricyclic ketoacetate 9 as the major product, presumably by a hydrogen shift in the intermediate diradical 11. Hydrolysis of the minor photoadduct 10 gave the dione 13.
Cyclopeptid‐Antibiotika aus Aspergillus‐Arten. Struktur der Echinocandine C und D
Authors: Traber René , Keller‐Juslén Camilla , Loosli Hans‐Rudolf , Kuhn Max , Von Wartburg Albert 
Published: December 2004

Cyclopeptide antibiotics from Aspergillus species. Structure of echinocandins C and DThe echinocandins B, C and D are antifungal antibiotics produced by a strain of Aspergillus rugulosus. All three metabolites are closely related representing cyclic oligopeptides composed of six amino acids and a linolic acid residue in an amide linkage. The complete structure of echinocandin B (1) has recently been established by X‐ray analysis. Structural assignments to the new minor metabolites C and D have now been made by hydrolytic and oxidative cleavage reactions, formation of N‐acyl‐α‐aminoethers as well as by chemical correlations and extensive NMR. examinations. Echinocandin C (2), C52H81N7O15, contains 3‐hydroxyhomotyrosine in the place of 3, 4‐dihydroxyhomotyrosine present in 1. Echinocandin D (3), C52H81N7O13, differs in two amino acids: 3, 4‐dihyroxyhomotyrosine and 4, 5‐dihydroxyornithine, unusual units of 1 being replaced by 3‐hydroxyhomotyrosine and ornithine.
Dérivés de sucres benzimidazoliques et benzothiazoliques
Authors: Tronchet Jean M. J. , Gentile Bernard 
Published: December 2004

Benzimidazole and benzothiazole sugar derivativesSimple aldehydosugars such as 1 or 2, by reaction with o‐phenylenediamine, gave the corresponding benzimidazoles 3 and 4. Whereas the unperturbed α, β‐unsaturated aldehydosugar D gave the benzodiazepine E upon treatment with o‐phenylenediamine, the formyl‐bearing alkenyl acetals 5 and 8 led, in the same conditions, to the benzimidazoles 6 and 9 respectively or, on reaction with o‐aminothiophenol, to the benzothiazoles 7 and 10 respectively. This difference in reactivity is explained by the electrondonor ability of the oxygen atom of the alkenyl acetal function as shown by the 13C‐RMN. spectra.
24‐Isopropylcholesterol and 22‐Dehydro‐24‐isopropylcholesterol, Novel Sterols from a Sponge
Authors: Hofheinz Werner , Oesterhelt Gottfried 
Published: December 2004

Abstract24‐Isopropycholesterol (1) and 22‐dehydro‐24‐isopropylcholesterol 2 have been isolated as the only sterols from an Australian sponge of the genus Pseudaxinyssa. Structures have been deduced from spectroscopic data.
Propellanes. L. Further support for control by secondary orbital overlap during Diels‐Alder reactions of certain propellanes,
Authors: Kaftory M. , Peled M. , Ginsburg D. 
Published: December 2004

AbstractIn contrast to the behavior of 4‐substituted‐1,2, 4‐triazoline‐3, 5‐diones which add to the syn‐face of the cyclohexadiene with respect to the hetero‐ring in propellanes of type 1, dienophiles containing a C, C double bond instead of an N, N double bond add exclusively to the anti‐face of the same substrates. This supports our thesis that these reactions are controlled by secondary orbital interaction between the N, N dienophiles and the hetero‐ring of the substrates, an interaction which cannot exist in the C, C dienophiles.
Polar Substituent Effects in the Solvolysis of Primary and Tertiary Alkyl Halides. Polar Effect IX
Authors: Grob Cyril A. , Waldner Adrian 
Published: December 2004

AbstractWhen the Hammett‐Taft equation log (k/ko)=ρq · σ is applied to the solvolysis of the 3‐substituted propyl bromides 6a‐6i in ethanol/water 4:1 (v/v) log k correlates linearly with σ except in cases where R exerts an anchimeric effect. The reaction constant ρq for 6 is − 0.12 and is typical for a nucleophilic solvent‐assisted ks process at a primary C‐atom. The tertiary halides 1 and 3, however, which react with little or no nucleophilic solvent assistance, i.e. by kc processes, lead to larger ρq values of −0.71 and −1.14, respectively. The reaction constant pq is therefore a sensitive gauge for charge development in the transition state for solvolysis of saturated compounds.
Micellar Solubilization of Biopolymers in Hydrocarbon Solvents III. Empirical Definition of an Acidity Scale in Reverse Micelles
Authors: Smith Robert E. , Luisi Pier L. 
Published: December 2004

AbstractThis paper deals with the problem of defining, and measuring, the pH inside the water pool (which we define as pHwp) of reverse micelles, i.e. micelles formed by surfactants dissolved in apolar solvents in the presence of minimal amounts of water. The conceptual and experimental difficulties are discussed, and it is argued that no absolute determination of pHwp is possible, mostly because water in the water pools of reverse micelles is a new solvent, for which no standardization of acidity is available. The problem can be approached only on the basis of an empirical acidity scale.An empirical acidity scale for water pools in reverse micelles of bis (2‐ethyl‐hexyl) sodium sulfosuccinate (AOT) in isooctane has been defined by measuring the 31P‐chemical shifts of phosphate buffers. The chemical shifts in bulk water were compared to those found in reverse micelles under the assumption that the pK of phosphate ion is the same in the two systems. It was found that in most cases there was little difference (less than 0.4 pH units) between pHwp and the pH of the starting buffer in bulk water (which we define as pHst). However, this difference between pHwp and pHst may become much larger in certain cases.The difference (pHwp–pHst) is measured under a variety of conditions, and this permits the determination of an operational acidity in the micelle water pools as a function of the pHst with which the aqueous micelles are prepared. The significance of such data for interpreting the behaviour of enzymes confined in the micelles water pool is discussed. Based on the pHwp scale, the apparent pKa of phenol‐red and 4‐nitrophenol were determined in reverse micelles containing different buffers and different water content. The pKa values obtained were rather sensitive to changes of both these factors, which was taken to signify that organic dies have only a very limited applicability to measure the acidity of the water pools of reverse micelles.
Iodine Oxidation of S‐Trityl‐ and S‐Acetamidomethyl‐cysteine‐peptides Containing Tryptophan: Conditions Leading to the Formation of Tryptophan‐2‐thioethers
Authors: Sieber Peter , Kamber Bruno , Riniker Bernhard , Rittel Werner 
Published: December 2004

AbstractCystine peptides are conveniently prepared from S‐acetamidomethyl‐ or S‐trityl‐protected cysteine derivatives by direct oxidation with iodine. Since the reaction proceeds through the formation of sulfenyl iodides, these highly reactive groups may substitute the indole ring of tryptophan residues, resulting in the formation of 2‐thioethers. During the synthesis of the peptide hormone somatostatin, we investigated this possible side reaction. By‐products of the tryptophan‐2‐thioether type can be produced under conditions which lead to a marked retardation of the disulfide bond formation. The largest amount of these compounds were formed when the oxidation was carried out in 90% aqueous trifluoroethanol.In model peptides in which tryptophan and cysteine residues were separated by 1 to 4 glycine residues, the ring size of the resulting thioether exerted a strong influence on the yield: in peptides with 1 and 2 glycines, only dimeric disulfides were formed. Incorporation of 3 and 4 glycine residues gave thioethers in yields of about 40% and 70% respectively. Conversely, under normal conditions of iodine oxidation, when disulfides are rapidly formed from the S‐acetamidomethyl‐ or S‐tritylcysteine residues, tryptophan‐2‐thioethers are produced only in insignificant amounts or not at all.
Synthese von (±)‐Diplodialid B und A
Authors: Shenvi Ashokkumar B. , Gerlach Hans 
Published: December 2004

Synthesis of (±)‐Diplodialide B and ATwo steroid hydroxylase inhibitors, diplodialide B (1) and A (2) have been synthesized in the following way: The lithium enolate 5 of S‐t‐butyl thioacetate (4) was added to (E)‐7‐(2′‐tetrahydropyranoxy)‐2‐octen‐1‐al (8) and the newly formed 3‐hydroxy group in the product 9 was protected as t‐butyl‐diphenyl silyl ether followed by selective hydrolysis of the tetrahydropyranyl ether to give 10. Treatment with AgNO3/H2O cleaved the S‐t‐butyl ester group in 10 to give the corresponding hydroxy carboxylic acid which was converted into the S‐2‐pyridyl thioester by treatment with di(2‐pyridyl)disulfide and triphenyl phosphine and cyclized with AgClO4 to give the (4E,3,9‐trans)‐ and (4E,3,9‐cis)‐lactone 11 and 12 (Rt‐Bu(C6H5)2Si) in 67% yield. Chromatographic separation of 11 and 12 and cleavage of the t‐butyl‐diphenyl silyl ether with tetrabutyl ammonium fluoride yielded (±)‐diplodialide B (1) with (4E,3,9‐trans)‐configuration and the (4E,3,9‐cis)‐isomer 12 (RH). Both isomers could be oxidized to diplodialide A (2) with manganese dioxide. The synthesis described above has also been carried out via the intermediates 10, 11 and 12 with RCOOCH2CH2Si(CH3)3.
Photochemical High‐yield Preparation of Tricyclo [3.3.0.02,8]octan‐3‐ones. Potential Synthons for Polycyclopentanoid Terpenes and Prostacyclin Analogs. Preliminary Communication
Authors: Demuth Martin , Raghavan Palaykotai R. , Carter Charles , Nakano Koichi , Schaffner Kurt 
Published: December 2004

AbstractThree‐step syntheses and the resolution into the enantiomers are reported for the tricyclo[3.3.0.02,8]octan‐3‐ones 7–9, which are destined to serve as synthons for polycyclopentanoid terpenes and prostacyclin analogs. Routine overall yields of ca. 75% for 7, 40% for 8, and 46% for 9 are obtained, with 2‐chloroacrylonitrile and 1,3‐cyclohexadiene (for 7) and 1‐methyl‐1,4‐cyclohexadiene (for 8 and 9) as the starting materials. The key step is the triplet‐sensitized oxadi‐π‐methane photorearrangement of the β,γ‐unsaturated ketones 1–3 which can be achieved in 80–90% yields of isolated product and quantum yields of 0.5–1.0. The racemates of both ketone 1 and its photoisomer 7 have been resolved via chromatographic separation of suitable diastereoisomeric acetal mixtures. On the other hand, sensitization of 1 with an optically active donor, (‐)‐14, gave only an impractical maximum enantiomeric excess of 10% (‐)‐7.
Methyl‐triisopropoxy‐titanium, a highly selective nucleophilic methylating reagent. Preliminary Communication
Authors: Weidmann Beat , Seebach Dieter 
Published: December 2004

AbstractReplacement of lithium or magnesium by titanium can furnish nucleophilic organometallic reagents of high selectivity as exemplified by the title compound 1 (see Tables 1–3).
The Synthesis of Stereoisomers of Arteannuin B
Authors: Goldberg Ora , Deja Irena , Rey Max , Dreiding André S. 
Published: December 2004

AbstractDie Synthese von Stereoisomeren des Arteannuins BWir beschreiben die Synthese von drei rac‐Diastereomeren 7A‐7C des Sesquiterpenlaktons Arteannuin B (I) auf dem in den Schemata 2 und 3 zusammengefassten Weg. Als Schlüsselstufe für den Aufbau des Ringsystems 6 wurde eine intramolekulare Reformatsky‐artige Reaktion verwendet, in der gleichzeitig ein Cyclohexanring und ein α‐Methylidenbutyrolaktonring gebildet werden (Schritte 3 und 6). Die Cyclisierung von 5A bzw. 5B oder von 9/10 führte vorwiegend zur cis, cis‐Verknüpfung der drei Ringe A/B/C, wie in 6A bzw. 6B. Daneben entstand aus 5B auch das trans, cis‐System 6C. Die Verlängerung der Seitenkette in 1A,B unter Ausbildung der für die Reformatsky‐artige Reaktion notwendigen Funktionalität (in 5 bzw. 9/10) wurde nach zwei Methoden ausgeführt, welche in den Schritten 1, 2 bzw. 5 beschrieben sind. Die Epoxydierung von 6A, 6B bzw. 6C zu 7A, 7B bzw. 7C (Schritt 4) war vollkommen regio‐ (an C(7′), C(8′)) und stereospezifisch. Die relative Konfiguration an den Zentren C(1′), C(4′), C(4a′) und C(8a′) der drei Diastereomeren A, B bzw. C von 6 und 7 wurde anhand der 1H‐NMR‐Spektren abgeleitet.
Microbial transformation of cannabinoids. Part 3: Major metabolites of (3R, 4R)‐Δ1‐tetrahydrocannabinol
Authors: Binder Michael , Popp Astrid 
Published: December 2004

AbstractThe metabolic transformations of the psychotropic cannabinoid (3R, 4R)‐Δ1‐tetrahydrocannabinol (5) (=Δ1‐THC) by cultures of Fusarium Nivale, Gibberella fujikuroi (both Ascomycetes) and Thamnidium elegans (Phycomycetes) were investigated. A number of metaboilites, 1–4 and 6–9 were isolated from the incubations, partly purified and their structures elucidated by combined gas chromatography/mass spectrometry. Four of these metabolites, 1″‐hydroxy‐Δ1‐THC (4) 2″‐hydroxy‐β1‐THC (1) 6Δ‐hydroxy‐ζ1‐THC (8) and 2″,6Δ‐dihydroxy‐Δ1‐THC (9) so far have not been reported as microbial transformation products of 5.
Mimulaxanthin, Hauptcarotinoid von Lamium montanum, und seine absolute Konfiguration; konfigurative Verknüpfung von Deepoxyneoxanthin mit Neoxanthin
Authors: Buchecker Richard , Eugster Conrad Hans 
Published: December 2004

Mimulaxanthin, the Main Carotenoid in Lamium montanum, Determination of its Absolute Configuration. Absolute Configuration of Deepoxyneoxanthin by its Correlation with NeoxanthinThe carotenoid mixture isolated from the yellow flowers of Lamium montanum PERS. (Labiatae) consists of more than 75% of carotenoids with allenic end groups. Besides 32% of neoxanthin/neochrome we isolated 44% of mimulaxanthin (1a), a very rare carotenoid so far only found in Mimulus sp. (Scrophulariaceae). Its absolute configuration was determined by oxidative degradation to the known ketone 3 (‘grasshopper ketone’) and by spectroscopic and chiroptical comparisons with neoxanthin (6). Mimulaxanthin (1a) therefore is (3S, 5R, 6R, 3′S, 5′R, 6′R)‐6,7,6′,7′‐tetradehydro‐5,6,5′,6′‐tetrahydro‐β, β‐carotene‐3,5,3′,5′‐tetraol. Deep‐oxyneoxanthin, which was reisolated from Mimulus sp. is (3S, 5R, 6R, 3′R)‐6,7‐didehydro‐6,7‐dihydro‐β, β‐carotene‐3,5,3′‐triol (2), as shown by spectroscopic and chemical correlation with neoxanthin (6; de‐epoxydation by BuLi/FeCl3).
The Synthesis of 4‐Decarboxy‐4‐phosphono‐O‐2‐isooxacephems, ‐isopenams and ‐isooxacephems Containing Phosphorus at the 3‐Position
Authors: Hakimelahi Gholam Hosein , Just George 
Published: December 2004

AbstractTwo new types of iso‐oxacephems have been synthesized in which a phosphonate group replaces either the carboxyl group or C(3). The latter compound exists as a stable trialkoxyphosphonium ylide.Potassium thioacetate and O2 in DMF are transformed in an autocatalytic, probably sulfur‐catalyzed process to CH3COOK and sulfur; the latter two reagents are sufficient to transform the methanesulfonate 7 to the isopenam 15.
High‐Pressure 17O‐NMR. Study of Vanadium (II) in Water: A Second Example of an Associative Interchange Mechanism (Ia) for Solvent Exchange on an Octahedral Divalent Transition‐Metal Ion
Authors: Ducommun Yves , Zbinden Donald , Murbach André E. 
Published: December 2004

AbstractThe water exchange of [V(H2O)6]Cl2 in aqueous solution has been studied as a function of temperature and pressure (up to 250 MPa), by measuring the 17O‐FT‐NMR. line‐widths of the free water resonance at 8.13 MHz. The kinetic parameters obtained are K = 87±4 s−1, ΔH* = +61.8 ± 0.7 kJ mo1−1 and ΔS* = −0.4±1.9 J mol−1 K−1. A pressure‐independent volume of activation ΔV* = −4.1±0.1 cm3 mol−1 is obtained, suggesting an associative interchange (Ia) mechanism for this early divalent metal ion.
Neue Synthesen von 1α,25‐Dihydroxycholesterin
Authors: Färst Andor , Labler Ludvik , Meier Werner 
Published: December 2004

New Syntheses of 1α,25‐DihydroxycholesterolFive convergent syntheses of 1α,25‐dihydroxycholesterol (2) essentially achieved by combining 1α‐hydroxylated C21− and C22−steroids with C4− or C5−side‐chain building blocks, are described. The l,3‐bis(tetrahydropyranyloxy)pregnen‐21‐ol‐Ptoluenesulfonate (4) was used as a C22−unit in three approaches involving sulfone 24 as a C4−, sulfone 43 and 2‐propynyl ether 49 as C5−side‐chain building blocks. In a further preparation, the 1,3‐diacetoxypregnen‐21 ‐al 5 and the phosphorane 59, a C22− and a C5−unit, respectively, were connected. For the last one, the 1,3‐bis(tetrahydropyranyloxy)pregnen‐20‐one (6), a C2l−unit and the C5−phosphorane building block 66 were chosen. Furthermore, new routes for the preparation of the 3‐hydroxy‐27‐norcholestenone (29) and of 25‐hydroxycholesterol (3) are described for which the p‐toluenesulfonates 21 and 23 served as the steroidal units and the sulfones 24 and 43, respectively, as the side chain fragments. Finally, the 1,3‐diacetoxypregnen‐21‐al (5) and the C5‐phosphorane unit 60 gave a novel approach to 1α‐hydroxycholesterol (53).
Synthese von 5,6‐Epimino‐5,6‐dihydro‐β‐jonon
Authors: Müller Ernst Peter 
Published: December 2004

Synthesis of 5,6‐Ephnino‐5,6‐dihydro‐β‐iononeIn order to synthesize the title compound 5 the 2‐azidoalcohols 3 and 4 were treated with various nucleophilic phosphorus compounds. It was found that the course of the reaction depends strongly upon the kind of nucleophilic phosphorus derivative used.
Organization of Carotenoid‐Phospholipid Bilayer Systems. Incorporation of Zeaxanthin, Astaxanthin, and their C50 Homologues into Dimyristoylphosphatidylcholine Vesicles
Authors: Milon Alain , Wolff Geneviève , Ourisson Guy , Nakatani Yoichi 
Published: December 2004

AbstractFour carotenoids (zeaxanthin 1, astaxanthin 2, and their C50 synthetic isoprene‐homologues 3 und 4) have been incorporated into bilayer unilamellar vescles of dimyristoylphospatidylcholine as proved by coelution on a Sepharose column. The incorporation into the bilayer proper has been proved by the sensitivity to phase transition of UV/VIS spectra and circular dichroism. The UV/VIS absorptions of the carotenoids are typical of a lipidic environment. At the temperature of phase transition occur both intermolecular phenomena (aggregation of carotenoid molecules) and intramolecular changes (conformational change). The relative solubilities of the various carotenoids in this phospholipid membrane can be fitted with molecular parameters (length of the lipophilic carotenoid segment vs. lipid bilayer thickness).
Synthesis and Properties of 1,5‐Dimethyltricyclo[3.3.0.02,8]octane‐ and 1,5‐Dimethyltetracyclo[3.3.0.02,804,6]octane Derivatives
Authors: Gleiter Rolf , Jähne Gerhard , Müller Georg , Nixdorf Matthias , Irngartinger Hermann 
Published: December 2004

AbstractThe synthesis of 1,5‐dimethyltricyclo[3.3.0.02,8]octane‐3,7‐dione (2), 1,5‐dimethyltetracyclo[3.3.0.02,804,6]‐octane‐3,7‐dione (3), the corresponding dienes 5 and 6 as well as the mixed enones 13–15 is reported. Using He(I) photoelectron spectroscopy (PE) as a tool, a considerable interaction between the n orbitals on the O‐atoms and the σ frame in 2 and 3 as well as of the double bonds in 5 and 6 and the σ frame is found. These interactions are also traced back by the electronic absorption spectra of these compounds. The molecular structures of 2 and 3 have been investigated by X‐ray analysis.