bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesen von (1R)‐cis‐3‐(2′,2′‐Dihalovinyl)‐2, 2‐dimethylcyclopropan‐carbonsäuren via Favorskii‐Umlagerung von optisch aktiven Cyclobutanonen
Authors: Greuter Hans , Dingwall John , Martin Pierre , Belluš Daniel 
Published: December 2004

Syntheses of (1R)‐cis‐3‐(2′,2′‐Dihalovinyl)‐2,2‐dimethylcyclopropane Carboxylic Acids via Favorskii‐rearrangement of Optically Active CyclobutanonesThe cis‐cyclobutanones 7 are resolved by means of optically active amine salts of their sodium hydrogen sulfite adducts. The desired (1R)‐cis‐carboxylic acids 9 are obtained from the (+)‐cis‐cyclobutanones 7 via Favorskii‐rearrangement and HX‐elimination. The recycling of undesired (−)‐cis‐cyclobutanones 7 is carried out in good yield by their racemization, thus rendering the total synthesis 1+2→9 chirally economic.
Photodimerization of Solid Pleiadiene; Isomerization and Cycloreversion of the Dimer
Authors: Hazell Alan C. , Pagni Richard M. , Persy Gabriele , Rommel Erika , Wirz Jakob 
Published: December 2004

AbstractIrradiation (λ>400 nm) of solid pleiadiene (1) yields a single, head‐to‐head [π4s+π4s]‐photodimer (2) the structure of which was determined by X‐ray analysis. The formation of 2 is entirely suppressed at 77 K, since properly oriented pairs of molecules arise only from thermal disorder in crystals of 1. Upon pyrolysis (80°), the strained photodimer 2 rearranges to the [π2s + π4s] dimer 3 by a ‘forbidden’ suprafacial [1,3]‐C‐atom migration. Both 2 and 3 are reconverted to 1 by UV. irradiation in solution, but the latter, ‘forbidden’ photoreaction is suppressed at 77 K. Discrepancies of the experimental observations with the predictive schemes of Kaupp or Michl are discussed.
Inductive and Polarizability Effects of an Exocyclic Diene‐Iron Tricarbonyl Group. The acetolyses of exo‐ and endo‐irontricarbonyl complexes of 5,6‐dimethylidene‐2‐exo‐norbornyl and 2,3‐dimethylidene‐7‐anti‐norbornyl parabromobenzenesulfonates
Authors: Barras Charles , Bell Larry G. , Roulet Raymond , Vogel Pierre 
Published: December 2004

AbstractThe exo‐ and endo‐irontricarbonyl complexes of 5,6‐dimethylidene‐2‐exo‐norbornyl alcohols 10x, 10n, p‐bromobenzenesulfonates 11x, 11n, acetate 12x and of the 2,3‐dimethylidene‐7‐anti‐norbornyl alcohols 17x, 17n, p‐bromobenzenesulfonates 19x, 19n and acetates 20x, 20n have been prepared. The SN1 buffered acetolyses of 11x, 19x and 19n gave 12x, 20x and 20n, respectively (retention of configuration). The first‐order rate constants of the acetolyses have been evaluated and compared with those of the acetolyses of the uncomplexed 5,6‐dimethylidene‐2‐exo‐norbornyl (14) and 2,3‐dimethylidene‐7‐anti‐norbornyl p‐bromobenzenesulfonates (18). A rate retardation effect of ca. 1.5 · 105 was measured for 11x → 12x (65°) compared with the acetolysis of 14. The retardation effect is larger (> 5 · 107) with 11n. Contrastingly, the acetolysis 19x → 20x was slightly accelerated with respect to that of the uncomplexed p‐bromobenzenesulfonate 18. An unsignificant rate‐retardation effect was measured for the acetolysis 19n → 20n. The results are interpreted in terms of competitive inductive destabilization and charge‐induced dipole stabilizing interaction by the exocyclic diene‐iron tricarbonyl fragment. PMO. arguments give a rationale for the difference in polarizability between the diene‐Fe(CO)3 group in 19 and that in the endo‐7‐norbornadienyl‐iron tricarbonyl system.
Stoffwechselprodukte von Mikroorganismen. 210. Mitteilung. Über die Avilurekanosen A and C and weitere Abbauprodukte Avilamycine A and C
Authors: Kupfer Ernst , Neupert‐Laves Katarina , Dobler Max , Keller‐Schierle Walter 
Published: December 2004

The Avileurekanoses A and C and Further Degradation Products of the Avilamycins A and CAlkaline hydrolysis of the orthosomycin antibiotics, avilamycins A ad C products similar t those earlier described for flambamycin. Among these avileurekanose c (15) became of particular importance because its acetate prisms suitable for an X‐ray structural determination. For the avilamycins A and C structural formulae 2 and 3, respectively, can now be drawn, in which only the configuration at C (16), one out of 32 asymmetric C‐atoms, is not yet determined.
Regioselectivity of the Diels‐Alder Additions of 2‐Substituted 5,6 Dimethylidenenorbornanes and‐bicyclo[2.2.2]octanes
Authors: Avenati Marco , Carrupt Pierre‐Alain , Quarroz Daniel , Vogel Pierre 
Published: December 2004

AbstractThe cycloadditions of methyl propynoate and methyl vinyl ketone to 5,6‐dimethylidene‐2‐norbornanone (6) are para′‐regioselective“Para” (p) designs in this paper the 4, 9‐disubstituted tricclo[6.2.1.02, 7] undecane‐ and 4, 9‐disubsstituted tricycle[6.2.202,7] dodecane derivatives, “meta” (m) design the corresponding 4, 10‐disubstituted compounds.
. A smaller para ‐regioselectivity is observed for the addition of methyl propynoate to 5,6‐dimethylidene‐2bicyclo[2.2.2]octanone (10). No regioselectivity is observed with 5,6‐dimethylidene‐2exo‐norbornyl alcohol (3), acetate (5) and 5,6‐dimethylidene‐2exo‐bicyclo[2.2.2]octanol (9). PMO arguments based on the shape of the HOMO's and subHOMO's of the dienes allow to rationalize these observations. Unpredictable para′‐ or ‘meta’regioselectivities are found for the Diels,‐Alder additions of 5,6‐dimethylidene‐2endo‐norbornyl alcohol (2), acetate (4) and 5,6‐dimethylidene‐2endo‐bicyclo[2.2.2]octanol (8). The carbonyl group of β,γ unsaturated ketones such as 6 and 10 can act as an electron donating homoconjugated substituent. The n(CO) ↔ σ[C(1), C(2)] ↔ π[C(5), C(6)] hyperconjugative interaction can override the usual electron‐withdrawing effect of this function.
Synthesis, Conformation, and Interactions with Small Molecules of Bis (Cyclic Dipeptides)
Authors: Tomiyasu Hiroshi , Kinjura Shunsaku , Imanishi Yukio 
Published: December 2004

AbstractBis (cyclic dipeptides), cyclo and S, S′‐bis(cyclo(hemiCys‐Pro)), were synthesized. These bis (cyclic dipeptides) very efficiently formed complexes with Ba2+ and Na+ owing to intramolecular cooperation of two cyclicdipeptide moieties, the bis‐effect. Cyclo stacked sodium 8‐anilino‐1‐naphthalensulfonate in aqueous solution. These properties of complexation were controlled by the nature of the bridge connecting two cyclic dipeptide moieties. The geometry of the complex between S, S′‐bis (cyclo (hemiCys‐Pro)) and metal ion was investigated with the help of circular dichroism, nuclear magnetic resonance, and Raman spectroscopy.
31P‐, 119Sn‐ and 195Pt‐NMR. Studies of Trichlorostannate Complexes of Pt(II) and Pd(II). 2J(119Sn, 117Sn)‐Values
Authors: Starzewski Karl H. A. Ostoja , Pregosin Paul S. , Rüegger Heinz 
Published: December 2004

AbstractThe synthesis and solution structures of new four‐ and five‐coordinate phosphine and arsine complexes of Pt and Pd containing the trichlorostannate ligand are described. Complexes containing two and three SnCl−3‐ligands have been identified from their 31P‐, 119Sn‐ and 195Pt‐NMR. spectra. The complexes trans‐[M (SnCl3)2L2] (M = Pt, L‐PEt3, PPr3, AsEt3; M = Pd, L = AsEt3) show unexpectedly large 2J(119Sn, 117Sn)‐values (34,674–37,164 Hz) with the trans‐orientation of these spins playing an important role. The heteronuclear coupling constant 2J(119Sn, 31P) in the five‐coordinate cationic complexes [Pt(SnCl3)(P(o‐AsPh2C6H4)3)]+ and [Pt(SnCl3)(As(o‐PPh2C6H4)3)]+ also shows a geometric dependence. New five‐coordinate anionic complexes of type [M (SnCl3)3L2]− (M = Pd, Pt; L = PEt3, AsEt3) may be prepared via addition of three mol‐equiv. of SnCl2 and one mol‐equiv. of (PPN)Cl to [MCl2L2] in acetone.
Zur Kenntnis des Faktors F430 aus methanogenen Bakterien: Struktur des porphinoiden Ligandsystems
Authors: Pfaltz Andreas , Jaun Bernhard , Fassler Alexander , Eschenmoser Albert , Jaenchen Rolf , Gilles Hans Harald , Diekert Gabriele , Thauer Rudolf K. 
Published: December 2004

Factor F430 from Methanogenic Bacteria: Structure of the Porphninoid Ligand SystemA structure is proposed for F430M, a non‐cristalline methanolysis product of isolates of the nickel‐containing, porphinoid factor F430 from Methanobacterium thermoautotrophicum.Crucial to the structure determination are five incorporation experiments with M. thermoautotrophicum (strain Marburg) in which the specifically mono‐13C‐labeled biosynthetic precursors (2‐13C), (3‐13C), (4‐13C)‐, (5‐13C) ALA (ALA = δ‐amino‐levulinic acid) and L‐(methyl‐13C)methionine were incorporated into F430 with high efficiency. The 13C‐NMR,‐spectra of the specifically labeled F430M samples derived therefrom, together with the UV./VIS. spectral data of F430M, contain all the information necessary for the deduction of the constitution of the F430M chromophore, assuming the established pattern of porphinoid biosynthesis to be operative in F430 biosynthesis. 1H‐NMR. spectroscopy and, in particular, 1H‐NMR.‐NOE‐difference spectroscopy corroborates and completes the constitutional assignments and, furthermore, makes possible an almost complete derivation of the molecule's relative configuration. Schemes 3 and 4 summarize the results of 1H‐NMR. spectroscopy, presenting them within the context of the proposed structure for F430M. The assignment of absolute configuration implied in the formula is given preference because of F430M's very close structural and (assumed) biosynthetic relationship to sirohydrochlorin and vitamin B12 (with respect to ring C, the assignment is based on degradative evidence).According to the proposed structure, the nickel complex F430M possesses an uroporphinoid (Type III) ligand skeleton with an additional carbocyclic ring and a chromophore system not previously encountered among natural porphinoids. It can be considered to be a (tetrahydro) derivative of the corphin system, combining structural elements of both porphyrins and corrins.
Effects of Remote Substitution on the Photo‐oxidation of Exocyclic s‐cis‐Butadienes Grafted onto Bicyclo [2.2.1]heptanes. Thermal and Rhodium Catalyzed Rearrangements of 3,6‐Dihydro‐1,2‐dioxines
Authors: Hagenbuch Jean‐Pierre , Birbaum Jean‐Luc , Métral Jean‐Luc , Vogel Pierre 
Published: December 2004

AbstractThe rates of photo‐oxidation of exocyclic S‐cis‐butadienes grafted onto bicyclo‐[2.2.1]heptanes and 7‐oxabicyclo[2.2.1]heptanes (1–6) are dependent upon remote modifications of the bicyclic skeletons. They correlate with the rates of Diels‐Alder additions of these dienes to strong dienophiles. The 2,3‐dimethylidenenorbornane (1), 5,6‐dimethylidene‐2‐norbornene (2) and 2,3‐dimethylidene‐7‐oxanorbornane (3) gave the corresponding endo‐peroxides (3,6‐dihydro‐1,2‐dioxines) 7–9 in good yield. The 2, 3, 5, 6‐tetramethylidene‐7‐oxanorbornane (4) gave the mono‐endo‐pe‐roxide 6, the latter did not react with a second equivalent of oxygen. Similarly, 5, 6‐dimethylidene‐7‐oxa‐2‐norbornene (5) was unreactive toward photo‐oxidation. Thermal isomerization of the endo‐peroxides 7 and 9 gave, the trans‐diepoxides 10 and 14, respectively, with high stereoselectivity. The endo‐peroxides 6, 7 and 9 were cleanly isomerized into the corresponding α, β‐unsaturated γ‐hydroxy aldehydes in the presence of catalytic amounts of Rh2(CO)4Cl2.
Electronic and Molecular Structure of Simple 3,3′‐Bicyclopropenyls. Photoelectron Spectroscopy and Model Calculations
Authors: Spanget‐Larsen Jens , De Korswagen Carla , Eckeri‐Maksie Mirjana , Gleiter Rolf 
Published: December 2004

AbstractThe electronic and molecular structure of 3,3′‐bicyclopropenyl (1) and its alkyl derivatives 3,3′‐dirnethyl‐3,3′‐bicyclopropenyl (2), dispiro [2.0.2.3]nona‐1,5‐diene (3), dispiro[2.0.2.4]deca‐1,5‐diene (4), dispiro [2.0.2.5]undeca‐1, 5‐diene (5), and dispiro [2.0.2.6]dodeca‐1, 5‐diene (6) are studied by means of photoelectron spectroscopy and model calculations. Through‐bond' effects in model compound 1 are analyzed in detail, illustrating a general difficulty with NDO models. Low‐energy photoelectron bands of 2–6 can be assigned to ejection of electrons from cyclo‐propenyl π‐ and Walsh‐orbitals. Strong ‘through‐bond’ coupling leads to splitting of the π‐bands in the range 1.0–1.5 eV, while the strongly conformation‐dependent splitting of the Walsh‐bands allows conclusions concerning the preferred torsional angles. The preference of a gauche‐conformation is predicted for 2 in the gas phase.
Chromatographische Trennung und Identifizierung diastereomerer Carotinoide mit grossem räumlichem Abstand der chiralen Zentren
Authors: Vecchi Max , Englert Gerhard , Mayer Hans 
Published: December 2004

Chroma to graphic Separation and Identification of Diastereomeric Carotinoids with Distant Chiral CentersThe high‐performance liquid chromatographic separation of diastereomeric C40‐carotinoids is described possessing chiral centers which are separated by 18 C‐atoms (nonaene system). The method is applied to the separation of the two diastereomers of 6,6′‐dihydrorhodoxanthin 1a and 1b (ε,ε‐carotene‐3,3′‐dione) and the six diastereomers of tunaxanlhin (ε,ε‐carotene‐3,3′‐diol; 2a–2f). Conditions for the separation of lutein [(3R, 3′R, 6′R)‐β,ε‐carotene‐3.3′‐diol, 3a], 3′‐epi‐lutein [(3R,3′S,6′R)‐β, ε‐carotene‐3,3′‐diol, 3b] and its 13′‐cis‐ (3c) and 13‐cis‐stereo‐isomers(3d) are also reported. Identification of the different chromatographic fractions was possible by use of authentic synthetic samples or by 1H‐NMR. spectroscopy.
Herstellung und Solvolyse von 3‐substituierten p‐Toluolsulfonsäure‐(1‐adamantyl)estern
Authors: Bielmann Rolf , Grob Cyril A. , Schaub Bruno 
Published: December 2004

The Preparation and Solvolysis of 3‐substituted 1‐Adamantyl ToluenesulfonatesMethods for the preparation of some hitherto unknown 3‐iubstitutetl 1‐adamantyl toluenesulfonates are evaluated. Their solvolysis products in dioxane/water 70:30 are reported.
17O‐NMR. of Enriched Acetic Acid, Glycine, Glutamic Acid and Aspartic Acid in Aqueous Solution. II. Relaxation Studies
Authors: Gerothanassis Ioannis P. , Hunston Roger , Laulenvein Jürgen 
Published: December 2004

AbstractThe 17O‐NMR. line widths of the enriched amino acids glycine, aspartic acid, glutamic acid and, for comparative reasons, acetic acid were measured in aqueous solution between pH 1 and 14. The 17O‐NMR. line‐width maxima of glycine at pH≈︁11 and acetic acid at pH≈︁5 are shown to arise from traces of paramagnetic metal ions. The increase in line width in case of glycine on going from the zwitterion 10 the cataion is attributed to an increase in the 17O‐quadrupole coupling constant. No evidence for an intermolecular or intramolecular association of glycine in the zwitterionic form was found. When the paramagnetic impurities were eliminated by addition of EDTA, both the longitudinal and transverse relaxation times remained unchanged on deprotonation of the amino group. The overlapping of the α, β‐ and α, γ‐carboxyl resonances of aspartic and glutamic acid, respectively, created difficulties for their line‐width analysis.
Stoffwechselprodukte von Mikroorganismen. 216. Mitteilung. Isolierung, Strukturaufklärung und Synthese von Ferrioxamin H
Authors: Adapa Srinivas , Hubtr Peter , Keller‐Schierlein Walter 
Published: December 2004

Metabolites of Microorganisms. 216. Isolation, Structure and Synthesis of Ferrioxamine HThe structure of ferrioxamine H, a minor component of the sideramine complex of actinomycetes, was determined by spectroscopic investigations, degradation and synthesis. Ferrioxamine H is the Fe (III)‐complex of 11,22‐dihydroxy‐4, 12, 15, 23‐tetraoxo‐5,11,16,22‐tetraazatetracosanoic acid (2).
Diterpenoide Drüsenfarbstoffe aus Labiaten: 22 neue Coleone und Royleanone aus Plectranthus lanuginosus
Authors: Schmid Jean Martin , Rüedi Peter , Eugster Conrad Hans 
Published: December 2004

Leaf‐gland Pigments from Labiatae: 22 Novel Diterpenoids (Coleons and Royleanones) from Plectranthus lanuginosusWe report the isolation and structure elucidation of 22 novel diterpenoids (named lanugones A, B, C, D, E, F, G, H, I, J, K, K′, L, M, N, O, P, Q, R, S and (155)‐coleon C (28) and (155)‐coleon D (29)) from the leaf‐glands of the above‐mentioned plant (see Table 1). Structurally they belong to the subgroups of royleanones and coleons with the following structural characteristics: 8‐hydroxy‐1‐methyl‐spi‐ro[2,5]oct‐5‐ene‐4,7‐diones, p‐quinomethanes, extended (vinylogous) quinones, di‐osphenols and diketones. Compounds 28 and 29 are (15S)‐epimers of the already known coleon C and coleon D (with (15 R)‐configuration), respectively. Furthermore, the already known 6,7‐didehydroroyleanone (1) has been isolated in small amount.The present investigation has uncovered the broadest range of diverse chromo‐phoric systems and oxydation levels so far found amongst diterpenoids in a single plant species. Most important for an understanding of the metabolic fate of an iso‐propyl group is the full range found with the following metabolic stages: isopropyl‐→ hydroxyisopropyl → dihydrofuran and spirocyclopropane → allyl‐ and 2‐hydroxypropyl groups.
A Stereocontrolied Entry to Racemic Eremophilane and Valencane Sesquiterpenes via an Intramolecular Diels‐Alder Reaction
Authors: Näf Ferdinand , Decorzant René , Thommen Walter 
Published: December 2004

AbstractA stereocontrolied route to racemic eremophilane and valencane sesquiterpenes is described via a common intermediate 15, accessible from an intramolecular Diels‐Alder reaction. 13C‐NMR.‐shift assignments of the bicyclic intermediates and products are presented.
Desoxy‐nitrozucker. 3. Mitteilung. Synthese von Ketosen durch Kettenverlängerung von 1‐Desoxy‐1‐nitro‐aldosen. Nucleophile Additionen und Solvolyse von Nitroaethern
Authors: Aebischer Bernard , Bieri Jost H. , Prewo Roland , Vasella Andrea 
Published: December 2004

Synthesis of Ketoses by Chain Elongation of 1‐Deoxy‐1‐nitroaldoses. Nucleophilic Additions and Solvolysis of Nitro EthersA method for the preparation of chain elongated uloses based upon the base‐catalyzed addition of 1‐deoxy‐1‐nitroaldoses to aldehydes and Michael acceptors and subsequent solvolytic replacement of the nitro group by a hydroxy group is described. Thus, addition of 1, 3 and 9 to formaldehyde, followed by solvolysis gave the chain elongated ulose derivatives 2, 8 and 10 (63–76%), respectively. The configuration at the anomeric center of the addition products was deduced from 13C–NMR. spectra and mutarotation. In the case of 3, the primary addition products 4 and 6 were isolated and acetylated to 5 and 7. The nitro derivatives 4–7 do not follow Hudson's rule of isorotation. Addition of 1 to benzaldehyde (44%) and to nonanal (74%) preceded with a small degree of diastereoselectivity to give 15a/15b, and 11/12, respectively. The configuration of the secondary hydroxyl group of 12 was determined by correlation with methyl 2‐hydroxydecanoate (14). Addition of 1 to the galacroaldehyde 16 gave a single compound 17 (78%). The structure of this dodecosulose was determined by X‐ray crystallography. Solvolysis of the acetylation product 18 in formamide gave the hemiacetal 19 (69%). Michael addition of 1 to acrylonitrile, methyl vinyl ketone and cyclohexenone under solvolytic conditions gave the hemiacetals 27, 30 and 31a,b (49%, 71% and 76%, respectively). Under non‐solvolytic conditions (Bu4NF), 1 reacted with acrylonitrile, and crotononitrile to give the anomeric nitro ethers 23 and 24 (67%) and 25 and 26 (84%). respectively. Similarly. 3 added to acrylonitrile to give 28 and 29 (55%, 4:1). This reaction appears to proceed under kinetic control. Addition of 1 to ethyl propiolate and solvolysis yielded the unsaturated spirolactone 32 (50%) and the hemiacetal 33 (17%). Hydrogenation of 32 gave the saturated spirolactone 34 (100%) which was also obtained from 1 and methyl acrylate (63%). Addition of 1 to dimethylmaleate gave the unsaturated ester 35 (48%).
New Peptide Lactones of the Streptogramin Family (Group B). Structures of Virginiamycin S5 and Viridogrisein II
Authors: Oberbäumer Ilse , Grell Ernst , Raschdorf Fritz , Richter Wilhelm J. 
Published: December 2004

AbstractVirginiamycin S5 and viridogrisein II were isolated by liquid chromatography from the crude antibiotics virginiamycin and viridogrisein, respectively. Their structures were elucidated by amino‐acid analysis and mass spectrometry.
Broad Nematic Phases with High Clearing Points
Authors: Osman Maged A. 
Published: December 2004

AbstractUnbranched 4‐(4′‐alkylbenzoyloxy)‐, 4‐(4′‐methylanlinobenzoyloxy)‐ and 4‐(4′dime thylaminobenzoyloxy)benzylidene‐4″‐cyanoanmlines were synthesized. They show broad nematic phases with high nematic isotropic transitions. Lateral Clsubstituents decrease the clearing points of these liquid crystals by about 80°. The intermediate 4‐(4′‐alkylbenzoyloxy)benzaldehydes are monotropic nematic.
‘Non‐Koopmans’ States in Stilbene Cations and a Remarkable Example to the «SDT‐Equation»: Indeno [2,1‐a]indene
Authors: Haselbach Edwin , Klemm Urs , Gschwind Rudolf , Bally Thomas , Chassot Laurant , Nitsche Stephan 
Published: December 2004

AbstractThe radical cations of indeno [2, 1‐a]indene (1), stilbene (2) and 3, 5, 3', 5'‐tetramethylstilbene (3) were prepared by γ‐irradiation of the neutral precursors in an electron‐scavenging matrix at 77 K. Their electronic spectra were recorded and compared to the photoelectron spectra (PE.) of the neutral precursors. The results show that either the fourth or the fifth excited doublet state of the cations is of «Non‐Koopmans» type, with specific doublet energy (D) D (2Bg)=2.74 eV (1+), =2.59 eV (2+), =2.49 eV (3+). Remarkably, 1+ possesses two electronic states in the 2.7‐2.8 eV energy range: 2Au («Koopmans»‐type) and 2Bg («Non ‐Koopmans»‐type). The «SDT»‐equation \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm D} = \sqrt {{\rm S} \cdot {\rm T}} $\end{document} approximately connecting excited singlet (S) and triplet (T) states of a neutral alternant system with the excited doublet (D) states of its radical cation ‐ provided e‐promotion occurs For all three excited states between the same (paired) orbitals‐is satisfyingly exemplified by 1: S1 = 3.92 eV and T1= 2.06 eV for 1, D4 or 5=2.74 eV for 1+.
Die Struktur des Curare‐Alkaloides Calebassinin‐1 183. Mitteilung uber organische Naturstoffe
Authors: Guggisberg Armin , Prewo Roland , Bieri Jost H. , Hesse Manfred 
Published: December 2004

The Structure of the Calabash Curare Alkaloid Calebassinine‐1The quaternary alkaloid calebassinine, isolated 1947 from Calabash Curare. has now been separated into calebassinine‐1 and ‐2. X‐ray structure determination of calebassinine‐1 led to structure 2 with relative configuration. A possible biogenetic pathway from 2,16‐dihydroakuammicine (3) as well as its pyrolytic decomposition to 3‐ethylpyridine (9), the quinoline derivative 8, methylchloride and norcale bassinine‐1 are discussed.
Aspects of the Reduction of Double Bonds Using Cob (I)alamin as Catalys
Authors: Fischli Albert 
Published: December 2004

AbstractThe olefinic system in 3β‐methoxy‐4‐cholesten‐6 a‐ol (2) is reduced using cob (I)alamin (1(I); see Scheme 1) as catalyst, aqueous acetic acid as solvent and metallic zinc as electron source (cf. Schemes 2 and 3). Experimental evidence for an attack of 1(I) on both faces of the double bond is presented. By the same catalyst (1 R)‐10, 10‐dimethyl‐2‐pinene‐ 10‐carbonitrile (9) is first transformed to the menthene derivative 11 (see Schemes 4 and 5). The ring opening is then followed by a fast saturation of the disubstituted olefinic system in 11, and ultimately the remaining double bond is reduced in a slow reaction. The cis‐configurated saturated menthane derivative 16 is the main final product (16/17 ≈ 10:1).