bluuebunny/crossref_metadata_2025_split huggingface dataset:
Acid‐Catalysed Dehydration of Tricyclic Unsaturated Alcohols
Authors: Hayakawa Kenji , Schmid Hans 
Published: December 2004

AbstractThe tricyclic alcohols 3–7, derived from the corresponding ketones 1 and 2 (Scheme 1), by action of acids underwent dehydration with skeletal rearrangements. Dehydration of 3 and 4 with POCl3/pyridine (procedure A) afforded the polycyclic hydrocarbons 9, 10, and 12, 13, respectively. With TsOH (procedure B), on the other hand, 3 and 4 gave homo‐triquinacenes 10 and 14 respectively, as well as the polycyclic ethers 11 and 15 (Scheme 2). Hydrocarbon 9 (or 12) was converted into 10 FSO3H to the tertiary alcohol 16 (Scheme 4). Plausible mechanisms for these transformations are summarized in Scheme 8. Dehydration of the secondary alcohols 5 and 7 was effected by procedure A. While treatment of alcohol 5 with POCl3/pyridine yielded two isomeric hydrocarbons 17 and 18, similar dehydration of its epimeric alcohol 7 afforded hydrocarbon 21 as the sole product. The tertiary alcohol 6 was dehydrated by both procedures to yield two isomeric hydrocarbons 19 and 20 (Scheme 5). Hydrocarbon 20 was converted into 19 by procedure B (mechanisms, Scheme 10). Reaction of ketone 2 with CF3COOH gave the addition product 22 converted into vinylsulfonyl fluorides 24 and 25 by treatment with FSO3H (Scheme 6). Homo‐triquinacenes 10 and 14 reacted smoothly with 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione to give the ‘ene’‐reaction products 26 and 27, respectively.
Über Reaktionen oxygenierter Kobalt(II)‐Komplexe. IX. Oxydative Eigenschaften von Tetrakis(äthylendiamin)‐μ‐peroxo‐μ‐hydroxo‐dikobalt(III)
Authors: Brüstlein‐Banks Pauline , Fallab Silvio 
Published: December 2004

Reactions of oxygenated cobalt(II) complexes. IX. Oxidative properties of tetrakis(ethylenediamine)‐μ‐peroxo‐μ‐hydroxo‐dicobalt(III)VIII s. [1].
[(en)2Co(O2, OH)Co(en)2]3+ (a) reacts with I− in acidic aqueous solution according to: CoIII(O2, OH)CoIII + 21− + 5H+ ⇀ 2CoIII + 3H2O + I2. Using I− in excess first order rate constants are obtained which, to a first approximation, are independent of [I−]. Comparison with kinetic data of deoxygenation of [(en)2Co(O2, OH)Co(en)2]3+ under analogous conditions suggests that both reactions have the same rate determining step. The singly bridged species [(en)2(H2O)CoO2Co(H2O) (en)2]4+ is shown to be the reactive intermediate in the iodide oxidation (Schema 2).
Stereospecific Formation of Pentaamine Complexes of Co(III) with Terdentate 2,6‐Bis(aminomethyl)pyridine
Authors: Tinner Ursula , Marty Werner 
Published: December 2004

AbstractSome pentaamine complexes of Co(III) with 2,6‐bis(aminomethyl)pyridine (bamp), a diamine ligand (or two ammonia ligands) and one unidentate ligand have been prepared (Table 1). In all these species, bamp remains coordinated meridionally under a variety of conditions as shown by 1H‐ and 13C‐NMR. spectroscopy and correlations by stereoretentive reaction cycles. The rates of amine proton exchange and of spontaneous aquation, Hg2+‐induced aquation and base hydrolysis of some chloropentaamine complexes have been determined. They essentially follow the patterns observed for complexes with purely aliphatic amine ligands; the presence of a pyridine donor in these complexes does not suggest deviations from the mechanistic schemes usually proposed for the solvolytic reactions investigated.
The Ionization Energies of Di‐n‐Alkyl Diacetylenes
Authors: Heilbronner Edgar , Jones Taylor B. , Maier John P. 
Published: December 2004

AbstractThe He(Iα) photoelectron spectra and the ionization energies of symmetrically substituted di‐n‐alkyl‐diacetylenes R‐(CC)2‐R (with R  CH3, C2H5, n‐C3H7, n‐C4H9) are presented. The effect of the alkyl substitutents is that the two acetylenic ionization energies, Iv,1 and Iv,2, shift by the same amount, i.e. their difference Iv,2 – Iv,1 remains constant (2.45 ± 0.05 eV). Between 12.5 eV and 17 eV the band system in the photoelectron spectrum of R‐(CC)2‐R is superimposable with that in the spectrum of the corresponding alkane, RH, with the exception of a uniformly small shift of all the bands to higher ionization energy.
Die Carotinoide der Blüten von Rosa foetida
Authors: Buchecker Richard , Eugster Conrad Hans 
Published: December 2004

Carotenoids in petals of Rosa foetidaThe petals of Rosa foetida, HERRM., a species of prime importance in the history of breeding true yellow garden roses, have been analysed for carotenoids for the first time. The following components were identified: β‐carotene (1, 4,5%), lutein (2, 8%), zeaxanthin (3, 17,4%), auroxanthin (4, 30,8%), luteoxanthin (5, 21,9%), violaxanthin (6, 9,2%) and neochrome (7, 4,1%). Not identified carotenoids (4,1%) contained probably mutatoxanthin, antheraxanthin and apocarotenals. Thus the brillant yellow colour of R. foetida flowers is due mainly to carotenoid epoxides.
Säurekatalysierte Umlagerungen von 1,5‐Dimethyl‐6‐methyliden‐tricyclo[3.2.1.02,7]oct‐3‐en‐8endo‐olen
Authors: Mukherjee‐Müller Gabriele , Gilgen Paul , Zsindely Janos , Schmid Hans 
Published: December 2004

Acid Catalysed Rearrangement of 1,5‐Dimethyl‐6‐methyliden‐tricyclo[3.2.1.02,7]oct‐3‐en‐8endo‐olsThe tricyclic alcohols 2,3,4 and 6 (Scheme 1) are synthesized by the reaction of the tricyclic ketone 1 with sodiumborohydrid or metalloorganic reagents. Their configuration at C(8) is determined by NMR. in the presence of Eu(fod)3. The exo‐attack of 1 by the nucleophil forming the endo‐alcohol is favored, the π‐electrons of C(3) = C(4) hindering the endo‐attack. On treatment with sulfuric acid in dioxane/water at 25° the tertiary alcohols yield aryl‐substituted ketones. 3 gives in 78.5% yield a mixture of the 3‐(dimethylphenyl)‐2‐butanones 12 and 13, in addition to 16.5% of (2,3,4‐trimethylphenyl)‐2‐propanon (14) (Scheme 2). The alcohols 4 and 6 yield mixtures of the 2‐(dimethylphenyl)‐3‐pentanones 19 and 20 (72%), and 2‐(dimethylphenyl)‐propiophenones 21 and 22 (68%), respectively (Scheme 2). In the case of the secondary alcohol 2 mainly products derived from hydration at the C(6), C(9) double bond are formed, namely the mixture of diols 23 and 24 (21%), and the mixture of the isomeric 2‐(dimethylphenyl)propanals 25, 26 and 27 (3%) (Scheme 3). ‐ The structures of 12–14, 19/20, 21/22, 23/24 and 25/26/27 were established by spectroscopic data. In the case of 12 and 13 the degradation of their mixture to the known 1‐(dimethylphenyl)ethanols 17/18 confirmed the assignment. ‐ The most probable mechanism for the rearrangement of 3 is shown in Schemes 4 and 5. The reaction proceeds from 3 through a, b and g to 12 and 13; 14 is formed via e, f and i. In the case of 4 and 6 only the reaction analogue to 3 → a → b → g ⇉12/13 takes place. The isomeric aldehyds 25–27 formed from 2 could have the structures s, t, and v. The former two could be generated in a similar way as 12/13 from 3, the latter one as shown in Scheme 8.
Crystal Structure of Metal‐Ion Complexes with neutral noncyclic Ionophores
Authors: Neupert‐Laves Katarina , Dobler Max 
Published: December 2004

AbstractCrystal structure determinations of two metal‐ion complexes with noncyclic ionophores are reported: (i) CaCl2 complex of N,N,N′,N′‐Tetrapropyl‐3,6‐dioxa‐octane diamide, space group Fddd, a = 14.659, b = 19.616, c = 33.173 Å; (ii) MnBr2 complex of N,N,N′,N′‐Tetrapropyl‐1,2‐cyclohexylenedioxydiacetamide, space group I4, a = b = 11.695, c = 21.299 Å.
Nucleophilicity and Basicity in the Quaternization of 4‐Substituted Quinuclidines. Polar effects. Part III
Authors: Grob Cyril A. , Schlageter Markus G. 
Published: December 2004

AbstractThe second order rate constants (k) for quaternization of thirty 4‐substituted quinuclidines (1) by methyl iodide in methanol have been measured. The effects of the substituents on rate are relatively small and indicate an early transition state with little charge separation. They also indicate less involvement of the nitrogen atom,i.e.a looser transition state, for quaternization by allyl halides than for the less reactive propyl halides. The logkvalues of 4‐substituted quinuclidines correlate moderately well with their pKavalues, the main reason being the imperfect correlation between nucleophilicity and basicity. The assumption that substituents exert equal effects on rates and equilibria is therefore only partly justified. Certain irregularities in the correlation can be attributed to a reduction of the nucleophilicity of nitrogen in1due to hydrogen bonding to the solvent methanol. Furthermore, quaternization is faster and responds more strongly to substituent effects in the aprotic solvent acetonitrile.
Nucleophilic Additions to Unactivated Carbon‐Carbon Double Bonds. Base‐Catalysed Ether Formation. Preliminary Communication
Authors: Ammann Willi , Ganter Camille 
Published: December 2004

AbstractSeveral examples (3 → 5, 4 → 7, 6 → 7, 9 → 10) of base‐catalysed intramolecular ether formation involving nucleophilic attack on an unactivated carbon‐carbon double bond are described.
Reactions of Tricyclic Vinylcyclopropanes with Metal Carbonyls
Authors: Hayakawa Kenji , Schmid Hans 
Published: December 2004

AbstractIrradiation of the tricyclic vinylcyclopropane 3 and Fe(CO)5 resulted in the formation of the s̀,π‐bonded iron complex 7 and the π,π‐bonded iron complex 8 (Scheme 2). Complex 8 was easily degraded with silica gel to give hydrocarbon 9, which reproduced 8 by photolysis in the presence of Fe(CO)5. Photolysis of 7 afforded a mixture of 3 (23%), 9 (27,5%), and three other hydrocarbons. Oxidative degradation of 7 with ceric ammonium nitrate in methanol gave the dimethoxy‐hydrocarbon 10. ‐ The tricyclic hydrocarbon 3 isomerized thermally to the bicyclic hydrocarbon 11 (with CH3C(9) in an exo position) via a homosigmatropic [1,5]‐H‐shift. On the other hand, 3 was converted into the other isomer 14 (with CH3C(9) in an endo position) by action of Mo(CO)6 or TsOH. Both isomers 11 and 14 reacted with 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione to give the isomeric Diels‐Alder adducts 12 and 15, respectively, which were photochemically converted into the cage compounds 13 and 16, respectively (Scheme 3). ‐ Photochemical reaction of the tricyclic vinylcyclopropane 6 with Fe(CO)5 gave the σ,π‐bonded iron complexes 17 and 18. Heating of 17 at 80° resulted in a loss of one mol of carbon monoxide to give 18 in quantitative yield. Oxidative degradation of 17 with ceric ammonium nitrate in ethanol afforded the polycyclic lactones 19 and 20 by a novel type of reaction (Scheme 4). ‐ The tricyclic ketone 21 was thermally converted into the α,β‐unsaturated ketone 22 via a homosigmatropic [1,5]‐H‐shift. The configuration at C(7) of 22 was confirmed to be same as that of 11 (CH3C(9) in an exo position) by chemical conversions: 22 was reduced with NaBH4 to alcohol 23 which, in turn, was dehydrated with POCl3/pyridine to 11 (Scheme 5). Reaction of ketone 21 with Mo(CO)6 gave the α,β‐unsaturated ketone 25 and a cage compound X, whose structure was not fully elucidated. ‐ Reaction of the polycyclic epoxide 26 with Fe2(CO)9 or Mo(CO)6 yielded the allyl alcohol 27 in a novel type of reaction. The epoxides 29 and 32 were similarly converted into the corresponding allyl alcohols 30 and 33, respectively (Scheme 6).
Oxiranylmethyl‐Fragmentierung zur Bildung von Cyclopentadecan‐1,5‐dion‐Derivaten. Eine Musconsynthese
Authors: Gray Robert W. , Dreiding André S. 
Published: December 2004

The Formation of Cyclopentadecane‐1,5‐dione Derivatives by an Oxiranylmethyl Fragmentation. A Synthesis of MusconeA new method for the preparation of cyclopentadecane‐1,5‐dione (11) and its 3‐methylderivative 12, compounds with a musk fragrance, is described. Starting from the readily available bicyclic enones 9 and 10, the epoxy‐p‐toluenesulfonate 15 and its methylderivatives 20A and 20B were prepared by reduction with diisobutyl‐aluminium hydride or sodium borohydride (to 13 and 18A, 18B), epoxidation with m‐chloroperbenzoic acid (to 14 and 19A, 19B), followed by tosylation. Heating of 15 and 20A or 20B with calcium carbonate in water/dioxane under reflux caused fragmentation leading to the diketones 11 and 12 in high yields. The same fragmentation also occurred with sodium hydrogencarbonate in dimethylsulfoxide at 160°, but in lower yields. The conversion of 12 into rac‐muscone (2) was accomplished by developing a method for selectively forming the monotosylhydrazone 27. The latter was reduced with sodium borohydride and the crude alcohol 28 oxidized to 2.Unexpectedly the pyrolysis of the epoxy‐acetate 29 at 350° in a sealed glass tube led to the bicyclic ketone 10. Treatment of 3‐methylcyclopentadecane‐1,5‐dione (12) with peracetic acid and boron trifluoride etherate gave the stable crystalline ozonide 33.
Un nouvel analogue synthétique de l'adénosine: La désoxy‐3′‐C‐dibromométhylidène‐3′‐adénosine
Authors: Tronchet Jean M. J. , Schwarzenbach Dominique 
Published: December 2004

A novel synthetic analog of adenosine: the 3′‐deoxy‐3′‐C‐dibromomenthylidene‐adenosineThe title compound (7) has been prepared by a sequence of classical synthetic steps from 3‐deoxy‐3‐C‐dibromomethylidene‐1,2: 5,6‐di‐O‐isopropylidene‐α‐D‐ribo‐hexofuranose (1). The β‐configuration of the nucleoside was established by formation of a cyclonucleoside. 7 is very slowly deaminated by adenosine deaminase. In contrast with its dichloro analog, it does not inhibit the growth of Escherichia coli.
Contribution à la phytochimie du genre Gentiana XXI; Les cinnamoyl‐C‐glucosylflavones et leurs O‐glucosides dans Gentiana punctataL.
Authors: Luong Minh Duc , Jacot‐Guillarmod André 
Published: December 2004

Phytochemistry of genus Gentiana XXI: The cinnamoyl‐C‐glucosylflavones and their O‐glucosides in Gentiana punctata L.Three new (1–3) and three previously identified (4–6) cinnamoyl‐C‐glucosyl‐flavones have been isolated from the leaves of Gentiana punctata L. The structures of the new compounds were established as: trans‐cafeoyl‐2″‐iso‐orientin‐4′‐O‐β‐D‐glucoside (1), trans‐feruloyl‐2″‐isovitexin‐4′‐O‐β‐D‐glucoside (2) and trans‐feruloyl‐2″‐isovitexin (3). Isoscoparine (8) and O‐β‐D‐glucosyl‐2″‐iso‐orientin (7) were also isolated and identified.
Der Stoffwechsel von Verbindungen mit Dreifachbindung. VII. Verteilung und Abbau der 9‐Octadecinsäure bei Ratten, ein Beitrag zur α‐Oxydation der C‐Kette
Authors: Reichlmeier Klaus , Graf Peter , Kaempf Ekkehard , Bernhard Karl 
Published: December 2004

Distribution and Metabolism of Octadec‐9‐ynoic acid in RatsOctadec‐9‐ynoic acid (stearolic acid) fed to rats leads to the metabolic excretion of six dicarboxylic acids with retained triple bond. The main metabolic steps are ω‐, β‐, and presumably α‐oxidation. Feeding of 14C‐stearolic acid proves that the α‐oxidative steps involves the methyl end of the original acid. It could further be shown that this acid is incorporated partially in the body lipids. To a substantial degree it is totally oxidized and expired as 14CCO2.
A Simple Equivalent Bond Orbital Model for the Rationalization of the C2s‐Photoelectron Spectra of the Higher n‐Alkanes, in Particular of Polyethylene
Authors: Heilbronner Edgar 
Published: December 2004

AbstractThe higher homologues of n‐alkanes H(CH2)NH with N > ∽ 13 yield photoelectron spectra in which the C2s‐bands merge to form a double humped, unresolved C2s‐band system in the interval of I=15 to 25 eV [1]. It is shown that with the help of an equivalent bond orbital model one can derive a closed formula, which gives the individual C2s‐band positions I=−εj in function of N and j with sufficient accuracy, assuming the validity of Koopmans' approximation. The calculated I values (j=1 to N) folded with an appropriate shape function for the individual C2s‐bands reproduce the observed Franck‐Condon envelope of the C2s‐band system within narrow limits of error. However, a comparison of the observed total width of the C2s‐band system with the computed one, indicate that for large n‐alkanes (N≥ ∽ 13), the simplification which consists of taking into account only the interaction matrix elements between vicinal bond orbitals [2], is no longer a satisfactory one.
Experimente zum kompetitiven Einbau der Stereoisomeren des Farnesols in Cantharidin. 6. Mitteilung zur Biosynthese des Cantharidins
Authors: Woggon Wolf‐Dietrich , Peter Martin G. , Schmid Hans 
Published: December 2004

Experiments on the competitive incorporation of farnesol‐stereoisomers into cantharidinFarnesol (2) has been demonstrated to be an efficient precursor for cantharidin (1), into which it is transformed by elimination of C(1), C(5), C(6), C(7) and C(7′) [1]. The following incorporation experiments with doubly labelled (3H and 14C) stereoisomers of farnesol present strong evidence that (E,E)‐ farnesol ((E,E)‐2) in fact is the precursor for cantharidin, whereas (2E, 6Z)‐2 and (Z,Z)‐2 are not utilized for the biosynthesis of cantharidin. A possible mechanism for the incorporation of (2Z,6E)‐farnesol ((2Z,6E)‐2) to an extent of 56,8% relative to (E,E)‐2 is discussed.
Über Pterinchemie. 64. Mitteilung. Die Kristallstruktur von 6‐Methyl‐7,8‐dihydropterin‐monohydrochlorid‐monohydrat
Authors: Bieri Jost H. 
Published: December 2004

The crystal structure of 6‐methyl‐7,8‐dihydropterine‐monohydrochloride‐monohydrateThe crystal structure of the title compound has been determined by X‐ray analysis (direct methods) and refined with 990 structure amplitudes to R = 0.025. The crystal system is triclinic, space group P1, with unit cell dimensions a = 5.859, b = 7.686, c = 12.107, α = 71.84, β = 76.35, γ = 85.80. The molecule is protonated at the N(5)‐position and is planar. The atoms H(19) and H(20) are with 0.818 Å above respectively with −0.705 Å under the plane.
Ionophore für Li+: Membranselektivität, Darstellung und Stabilitätskonstanten in Äthanol
Authors: Kirsch Norbert N. L. , Funck Robert J. J. , Pretsch Ernö , Simon Wilhelm 
Published: December 2004

Membrane Selectivity and Syntheses of Ionophores for Li+. Stability Constants in EthanolElectrically neutral, lipophilic complexing agents were prepared which induce Li+ selectivity in solvent polymeric membranes. Stability constants for group IA and IIA cations of one such ligand in ethanol have been determined. The selectivity behaviour of this ligand in membranes as well as in extraction systems is studied and discussed in terms of model considerations.
A Flexible Stereoselective Synthesis of the Spirosesquiterpenes (±)‐β‐Acorenol, (±)‐β‐Acoradiene, (±)‐Acorenone‐B and (±)‐Acorenone via an Intramolecular Ene‐Reaction
Authors: Oppolzer Wolfgang , Mahalanabis Kumar K. , Bättig Kurt 
Published: December 2004

AbstractThe racemic spirosesquiterpenes β‐acorenol (1), β‐acoradiene (2), acorenone‐B (3) and acorenone (4) (Scheme 2) have been synthesized in a simple, flexible and highly stereoselective manner from the ester 5. The key step (Schemes 3 and 4), an intramolecular thermal ene reaction of the 1,6‐diene 6, proceeded with 100% endo‐selectivity to give the separable and interconvertible epimers 7a and 7b. Transformation of the ‘trans’‐ester 7a to (±)‐1 and (±)‐2 via the enone 9 (Scheme 5) involved either a thermal retro‐ene reaction 10 → 12 or, alternatively, an acid‐catalysed elimination 11 → 13 + 14 followed by conversion to the 2‐propanols 16 and 17 and their reduction with sodium in ammonia into 1 which was then dehydrated to 2. The conversion of the ‘cis’‐ester 7b to either 3 (Scheme 6) or 4 (Scheme 7) was accomplished by transforming firstly the carbethoxy group to an isopropyl group via 7b → 18 → 19 → 20, oxidation of 20 to 21, then alkylative 1,2‐enone transposition 21 → 22 → 23 → 3. By regioselective hydroboration and oxidation, the same precursor 20 gave a single ketone 25 which was subjected to the regioselective sulfenylation‐alkylation‐desulfenylation sequence 25 → 26 → 27 → 4.
Zur Stereochemie der aromatischen Claisen‐Umlagerung. Thermische Umlagerung von erythroiden und threoiden ortho‐Dienonen
Authors: Wunderli Alfred , Winkler Tammo , Hansen Hans‐Jürgen 
Published: December 2004

On the Stereochemistry of the Aromatic Claisen Rearrangement. Thermal Rearrangement of erythroid and threoid ortho‐Dienones.Erythro‐ and threo‐1‐methyl‐1‐(1′‐methyl‐2′‐propynyl)‐2‐oxo‐1,2‐dihydronaph‐thalene (erythro‐ and threo‐6) as well as erythro‐ and threo‐2,6‐dimethyl‐6‐(1′‐methyl‐2′‐propynyl)‐cyclohexa‐2,4‐dien‐1‐one (erythro‐ and threo‐8) were obtained together with the corresponding aromatic ethers 5 and 7 by alkylation of 1‐methyl‐2‐naphthol and 2,6‐dimethyl‐phenol, respectively in alcoholic potassium hydroxide solution with 1‐methyl‐2‐propynyl p‐toluenesulfonate (Scheme 2). The diastereoisomeric dienones 6 and 8 were easily separated by column chromatography on silica gel and its relative configuration at C(1) or C(6) and C(1′) deduced from the chemical shifts in their 1H‐NMR.‐spectra (Table 1). Hydrogenation of 6 and 8 using Lindlar catalyst yielded the corresponding erythro‐ and threo‐configurated (1′‐methyl‐2′‐propenyl)‐dienones 10 and 13, respectively (Scheme 3) the thermal rearrangement of which were studied. The following results were obtained: threo‐10 rearranged in benzene at 85–105° preferentially via a chair‐like (C) transition state to yield 99,5% (E)‐ and 0,5% (Z)‐(2′‐butenyl) 1‐methyl‐2‐naphthyl ether ((E)‐ and (Z)‐14; ΔΔG (C/B) = −4,0 kcal/mol). On the other hand, erythro‐10 when heated at 105‐125° in benzene gave 84,7% (E)‐ and 15,3% (Z)‐14, i.e. in this case a boat‐like (B) transition state is favoured (G (C/B) = + 1,3 kcal/mol) (Scheme 5 and Table 2). The thermal rearrangement of dienones 13 led to the corresponding ethers 12 as well as p‐allyl‐phenols 11. Thus, heating of threo‐13 at 20–42° in cyclohexane resulted in the formation of 2,5% of ether 12, consisting of 98% of the (E)‐ and 2% of the (Z)‐isomer, and 97,5% of (E)‐11 which contained, at a maximum, 0,5% of the (Z)‐isomer, (Scheme 6 and Table 3). This means that both rearrangements occurred with a strong preference of the C transition state (G (C/B, phenol) = −3,3 kcal/mol). On the contrary, erythro‐13 when heated at 42–68° in cyclohexane yielded a 3:2 mixture of ether 12 and phenol 11 (Scheme 6). The ethereal part consisted of 88,0% of the (E)‐ and 12,0% of the (Z)‐isomer which again shows that the B geometry predominated in the erythro transition state leading to the ether (G (C/B)= + 1,3 kcal/mol). In the phenolic part 36–40% of the (E)‐isomer and 64–60% of (Z)‐isomer were found which means that in the para‐Claisen rearrangement of erythro‐13 the C arrangement is only slightly favoured (ΔΔG (C/B)= −0,36 kcal/mol).
Synthese und IR.‐spektroskopische Identifizierung epimerer 3‐Äthinyl‐5 α‐cholestan‐3‐ole
Authors: Berbalk Hans , Eichinger Karl , Schuster Rudolf 
Published: December 2004

Synthesis and IR. Spectroscopic Identification of Epimeric 3‐Ethinyl‐5α‐cholestan‐3‐olsThe syntheses of the 3β‐ethinyl‐5α‐cholestan‐3α‐ols 2a, 2b, 2c and of the corresponding epimeric 3α‐ethinyl‐5 α‐cholestan‐3 β‐ols 3a, 3b, 3c are described. Bands at 1000 cm−1 for the α‐alcohols and at 1030 cm−1 for the β‐alcohols are found to be useful for the IR. spectroscopic identification of epimeric 3‐ethinyl‐5α‐cholestan‐3‐ols.
The Photoenolization of 2‐Methylacetophenone and Related Compounds
Authors: Haag Roland , Wirz Jakob , Wagner Peter J. 
Published: December 2004

AbstractA reinvestigation of 2‐methylacetophenone (1) by ns flash photolysis has provided detailed evidence for the reaction sequence of photoenolization. The triplet reaction proceeds adiabatically from the lowest excited triplet state of the ketone, 3K (1), to the enol excited triplet state, 3E (1), which decays both to enol and ketone ground state. The Z‐ and E‐isomers of the photoenol, Z‐E (1) and E‐E (1) are formed in about equal yield by the triplet pathway, while direct enolization from the lowest excited singlet state of 1 yields (predominantly) the Z‐isomer. Intramolecular reketonization from Z‐E (1) to 1 proceeds at a rate of ca. 108s−1 in cyclohexane, but can be retarded to ca. 104s−1 in hydrogen‐bond‐acceptor solvents. The proposed mechanism is summarized in Scheme 1 and rationalized on the basis of a state correlation diagram, Scheme 2. 3,3,6,8‐Tetramethyl‐1‐tetralone (2) was used as a reference compound with fixed conformational position of the carbonyl group, and some results from a brief investigation of 2,4‐dimethylbenzophenone (3) are also reported.