bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diastereoselektivität der Geruchswahrnehmung von Alkoholen der Iononreihe
Authors: Schulte‐Elte Karl H. , Giersch Wolfgang , Winter Beat , Pamingle Hervé , Ohloff Günther 
Published: December 2004

Diastereoselective Odor Perception of Alcohols in the Ionone SeriesThe characteristic odor of the diastereoisomers 1 and 2 of 1‐(2,2,6‐trimethylcyclohexyl)‐3‐hexanol is configuration dependent, the trans‐alcohol 1 being identified as the sensorily active component. Structure modification of model 1/2, for example substitution on C(2), C(13), and C(14) (ionon numbering) by CH3 groups, introduction of double bonds in the 3‐ or 4‐position, and isosteric substitution of C(7) by an O‐atom, leads to analogues revealing an unequivocal relation between stereochemistry and odor. The specific odor of alcohol 1 is generally released when all substituents are in an equatorial position; the resulting analogy with the molecular size and shape of odoriferous steroids suggests that the release of the particular scent can be correlated with a steroid‐resembling receptor event.
Nucleophilic 1,2‐Shifts of Carboxamide Groups in the Benzil‐Benzilic Acid Type Rearrangement of 4‐Aryl‐2,3‐dioxobutyramides and of Quinisatine
Authors: Gowal Heike , Spiess Anita , Ballenegger Marc , Due Laurent , Moll Hans , Schlunke Hans‐Peter , Dahn Hans 
Published: December 2004

Abstract4‐Aryl‐2,3‐dioxobutyramide hydrates 1, undergo the benzil‐benzilic acid rearrangement to form (substituted) benzyltartronate monoamides 2. For compound 1a (Ar = Ph), it is demonstrated by isotopic labelling that the reaction occurs exclusively by migration of the CONH2 group. Kinetic measurements with 1a‐c and with the cyclic amide quinisatine 6 show that the rearrangement of the carboxamide group, proceeding via an alkali‐catalysed step, can reach a plateau in the kobs./[OH−] diagram (cf. the Fig.), due to complete formation of a mono‐anion, and a further increase of rate attributable to the rearrangement of a bis‐anion. Comparisons suggest that rearrangements involving an amide group are slower than those involving an ester group, and that, for this effect (as for others), the pre‐equilibrium deprotonation of the hydrate is more important than a specific migration tendency.
Nucleophilic addition to C,Cdouble bonds. Part IX. Kinetics and mechanism of the base‐catalyzed intramolecular cyclization of olefinic alcohols
Authors: Tombo Gerardo M. Ramos , Ganter Camille 
Published: December 2004

AbstractThe base‐catalyzed intramolecular cyclization of polycyclic olefinic alcohols of type a (10‐endo‐hydroxy‐anti9,10‐tricyclo [4.2.1.12,5]dec‐7‐en‐9‐ones (type h), anti9,10‐tricyclo[4.2.1.12,5] dec‐3‐en‐9‐endo‐ols (type j), and anti10,11‐tricyclo[4.3.1.12,5]undec‐3‐en‐10‐endo‐ols (type 1)) to the ethers d and f, resp., has been studied. A mechanism for the nucleophilic addition of the corresponding alkoxide anion b to the isolated C,Cdouble bond is discussed. It is proposed that b is formed (fast acid/base equilibrium) in the first step. For the subsequent reaction sequence, there are two well distinguishable pathways: (a) Compounds with an additional carbonyl group (h) cyclize via a homoenolate‐like intermediate c, which is protonated stereoselectively on the exo‐side by the hydroxylic solvent. (b) Compounds without a carbonyl group (j and l) cyclize 102‐104 times slower, and the reaction proceeds via a carbanion‐like transition state e. The proton transfer from the hydroxylic solvent is clearly coupled with the C,Obond formation. Steric compression in the olefinic alcohols a influences the cyclization rate: (a) Alcohols with a smaller ring (h, X = CH2CH2) cyclize 70–200 times faster than the ones with a larger ring (1, X = CH2CH2CH2). (b) Replacement of the H‐atom at the carbinol C‐atom by a CH3 group enhances the rate of ether formation by a factor of 50–100. Due to through‐bond interactions between the C,C‐double bonds, olefinic alcohols with an additional endocyclic C,C‐double bond (h and j, X = CHCH) cyclize 20–300 times faster than the corresponding monoolefinic ones (h and j, X = CH2CH2).
Formation of the 5‐Azoniafulvene Ion and its Benzo‐annellated Analogue from N‐Mannich Bases of Pyrrole and Indole
Authors: Burger Ulrich , Bringhen Alain O. , Wirthner Philippe J. , Schärer Jean‐Claude 
Published: December 2004

Abstract1‐Dialkylaminomethylpyrroles are shown to behave in many respects like aminals. Acylation by an acid chloride, for instance, occurs normally at the amine‐type N‐atom rather than at the pyrrole ring. Spontaneous cleavage of the resulting quaternary acylammonium salts affords the 5‐azoniafulvene ion (3). This higly reactive iminium ion, and its benzo‐annellated analogue (4) can be trapped by electron rich aromatic compounds such as N‐methylpyrrole or N,N‐dimethylaniline. More elaborate N‐Mannich bases are accessible by addition of indoles to enamines.
Ion‐Transport Properties of Ionophores in Asymmetric Membranes
Authors: Morf Werner E. , Ruprecht Heidi , Simon Wilhelm 
Published: December 2004

AbstractThe selectivity and the permeability of neutral‐carrier‐based membranes for substrate ions not only depend on the complexation behavior of the ionophores used, but also on their environment. In asymmetric membranes, ionophores may generally exhibit asymmetric transport properties. Such asymmetric bulk membranes were prepared from two PVC half‐membranes incorporating synthetic cation‐carriers in different plasticizers. The results of potentiometric and electrodialytic studies are discussed on the basis of a theoretical analysis of the carrier‐mediated electrical properties of asymmetric bulk and bilayer membranes.
Stereoselective Double Friedel‐Crafts Acylation of trans‐μ‐(2,3,6,7‐Tetramethylidenebicyclo[3.2.1]octane)bis(tricarbonyliron). Crystal Structure of trans‐μ‐{(1RS,2RS,3SR,5RS,6SR,7SR)‐C,2,3,C‐η:C,6,7,C‐η‐[(Z,Z)‐1,1′‐(3,7‐Dimethylidenebicyclo[3.2.1]octane‐2,6‐diylidene)di(2‐propanone)]}bis(tricarbonyliron)
Authors: Alan Pinkerton A. , Schwarzenbach Dieter , Gabioud Raphy , Vogel Pierre 
Published: December 2004

AbstractThe Friedel‐Crafts mono and double acylations of trans‐μ‐[(1RS,2RS,3SR,5RS,6SR,7SR)‐C,2,3,C‐η:C,6,7,C‐η‐(2,3,6,7‐tetramethylidenebicyclo[3.2.1]octane)]bis(tricarbonyliron) (4) are highly stereoselective and yield trans‐μ‐{(1RS,2RS,3SR,5RS,6SR,7RS)‐C,2,3,C‐η :C,6,7,C‐η‐[(Z)‐1‐(3,6,7‐trimethylidenebicyclo[3.2.1]‐oct‐2‐ylidene)‐2‐propanone]}bis(tricarbonyliron) (5) and trans‐μ‐{(1RS,2RS,3SR,5RS,6SR,7SR)‐C,2,3,C‐η :C,6,7,C‐η‐[(Z,Z)‐1,1′‐(3,7‐dimethylidenebicyclo [3.2.1] octane‐2,6‐diylidene)di(2‐propanone)]}bis(tricarbonyliron) (6) whose structure has been established by single‐crystal X‐ray diffraction.
2,5‐Chinonmethide des 1,6‐Methano[10]annulens mit S,N‐ und N,N‐Acylketenacetal Struktur
Authors: Neidlein Richard , Hartz Georg 
Published: December 2004

2,5‐Quinonemethides of 1,6‐Methano[10]annulene with the Structures of S,N‐ and N,N‐Acylketene AcetalsInvestigation on the chemical reactivities of 2‐(tert ‐butoxy)‐1,6‐methano[10]annulene and the syntheses of the compounds 2, 4, 6–8, 11, 13–22 are described; the results of 1H‐ and 13C‐NMR‐spectroscopic measurements are reported.
(Cholestanyloxycarbonyl)benzyl esters as peptide substituents: Conformational properties of fully protected oligo‐L‐lysines with C‐terminal (cholestanyloxycarbonyl)benzyl and benzyl ester moieties
Authors: Toniolo Claudio , Bonora Gian Maria , Moretto Vittorio , Schneider Conrad H. , Rolli Hanspeter , Jung Marina , Izdebski Jan 
Published: December 2004

AbstractThis study involves L‐lysine oligo peptides, protected at the N‐terminus by the Nps and at the ε‐amino functions by Boc groups. Two series were prepared from dimer to octamer, one containing the p‐[(cholestan‐3β‐yloxy)carbonyl]benzyl, the other one the benzyl ester group at the C‐terminus. Conformational analyses were performed by IR absorption. The occurrence of the intermolecular β‐structure in the solid state and in CH2Cl2 solution was demonstrated for the highest oligomers. The relative stabilities of the self‐associated species were determined by adding a variety of polar solvents to the CH2Cl2 solutions. The cholestanyl‐containing peptides have a lower propensity to self‐aggregate than the benzyl‐ester analogues. Self‐aggregation and decreasing solubility run in parallel. It was also directly shown that soluble urea derivatives may disrupt intermolecular H‐bonds in CH2Cl2, a point of practical interest, particularly in solid‐phase peptide synthesis.
Optical Resolution of (RS)‐Pantolactone through Amide Formation
Authors: Fizet Christian 
Published: December 2004

AbstractThe optical resolution of (RS)‐pantolactone (1) is carried out through formation of diastereoisomeric amides. These are separated by a single hot washing with CH2C12 or CHC13. The used asymmetric amine, (1R)‐3‐endo‐aminoborneol (4), is readily accessible and can be recovered almost quantitatively after resolution.
Der Sterische Verlauf der nucleophilen Cyclopropanöffnung an den vier im Spiro(methylcyclopropan)‐Ring Diastereoisomeren Lanugonen J (Spirocoleonen)
Authors: Buss Peter , Prewo Roland , Bieri Jost. H. , Rüedi Peter 
Published: December 2004

The Stereochemistry of the Nucleophilie Opening of the Cyclopropane Ring in the four Diastereoisomeric Lanugons J (Spirocoleons)Methanolysis of the spiro(methylcyclopropane) moiety in the four diastereoisomeric lanugons J 3 (13S, 15R), 4 (13R,15R), 5 (13S,15S), and 6 (13R,15S) is shown to proceed stereospecifically with inversion of the configuration at the attacked C‐atom (C(15)). The resulting epimeric 2‐methoxypropyl‐substituted hydroxy‐1,4‐benzoquinones (royleanones) 7a/8a (monomethoxy derivatives) and 7b/8b (dimethoxy derivatives) could be separated by HPLC using the recently described ‘Non‐Aqueous Cation Exchange System’. Respective pairs of 1H‐NMR spectra exhibit minute but significant differences in the ABMX3 part of the 2‐methoxypropyl group. The final structure assignment is based on a single‐crystal X‐ray analysis of the dimethoxyroyleanone 7b, whose absolute configuration was established by chiroptical correlation with known abietanoids. Thus, methanolysis of 3 and 4 ((R)‐configuration at the reaction centre) yielded the royleanones 7a and 7b with (S)‐configuration, whereas analogous treatment of 5 and 6 ((S)‐configuration at the reaction centre) led to the corresponding derivatives 8a and 8b both having the (R)‐configuration in the 2‐methoxypropyl side chain.
Über Dienketene aus o‐Chinolacetaten
Authors: Quinkert Gerhard , Kleiner Erna , Freitag Bernd‐Jürgen , Glenneberg Jürgen , Billhardt Uta‐Maria , Cech Franz , Schmieder Klaus R. , Schudok Clemens , Steinmetzer Hans‐Christian , Bats Jan W. , Zimmermann Gottfried , Dürner Gerd , Rehm Dieter , Paulus Erich F. 
Published: December 2004

On Dien‐Ketenes from o‐Quinol‐AcetatesA detailed picture of the photochemistry of o‐quinol‐acetates is presented. (RS)‐6‐Acetoxy‐6‐methyl‐, (RS)‐6‐acetoxy‐2,6‐dimethyl‐, (RS)‐6‐acetoxy‐5,6‐dimethyl‐, (RS)‐6‐acetoxy‐2,4,6‐trimethyl‐, (RS)‐6‐acetoxy‐2,3,4,6‐tetramethyl‐, and (RS)‐6‐acetoxy‐2,3,4,5,6‐pentamethyl‐2,4‐cyclohexadien‐1‐ones serve as representative educts. There are two separate main photochemical routes conveniently designated as 1(π*, n) or 3(π*, π) tracks. The latter may also be attained by sensitization and leads to phenols. The former, by α‐cleavage furnishes dienketens as indispensable phototransients. Photolysis of dien‐ketens follows one or more of three reaction channels, each of which yields a particular type of photoproduct: heat‐induced monocyclization affords 2,4‐cyclohexadien‐1‐ones, heat‐induced bicyclization stereoselectively furnishes bicyclo[3.1.0]hex‐3‐en‐2‐ones, and multi‐step addition of protic nucleophiles stereoselectively gives 1,4‐, 1,6‐ and/or 1,2‐adducts. By X‐ray analysis or NOE studies, the structure of isolated photoproducts is established. Conventional spectroscopy at low or flash spectroscopy at normal temperature yield information on the formation and decay of kinetically unstable intermediates. Photoproduct composition depends on the pattern of substitution of the educts, on the solvents, and on the nucleophiles that might be present. Substituents primarily exert an influence upon the population of the various conformers of the dien‐keten. Solvents affect the rate of the divers reaction paths competing for the phototransient. Nucleophiles play more than a trivial role when adducts are formed. With the detailed view of a dien‐keten's role on hand, the photoproduct from a given o‐quinol‐acetate or more general from a linear conjugated cyclohexadienone is now predictable.
Partial Purification and Characterization of Raucaffricine β‐D‐Glucosidase from Plant Cell‐Suspension Cultures of Rauwolfia serpentina BENTH
Authors: Schübel Helmut , Stöckigt Joachim , Feicht Richard , Simon Helmut 
Published: December 2004

AbstractA novel highly substrate‐specific Rauwolfia enzyme, raucaffricine β‐D‐glucosidase, was isolated from cell‐suspension cultures of R. serpentina. The enzyme has been purified ca. 1350‐fold, its major characteristics such as Mr = 66600 ± 5%, pH optimum 5.1, temperature optimum 38°, and inhibition of its activity by glucose and fructose were investigated. Its limited distribution in different cell cultures and differentiated plants indicates that the enzyme is present in significant amounts exclusively in cultured Rauwolfia cells.
Synthesis of anti‐9‐Bromo‐ and anti‐9‐Chlorobicyclo[4.2.1]nonatriene via Bicyclo[4.2.1]nonatriene→Bicyclo[4.2.1]nonatriene Rearrangement
Authors: Goldstein Melvin J. , Barren James P. 
Published: December 2004

AbstractThe first syntheses of 9‐bromo‐ and 9‐chlorobicyclo[4.2.1]nona‐2,4,6‐trienes were each achieved in three stereoselective steps from the 9,9‐bis(selenophenyl) derivative 9 in 79% overall yield for the bromide and 64% for the chloride. A deuterium‐labeling experiment reveals the first rearrangement of a bicyclo[4.2.1]nonatriene which leaves the ring system intact.
Remarkable Enhancement of the Rate of Cathodic Reduction of Hydrocarbonate Anions at Palladium in the Presence of Caesium Cations
Authors: Spichiger‐Ulmann Martine , Augustynski Jan 
Published: December 2004

AbstractSteady‐state polarization curves, representative of the electrochemical reduction of HCO ions at a smooth palladium cathode, obtained in CsHCO3 and NaHCO3 solutions, are compared. The net current densities, associated with the electroreduction of HCO anions, measured in 1M CsHCO3 solution are shown to be up to 9 times larger than those observed in 1M NaHCO3 solution. This result is interpreted in terms of a direct involvement of the Cs+ cations in the reaction at the cathode through the formation of ion pairs with the HCO anions.
C45‐ und C50‐Carotinoide. 4. Mitteilung. Synthese von optisch aktiven cyclischen C20‐Bausteinen und von (2R,2′R)‐2,2′‐Bis(4‐hydroxy‐3‐methyl‐2‐butenyl)‐β,β‐carotin ( = C.p. 450)
Authors: Wolleb Heinz , Pfander Hanspeter 
Published: December 2004

C45‐ and C50‐Carotenoids: Synthesis of Optically Active Cyclic C20‐Building Blocks and of (2R,2′R)‐2,2′‐Bis(4‐hydroxy‐3‐methyl‐2‐butenyl)‐β,β‐carotene ( = C.p. 450)The synthesis of the optically active C20‐building blocks (R)‐26 and (R)‐39 and of the optically active cyclic C50‐carotenoid C.p. 450 (3) starting from (−)‐β‐pinene is reported.
Sequence dependence of secondary‐structure formation part IV Helix‐forming potential of amphiphilic oligopeptides containing aib residues
Authors: Mutter Manfred , Altmann Karl‐Heinz , Flörsheimer Andreas , Herbert JüRgen 
Published: December 2004

AbstractThe conformational properties of Aib‐containing oligopeptides having the propensity to adopt amphiphilic helical conformations were investigated by CD spectroscopy in solution. The peptides CF3COOH.H‐Pro‐Glu‐[Ala‐Aib‐Glu‐Aib‐]4Gly‐OH (I), HCl.H‐Pro‐Ala‐Aib‐[Gul‐Ala‐Ala‐Aib‐]2Glu‐Ala‐Aib‐Gly‐PEGM (II), and CF3COOH.H‐Ala‐Aib‐[Glu‐Glu‐Ala‐Aib‐]3PEGM (III) were synthesized according to the general principles of the liquid‐phase method for peptide synthesis. Peptides I‐III exhibit helical conformations in CF3CH2OH, MeOH, and in H2O at acidic pH; however, at pH 7, only II forms a stable helix, whereas I and III are predominantly in an unordered conformation. Some general features for the construction of amphiphilic helices are discussed in the light of the experimental data.
Stereoselective Reduction of δ‐Hydroxy‐β‐ketoesters
Authors: Kathawala Faizulla G. , Prager Bernhard , Prasad Kapa , Repič Oljan , Shapiro Michael J. , Stabler Russell S. , Widler Leo 
Published: December 2004

AbstractThe reduction of δ‐hydroxy‐β‐ketoesters 1 was investigated with three different reducing agents. In several instances, high selectivity in favor of syn‐1,3‐diols was observed.
Konfigurationsbestimmung von geometrischen Isomeren mittels selektiver 13C{1H}‐NOE‐Differenzspektroskopie
Authors: Neidlein Richard , Kramer Walter , Ullrich Volker 
Published: December 2004

Application of Selective 13C{1H}‐NOE Difference Spectroscopy in Determination of the Configuration of (Z)/(E)‐IsomersHeteronuclear 13C{1H}‐NOE studies have been performed to elucidate the configuration at the imino double bond in N,N′‐Dicyanoquinonediimines. Selective low‐power irradiation of the neighbouring ring protons in compounds 1–5 increases the signal intensities of CN as well as of the imino‐C‐atoms in the 13C‐NMR spectra. The increase of signal intensity can easily be detected by the difference spectroscopy. The results of this investigation are in good agreement with a recently published study on the stereochemistry of N,N′‐Dicyanoquinonediimines, based on the interpretation of 13C‐chemical shifts.
Desoxy‐nitrozucker 14. Mitteilung 1‐C‐Nitroglycale. Herstellung und Umsetzung mit einigen Stickstoff‐Nucleophilen
Authors: Baumberger Franz , Beer Dieter , Christen Markus , Prewo Roland , Vasella Andrea 
Published: December 2004

1‐C‐Nitroglycals. Preparation and Reaction with Some Nitrogen NucleophilesAcetylation of the 1‐deoxy‐1‐nitromannopyranoses 2 and 6 was accompagnied by spontanous β‐elimination to give the 1‐C‐nitroglucals 3 and 7, respectively, while acetylation of the gluco‐ and galacto‐configurated 1‐deoxy‐1‐nitropyranoses 8 and 14 gave the acetates 9 and 15, respectively (Scheme 1). The acetylation of the ribo‐ and arabino‐configurated 1‐deoxy‐1‐nitrofuranoses 19 and 21 also occurred without β‐elimination to give the acetates 20 and 22, respectively (Scheme 2). Mild base treatment of the previously described O‐acetylnitro‐β‐D‐glucose 4, the O‐acetylnitro‐β‐D‐pyranoses 9 and 15, and the O‐acetylnitro‐β‐D‐furanoses 17, 20, and 22 gave the 1‐C‐nitroglycals 3, 10, 16, 18 and 23, respectively (Scheme 1 and 2). The previously obtained 1‐C‐nitroglucal 3 was deacetylated by treatment with MeOH in the presence of KCN or sodium m‐nitrophenolate to give the free nitroglucal 5. Deacetylation of the benzylidene protected 1‐C‐nitroglucal 10 (MeOH, NaOMe) gave the 4,6‐O‐benzylidene‐1‐C‐nitroglucal 11 and traces of the 2‐O‐methyl‐1‐C‐nitromannoses 12 and 13. The UV, IR, 1H‐NMR and 13C‐NMR spectra of the 1‐C‐nitroglycals are discussed. In solution, the 1‐C‐nitroglycals 1, 5, 7, 10, 11, and 16 adopt approximately a 4H5− and 3 a flattened 4H5 conformation. The structure of 5 was established by X‐ray analysis. In the solid state, 5 adopts a sofa conformation, which is stabilized by an intramolecular H‐bond. The β‐addition of NH3 to the 1‐C‐nitroglucals 7 and 10 was followed by an O→ N acetyl migration to give exclusively anomeric pairs of the N‐acetyl‐1‐nitromannosamine derivatives 24/25 and 26/27, respectively (Scheme 3). The β‐addition of methylamine, octadecylamine, and tryptamine to the 1‐C‐nitroglucal 11 also stereoelectronically controlled and gave the crystalline N‐alkyl‐1‐nitromannosamines 28, 29, and 30, respectively. The stereoelectronically controlled β‐addition of NH3 to the 1‐C‐nitrogalactal 16, followed by acetylation, yielded exclusively the talosamine derivative 31, while the reversible β‐addition of azide ions to 16 gave the anomeric 2‐azido‐1‐nitrogalactoses 32 and 33. The β‐addition of azide ions to the 1‐C‐nitroglucal 1 led to the 2‐azido‐1‐nitromannose 34. In the presence of excess formaldehyde, this addition was followed by a Henry reaction. Chromatography of the crude product was accompagnied by solvolytic removal of the NO2 group to give the 3‐azidomannoheptulose 35 in high yields (Scheme 4).
Synthese von (Methylthio)penam‐Derivaten durch Keten‐Addition an 4,5‐Dihydro‐5‐(methylthio)‐1,3‐thiazole
Authors: Jenny Christjohannes , Prewo Roland , Bieri Jost H. , Heimgartner Heinz 
Published: December 2004

Synthesis of (Methylthio)penam Derivatives via Keten Addition onto 4,5‐Dihydro‐5‐(methylthio)‐1,3‐thiazolesThe 4,5‐dihydro‐5‐(methylthio)‐2‐phenyl‐1,3‐thiazoles 3a and 3b, easily prepared from the corresponding 1,3‐thiazol‐5(4H)‐thiones and MeLi, react with dichloroacetyl chloride (5a) and acidoacetyl chloride (5b) in the presence of Et3N to give (methylthio)penam derivatives 6 (Table 1). The reaction mechanism is either a [2 + 2] cycloaddition of in situ generated ketene or a two‐step reaction (Scheme 2). The structure of 6f has been confirmed by X‐ray crystallography (Fig. 2). The relative configuration of 6a‐e follow from comparison of their 1H‐NMR spectra with those of 6f (Fig. 1). The 6‐azidopenams 6d and 6f have been reduced to aminopenams 8a and 8b, respectively. Acylation of 8a with phenacetyl chloride yields 9 (Scheme 4).
Preparation of Enantiomerically Pure β‐Silylcarboxyl Derivatives by Asymmetric 1,4‐Addition to N‐Enoyl‐sultams. Preliminary Communication
Authors: Oppolzer Wolfgang , Mills Robert J. , Pachinger Werner , Stevenson Thomas 
Published: December 2004

AbstractEtAlCl2‐promoted additions of organocopper reagents to camphor‐derived, conjugated N‐enoyl‐sultams gave saturated and olefinic β‐silylcarboxyl derivatives with high diastereodifferentiation. Nondestructive removal of the chiral auxiliary followed by oxidative Si‐C bond cleavage furnished enantiomerically pure acetate‐derived aldols and propionate‐derived ‘anti’ ‐aldols (via silyl‐directed α‐methylation).
Struktur und Reaktivität von Xanthocorrinoiden. 4. Mitteilung. Hydroxylierung an C(15) des Corrin‐Chromophors bei der Reaktion von Cyanocob(III)alamin mit Udenfriend‐Reagenz
Authors: Holze Gerhard , Gossauer Albert , Ernst Ludger 
Published: December 2004

Structure and Reactivity of Xanthocorrinoids. C(15) Hydroxylation of the Corrin Chromophore on Reaction of Cyanocob(III)alamin with Udenfriend's ReagentHydroxy‐corrinoid 4 represents a new type of corrin derivatives whose chromophore is identical with that of products formed on bacterial degradation of cyanocob(III)alamin (1). In vitro, 4 is obtained by O2 oxidation of 1 in the presence of ascorbic acid and cupric ions.
Thermal Methyl‐Group Transfer between Methylcobalt(III) Corrinates and Cobalt(II) Corrinates. Equilibration Experiments with Heptamethyl Cobyrinates and Cobalamins
Authors: Kräutler Bernhard , Hughes Mark , Caderas Christian 
Published: December 2004

AbstractSeparate neutral aqueous solutions of either (a) methylcob(III)alamin (2) and (heptamethyl cob(II)yrinate) perchlorate (3) or of b) cob(II)alamin ( = vitamin B12r; (4) and [Coβ‐methyl(heptamethyl cob(III)yrinate)] perchlorate (5) equilibrated thermally at r.t. according to 2 + 3 ⇄ 4 + 5. The corresponding equilibrium constant Ke was determined (Ke = 0.63 ± 0.15). This equilibration experiment indicates that the coordination of the nucleotide function in methylcob(II)alamin (2) hardly affects the thermodynamics of the CoC bond homolysis in aqeous solution when compared to nucleotide‐free methylcorrinoids such as 5.