bluuebunny/crossref_metadata_2025 huggingface dataset:
The Versatile Chemistry of 1,4‐Diazines: Organic, Inorganic and Biochemical Aspects
Authors: Kaim Wolfgang
Published: December 2003

In chemical research attention is increasingly being focussed on composite “complex” systems with special properties and functions. As components of such systems 1,4‐diazines are steadily gaining in popularity. Here, 1,4‐diazines means pyrazine and its derivatives as well as compounds with partial pyrazine structure; examples are quinoxaline, phenazine, pteridine, flavin and their derivatives. All these compounds are characterized by a low lying unoccupied π‐molecular orbital and by the ability to act as bridging ligand. Due to these two properties 1,4‐diazines, and especially their parent compound pyrazine, possess a characteristic reactivity. 1,4‐Diazines may be employed to study inter‐ and intramolecular electron transfer in organic, inorganic and biochemical reactions. In the redox system of 1,4‐diazines the paramagnetic 7π‐electron intermediate exhibits exceptional stability, whereas the 1,4‐dihydro‐1,4‐diazines with 8π‐electrons in a six‐membered ring are not generally accessible due to their potential antiaromaticity and their large excess of π electrons. Its inherent bifunctionality and the low lying unoccupied molecular orbital permit pyrazine to form coordination polymers having unusual electrical and magnetic properties. Finally, the phenomena observed for pyrazines may be used in the interpretation of the reactivity of naturally occurring 1,4‐diazines, such as flavins and bioluminescent natural products.
Symmetry Breaking and Non‐Born‐Oppenheimer Effects in Radical Cations
Authors: Köppel Horst , Cederbaum Lorenz S. , Domcke Wolfgang , Shaik Sason S.
Published: December 2003

The various electronic states in which molecules can exist are often considered to be independent. In this article we turn our attention to the limitations of this assumption, namely the interaction between different electronic states through the nuclear motion. This interaction can have several important consequences, two of which are discussed in some detail. One is a distortion of the molecular framework, leading to a lowering of the symmetry of a molecule in excited or ionic states compared to the neutral ground state. General aspects of this symmetry lowering are outlined and interpreted with the aid of typical examples. The other consequence considered is the ability of the nuclei to “jump” between different molecular potential energy surfaces (non‐Born‐Oppenheimer effects). The nature of this behavior is analyzed and it is argued that the “jumping” can be very fast and efficient, dominating completely the nuclear motion. To exemplify our general ideas we refer to the photoelectron spectra of ethylene and related compounds and demonstrate that they are governed by strong non‐Born‐Oppenheimer effects. It emerges that the Franck‐Condon principle fails in the analysis of their vibronic structure.
Direct Synthesis of a [13]Annulenide Ion
Authors: Becker Bernd C. , Neumann Gerd , Schmickler Hans , Müllen Klaus
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 282. DOI:10.1002/anie.198302820
Carbonyl Olefinations with Organomolybdenum Compounds
Authors: Kauffmann Thomas , Ennen Beate , Sander Jörg , Wieschollek Raphael
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 222. DOI:10.1002/anie.198302220
Zircona‐ and Hafnacyclobutenes—A New Route to Metallacyclobutanes
Authors: Seetz Johannes W. F. L. , Schat Gerrit , Akkerman Otto S. , Bickelhaupt Friedrich
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 234. DOI:10.1002/anie.198302340
Synthesis and Structure of [AsPh4][Ru6H(μ‐OCNMe2)2(μ‐CO)4‐(CO)14]·Me2CO; A Cyclic Hydrido‐Hexametallic Anion
Authors: Boag Neil M. , Knobler Carolyn B. , Kaesz Herbert D.
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 198. DOI:10.1002/anie.198301980
1,5‐Dimethylverdazyls, Hydrazidinyl Radicals with Pyramidal 1,5‐Nitrogen Atoms
Authors: Neugebauer Franz A. , Siegel Rolf
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 457. DOI:10.1002/anie.198304570
Enantioselective Hydrosilylation of Acetophenone with Rhodium/Thiazolidine Catalysts
Authors: Brunner Henri , Riepl Georg , Weitzer Helgard
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 445. DOI:10.1002/anie.198304450
A Novel Planar Antiaromatic Dibenzo[8]annulene
Authors: Dürr Heinz , Klauck Günter , Peters Karl , von Schnering Hans Georg
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 347. DOI:10.1002/anie.198303470
Homolytic Cyclizations of N‐Chloroalkenylamines
Authors: Stella Lucien
Published: December 2003

Many N‐chloroalkylamines with double bond(s) dissociate homolytically to give chlorine atoms and aminyl radicals which undergo intramolecular cyclization reactions. Here, the nature of the aminyl radicals (neutral, protonated, or complexed to metal salts) appears to be important. The reactivity varies strongly from one species to another, and their selectivities can be different towards addition, substitution, abstraction, or dimerization reactions. A good synthetic tool appears to be the “complexed radical”, which is generated under mild conditions. A variety of β‐functionalized, substituted, fused, or bridged azaheterocycles with alkaloid part structures thus become easily accessible in high yields, in a regio‐ and, possibly, stereoselective manner. Many examples are discussed illustrating the synthetic possibilities, limitations, and mechanistic features of this cyclization process.
Stable Carbodications
Authors: Prakash G. K. Surya , Rawdah Tarik N. , Olah George A.
Published: December 2003

Methods developed for the generation and study of stable carbomonocations can also be employed for similar investigations on carbodications. Trivalent (classical) as well as hexacoordinate (non‐classical) carbodications studied under long‐lived ion conditions are reviewed with special emphasis on their structural features, and investigated primarily by 1H‐ and 13C‐NMR spectroscopy.
(Z)‐2‐Methoxy‐1,2‐diphenylvinyl Alcohol, A Remarkably Stable Enol
Authors: McGarrity John F. , Cretton Alex , Pinkerton Alan A. , Schwarzenbach Dieter , Flack Howard D.
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 551. DOI:10.1002/anie.198305510
A Novel Type of Ionic Clathrands for Numerous Inclusion Compounds
Authors: Vögtle Fritz , Löhr Hans‐Gerd , Puff Heinrich , Schuh Willi
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 527. DOI:10.1002/anie.198305270
Addition of a Phosphaalkyne to Metal‐Metal Multiple Bonds
Authors: Becker Gerd , Herrmann Wolfgang A. , Kalcher Willibald , Kriechbaum Gangolf W. , Pahl Claudia , Wagner C. Thomas , Ziegler Manfred L.
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 501. DOI:10.1002/anie.198305010
Reactions at the Counter Electrode in Electroreductions under Aprotic Conditions in One‐Compartment Cells
Authors: Engels Rainer , Smit Cornelis J. , van Tilborg Wim J. M.
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 691. DOI:10.1002/anie.198306910
Novel η3, σ‐Sulfur Double‐Ylide Chromium Complexes by endo‐Hydride Addition to Cationic (λ6‐Thiabenzene 1‐Oxide)chromium Complexes
Authors: Weber Lothar , Boese Roland
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 620. DOI:10.1002/anie.198306200
Four‐Membered Ring Peroxides as Excited State Equivalents: A New Dimension in Bioorganic Chemistry
Authors: Adam Waldemar , Cilento Giuseppe
Published: December 2003

Consideration of chemiluminescent and bioluminescent processes invariably brings to mind the four‐membered ring peroxides, 1,2‐dioxetanes and α‐peroxylactones. Nevertheless, while chemiluminescence and bioluminescence are well established fields of scientific study, isolable and characterized “high‐energy” molecules such as the 1,2‐dioxetanes and α‐peroxylactones are of relatively recent vintage, about a decade. These intriguing compounds produce electronically excited products which manifest themselves by light emission during their thermal decay; more importantly, these transformations are involved in luminescent as well as dark enzymatic processes. It is not our intention to present a comprehensive overview in this progress report, but rather to focus on those aspects which require further study.
Complex Reducing Agents (CRA's)—Versatile, Novel Ways of Using Sodium Hydride in Organic Synthesis
Authors: Caubère Paul
Published: December 2003

Why do we hardly use the simplest and, at the same time, inexpensive reducing agent sodium hydride in organic chemistry? To this question the answer is invariably: “It is too basic”. In this progress report we describe work we have performed aimed at controlling the basicity of NaH using sodium alcoholates and metal salts. The complex reducing agents (CRA's) developed (symbolized NaH‐RONa‐MXn) allow organic halides, alkenes, alkynes and ketones to be reduced selectively. Highly regioselective 1,4‐ and 1,2‐reductions of α,β‐unsaturated ketones are easily performed using appropriate metal salts. Modified CRA's have proved to be excellent hydrosilylating reagents for carbonyl groups, non‐pyrophoric heterogeneous hydrogenation catalysts, coupling reagents for aryl and vinyl halides, and reagents for the carbonylation of organic halides under very mild conditions. The study of these reactions opened up the field to phase‐transfer‐catalyzed photostimulated carbonylations as well as to SRN1 reactions of metalates.–Thus, starting from the simple sodium hydride a large number of useful reagents have become accessible.
Surfactants with Novel Structural Characteristics
Authors: Weber Edwin
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 840. DOI:10.1002/anie.198308400
Solution‐Phase Metal Atom Preparation of Catalytically Active Zeolite‐Encapsulated Metal Clusters; Characterization and Application to the Selective Reduction of CO to Butene
Authors: Nazar Linda F. , Ozin Geoffrey A. , Hugues François , Godber John , Rancourt Denis
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 898. DOI:10.1002/anie.198308980
Turgorins, Hormones of the Endogeneous Daily Rhythms of Higher Organized Plants—Detection, Isolation, Structure, Synthesis, and Activity
Authors: Schildknecht Hermann
Published: December 2003

Probably the most fascinating biological phenomenon is the movement which is so impressively observed in higher organized plants when, e.g., in a sort of “quick retreat”, the sensitive plant apparently vanishes on touching, or when all the pinnules of an acacia fold together pairwise at dusk, as though the whole tree were going to “sleep”. Such plants and trees do not possess muscles for the movement of their organs; instead of the contraction of a “still primitive” actomyosin system in this movement the hydrostatic internal pressure of the vacuoles—the turgor—in the parenchymal cells of the motile organs is often drastically and unilaterally reduced. After preception of an external stimulus there follows a gradual or sudden change in the semipermeability of the boundry plasma layers, and, mediated by a stimulus conduction, also of all the symplasts of a multicellular plant organism. The phytohormones which form the molecular basis of the physiology of movement discussed here have now been isolated and structurally elucidated. The chemical agonists of phytodynamics, referred to as turgorins, elicit leaf movement; moreover, they very probably also regulate—perhaps together with other phytohormones—the mechanism of change of aperture in stomatal transpiration. Hence, the turgorins facilitate not only a regulation of temperature, but even their own transport in the sap of the whole plant body.
Regiocontrolled Prenylations and Alkylations of Furans: Preparation of Rosefuran and Novel Analogues
Authors: Ismail Zeinhom M. , Hoffmann H. M. R.
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 985. DOI:10.1002/anie.198309850
[Me3Si(py)]⊕X⊖ (X = Br,I): X‐Ray Structural Analysis of the 1:1‐Adducts of Bromo‐ or Iodotrimethylsilane and Pyridine
Authors: Hensen Karl , Zengerly Thomas , Pickel Peter , Klebe Gerhard
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 973. DOI:10.1002/anie.198309730
Derivatization‐Free Enantiomer Resolution of Chiral Alcohols and Ketones by High‐Resolution Complexation Gas Chromatography
Authors: Schurig Volker , Weber Roland
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1130. DOI:10.1002/anie.198311300
A New Route to Tellurium‐Nitrogen Compounds
Authors: Thrasher Joseph S. , Seppelt Konrad
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1106. DOI:10.1002/anie.198311060
Unprecedented Oxidative Addition of the P4S3 Cage Molecule with Phosphorus‐Phosphorus Bond Cleavage; Synthesis and Molecular Structure of [Ir(μ‐P4S3)(PPh3)Cl(CO)]2
Authors: Ghilardi Carlo A. , Midollini Stefano , Orlandini Annabella
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1066. DOI:10.1002/anie.198310660
Novel Catalytic Application of a Transition‐Metal Cluster: Spirocyclization of Alkyl Isocyanates
Authors: Süss‐Fink Georg , Herrmann Gerhard , Thewalt Ulf
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1203. DOI:10.1002/anie.198312030
1,2,4‐Thiadiazole‐3,5‐dicarbonitrile by Reaction of Cyanogen with Sulfur
Authors: Roesky Herbert W. , Keller Klaus , Bats Jan. W.
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1323. DOI:10.1002/anie.198313230
Flip‐Flop Hydrogen Bonds in β‐Cyclodextrin—A Generally Valid Principle in Polysaccharides?
Authors: Saenger Wolfram , Betzel Christian , Hingerty Brian , Brown George M.
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1191. DOI:10.1002/anie.198311910
[Ph4P]2[V2(SC2H4S)4]·4MeOH: The First Polynuclear Vanadium‐Sulfur Complex with Pure Sulfur Coordination
Authors: Szeymies Detlef , Krebs Bernt , Henkel Gerald
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1176. DOI:10.1002/anie.198311760
Radical Products in Single Electron Transfer Reactions of Lithium Triethylhydridoborate Detected by ESR and Multinuclear (1H, 10B, 11B, 14N)‐ENDOR Spectroscopy
Authors: Kaim Wolfgang , Lubitz Wolfgang
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1209. DOI:10.1002/anie.198312090
Phosphorus Ylides in the Coordination Sphere of Transition Metals: An Inventory
Authors: Schmidbaur Hubert
Published: December 2003

Phosphorus ylides are not only classical reagents in organic chemistry, but also play an increasingly important role as novel components in organometallic compounds. These metallic “ylide complexes” are either synthesized from “preformed ylides” and coordination compounds by addition or substitution, on the building block principle, or they are formed, in sometimes complicated reactions, from phosphanes, metal complexes, and C1 substrates in the coordination sphere of the metals. The resulting metal‐carbon bonds are greatly modified in their properties by the immediate presence of the phosphonium center and often belong to the most stable of M‐C structural units. The metal can come from any group of the periodic table, including the lanthanoids and actinoids. Numerous preparative and structural studies are gradually enabling us to gain an overall picture of the scope of this area of research.
Conversion of Imidazole into μ‐2,3‐Dihydro‐1H‐imidazole‐1,2,2‐triyl Ligands
Authors: Müller Jörn , Stock Rainer
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1537. DOI:10.1002/anie.198315370
A Novel and General Route to (η5‐Borole) metal Complexes: Compounds of Manganese, Ruthenium, and Rhodium
Authors: Herberich Gerhard E. , Hessner Bernd , Boveleth Wilfried , Lüthe Herbert , Saive Roland , Zelenka Ljerka
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1503. DOI:10.1002/anie.198315030
Metal‐Induced CC Coupling by Reductive Dimerization of Thioaroyl Groups
Authors: Lindner Ekkehard , Butz Ingobert P. , Hiller Wolfgang , Fawzi Raid , Hoehne Sigurd
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1388. DOI:10.1002/anie.198313880
Conformational Inversion of Tetraisopropylethylene: No Cog‐Wheel Mechanism!
Authors: Ermer Otto
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1353. DOI:10.1002/anie.198313530
Octalene—Bicyclo[6.2.0]decapentaene Conversion Mediated by Transition‐Metal Complexes
Authors: Kawka Dieter , Mues Peter , Vogel Emanuel
Published: December 2003

The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1983, 1371. DOI:10.1002/anie.198313710
The Cycloaddition of Allyl Cations to 1,3‐Dienes: General Method for the Synthesis of Seven‐Membered Carbocycles. New Synthetic Methods (40)
Authors: Hoffmann H. M. R.
Published: December 2003

The reaction of allyl cations and 1,3‐dienes affords seven‐, five‐, and six ‐membered rings as well as products of electrophilic substitution and linear 1:1‐adducts. In this review article, preparative and mechanistic advances are summarized with special emphasis on the synthesis of seven‐membered carbocycles. For the first time, a comprehensive mechanistic description is presented: Three classes A, B, and C correlate product type and stereochemistry with the nucleophilicity of the diene, the electrophilicity of the allyl cation intermediate, and the donor capacity of the group Y attached to the central carbon of the allylic moiety. The problem “allylic resonance versus nucleophilic participation of Y” is discussed and experimental evidence is adduced for some participation of Y as a function of its nucleophilicity. For cyclopentenyl cations, enhanced charge separation and electrophilicity are postulated, even when Y is a good donor, due to the structurally enforced polarity of the π‐allyl system.
N,N‐Bis(trimethylsilyl)aminomethylation of Grignard Compounds — A Versatile Amine Synthesis
Authors: Bestmann Hans Jürgen , Wölfel Gerhard
Published: December 2003

The conversion of Grignard compounds into homologous amines has proven possible by aminomethylation with the alkoxymethylamine 1. The reaction is widely applicable; R = alkyl, alkenyl, alkynyl, aryl.
equation image
(Ph4As)2[Cl5W(μ‐N4)WCl5], a μ‐Isotetrazenido(4–) Complex of Tungsten(VI)
Authors: Massa Werner , Kujanek Richard , Baum Gerhard , Dehnicke Kurt
Published: December 2003

A planar N4 star, which is bonded at two points to WCl5 moieties, is contained in the novel complex 1. This first isotetrazene derivative of a transition metal was characterized by X‐ray structure analysis. Compounds of this type are precusors of N,N‐bridge complexes.
equation image
Phospholipids as Functional Constituents of Biomembranes
Authors: Eibl Hansjörg
Published: December 2003

This article describes new methods for the synthesis of biologically active phospholipids. The physical properties of such compounds are directly related to their chemical structure, the position of the substituents esterified with glycerol not only influencing the physical properties but also the biological function of the phospholipids. Phase transitions can be induced by temperature changes and—in biological systems—by changes in the surface charge or the degree of protonation. In model studies, the properties of lipid phases differ sufficiently to influence and control biological membrane processes. Alkyl glycerides can modify the properties of biological membranes quickly and reversibly to increase the permeation of active compounds. An important example is the improved transport of cytostatic drugs across the blood‐brain barrier. Knowledge about the substrate specificity of enzymes that metabolize phospholipids allows the synthesis of tailored cytotoxic phospholipids which selectively accumulate in malignant tissues. Thus, the interplay of chemical synthesis and investigations of physical structure lays a foundation for the understanding of simple membrane processes on a molecular level, and the experience gained with such model systems can, in turn, be used to influence natural membranes, such as those of the blood‐brain barrier or of tumors, in a directed way.
Chemical Bonding in Higher Main Group Elements
Authors: Kutzelnigg Werner
Published: December 2003

Many concepts used for a qualitative description of chemical bonding that originated in the early days of theoretical chemistry have been vindicated recently by quantum chemical calculations, at least as far as first row elements are concerned. However, many concepts that have been justified for first row elements (Li to Ne) cannot—contrary to widespread belief—be generalized to the higher main group elements. This applies particularly to the concept of hybridization, which should be viewed with considerable caution. The essential difference between the atoms of the first and higher rows is that the cores of the former contain only s‐AOs, whereas the cores of the latter include at least s‐ and p‐AOs. As a consequence, the s and p valence AOs of first row atoms are localized in roughly the same region of space, while the p valence AOs of higher row atoms are much more extended in space. This has the consequence that for the light main group elements both lone‐pair repulsion and isovalent hybridization play a greater role than for the heavy main group elements. Furthermore, this implies that single bonds between first row elements are weak and multiple bonds are strong, whereas for the second or higher row elements single bonds are strong and multiple bonds weak. The “extended valence” (violation of the octet rule) observed in compounds of higher main group elements has very little to do with the availability of d‐AOs but is due rather to the size of these atoms and thus to the reduced steric hindrance between ligands and, to a lesser extent, also to the lower electronegativity of the heavy atoms. A model based on the concept of electron‐rich multicenter bonds is certainly closer to reality than one involving hybrids with the participation of d‐AOs. The XO bonds in phosphane oxides, sulfoxides, oxo acids and related compounds are better formulated as semipolar rather than as true double bonds, even if they behave in some respects like double bonds.—The growing interest of theorists in compounds of higher main group elements parallels new and, in some instances, spectacular results of experimental research on the chemistry of these elements.
X‐Ray Spectroscopic Studies of the Surface Species in CoMoAl2O3 Hydrodesulphurization Catalysts
Authors: Sarode P. R. , Sankar G. , Srinivasan A. , Vasudevan S. , Rao C. N. R. , Thomas J. M.
Published: December 2003

Octahedrally coordinated CoII and MoIV species are present on the surfaces of sulfided CoMoAl2O3 catalysts used for hydrodesulfurization. They were characterized by XPE, EXAFS and XANES data. An “excess” of sulfur in the surface species can be explained in terms of the presence of S ions. Disulfide bridges could play a role in the hydrodesulfurization.
Remarks on Simon's Review Article “Intermetallic Compounds and the Use of Atomic Radii in Their Description”—Cell Dimensions of Phases with a Given Crystal Structure Do Not Generally Form a Homogeneous Data‐Set
Authors: Hellner Erwin , Pearson William B.
Published: December 2003

Remarks on Simon's Review Article “Intermetallic Compounds and the Use of Atomic Radii in Their Description”—Cell Dimensions of Phases with a Given Crystal Structure Do Not Generally Form a Homogeneous Data‐Set.
Intermetallic Compounds and the Use of Atomic Radii in Their Description—Reply
Authors: Simon Arndt
Published: December 2003

Intermetallic Compounds and the Use of Atomic Radii in Their Description—Reply
Bonding Attitudes in Crystalline SeF4 and TeF4
Authors: Kniep Rüdiger , Korte Lutz , Kryschi Rainer , Poll Wolfgang
Published: December 2003

Solid SeF4 is monomeric, and not—like solid TeF4—polymeric. The differences in the bonding can be ascribed to the respective degrees of hybridization of the chalcogens and can be described in terms of sp3d (SeF4, pseudo trigonal bipyramidal) and sp3d2 states (TeF4, pseudo‐octahedral).
Pyrylium Mediated Transformations of Primary Amino Groups into Other Functional Groups. New Synthetic Methods (41)
Authors: Katritzky Alan R. , Marson Charles M.
Published: December 2003

The first pyrylium salt was isolated some 80 years ago, yet up to the 1950s only moderate interest was taken in the preparation, properties and uses of such salts. However, the past thirty years has seen a phenomenal growth in the literature pertinent to this area of chemistry: the importance of pyrylium salts as intermediates has been realized. They are readily prepared by a variety of generally applicable routes, and they are highly reactive towards nucleophiles. Together, this enables the convenient synthesis of a great variety of acyclic and heterocyclic compounds. We have used highly substituted pyrylium salts for the two‐step conversion of the amino group in alkylamines RNH2 into numerous other functionalities. In the first step, the pyrylium salts are converted with the amines into N‐substituted pyridinium salts, which, in the second step, react with Nu⊖ to give the desired products RNu. In some cases the R moiety is also changed, e.g. by elimination. Studies of the reactions of these pyridinium salts have allowed interesting insights into the mechanisms of nucleophilic substitution, in addition to rendering aliphatic amines important synthetic intermediates. Thus, the method complements the diazotization procedure for the transformation of arylamines.
Mycotoxins from Mold Fungi — Weapons of Uninivited Fellow‐Boarders of Man and Animal: Structures, Biological Activity, Biosynthesis, and Precautions
Authors: Franck Burchard
Published: December 2003

In addition to the antibiotics, mycotoxins represent a second large group of biologically active substances of microbial origin. Over 300 mycotoxins are so far known and can be subdivided into 25 structural types. They are formed by approximately 350 molds of which there are 10 000 different strains. As mycotoxin‐producing molds tend to spread aggressively on foodstuffs, they can cause epidemic mycotoxicoses.—The mycotoxins have been isolated, their structures determined, and their biological activities investigated; their biosynthesis has now also largely been elucidated. Accordingly, mycotoxins are derived from only three groups of key biogenetic building blocks: polyketides, isopentenyl pyrophosphate, and amino acids. Mycotoxins are mainly non‐polar, chemically stable, are formed in high concentrations, and do not contain—unlike antibiotics—any sugars. Mycotoxins display an enormous variety of toxic‐pharmacological activities, e.g. liver degradation, hemorrhages, carcinomas. The identification of mycotoxicoses is impeded by their long incubation periods and the fact that the mycotoxins tend to accumulate in the mammalian organism, which means that even very low concentrations in food are a potential danger. The particularly dangerous aflatoxin B1 1 may not exceed a limit in food of 5 ppb (5 μg/kg), which is difficult to control.
Mechanism of the Cyclocotrimerization of Diethyl(hydrido)thiophosphorus with Alkynes
Authors: Lindner Ekkehard , Krieg Claus‐Peter , Hiller Wolfgang , Fawzi Riad
Published: December 2003

All the intermediates in the (σ‐C3F7)Fe(CO)4I‐catalyzed reaction of SPHEt2 with electron‐deficient alkynes could be characterized by complete elemental analysis and by IR, 31P‐NMR, and mass spectroscopy: X‐ray structure analyses could also be performed on some of these complexes. The reaction affords highly substituted heterocycles. All intermediates contain the fragment (σ‐C3F7)Fe(CO)2.
Cobalt‐Mediated [2 + 2 + 2]‐Cycloadditions: A Maturing Synthetic Strategy [New Synthetic Methods (43)]
Authors: Vollhardt K. Peter C.
Published: December 2003

Dicarbonyl (η5‐cyclopentadienyl)cobalt functions as a matrix on which a variety of unsaturated organic substrates undergo mutual bond formation. In this way α,ω‐diynes cocyclize with monoalkynes to give annelated benzenes, while o‐diethynylbenzenes furnish biphenylenes, and α,ω‐enynes lead to the formation of complexed bi‐and tricyclic dienes. Nitriles cocyclize with two alkynyl groups to give pyridines and other heterocycles, isocyanates allow access to annelated 2‐pyridones, and incorporation of carbon monoxide provides complexed cyclopentadienones. In many cases remarkable chemo‐, regio‐, and stereoselectivity are observed, partially facilitated by use of the trimethylsilyl substituent as a controlling group. The scope and level of maturity of the method are demonstrated by the synthesis of a series of hitherto inaccessible, novel, and theoretically interesting molecules, and by its utilization in several unique approaches to a variety of natural products, e.g. protoberberines, steroids, vitamin B6, and camptothecin.
Chelation or Non‐Chelation Control in Addition Reactions of Chiral α‐ and β‐ Alkoxy Carbonyl Compounds [New Synthetic Methods (44)]
Authors: Reetz Manfred T.
Published: December 2003

The addition of C‐nucleophiles such as Grignard reagents or enolates to chiral α‐ or β‐alkoxy aldehydes or ketones creates a new center of chirality and is therefore diastereogenic. In order to control stereoselectivity, two strategies have been developed: (1) Use of Lewisacidic reagents which form intermediate chelates, these being attacked stereoselectively from the less hindered side (chelation control); (2) use of reagents incapable of chelation, stereoselective attack being governed by electronic and/or steric factors (non‐chelation control). Generally, the two methods lead to the opposite sense of diastereoselectivity. It is possible to predict the outcome by careful choice of organometallic reagents containing elements such as Li, Mg, B, Si, Sn, Cu, Zn, or Ti.

For corrigendum see DOI:10.1002/anie.198407461
Chemical Bonds without Bonding Electron Density — Does the Difference Electron‐Density Analysis Suffice for a Description of the Chemical Bond?
Authors: Cremer Dieter , Kraka Elfi
Published: December 2003

Formation of a covalent bond is not necessarily associated with an increase in electron density in the bonding region. This can be established by analysis of the single electron density distributions ρ(r) with the aid of the assigned Laplace field ▽2ρ(r). For “bonds without bonding electron density ρ(r)”, it is decisive that the density ρ(r) actually present in the region between the atoms results in a decrease in the local energy density and, hence, produces a stabilizing effect.
CP/MAS‐13C‐NMR Spectra of Sclerotized Insect Cuticle and of Chitin
Authors: Peter Martin G. , Grün Lothar , Förster Hans
Published: December 2003

A nondestructive method for investigating the exoskeleton of insects has facilitated structural information to be gained about the insoluble, fully sclerotized cuticle and about the highly polymeric chitin. It was known that the exoskeleton consists of chitin, proteins, and polyarenes. In contrast to previous suppositions, however, the transformation products of sclerotizating agents with 3,4‐dihydroxyphenyl groups are predominantly present in the reduced state.
Organic Polymeric and Non‐Polymeric Materials with Large Optical Nonlinearities
Authors: Williams David J.
Published: December 2003

Nonlinear optical properties are a sensitive probe of the electronic and solid‐state structure of organic compounds and as a consequence find various applications in many areas of optoelectronics including optical communications, laser scanning and control functions, and integrated optics technology. Because of their strongly delocalized π electronic systems, polymeric and non‐polymeric aromatic compounds show highly nonlinear optical effects. Nowadays, polymer chemists are able to tailor specific materials properties for various applications. Some organic substances with π electronic systems exhibit the largest known nonlinear coefficients, often considerably larger than those of the more conventional inorganic dielectrics and semiconductors, and thus show promise for thin‐film fabrication, allowing the enormous function and cost advantages of integrated electronic circuitry. The electronic origins of nonlinear optical effects in organic π electronic systems are reviewed, with special emphasis being given to second‐order nonlinear optical effects. Methods for measuring nonlinear optical responses are outlined, and the critical relationships of the propagation characteristics of light to observed nonlinear optical effects and to solid‐state structure are discussed. Finally, the synthesis and characterization of organic crystals and polymer films with large second‐order optical nonlinearities are summarized.
Facile Synthesis of Heteroalkenes CF3ECF2 (EP, As)
Authors: Grobe Joseph , Le Van Duc
Published: December 2003

A general entry to E  C(p‐p)π systems might be afforded by the elimination of Me3SnF from stannylated trifluoromethylelement compounds. Thus, the phosphane 1a (E  P) and the arsane 1b (E  As) react in the gas phase at 10−3 torr and 300—340oC to give the heteroalkenes 2a and 2b, respectively, in quantitative yield. CF3As  CF2 is the smallest molecule known so far with As  C bonding.—Further examples of species thus generated are S  CF2, Se  CF2, and Me3SnP  CF2.
equation image
TMEDA Adducts of CpMnCl and Manganocene
Authors: Heck Jürgen , Massa Werner , Weinig Peter
Published: December 2003

The base‐stabilized manganese(II) half‐sandwich complex 1, the first unsubstituted cyclopentadienylmanganese(II) halide, was synthesized via the route depicted below. 1 could find wide application as a CpMn transfer agent, e.g. for the synthesis of unsymmetrical sandwich compounds, especially “mixed” manganocenes, which should enable a detailed study of the high‐spin—low‐spin equilibrium. The thermolysis of 1 leads to Cp2Mn(TMEDA), the first Mn11 compound known to contain a η5‐ and a η1‐ligand (TMEDA Me2NCH2CH2NMe2, Cp  C5H5).
equation image
OPCl and SPCl: Gas‐Phase Ionization
Authors: Binnewies Michael , Solouki Bahman , Bock Hans , Becherer Ralf , Ahlrichs Reinhart
Published: December 2003

The ionization bands of OPCl and SPCl in the PE spectrum cold be assigned by ab initio‐SCF calculations. The structural data calculated for the minimum of the total energy differ very little from those of the educts OPCl3 and SPCl3. The influence of the electron pair at the P atom manifests itself, according to the calculations, in the contraction of the OPCl and SPCl angles from 115 to 109o and from 116 to 110o, respectively; the P  O and P  S bonds are about 1—2 pm shorter and the P–Cl distances about 6 pm longer than in the educts.
Reactivity of CH2XCH (X  Cl, Br) with Electrophiles and Nucleophiles in the Gas Phase, a Fourier Transform Ion Cyclotron Resonance Investigation
Authors: Weiske Thomas , van der Wel Hans , Nibbering Nico M. M. , Schwarz Helmut
Published: December 2003

Nonclassical chloronium radical ions such as 1 are accessible by electron impact ionization from ClCH2–COOMe. According to ab initio calculations, 1 can be described as an ion‐dipole complex. The expected well‐defined reactions of such a complex have been demonstrated in an FT‐ICR experiment.
equation image
Chiral Macrocycles as Reagents and Catalysts
Authors: Kellogg Richard M.
Published: December 2003

Ionophores, whether of natural or synthetic origin, encapsulate their ionic “guests” using noncovalent bonding. This encapsulation process resembles, at least superficially, the bonding of a substrate by an enzyme‐active site. The analogy to enzymes can be extended further if the ionophore is provided with functional groups that can react with a suitable guest molecule bound in the cavity of the ionophore. We have embedded in the periphery of a macrocycle a 1,4‐dihydropyridine, a mimic of the coenzyme NADH. The macrocycle, in addition to having (weak) ionophoric properties, is chiral. The strategy has led to compounds that react as artificial hydrogenases and which are capable of distinguishing, in a predictable fashion, between the prochiral faces of suitable carbonyl substrates. Ancillary developments from this approach have been many. A remarkably general method for the preparation of a wide variety of macrocycles has been developed which depends on some remarkable chemical idiosyncrasies of the cesium ion. In attempts to exploit the chemical possibilities of these macrocycles, unusual chemistry, possibly relevant to the action of the enzyme, 3‐phosphoglyceraldehyde dehydrogenase, has been uncovered. In a similar vein, study of macrocycles has led to variants of the aldol condensation on chiral templates. Finally, catalytic CC bond formation mediated by transition metals is revealed to be an area in which chiral macrocycles can play a useful role by acting as chiral ligands for the transition metal.
P4‐Degradation with and without Disproportionation
Authors: Schmidpeter Alfred , Burget Günther , von Schnering Hans Georg , Weber Dieter
Published: December 2003

The cleavage of P4 by diphenyl or diethyl phosphinite OPR proceeds with or without disproprotionation, depending upon the molar ratio. With 0.9 OPR, P4 also gives the OP(R2)PP(R2)O⊖ ions 1 and P; with 2.4 OPR, 1 is likewise formed, but along with P. With a molar ratio of 1 :4, on the other hand, P4 is degraded without disproportionation. The two P2‐halves are stabilized as the OP(R2)PPP(R2)O2⊖ ion.
[Li(tmeda)]3P7—A Solvated Ion Complex of Trilithium Heptaphosphide
Authors: Hönle Wolfgang , von Schnering Hans Georg , Schmidpeter Alfred , Burget Günther
Published: December 2003

A nice example for the stepwise transition from the polymeric solid to a solution in which solvated and separated ions predominate is provided by the Li3P7 system. In solvent‐free Li3P7, all the P atoms participate in the coordination of the Li atoms, and the Li atoms always belong to several P7 groups, whereas in [Li(tmeda)]3P7 the Li atoms are only coordinated by the twofold bonded P⊖ atoms of one P7‐group and by the solvent. The title complex can be regarded as a model for the species in solution. In this case the Li atoms would be of significance for the valence fluctuation in P.
Prostaglandin Syntheses by Three‐Component Coupling. New Synthetic Methods (49)
Authors: Noyori Ryoji , Suzuki Masaaki
Published: December 2003

The role played by prostaglandins (PGs) in the human body is bewitching. Following the elucidation of their structures in the early 1960s, tremendous efforts were made for the realization of an efficient chemical synthesis, since a sufficient supply of such very rare, naturally occurring local hormones relies solely on their total synthesis. Of the many synthetic routes described in the literature, the majority of which are linear or sequential in nature, the Corey synthesis is perhaps the most versatile; so far more than 5000 prostaglandin analogues have been prepared and have been tested biologically. Some natural prostaglandins and their analogues are already in clinical use. In view of the continuing expansion of this field, we have been fascinated with the concept of developing a highly convergent entry to prostaglandins based on a new strategy. The discovery of a highly enantioselective method for the reduction of prochiral ketones and the elaboration of a procedure for double vicinal CC‐coupling with enones have enabled a one‐pot synthesis of the complete prostaglandin skeleton by linking a chiral 4‐oxygenated 2‐cyclopentenone unit and two side‐chain blocks. This approach is efficient and flexible and allows the direct production of all the naturally occuring prostaglandins and a wide spectrum of analogues.
A Binuclear, Mixed‐Valence MoVI/V‐Complex; The Crystal Structure of [(C9H21N3)2Mo2VIO5](Br3)2
Authors: Wieghardt Karl , Backes‐Dahmann Gabriele , Herrmann Willy , Weiss Johannes
Published: December 2003

Chemical or electrochemical reduction of the binuclear MoVI complex ion 1 affords the mixed valence MoVI/V ion 2, which can be reduced to the MoV species 3. 2 is the first binuclear μ‐oxo‐bridged MoVI/V complex. Such systems are under discussion as active centers in the enzymes nitrate reductase as well as sulfite oxidase and xanthine oxidase.
equation image
Second Order Jahn‐Teller Effect in Hexahalogenotellurates(IV): Statically Distorted Anion in Ca(H2O,HF)7TeBr6
Authors: Abriel Walter , Ehrhardt Hartmut
Published: December 2003

The transition from the dynamic to the static distorted structure (point symmetry Oh and C2v, respectively) could be detected for the first time in structural investigations on the TeBr⊖ ion. In the title compound, which is characterized by a strongly polarizing cation, the static distorted structure could be stabilized by reduced symmetry of the crystal field. This means that the privileged position assigned to the AX6E system according to Gillespie's VEPA theory is also refuted.
Simple Model for Radical Additions
Authors: Höweler Udo , Klessinger Martin
Published: December 2003

Energies and geometries of the transition states as well as substituent effects in radical additions to alkenes can be reliably estimated with the model for nonpolar radical reactions. According to the model, thermal additions preferentially proceed via transition states in which the length of the educt bond is almost unchanged.
Synthesis and Structure of the 7‐Trifluoromethyl‐1,3,5,2,4,6,8‐trithiatetrazocine Cation
Authors: Höfs Hans‐Ulrich , Hartmann Gabriele , Mews Rüdiger , Sheldrick George M.
Published: December 2003

For corrigendum see DOI:10.1002/anie.198500761
Synthesis of Cyclosporine and Analogues: Structural Requirements for Immunosuppressive Activity
Authors: Wenger Roland Maurice
Published: December 2003

Cyclosporine is a new immunosuppressive drug which was first marketed in 1983 under the trade name Sandimmune®. This compound, an innovation in selective immune modulation, was isolated from a fungal culture and characterized as a cyclic undecapeptide containing a novel amino acid together with several N‐methylated amino acids. The new amino acid (4R)‐4‐[(E)‐2‐butenyl]‐4,N‐dimethyl‐L‐threonine (MeBmt) was the only unknown amino acid of cyclosporine and there had previously been no means for its isolation. For this reason and because it seemed possible that MeBmt could play a significant role in determining the pharmacological activity of cyclosporine, its synthesis in enantiomerically pure form was undertaken. The next step was the development of a total synthesis of cycloporine, which appeared attractive, not only for its intrinsic worth, but also as an important tool for investigating the relationships between structure and immunosuppressive activity. Essential for the immunosuppression are the amino acids MeBmt, Abu, Sar, and MeVal in the positions 1, 2, 3 and 11, but probably also still larger parts of the molecule. Such information could be valuable for finding new chemical leads or drugs with a new activity profile.
Synthesis and Biological Activity of α‐Methylene‐γ‐butyrolactones
Authors: Hoffmann H. M. R. , Rabe Jürgen
Published: December 2003

α‐Methylene‐γ‐butyrolactones [dihydro‐3‐methylene‐2(3H)furanones] constitute an important group of natural products and possess wide‐ranging biological activities. Progress in the synthesis of the heterocycle and the classification of the synthetic methods are not only of practical interest, but also fundamentally important as a current example for the construction of an unusual 1,4‐functionality distance and an α‐substituted acrylic ester moiety which is susceptible to nucleophilic attack.
Monoclonal Antibodies: Their Chemistry, Functions, and Possible Uses
Authors: Seiler Friedrich Robert , Gronski Peter , Kurrle Roland , Lüben Gerhard , Harthus Hans‐Peter , Ax Wolfgang , Bosslet Klaus , Schwick Hans‐Gerhard
Published: December 2003

In December of last year the Nobel Prize for Medicine or Physiology was awarded to the natural scientists N. K. Jerne, C. Milstein, and G. Köhler. These three immunologists have contributed fundamentally to our understanding of antibody synthesis by the individual immune cell. They confirmed the rule, established in the sixties, that only one antibody comes from each type of immune cell, thus giving it the status of a dogma. Jerne worked out the basic understanding of the great variety of antibodies, and his Jerne‐Plaque‐Test (1963) has enabled us to describe and analyze a single antibody‐producing immune cell in vitro. Thus, the study of immune cell interaction and the cooperation of lymphocyte subpopulations, which leads to the formation of antibodies, received decisive impulses and important methodological prerequisites. In 1975 Köhler and Milstein succeeded in permanently stabilizing, i.e., immortalizing, the antibody production of an already immunologically specifically primed mortal immune cell by means of cell fusion (hybridization) with an immortal, cancerous immune cell (myeloma cell). The hybrid cell and the hybrid cell clone grown from it in cell culture produced a homogeneous antibody, having the desired constant binding specificity, in a practically unlimited fashion and independently of an animal organism, a monoclonal antibody. This scientific breakthrough was the beginning of a tremendously stimulating new biotechnological development, which very quickly spread to laboratories in diverse fields and which today enables us to take up, and in part even solve, scientific, technical, and medical problems that would otherwise not have been analyzable at present.
Hexafluoropropene Oxide — A Key Compound in Organofluorine Chemistry
Authors: Millauer Hans , Schwertfeger Werner , Siegemund Günter
Published: December 2003

Of the important C3‐compounds in organofluorine chemistry, namely hexafluoropropene, hexafluoroacetone and hexafluoropropene oxide, the latter is chemically the most versatile compound. Hexafluoropropene oxide provides another example of the frequently observed change in reactivity when hydrocarbon compounds are converted into their perfluorinated derivatives. The overwhelming majority of the known reactions of hexafluoropropene oxide are initiated through attack by a nucleophile. The conversion of hexafluoropropene oxide into hexafluoroacetone in the presence of Lewis acids is the basis of further development of the chemistry of this synthetic chemical. Hexafluoropropene oxide is also regarded as a convenient source of difluorocarbene. In industrial chemistry it now plays a significant part in the manufacture of high‐grade organofluorine products.