bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractSelective 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

AbstractVarious 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

AbstractThe 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 DerivativesChiral, 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 UrineThe 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

AbstractPure 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 EstersIrradiation 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‐EpikarpoxanthinA 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

AbstractThe 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 endochryseaThe 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

AbstractThe 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

AbstractA 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

AbstractIt 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

AbstractIt 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

AbstractThe 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

AbstractOn 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

Abstract14N‐ 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’ TomatoFrom ‘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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractLaser‐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 BThe 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

AbstractUnder 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

AbstractThe 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

AbstractThe 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

AbstractOn 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

AbstractChanges 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

AbstractOptically 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

AbstractThe 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.