bluuebunny/crossref_metadata_2025 huggingface dataset:
Bicyclo[2.2.2]octanes. Syntheses and Hydrolyses of 6‐exo‐substituted 2‐exo‐ and 2‐endo‐Bicyclo[2.2.2]octyl p‐Toluenesulfnates. Part 9
Authors: Grob Cyril A. , Sawlewicz Pawel
Published: December 2004

The synthesis of the title compounds and their hydrolysis products in 70% dioxane are described.
Cob(I)alamin‐Catalyzed Skeletal Migrations Observed during the Reduction of 4β‐(tert‐Butyl)‐1α‐(1‐methylvinyl)cyclohexanecarbaldehyde
Authors: Wan Terence S. , Fischli Albert
Published: December 2004

The cob(I) alamin(1(I))‐catalyzed2 transformation of the aldehyde 2 has been studied (cf. Table 1). Kinetic examinations showed a rapid isomerization of 2 to 3 (cf. Fig. 1 and 2). From the transformations in glacial AcOH, the two cyclopropanols 5 and 7 were isolated as main products (cf. Tables 1–3 and Fig. 1 and 2). Using large amounts of 1(I), the aldehyde 4 was very slowly transformed. Accepting the intermediate formation of 6 interconnected Co‐complexes, i. e. A, B, C, D, E and F (cf. Scheme), the generation of all the products observed can be explained.
Studies on Monoterpene Glucosides and Related Natural Products Part 51. Absolute Structures of Hydrangenosides A, B, C, D, E, F, and G. Novel Type Secoiridoid Glucosides from Two Hydrangea Plants
Authors: Uesato Shinichi , Takeda Yoshio , Hashimoto Toshihiro , Uobe Kenichi , Inouye Hiroyuki , Taguchi Heihachiro , Endo Toru
Published: December 2004

From Hydrangea macrophylla var. Macrophylla, four new secoiridoid glucosides, hydrangenosies A, B, C and D, were isolated, along with the known iridoid glucosides loganin, secologanin, secologanic acid and sweroside. Moreover, hydrangenosides E, F, and G, the glucosides of the same class, were isolated together with hydrangenosides C and D from Hydrangea Scandens. Based on spectroscopic and chemical methods, the novel structures of the new glucosides consisting of secologanin and a shikimate‐malonate‐derived unit which are joined by a CC bond were elucidated. However, seven other Hydrangea plants were tested and found not to contain hydrangenoside‐type glucosides.
Effect of Substituents, Solvent, and Temperature on the Reactivity of the Zwitterionic Peroxides Arising from the Photo‐Oxygenation of 2‐(Methoxymethylidene)‐ and 2‐(Phenoxymethylidene)adamantane
Authors: Jefford Charles W. , Grant Hamish G. , Jaggi Danielle , Boukouvalas John , Kohmoto Shigeo
Published: December 2004

The photo‐oxygenation of 2‐(methoxymethylidene)adamantane (3) creates a zwitterionic peroxide which may be captured by acetaldehyde to give the corresponding pair of diastereoisomeric tricyclo[3.3.1.13,7]decane‐2‐spiro‐6′ ‐(3′ ‐methyl‐5′ ‐methoxyl′, 2′, 4′ ‐trioxanes) (4). Ease of capture depends strongly on solvent polarity and temperature. When these are low, yields of trioxine are high (∼ 80%). Conversely, 1,2‐dioxetane formation is favoured at high temperature and solvent polarity. 2‐(Phenoxymethylidene)adamantane (5), on photo‐oxygenation, only gives the corresponding 1,2‐dioxetene, even in the presence of acetaldehyde. From a Hammett, study of the‐oxygenation of the enol ether 5 and p‐methoxy, p‐methyl, p‐chloro and m‐chloro derivatives, 9, 11, 13, and (15), a good linear relation was found between substituent constants and oxygenation rates which yielded reaction constants (ρ) of 2.59, −2.40, −1.09, and −0.90 in benzene, AcOET, CH2Cl2, and MeOH respectively. This data to the formation of a zwitterionic peroxide which enjoys stabilization from its won substituents and by competing solvation and further explains the predominance of dioxetane to the detriment of trioxane formation.
Biogenetic‐Type Total Synthesis of (±)‐2‐Deoxystemodinone. Preliminary Communication
Authors: Lupi Alessandro , Patamia Maria , Grgurina Ingeborg , Bettolo Rinaldo Marini , Di Leo Ornella , Gioia Patrizia , Autnaroli Simonetta
Published: December 2004

A biogenetic‐type total synthesis of(±)‐2‐deoxystemodinone (1), by solvolytic rearrangement of the 1‐methyl[2.2.2]oct‐2‐yl methanesulphonate 4, is described.
Probes for a Regulatory Site on the Nicotinic Acetylcholine Receptor‐Channel. Synthesis of (±)‐7‐Debutylperhydrohistrionicotoxin, (±)‐2‐Depentyl‐7‐debutylperhydrohistrionicotoxin, and their Analogues
Authors: Gessner Wieslaw , Takahashi Kimio , Witkop Bernhard , Brossi Arnold , Albuquerque Edson X.
Published: December 2004

Reaction of glutarimide with pent‐4‐enylmagnesium bromide, followed by cyclization of intermediate ketoamide, and hydrolysis of the formates 10 and 13 led to the mixture of the hydroxylactams 11 (cis) and 14 (trans) which could be separated via their benzenecarbamates. Reduction of cis‐hydroxylactam 11 with LiAlH4 yielded 2‐depentyl‐7‐debutylperhydrohistrionicotoxin (6), whereas reduction of trans‐isomer 14 gave the epimeric alcohol 9. cis‐Hydroxylactam 11 was converted via thiolactam 17 and the methylthio derivative 18 to ketimine 19 which was reduced with NaBH4 yielding a mixture of natural 4 and unnatural 7, analogues of perhydrohistrionicotoxin (2). Reduction of 4 with H2 in the presence of Pd/C yielded (±)‐7‐debutylperhydrohistrionicotoxin (5).
Halochrome Molekeln. 5. Mitteilung. Synthese substituierter 6H‐Chromeno[4,3‐b]indolizine und ihrer Aza‐analogen
Authors: Gunzenhauser Sigmund , Balli Heinz
Published: December 2004

Halochromic Molecules. Synthesis of Substituted 6H‐Chromeno[4,3‐b]indolizines and their Aza‐analogues

We have synthesized a series of substituted chromeno[4,3‐b]indolizines and their respective aza‐analogues. Dyes generated from them contain the electrondonating 2‐(2‐hydroxy‐5‐methylphenyl)indolizin‐3‐yl moiety. The 90 MHz FT 1H‐NMR spectra of starting and final products supported the postulated structures. Fragmentations in the mass spectra also were consistent with the assumed structures.
Syntheses of Racemic Diaminosugar Derivatives Starting from 1,2‐Dihydropyridines and from Nitrosobenzene
Authors: Augelmann Gérard , Streith Jacques , Fritz Hans
Published: December 2004

Racemic diaminosugars were easily obtained by a regio‐ and stereoselective three‐step synthetis. In the first step, regiospecific hetero‐Diels‐Alder cycloadditions between 1,2‐dihydropyridines 1a and 10 and nitrosobenzene led to the bicyclic compounds 2a and 11, respectively, cis‐Glycol formation starting from these latter adducts, followed by hydrogenolysis of the NO bond and by exhaustive acetylation of the OH‐groups, led to the diaminolyxose 5, the diaminomannose 14 and the diaminoallose 15. When starting from benzyl 1,2‐dihydropyridine‐1‐carboxylate (1b) and using the same reaction sequence, the racemic piperidine derivative 8 was obtained.
Steric Effects on Reaction Rates. VI. Application of a New MM2 Force‐Field for Carbenium Ions to Solvolysis Rates of Secondary p‐Toluenesulfonates
Authors: Müller Paul , Mareda Jiri
Published: December 2004

An empirical force‐field for carbenium ions has been incorporated in Allinger's MM2 programme. Structural parameters of secondary carbenium ions calculated by this method are compared with those obtained with Schleyer's BIGSTRN calculations. The strain changes occurring upon solvolysis of secondary p‐toluenesulfonates are evaluated by means of this force‐field and correlated with the rate constants for solvolysis. The equation for correlation of acetolysis, relative to cyclohexyl p‐toluenesulfonate, of 28 kc substrates is ΔG = 0.67 ΔEst ‐ 0.20 (r = 0.958).
Alkylierung in der 2‐Stellung von (2S, 4R)‐ 4‐Hydroxyprolin unter Retention
Authors: Weber Theodor , Seebach Dieter
Published: December 2004

Alkylation in the 2‐Position of (2S, 4R)‐4‐Hydroxyproline with Retention of Configuration

O‐Acetyl‐4‐hydroxyproline (1b) is condensed with pivalaldehyde to give a single stereoisomer of the 2‐(tert‐butyl)‐4‐oxo‐3‐oxa‐1‐azabicyclo[3.3.0]oct‐7‐yl acetate (3). This is converted to the enolates 4 or 5, reactions of which with alkyl halides, aldehydes, and acetone (→6,9,10,11) are diastereoselective (lk‐1,3‐induction). Cleavage of the corresponding products furnishes the enantiomerically pure 2‐deuterio‐, 2‐methyl‐, 2‐allyl‐, and 2‐benzyl‐substituted 4‐hydroxyprolines 2a–2d.
d6 and d8 Metal Carbonyl Complexes of 7,7‐Dimethoxy‐5,6‐dimethylidenebicyclo[2.2.1]hept‐2‐ene. Stereoselective Hydroformylation of an [Fe(CO)4(olefin)] Complex
Authors: Loset Jacques , Roulet Raymond
Published: December 2004

Reaction of 7,7‐dimethoxy‐5,6‐dimethylidenebicyclo[2.2.1]hept‐2‐ene (2) with various metal carbonyls and their derivatives gave the η2‐M(CO)4 (M = Fe (17), Ru (18)), η4‐M(CO)3 (M = Fe (19x, 19n), Ru (20n)), and η2‐M(CO)5 and η6‐M(CO)3 (M = Cr, Mo, W) complexes. The trigonal bipyramidal η2‐M(CO)4 complexes present an exceptional C3v symmetry at the metal with the C,C‐double bond in an axial position. In all the η2‐complexes, this double bond is stereospecifically coordinated by its exo‐vs. endo‐η4‐Fe(CO)3 configuration was established by chemical correlation (hydrolysis, hydrogenation) with the corresponding complexes (24x, 24n) of 7,7‐dimethoxy‐2,3‐dimethylidenebicyclo[2.2.1]heptane (5). The relative rates of hydrolysis (AcOH/H2O 2:1, 50°C) of ligands 2 and 5 and of complexes 19x, 19n, 24x, and 24n to the corresponding ketones showed an acceleration effect only when the metal is coordinated to the exo‐face. This was attributed to an F‐strain effect on the leaving group of the substrate. Compound 17 was further metallated by [Fe2(CO)9] giving the bimetallic isomers 21xn and 21xx. The endocyclic C,C‐double bond of the latter can be stereospecifically hydroformylated (1 atm CO, AcOH/H2O, 25°C) giving 29x (49%). Hydroformylation of 17 gave the corresponding uncoordinated aldehydes 30x/30n in better yields (76%) but with lower selectivity (3:1). These are the first examples of hydroformylation of an isolated [Fe(CO)4(olefin)] complex.
Investigation of the Cyclopentenone Formation via the α‐Alkynone Cyclisation: Synthesis of the Acorone Intermediate 8‐Methylspiro[4.5]deca‐3,7‐dien‐2‐one
Authors: Ackroyd John , Karpf Martin , Dreiding André S.
Published: December 2004

As a further application of the cyclopentenone formation A→C via the thermal α‐alkynone cyclisation B→C and in order to test the fate of an isolated C,C‐double bond within a molecule under these conditions, we investigated the synthesis of the acorone intermediate 3starting from the known carboxylic acid 1. The α‐alkynone 2 was obtained from 1 via the acyl chloride 6 and a Pd(II)‐catalysed route (22%). The thermolysis of 2 at 550° provided the target molecule 3 (48%) together with the product 9 (20%) of a competing intramolecular ene reaction and its dimer 10 (4%). At a higher thermolysis temperature (650°), the spiro ketone 3 was found to be unstable, affording the retro‐Diels‐Alder fragments 4‐methylidene‐2‐cyclopentenone (12) (33%) and isoprene (32%). A further example of the influence of an isolated double bond on the yield of the cyclopentenone‐formation sequence A→C was provided by the comparison of the annelation 14→20 (5% overall with Pd(II)‐catalysed acylation) with that of its non‐olefinic analogue 17→21 (53% overall with Friedel‐Crafts acylation).
Light‐Induced and Thermal π‐Skeletal Rearrangement of Heptalenes with Retention of Configuration
Authors: Bernhard Werner , Brügger Paul , Schönholzer Peter , Weber Roland H. , Hansen Hans‐Jürgen
Published: December 2004

It is shown that dimethyl 5, 6, 8, 10‐tetramethyl‐ (3) and 8‐ (tert‐butyl)‐5,6,10‐trimethylheptalene‐1, 2‐dicarboxylate (5), and their derivatives rearrange reversibly on irradiation or on heating to yield the corresponding 1,6,8,10‐tetramethyl‐ (4) and 8‐(tert‐butyl)‐1,6,10‐trimethylheptalene‐1,2‐dicarboxylate (6), and their derivatives by double‐bond shift (π‐skeletal rearrangement) via a transition state with D2 symmetry as the highest possible one. This follows from the fact that (−)‐(P)‐3 is photochemically as well as thermally rearranged to give (−)‐(P)‐4 i.e. the π‐skeletal rearrangement occurs with retention of configuration of the heptalene skeleton and without loss of optical purity.
Peptide conformations. Part 30. Assignment of the 1H‐, 13C‐, and 15N‐NMR spectra of cyclosporin A in CDCl3 and C6D6 by a combination of homo‐ and heteronuclear two‐dimensional techniques
Authors: Kessler Horst , Loosli Hans‐Rudolf , Oschkinat Hartmut
Published: December 2004

The 1H‐, 13C‐, and 15N‐NMR spectra of the immunosuppressive cyclic undecapeptide cyclosporin A (1) have been analyzed at 300 MHz in CDCl3, C6D6, and mixtures of these solvents. A combination of different homo‐ and heteronuclear two‐dimensional NMR techniques enable complete assignment of all H‐, C‐ and 4 N‐signals. Recognition of the proton spin systems has been achieved via 1H,1H–COSY and double‐quantum‐1H‐NMR spectroscopy. NOESY spectra yield some sequence assignments, but two techniques using coupling across amide bonds have been applied to get independent assignments of all amino acids in the sequence: (i) An 1H,1H‐COSY spectrum optimized for small coupling constants enables the detection of long‐range couplings from N‐methyl groups to both α‐protons attached to that amide bond. (ii) An 1H, 13C‐COSY spectrum optimized for C,H‐long‐range couplings (J = 5 to 10 Hz) to the eleven CO groups again yields coupling to both α‐protons attached to that amide bond. Additionally these two experiments yield the assignment of N‐methyl protons and carbonyl C‐atoms. Normal and relayed 1H,13C‐COSY in both solvents have been applied to assign all C‐atoms via their directly attached and remote protons. An 1H,13C‐COLOC spectrum at 500 MHz in CDCl3, which uses H,C‐long‐range couplings confirms the assignment of all proton spin systems as well as the C‐signals of each individual amino acid. Ambiguities in the assignment of the C(δ)'s of MeLeu have thus been removed. An 1H,15N‐COSY spectrum enables the assignment of the 4 NH N‐atoms.
Peptide conformations. Part 31. The conformation of cyclosporin a in the crystal and in solution
Authors: Loosli Hans‐Rudolf , Kessler Horst , Oschkinat Hartmut , Weber Hans‐Peter , Petcher Trevor J. , Widmer Armin
Published: December 2004

The all‐light‐atom X‐ray crystal‐structure analysis of cyclosporin A (1), a cyclic undecapeptide containing seven N‐methylated amino acids, reveals a conformation very similar to that of the previously analysed iodo derivative which is characterised by a twisted β‐pleated sheet involving the residues Me‐Val‐11, MeBmt‐1, Abu‐2, Sar‐3, MeLeu‐4, Val‐5, MeLeu‐6, and Ala‐7. The β‐bend at Sar‐MeLeu‐4 is of type II′, and the loop of the residual amino acids involves a cis‐peptide bond between MeLeu‐9 and MeLeu‐10. The NH proton of D‐Ala‐8 closes a yi‐bend with a H‐bond to the MeLeu‐6 CO group. The crystal was grown from acetone. A closely similar backbone conformation in apolar solvents such as CDCl3 or C6D6 has been derived from the interpretation of the NMR spectral parameters (homo‐ and heteronuclear NOE effects, coupling constants, chemical‐shift values of the C‐, H‐, and N‐atoms). A minor variation in the backbone conformation between crystal and solution is observed in the region of D‐Ala‐8, where in solution a 3‐center H‐bond is established between the NH of D‐Ala‐8 und the carbonyl O‐atoms of both MeLeu‐6 (yi‐turn) and D‐Ala‐8 (C5‐bend). A recently proposed technique to identify intramolecular H‐bond via heteronuclear NOE from NH proton to carbonyl C‐atoms is critically analysed. The main difference between crystal and solution conformations lies in the orientation of the side chains of the unusual amino acid MeBmt (χ1 = +60° in solution, ‐168° in the crystal) and of MeLeu‐10 (X1 = −60° in solution, +60° in the crystal). The differences in crystal and solution are caused by the break of the intermolecular H‐bond of the OH group of MeBmt on dissolution of the crystal. The bifurcated H‐bond of D‐Ala‐8 twists the backbone in this region. Molecular modeling demonstrates that this is the origin of the change in the side chain conformation of MeLeu‐10. The intramolecular flexibility in the crystal indicated by the thermal parameters obtained from the X‐ray refinement, and in solution by an analysis of spin‐lattice relaxation times in the NMR experiments, indicate a fairly rigid backbone and fixed conformations for all the side chains except for that of Abu‐2 and the distal atoms of MeBmt.
Synthesis of 1H‐Cyclopropa[b]naphthalenes via Trapping of o‐Benzoquinodimethanes
Authors: Müller Paul , Rodriguez Domingo
Published: December 2004

1H‐Cyclopropa[b]naphthalene (10a) and 3‐methyl or dimethyl derivatives have been synthesized by interception of appropriately substituted o‐quinodimethanes 3 with 1‐bromo‐2‐chlorocyclopropene 5, and subsequent dehydrohalogenation of the adducts. The o‐quinodimethane derivatives 3 in turn were obtained from the diynes 7 via base‐induced isomerization to bisallenes 8 and thermal electrocyclic ring closure.
Photooxygenolytic Degradation of the Vitamin‐B12 Derivative Heptamethyl Coα,Coβ‐Dicyanocobyrinate. Efficient Preparation of Bicyclic Fragments
Authors: Kräutler Bernhard , Stepánek René
Published: December 2004

The methylene‐blue sensitized photooxygenation of heptamethyl Coα,Coβ‐dicyanocobyrinate (1, cobester) at ca. −45° and in (D3)acetonitrile solution proceeds readily to the stage of selective double cleavage of the corrin macrocycle. It furnishes the bisected heptamethyl Coα,Coβ‐dicyano‐5,6:14,15‐tetraoxo‐5,6:14,15‐disecocobyrinate (3) in 91% yield after warming the photooxygenation mixture to room temperature. Complex 3 is also obtained by photooxygenation of the secocorrinoid oxygenation products of 1, namely of heptamethyl Coα,Coβ‐dicyano‐5,6‐dioxo‐5,6‐secocobyrinate (2a) and of its isomer heptamethyl Coα,Coβ‐dicyano‐14,15‐dioxo‐14,15‐secocobyrinate (2b). When the raw photooxygenation product of 1 is kept at low temperature, 3 is not formed in a significant amount; spectral analysis reveals 4 as intermediate that is transformed into 3 quantitatively upon warm‐up and storage at r.t. Compound 4 is assigned the structure of heptamethyl Coα,Coβ‐dicyano‐5,6‐epidioxy‐5,6‐dihydro‐14,15‐dioxo‐14,15‐secocobyrinate, based on NMR‐spectral data and since 4 is also formed cleanly in the corresponding low‐temperature photooxygenation of 2b. Catalytic reduction of the Co(III) complex 3 (H2, Pt/C) in the presence of EDTA produces a colourless oil, from which the bicyclic fragments 5 (corresponding to rings A and D of 1) and 6 (corresponding to rings B and C of 1) are obtained in 99 and 91% yield, respectively, after chromatographic separation.
Untersuchungen zur Carotinoidzusammensetzung in Blüten der Gartenhybride Narcissus cvv ‘Golden Harvest’
Authors: Berset Daniel , Pfander Hanspeter
Published: December 2004

Investigation of the Carotenoid Composition in the Petals of a Garden Hybrid Narcissus cvv ‘Golden Harvest’

The carotenoid composition of the petals of a yellow garden hybrid Daffodil is reported. As major compound (all‐E)‐lutein was isolated. As minor compounds phytoene, phytofluene, (all‐E)‐β‐carotene, (9Z)‐lutein, (9′Z)‐lutein, (13Z)‐lutein, violaxanthin, and luteoxanthin were identified. The position of the (Z)‐double bond of the different isomers of lutein could be proved by 1H‐NMR spectroscopy.
Physicochemical Properties of Deuterated Compounds. 8th Communication. The kinetic isotope effect for the reaction of hydrogen atoms with methylcyclohexane and perdeuteromethylcyclohexane in the gas phase
Authors: Fujisaki Noboru , Ruf Amanz , Gäumann Tino
Published: December 2004

Using H‐atoms produced in the radiolysis of water vapour, we determined the kinetic isotope effect for the reaction

where RH and R′D are methylcyclohexane and perdeuterated methylcyclohexane, respectively. The result obtained from the isotope competitive method can be expressed with the Arrhenius‐type equation kH/kD = (0.51 ± 0.04) exp[(8.58 ± 0.25) kJ mol−1/RT] over the temperature range from 363 to 483 K. The occurrence of H abstraction from primary, secondary, and tertiary CH bonds in methylcyclohexane is taken into consideration in the interpretation of the Arrhenius‐type expression obtained. Theoretical interpretation of the kinetic isotope effect has been achieved on the basis of the transition‐state theory and a semiempirical London‐Eyring‐Polanyi‐Sato potential‐energy surface. The tunnel effect is found to play a role in the H‐abstraction. Several methods for estimating the tunnel correction factors have been discussed.
Face Selectivity of the Diels‐Alder Reaction of Hexadienone Moieties Grafted onto the Bicyclo[2.2.2]octene Skeleton and Perturbed by a Remote Tricarbonylbutadieneiron Group
Authors: Tagliaferri Enrico , Hänisch Ulrich , Roulet Raymond , Vogel Pierre , Schenk Kurt J.
Published: December 2004

Selective oxidations of bis(tricarbonyliron) complexes of methyl (3,7,8‐trimethylidenebicyclo[2.2.2]oct‐5‐en‐2‐ylidene)methyl ketones 15–17 afforded selectively the tricarbonyl {(1RS,4SR,7SR,8RS)‐C,7,8,C‐η‐[methyl (3,7,8‐trimethylidenebicyclo[2.2.2]oct‐5‐en‐(2Z)‐2‐ylidene)methyl ketone]}iron (12), the corresponding (2E)‐derivative 13 and the tricarbonyl{(1RS,2RS,3SR,4SR)‐C,2,3,C‐η‐[methyl (3,7,8‐trimethylidenebicyclo[2.2.2]oct‐5‐en‐(2Z)‐2‐ylidene)methyl ketone]}iron (18). The stereoselectivity of the Diels‐Alder reactions of the uncomplexed (Z)‐ and (E)‐hexadienone 12 and 13, respectively, was established. The face of the diene syn with respect to the C(5), C(6) etheno bridge was preferred for the cycloadditions of N‐phenyltriazolinedione (NPTAD). In contrast, the reactions of dimethyl acetylenedicarboxylate (DMAD) and methyl propynoate showed a slight preference for addtion to the face of the hexadienones anti with respect to the etheno bridges of 12 and 13. The crystal structure of the adduct 25 resulting from the cycloaddition of NPTAD to 12 is reported.
The Synthesis and Liquid‐Crystal Transition Temperatures of Some Fluoro‐Substituted Benzonitriles
Authors: Kelly Stephen M. , Schad Hanspeter
Published: December 2004

Various laterally fluoro‐substituted benzonitriles have been prepared containing a trans‐4‐(n‐alkyl)cyclohexane ring linked to the 4‐position of the benzonitriles either through a methyleneoxy (CH2O–) or an ethylene (CH2CH2‐) bridge. The bridging group links the benzonitrile and cyclohexane rings either directly or through an additional 1,4‐bonded cyclohexane or benzene ring. The synthesis and liquid‐crystal transition temperatures of these new compounds are described. In several cases the nematic‐isotropic transition temperatures of F‐substituted benzonitriles are found to be higher than those of the non‐laterally substituted analogues.
Hydrogen Migration in Transition Metal Alkyne and Related Complexes
Authors: Silvestre Jérôme , Hoffmann Roald
Published: December 2004

The electronic and structural characteristics of the reaction interconverting a l‐alkyne complex into a vinylideneviaa 1,2 hydrogen shift are examined. In a mononuclear system, initial slippage of the alkyne to an η1geometry is indicated. The subsequent step is shown to be analogous to the isomerization of a methylvinyl cation. We conclude that an alternative route involving a hydrido‐acetylide species will be of much higher energy. A concerted shift in binuclear and trinuclear systems is ruled out, based on the loss of a strong bonding interaction between the alkyne and the metallic piece, in the transition state. In trinuclear systems, a mechanism for the isomerization is suggested involving prior oxidative addition of the CH bond across a metal‐metal bond. The metallic piece in this case assists the transformation. The discussion is extended to other reactions featuring hydrogen shifts; these include the intramolecular formation of a binuclear vinylidene from a 1,2‐hydrido‐acetylide complex, the isomerization of a binuclear μ‐alkylidyne into a μ‐vinyl geometry and the transfer of a bridging hydrogen onto a capping hydrocarbon fragment in trinuclear cluster complexes.
Asymmetrische Michael‐Additionen. Stereoselektive Alkylierung chiraler, nicht racemischer Enolate durch Nitroolefine. Herstellung enantiomerenreiner γ‐Aminobuttersäure‐ und Bernsteinsäure‐Derivate
Authors: Calderari Giorgio , Seebach Dieter
Published: December 2004

Asymmetric Michael‐Additions. Stereoselective Alkylation of Chiral, Non‐racemic Enolates by Nitroolefins. Preparation of Enantiomerically Pure γ‐Aminobutyric and Succinic Acid Derivatives

Chiral, non‐racemic lithium enolates (E,F,G) of 1,3‐dioxolan‐4‐ones, methyl 1,3‐oxazolidin‐4‐carboxylates, methyl 1,3‐oxazolin‐4‐carboxylates, 1,3‐oxazolidin‐5‐ones, and 1,3‐imidazolidin‐4‐ones derived from (S)‐lactic acid (2a), (S)‐mandelic acid (2b), and (S)‐malic acid (2c), or from (S)‐alanine (10), (S)‐proline (11), (S)‐serine (12), and (S)‐threonine (13), are added to nitroolefins. Michael adducts (3–9, 14–18) are formed (40–80%) with selectivities generally above 90% ds of one of the four possible stereoisomers. Conversions of these nitroalkylated products furnish the α‐branched α‐hydroxysuccinic acids 28 and 29, the α‐hydroxy‐γ‐amino acid 25, the α,γ‐di‐amino acid 32, the substituted γ‐lactames 19–22, and the pyrrolidine 23. The relative and absolute configuration of the products from dioxolanones and nitropropene are derived by chemical correlation and NOE measurements indicating that the steric course of reaction is to be specified as 1k, ul‐1,3. The mechanism is discussed.
Furancarbonsäuren aus Rinderharn
Authors: Bauer Sonja , Spiteller Gerhard
Published: December 2004

Furancarboxylic Acids in Cattle Urine

The urine of cattle contains large amounts of furancarboxylic acids. The same acids were isolated from rats after feeding with methyl esters of the so‐called F‐acids. Since the F‐acids were not detected in cattle‐food, they must be produced somewhere in the body of cattle.
Pterinechemistry. Part 84. A new, regiospecific synthesis of L‐biopterin
Authors: Schircks Bernhard , Bieri Jost H. , Viscontini Max
Published: December 2004

Pure L‐biopterin was obtained in 42% yield by the condensation of 5‐deoxy‐L‐arabinose‐phenylhydrazone‐triacetate with 4‐hydroxy‐2,5,6‐triaminopyrimidine, followed by iodine oxidation of the formed tetrahydropterin derivative to 1′,2′‐O‐diacetyl‐L‐biopterin. Deacetylation was carried out with NH4OH.
Triaziridine. 4. Mitteilung. Synthese von cis‐2,3‐Diisopropyltriaziridin‐1‐carbonsäureestern
Authors: Hilpert Hans , Hoesch Lienhard , Dreiding André S.
Published: December 2004

Triaziridines. Synthesis of cis‐2,3‐Diisopropyltriaziridine‐1‐carboxylic Esters

Irradiation of the (Z)‐azimines 1a, b in Et2O with a Hg high pressure lamp through Corex yielded (besides 30% of the previously described trans‐triaziridines 3a, b) 15% of the new cis‐triaziridines 4a, b. The same irradiation of the (E)‐azimines 2a, b afforded only 15–18% of 3a, b but 20–23% of 4a, b. Thus, these azimine photocyclizations show some stereospecificity. The triaziridines 3a, b and 4a, b formed in this way were always accompanied by the same three types of by‐products, namely 10–15% of the ‘triazones’ 5a, b, 11–20% of the carbamic esters 6a, b, and 5–10% of the ether/nitrene insertion products 7a, b. The constitution and configuration of the new cis‐triaziridines 4 followed from their spectral properties. Of particular interest are the symmetry properties of 4 derived from the 1H‐, 13C‐, and 15N‐NMR spectra: The stereoisomers 3 and 4 differ only in that the isochronicity of the two constitutionally equivalent molecular halves is temperature dependent in 3 but independent in 4. Both triaziridines 3 and 4 exhibit the IR CO band at (for carbamates) remarkably high frequency. The results confirm that the alkyl‐substituted N‐atoms of triaziridines are pyramidally stable, that the corresponding acyl‐substituted N‐atoms (N(1)) are also pyramidal, but can invert more readily, and that rotation around the N(1), C(O) bond is rapid. Thus, there can be only little amide‐type delocalization between a triaziridine N‐atom and an acyl substituent of the carbamate type attached to it.
Karpoxanthin und 6‐Epikarpoxanthin
Authors: Märki‐Fischer Edith , Eugster Conrad Hans
Published: December 2004

Karpoxanthin and 6‐Epikarpoxanthin

A tetrahydroxy‐β,β‐carotene previously isolated in minute amounts from ripe hips of Rosa pomifera was now identified as (3S,5R,6R,3′R)‐5,6‐dihydro‐β,β‐carotene‐3,5,6,3′‐tetrol (2). Acid hydrolysis of (9Z)‐antheraxanthin (3) gave 2 and its C(6)‐epimer 4. Tetrol 2 is named karpoxanthin.
Face Selectivity in the Diels‐Alder Additions and Chelotropic Addition of Sulfur Dioxide to 2‐(D)Methylidene‐3‐methylidenebicyclo[2.2.1]heptane
Authors: Carrupt Pierre‐Alain , Berchier Fabienne , Vogel Pierre
Published: December 2004

The stereoselectivity of the cycloadditions of 2‐(D)methylidene‐3‐methylidenebicyclo[2.2.1]heptane (4) to various dienophiles has been determined. The exo‐ vs. endo‐face selectivity depends on the type of dienophiles, and for olefinic ones, on the mode of attack (Alder‐ vs. anti‐Alder endo rule). It is > 9:1 with N‐phenyltriazolinedione (NPTAD) and ethylenetetracarbonitrile (TCNE), < 1:9 with dimethyl acetylenedicarboxylate (DMAD), 30 ± 5:70 ± 5 with DMAD in the presence of AlCl3, 15 ± 5:85 ± 5 with dehydrobenzene and 40 ± 5:60 ± 5 with 1O2 generated photochemically (Table 1). With para‐benzoquinone and maleic anhydride, the exo‐ vs. endo‐ face selectivity is < 1:9 and 20 ± 5:80 ± 5, respectively, for their anti‐Alder mode of attack; it is 50 ± 5:50 ± 5 and 55 ± 5:45 ± 5, respectively, for their Alder mode of reaction. Under conditions of kinetic control, the chelotropic addition of SO2 to 4 is endo‐face selective.
Synthèse des pseudocyphellarines A et B, deux depsides du lichen Pseudocyphellaria endochrysea
Authors: Pulgarin César , Gunzinger Jan , Tabacchi Raffaele
Published: December 2004

Synthesis of Pseudocyphellarins A and B, Two Depsides from the Lichen Pseudocyphellaria endochrysea

The total synthesis of the depsides pseudocyphellarin A (= 3‐hydroxy‐4‐methoxycarbonyl‐2,5,6‐trimethyl‐phenyl 3‐formyl‐2,4‐dihydroxy‐5,6‐dimethylbenzoate; 11) and pseudocyphellarin B (3‐hydroxy‐4‐methoxycarbonyl‐2,5,6‐trimethylphenyl 2,4‐dihydroxy‐3‐hydroxymethyl‐5,6‐dimethyl benzoate; 12) is described.
Cyclic Acetals. Structural Analysis of 1,3‐Dioxepine and Related Compounds
Authors: Jørgensen Flemming S. , Gajhede Michael , Frei Bruno
Published: December 2004

The He(I) PE spectra of 1,3‐dioxepine (1) and the related bicyclic acetals 1,3,7,7‐tetramethyl‐2,11‐dioxabicyclo[4.41]undeca‐3,5‐dien‐10‐one (2) and 1,3,7,7‐tetramethyl‐10‐methylidene‐2,11‐dioxabicyclo[4.4.1]undeca‐3,5‐diene (3) have been recorded and analyzed. Interpretation of the PE data indicate strong orbital interactions between the diene and acetal moieties in1. Different conformations have been evaluated by a joint MMP2 molecular mechanics andab initiomolecular orbital analysis, which shows1to prefer a slightly boat‐shaped conformation with the diene part being planar and the CH2group placed considerably out‐of‐plane. The bicyclic acetals2and3show a frontier orbital picture similar to1superimposed with the characteristics of the CO and CC groups, respectively. The crystal structure of the keto‐acetal2was determined by an X‐ray analysis.
Preparation and Some Reactions of 1H‐1,4‐Benzothiazine Ylides (= 1H‐1,4‐Benzothioniaazin‐4‐ide)
Authors: Iskander George M. , Khawad Ibrahim E. , Yousif Ghariballa , Fisher Keith , Fair C. Kay , Schlemper Elmer O.
Published: December 2004

A series of fifteen 1H‐1,4‐benzothiazine ylides were obtained by alkylation of the corresponding 4H‐1,4‐benzothiazines 1. Ylides of type 2g–r showed slight [1,2] rearrangements upon thermolysis besides main dealkylation to 1 and olefin production. The ylides of this type underwent redox reactions when treated with hydrazine hydrate alone, giving 3,4‐dihydro‐2H‐1,4‐benzothiazines mainly, while ylides of type 2a–f failed to react.
Enantiomer‐Differentiation Induced by an Enantiomeric Excess during Chromatography with Achiral Phases
Authors: Tsai Wen‐Liang , Hermann Kurt , Hug Erhard , Rohde Bernhard , Dreiding André S.
Published: December 2004

It is shown, in the case of the diketone 2, that chromatography with achiral phases of a non‐racemic mixture of enantiomers can furnish fractions which differ in enantiomeric excess. Such chromatography may, therefore, be used to further enrich a sample in one enantiomer. By the same token, chromatography is not a generally safe method for the purification of the product of an enantio‐differentiating process, if the enantiomeric excess of a purified portion of that product is taken to be a measure of the efficiency of the process. The described effect represents an enantiomer differentiation induced solely by an alredy existing enantiomeric excess during chromatography. It thus belongs to a class of effects where the relative amounts of two enantiomers induce an observable difference between them. Such effects are called EE effects. The common principle underlying EE effects is explained by a simple symmetry argument. Since EE effects can also occur during reactions with achiral reagents, further transformations of an enantiomer‐enriched product may furnish false information on its enantiomeric excess.
A Short Synthesis of Allene‐ and [3] Cumulenecarboxylates
Authors: Kohl‐Mines Elisabeth , Hansen Hans‐Jürgen
Published: December 2004

It is shown that carboxylic acids, in the presence of Bu3N and 2‐chloro‐1‐methylpyridinium iodide in toluene or CH2Cl2, react with [(alkoxycarbonyl)methylidene]phosphoranes to yield the corresponding esters of allene carboxylic acids (ef. Scheme 1 and Table 1). This procedure can also be applied to cinnamic acids which form [3]cumulenecarboxylates in low yield (Table 3). Under the same conditions 4‐methyl‐2‐pentynoic acid can be transformed into (2E)‐4‐chloro‐2,6‐dimethylhepta‐2,4,5‐trienoate (Scheme 4).
Diastereoselectivity in the Reaction of N‐Glycosyl‐nitrones: 1,3‐Dipolar Cycloaddition and Addition of Phosphite Anion
Authors: Bernet Bruno , Krawczyk Ewa , Vasella Andrea
Published: December 2004

The direction of approach of dibenzyl phosphite on the one hand and of dipolarophiles on the other hand to the spironitrone 7 was examined. The nitrone 7 was prepared from the lactone 3. The nucleophilic addition of dibenzyl phosphite gave 8 as a single adduct (86%). Its structure was established by X‐ray analysis. From the cycloaddition of methyl methacrylate, the products 9a, 9b, 11a, and 11b (83:2:7.5:7.5, 81%) were isolated. The structure of the main adduct 9a was established by an X‐ray analysis of a derivative of it, and the structures of the other adducts were deduced from their NMR spectra. The cycloaddition of 7 and methyl acrylate gave the adducts 10a, 10b, 12a, 13a, 13b, and 14a (27:10:54:1:2:6, 87%). The structures of these compounds were deduced from their NMR spectra. The results are discussed in relation to prior hypothesis.
Photochemistry of 5,5‐Dimethyl‐2(5H)‐thiophenone
Authors: Kiesewetter René , Margaretha Paul
Published: December 2004

On irradiation (λ > 305 nm) in alcohols, 5,5‐dimethyl‐2(5H)‐thiophenone (1b) is converted to (E)‐4‐mercapto‐4‐methyl‐2‐pentenoates 8. These esters undergo a consecutive light‐induced reaction affording thiolanes when irradiated in the presence of alkenes, and either 2,3‐dihydrothiophenes or 3‐thiabicyclo[3.1.0]hexanes with alkynes.
Nitrogen‐NMR Studies on the Protonation of 2‐(Aminomethyl)pyridine and Tris[(2‐pyridyl)methyl]amine
Authors: Anderegg Giorgio , Popov Konstantin , Pregosin Paul S.
Published: December 2004

14N‐ and 15N‐NMR spectra have been recorded for 2‐(aminomethyl)pyridine (1), tris[(2‐pyridyl)methyl]amine (2), and some of their protonated forms. For 1, the most basic site is the aliphatic N‐atom, whereas for 2 the pyridine N‐atoms are more basic, in contrast to what might be expected for a tertiary aliphatic amine.
1,2‐Epoxycarotinoide. 6. Mitteilung. Isolierung von 1′,2′‐Epoxy‐1′,2′‐dihydro‐ε,ψ‐carotin aus der ‘Delta‐Mutanten’‐Tomate
Authors: Berset Daniel , Pfander Hanspeter
Published: December 2004

1,2‐Epoxycarotenoids Isolation of 1′,2′‐Epoxy‐1′,2′‐dihydro‐ε,ψ‐carotene from a ‘Delta Mutant’ Tomato

From ‘Delta Mutant’ tomatoes, optically active 1′,2′‐epoxy‐1′,2′‐dihydro‐ε,ψ‐carotene (7) was isolated. According to the CD data, the configuration is 6R and presumably 2′S.
Three Novel Spin‐Labeled Substrates for Enzymatic Incorporation into Nucleic Acid Lattices
Authors: Toppin Charles R. , Pauly Gary T. , Devanesan Prabu , Kryak David , Bobst Albert M.
Published: December 2004

The synthesis of one C(4)‐spin‐labeled uridine‐5′‐diphosphate (C(4)‐UDP) and two nitroxide‐containing 2′‐deoxyuridine‐5′‐triphosphate (dUTP) analogs are reported. The C(4)‐UDP derivative was incorporated into copolymers by polynucleotide phosphoxylase (PNPase); one of the two dUTP analogs, substituted at position C(4), was a good substrate for TdT, whereas the other one, substituted at position C(5), served as substrate for E. coli DNA polymerase (Pol I).
On the Conformation of a Sterically Congested Amide Group in the Crystalline State and in Solution
Authors: Mühlebach Andreas , Lorenzi Gian Paolo , Gramlich Volker
Published: December 2004

The conformation in the crystalline state and in solution of the sterically congested tetramethylpiperidinederived amide group of the symmetric diamide I formed from 2,2,6,6‐tetramethylpiperidine (b) and 1,2,5‐thiadiazole‐3,4‐dicarbonyl dichloride (c), and of the mixed diamide II derived from b, c, and piperidine (a) has been investigated. In crystals, as observed with II, this group is strongly bent out‐of‐plane at both the N‐atom and the carbonyl C‐atom, and there is also a sizable twisting around the amide bond. Furthermore, the amide bond is abnormally long (1.37 Å). In CD2Cl2 (or CDCl3) solution, the group is apparently planar in its ground‐state conformation, but the energy barrier to rotation around the amide bond is low. This conclusion is based on low‐temperature 1H‐NMR measurements on I, II, and on the symmetric diamide III derived from a and c.
Preparation of Vicinal Azidohydrins by Reaction of Oxiranes with Triethylaluminium/Hydrogen Azide
Authors: Babu Mereyala Hari , Frei Bruno
Published: December 2004

A novel, mild, and highly stereoselective transformation of epoxides to azidohydrins by treatment with Et3Al/HN3 in toluene is described. As an example for the versatility of the reaction, a polyfunctional compound, 14,15‐epoxy‐14,15‐dihydromilbemycin D (1), was transformed to 14‐azido‐14,15‐dihydro‐15‐hydroxymilbemycin D (2) in 61% yield.
Photoinduced Electron‐Transfer Reactions of Perylene in Acetonitrile
Authors: Vauthey Eric , Suppan Paul , Haselbach Edwin , Stephen Davidson Robert
Published: December 2004

Laser‐flash‐photolysis experiments show that, in MeCN at 20°, perylene (P) undergoes three distinct electron‐transfer reactions:
equation image
These processes originate probably from the thermally relaxed excited states of P.
Die Gasphasen‐Flussthermolyse von 1‐Isobutenyl‐ und 2‐Methylphenyl‐alkinyl‐ketonen. Eine Synthese von Methylenomycin B
Authors: Koller Manuel , Karpf Martin , Dreiding André S.
Published: December 2004

The Gas‐Flow Thermolysis of 1‐Isobutenyl Alkynyl and 2‐Methylphenyl Alkynyl Ketones. Synthesis of Methylenomycin B

The gas‐flow thermolysis of 1‐isobutenyl alkynyl or 2‐methylphenyl alkynyl ketones were found to lead to phenols and cyclopentenones or to naphthols and indanones, respectively. These conversions involve two cyclization processes so far unknown with α‐alkynones; they are interpreted as intramolecular additions of an allylic or a benzylic C,H bond to a triple bond which may occur in two directions. In addition, the cyclopentenones formed by the α‐alkynone cyclization, a known carbene process yielding 5‐rings, were also found. The available evidence ruled out a carbene process yielding 6‐rings. The addition process yielding 5‐rings was applied to a short (but low yield) synthesis of methylenomycin B.
Diastereoselective Aldol Addition Using Boron Trichloride or Alkoxydichloroborane
Authors: Chow Hak‐Fun , Seebach Dieter
Published: December 2004

Under carefully controlled conditions, boron trichloride or alkoxydichloroborane/ethyldiisopropylamine in CH2Cl2 can be used to effect diastereoselective aldol additions of ethyl ketones to saturated, α, β‐unsaturated, or aromatic aldehydes. The CC bond formation takes place with relative topicity ul (‘syn,’ configuration of the aldols), in selectivities ranging from 90 to 99% ds (Tables 1–3). Mechanistic aspects of the reaction are discussed.
Asymmetric Synthesis of α‐Hydroxy‐Esters via Ester Enolates with Very High Diastereoselectivity
Authors: Gamboni Remo , Tamm Christoph
Published: December 2004

The α‐hydroxylation of chiral esters of 3‐phenylpropionic acid by MoO5·Py·HMPT was optimized to 98% de and 73% yield by systematic variation of the reaction conditions. The addition of at least 3 equiv. of K(sec‐BuO) proved to be essential.
Stereocontrolled Synthesis of an Epimer of the C(19)‐to‐C(27) Segment of Rifamycin S
Authors: Tschamber Théophile , Waespe‐S̆arčevic̀ Nada , Tamm Christoph
Published: December 2004

The synthesis of the ansa chain of rifamycin S (1), corresponding to the C(19) to C(27) moiety, epimeric at C(23), is described starting from dimethyl xylo‐3‐hydroxy‐2,4‐dimethylglutarate (4). The diester 4 was transformed to the C10‐diester 16 by two threo‐aldol condensations with 2,6‐dimethylphenyl propionate (5).
Photochemical Rearrangements of 5,6‐Epimino‐5,6‐dihydro‐β‐ionone and Derivatives
Authors: Müller Ernst Peter
Published: December 2004

On irradiation at −20°, 5,6‐epimino‐5,6‐dihydro‐β‐ionone (E)−3 rearranges to the products 6 and 7. The N‐methyl derivative (E)‐4 does not lead to any photoproduct upon brief irradiation; on prolonged irradiation, only unspecific photodecomposition is observed. The N‐acylated derivative (E)‐5 undergoes rapid (E)/(Z)‐isomerization and slow rearrangement to 12 and 13.
Ionization Shifts in 1H‐NMR Spectra of α,β‐Unsaturated Carboxylic Acids
Authors: Jaroszewski Jerzy W. , Grossen Peter , Mohr Peter , Tamm Christoph
Published: December 2004

Changes in chemical shifts of olefinic protons in a number of α,β‐ and α,β,γ,δ‐unsaturated carboxylic acids caused by ionization of the COOH group were investigated. The ionization shifts of α‐H‐atoms are −0.09 to 0.07 ppm, those of β‐H‐atoms are 0.32−0.47 ppm. The ionization shifts of δ‐H‐atoms are substantially larger than those of γ‐H‐atoms. The ionization shifts can be used for immediate determination of the esterification site in monoesters of (2E,4Z)‐2,4‐hexadienedioic (muconic) acid, which are of interest in connection with synthetic studies on verrucarins. Thus, isomerization by heating in aqueous solution of monoesters of (2Z,4Z)‐2,4‐hexadienedioic acid yields 1‐monoesters rather than 6‐monoesters of (2E,4Z)‐2,4‐hexadienedioic acid, in accordance with the isomerization mechanism involving anchimeric assistance of the free COOH group. Solutions of the ABXY spectra of olefinic protons of monomethyl (2E,4E)‐ and (2Z,4Z)‐2,4‐hexadienedioate are reported.
Structure of Tricarbonyl(diene)iron Complexes in Solution. Variable‐Temperature Circular Dichroism of trans‐μ‐(2,3,5,6‐Tetramethylidenebicyclo[2.2.2]octane)bis(tricarbonyliron) Complexes
Authors: Gabioud Raphy , Vogel Pierre
Published: December 2004

Optically pure (−)‐trans‐μ‐[(1R,2R,3S,4S,5S,6R)‐C,2,3,C‐η:C,5,6,C‐η‐(2,3,5,6,7‐pentamethylidenebicyclo[2.2.2]octane)]bis(tricarbonyliron) ((−)‐9), (−)‐trans‐μ‐[(1R,2R,3S,4S,5S,6R,7S)‐C,2,3,C‐η:C,5,6,C‐η‐(7‐methyl‐2,3,5,6‐tetramethylidenebicyclo[2.2.2]octane)]bis(tricarbonyliron) ((−)‐10), and (−)‐trans‐μ‐[(1R,2R,3S,4S,5S,6R,7R)‐C,2,3,C‐η:C,5,6,C‐η‐(2,3,5,6‐tetramethylidene(7D)bicyclo[2.2.2]octane)]bis(tricarbonyliron) ((−)‐16) have been prepared. Their CD spectra were solvent‐ and concentration‐independent, but temperature‐dependent, in accord with the existence of equilibria between rapidly interconverting diastereoisomeric species which can be interpreted as arising from distortions of the tricarbonyl(diene)iron units from the Cs symmetry.
Synthesis of 2,2‐Dimethyl‐1,2‐Dihydro‐3H‐pyrrol‐3‐one Preliminary Communication
Authors: Patjens Jan , Ghaffari‐Tabrizi Ramin , Margaretha Paul
Published: December 2004

The title compound 3g is obtained via two different routes, either in a multistep synthesis starting from 2‐amino‐2‐methylpropionic acid (methylalanine) or by light‐induced, oxidative dealkylation of the corresponding N‐isopropyl derivative 3c.
Intramolekulare 1,3‐dipolare Cycloadditionen mit alkenyl‐substituierten 3,4‐Diarylsydnonen
Authors: Meier Hansruedi , Heimgartner Heinz
Published: December 2004

Intramolecular 1,3‐Dipolar Cycloaddition Reactions of Alkenyl‐substituted 3,4‐Diarylsydnones

The 3,4‐diarylsydnones1and12a–ewith an allyl or alkenyloxy substituent on the N(3)‐phenyl group have been synthesized by classical methods starting from 2‐allylaniline and the corresponding alkenyloxyanilines, respectively (Schemes 2and3). Whereas the allyl‐substituted sydnone1undergoes an intramolecular 1,3‐dipolar cycloaddition at room temperature in solution to yield13(Scheme 4), the alkenyloxy‐substituted sydnones12a–eare thermally stable. On irradiation of1and12a–d, formation of the fused dihydropyrazoles2and14a–d(Schemes 1and5) is observed. In the case of12d, the yield of14dis very low, and the symmetric 1,2,3‐triazole15ahas been isolated as the main product. A very likely reaction mechanism for the formation of the photoproducts involves decarboxylation of the sydnones to give a nitrile‐imine which undergoes an intramolecular 1,3‐dipolar cycloaddition onto the CC bond.
Pteridine. Teil LXXXII. Synthese und Reaktivität von Lumazin‐7‐sulfensäuren
Authors: Heckel Armin , Pfleiderer Wolfgang
Published: December 2004

Synthesis and Reactivity of Lumazine‐7‐sulfenic Acids

The chemical synthesis of the pteridine‐7‐sulfenic acids 13–16 is described (Scheme 1). The 1,2,3,4‐tetrahydro‐1,3,6‐trimethyl‐2,4‐dioxopteridine‐7‐sulfenic acid (14) was isolated as a stable crystalline solid. Its chemical reactivity was investigated and the physical properties determined. In the solid state, the S‐oxide form 14A predominates, but in protic solvents the S‐OH tautomer 14 exists most likely. In basic medium, the pteridine‐7‐sulfenate species is stable, whereas a low pH gives rise to a disproportionation to the disulfide 10 and the corresponding pteridine‐7‐sulfinic acid 37 (Scheme 4). Reaction of 14 with ethyl propiolate leads, under cis‐addition, to 36, oxidation with KMnO4 forms 1,2,3,4‐tetrahydro‐1,3,6‐trimethyl‐2,4‐dioxopteridine‐7‐sulfonic acid (38) and NaBH4 reduction the corresponding 7‐mercaptopteridine dione 18 (Scheme 4).
Selective Transport Membranes and their Applicability for Novel Sensors
Authors: Morf Werner E. , Huser Marin , Lindemann Bernhard , Schulthess Peter , Simon Wilhelm
Published: December 2004

Selective transport of given substrates through artificial membranes can be achieved by incorporation of electrically neutral or charged carriers. Such mediated transport described for alkali and alkaline‐earth metal cations is reported here for the first time for certain anions using cobyrinate‐type ionophores, and it is also conceivable to be realized for nonionic substrates (e.g. glucose). The fundamental requirements for corresponding co‐transport and counter‐transport membrane systems are set forth in view of a design of novel substrate‐selective sensors for analytical‐chemical applications.
Methionin als Vorläufer zur enantioselektiven Synthese α‐verzweigter Vinylglycine und anderer Aminosäuren
Authors: Weber Theodor , Aeschimann Roland , Maetzke Thomas , Seebach Dieter
Published: December 2004

Methionine as Precursor for the Enantioselective Synthesis of α‐Branched Vinylglycines and of Other Amino Acids

Methionine is converted by previously published methods into the diastereoisomerically pure 3‐thiabutyl‐substituted oxazolidinone (7) and imidazolidinones 5 and 6. An X‐ray crystal structure determination of cis‐3‐benzoyl‐2‐(tert‐butyl)‐4‐(3‐thiabutyl)oxazolidin‐5‐one (7) confirms the configurational assignments made by NOE‐NMR measurements. Oxidation to sulfoxides and pyrolytic elimination produce vinyl‐substituted heterocycles (see 19, 21). Diastereoselective alkylations of the enolate 14 from the imidazolidinone 5 and of the dienolate 23 from the vinyl derivative 19 give geminally alkyl‐ and/or vinyl‐substituted heterocycles. Some of these products were hydrolyzed to free amino acids, such as (R)‐2‐methyl‐ (25a) and (R)‐2‐ethyl‐2‐vinylglycine (25b) (R)‐2‐methylhomoserine (27). Raney‐Ni desulfurization of 5 and oxidative degradation of 19 lead to enantiomerically pure derivatives of α‐aminobutyric acid (see 28) and of glycine (see 31), respectively.