bluuebunny/crossref_metadata_2025 huggingface dataset:
Über Metallalkyl‐ und ‐arylverbindungen, 48 Monomeres, tetrameres und polymeres Natriumfluorenid S [S = Me2N(CH2)2N(Me)(CH2)2NMe2, Me2N(CH2)nNMe2 (n = 2, 3)]
Authors: Corbelin Siegfried , Kopf Jürgen , Weiss Erwin
Published: July 2007

Monomeric, Tetrameric, and Polymeric Sodium Fluorenide · S [S = Me2N(CH2)2N(Me)(CH2)2NMe2, Me2N(CH2)nNMe2 (n = 2, 3)]

The metallation of fluorene with sodium butanide (NanBu) in the presence of N bases yields solvated sodium fluorenide. Base adducts with bi‐ and tridentate N‐chelating ligands have been isolated: Na(fluorenide)(pmdta) (1 [PMDTA = Me2N(CH2)2N(Me)(CH2)2NMe2], [Na(fluorenide)(tmeda)]n (2) [TMEDA = Me2N(CH2)2N(Me)(CH2)2NMe2], [Na(fluorenide)(tmeda)]4) (3) [TMPDA = Me2N(CH2)3NMe2]. According to X‐ray diffraction studies monomeric (1), polymeric (2), and cyclic‐tetrameric (3) structures are present in the crystal. These pronounced structural variations are explained on the basis of ionic contact aggregates where together with coulomb interactions the steric requirements of the ligands become rather important. Contact distances between Na ions and several C atoms of the carbanion may vary (ca. 260—300 pm) and definite coordination numbers become meaningless.
3‐Methyl‐4,6‐diphenylfuro[3,4‐d]isoxazol – Ein neues heterocyclisches System
Authors: Aßmann Lutz , Palm Ludger , Friedrichsen Willy , Zander Maximilian
Published: July 2007

3‐Methyl‐4,6‐diphenylfuro[3,4‐d]isoxazole – A New Heterocyclic System Metal‐catalyzed nitrogen extrusion from the diazo compound 8 yields 3‐methyl‐4,6‐diphenylfuro[3,4‐d]isoxazole (9). Compound 9 has been investigated by luminescence spectroscopy. Ab initio and/or semiempirical (PM3) quantum‐chemical calculations on the parent compounds 1a, 2a, 3a, b, the phenylsubstituted derivatives 1b, 2b, 9, and on 4 in ground and excited states are performed.
Die Berechnung von Resonanzenergien; das MM2ERW‐Kraftfeld
Authors: Roth Wolfgang R. , Adamczak Oliver , Breuckmann Rolf , Lennartz Hans‐Werner , Boese Roland
Published: July 2007

Resonance Energy Calculation; the MM2ERW Force Field*

The additivity of the thermochemical conjugation energy in acyclic systems allows one to extend force‐field calculations to conjugated π systems without embarking on quantum‐mechanical methods. The approach fails with cyclic delocalized systems, where resonance effects become important. Here the method provides the reference value needed to calculate resonance energies.
Retention of Configuration in Two Photochemical Reactions: Formation of Cyclopropanimines by Extrusion of Molecular Nitrogen from Tetraalkyl‐4‐imino‐1‐pyrazolines and [2 + 1] Cycloreversion of Cyclopropanimines to Isocyanides and Alkenes
Authors: Quast Helmut , Fuß Andreas , Heublein Alfred , Jakobi Harald , Seiferling Bernhard
Published: July 2007

The 1‐pyrazolin‐4‐ones 7 and 9 and the pyrazolidin‐4‐one 13 are condensed with alkanamines 8 to produce the imines 3,10 and 12 in high yields. Direct irradiation of 3 with 350‐nm light at 90°C in deuterated hydrocarbon solvents affords the cyclo‐propanimines 4 in almost quantitative yields besides molecular nitrogen and small amounts of the imines 12 as a result of photoreduction. In [D6]acetone, the cyclopropanimine 4b isomerizes in part of the α,β‐unsaturated imine 14. Direct irradiation of 3 with the unfiltered light of the high‐pressure mercury lamp results in quantitative [2 + 1] cycloreversion of the primary photoproducts 4 into the alkene 6 and an isocyanide 5. At low temperature (10°C), photolysis of 3 occurs much more slowly giving rise to photoextrusion of nitrogen (→4) and photoreduction (→12) to about the same extent. – Photolysis of the stereochemically labelled iminopyrazolines cis‐ and trans‐10 (d.e. 99%) at 90°C produces the cyclopropanimines cis‐ and trans‐16 (d.e. 94%) with high stereospecificity. The configuration of cis‐ and trans‐16 is established by a comparison with the corresponding methylenecyclopropanes cis‐ and trans‐19 and the quantitative and completely stereospecific [2 + 1] cycloreversion into methyl isocyanide (5a) and the 3,4‐ dimethyl‐3‐hexenes (Z)‐ and (E)‐17 on irradiation with the unfiltered light of the mercury arc. The necessity of thermal activation for efficient nitrogen extrusion from the 1(n,π*) state of 3 and 10 is indicative of a considerable energy barrier towards the transition into a dissociative state. At low temperature, hydrogen abstraction from the solvent or other molecules becomes important for the deactivation of the 1(n,π*) state, in addition to decay and fluorescence. The stereospecific formation of cis‐ and trans‐16 is interpreted in terms of diastereomeric bis‐orthogonal azatrimethylenemethane diradicals as intermediates which retain the configuration on cyclization. The minor non‐stereospecific path may involve mono‐orthogonal azatrimethylenemethane diradicals. Thus, mechanisms that involve the same types of diradical intermediates can rationalize the photolysis of the iminopyrazolines 3, 10 and of the methylenetriazoline 1 as well. The [2 + 1] cycloreversion of cis‐ and trans‐16 into the alkenes (Z)‐ and (E)‐17 and methyl isocyanide (5a) demonstrates for the first time that such photoreactions can be entirely stereospecific.
Anwendung der Isonitril‐Nitril‐Umlagerung zur Synthese von 2,2,5,5‐Tetramethylcyclopentancarbonsäure, einem Baustein für Süßstoffe auf Aminosäurebasis
Authors: Lüning Ulrich , Müller Michael , Gelbert Markus , Rüchardt Christoph
Published: July 2007

Use of the Isonitrile‐Nitrile Rearrangement for the Synthesis of 2,2,5,5‐Tetramethylcyclopentanecarboxylic Acid, a Building Block for Sweeteners on the Basis of Amino Acids1)

2,2,5,5‐Tetramethylcyclopentanecarboxylic acid (7) was synthesized in four steps from 2,2,5,5‐tetramethylcyclopentanone (3). The key step of the reaction is the gas‐phase rearrangement of 2,2,5,5‐tetramethylcyclopentyl isocyanide (5) to 2,2,5,5‐tetra‐methylcyclopentanecarbonitrile (6), which is hydrolyzed to 7.
Wasserstoffübertragungen, 18 Zur cis‐Selektivität bei der Dehydrierung mit Chinonen
Authors: Wehage Hubert , Heesing Albert
Published: July 2007

Hydrogen Transfer Reactions, 181). — The cis Selectivity in Dehydrogenation by Quinones

In contrast to literature results the dehydrogenation of [cis‐ 5,6‐D2]‐1,3‐cyclohexadiene by o‐chloranile proceeds stereo‐selectively. Fast 1,5‐hydrogen shifts in the last pyrolytic step of the synthesis are the cause of the contrary report.
Phosphinalkylene, 491) Chemie und Stereochemie des 9,10,19,20‐Tetrahydro‐tetrabenzo[a,c,g,i]cyclododecens und einiger seiner Derivate
Authors: Bestman Hans Jürgen , Schaper Wolfgang , Ruppert Dieter , Zimmermann Reiner , Burzlaff Hans
Published: July 2007

Phosphine Alkylidenes, 491). – Chemistry and Stereochemistry of 9,10,19,20‐Tetrahydrotetrabenzo[a,c,g,i]cyclododecene and of Some Derivatives

Twofold intermolecular C alkylation of the bis‐ylide 4 with the dibromide 5 and subsequent hydrolysis yields meso‐9,10,19,20‐tetrahydrotetrabenzo[a,c,g,i]cyclododecene (1 b), which isomerizes on heating to give the racemate 1a. From 1a and 1b the isomeric dibromides 7–10 are synthesized. Reaction of 7–10 with phenyllithium leads to the formation of the polycyclic compounds 11, 12, 13, from which 12 may be dehydrogenated to the unsaturated compound 14. Reaction of the dibromides 7–10 with silver acetate occurs with retention yielding the acetates 15–18, which may be hydrolysed to the corresponding alcohols. With the knowledge of the structures of compounds 15–22 the stereochemistry of the synthesis and the Wittig ether rearrangement of the diethers 24 can be elucidated. In the reaction of the dibromides 7–10 with sodium acetate elimination takes place instead of substitution. Starting from 7 and 8 the polycyclic hydrocarbon 31 is formed via the carbenium ion intermediate 26 and subsequent transannular reaction. 31 is dehydrogenated to yield 32, whose X‐ray structural analysis shows a multi helical structure. Reaction of the base potassium tert‐butylate with the dibromides 7–10 leads to the formation of isomers of the diolefin 2.
Are Charge‐Transfer Complexes Intermediates in Diels‐Alder Reactions? A Case Study of the Reaction of 1,2‐Dimethylenecyclopentane with Tetracyanoethylene
Authors: Sustmann Reiner , Korth Hans‐Gert , Nüchter Ursula , Siangouri‐Feulner Joana , Sicking Willi
Published: July 2007

The Diels‐Alder reaction of 1,2‐dimethylenecyclopentane (1) and tetracyanoethylene (TCNE) is kinetically studied by conventional and stopped‐flow UV/Vis absorption‐spectroscopic techniques. A transient charge‐transfer (CT) absorption band with λmmax=490 nm (half‐life at 20°C ca. 3.4 × 10‐2 s) is detected in dichloromethane solution. For the molar extinction coefficient a value of e490=310 M‐1 cm‐1 has been determined from measurements of the optical densitity at zero time as a function of excess diene concentration. With the aid of computer simulation the combined kinetic analysis of the disappearance of reactants and CT complex reveals that the data obtained from experiments at equimolar concentration and at a single temperature (20°C) can be interpreted equally well by both the model where the CT complex is an intermediate on the reaction path and where it is in a nonreactive side equilibrium with the reactants. Activation parameters have been determined for the disappearance of the starting compounds and of the CT complex. Contrary to what is expected for a CT complex being an intermediate in a concerted Diels‐Alder reaction a more negative activation entropy for the decay of the CT complex than for the disappearance of the reactants is found. This suggests that the CT complex is unlikely to exhibit a transition‐state‐like structure as is required for a concerted cycloaddition. Experiments under pseudo‐first‐order conditions have led to an extension of the reaction scheme by a second‐order reaction of the CT complex with the excess diene, the rate constant of which is virtually identical to that for the direct bimolecular cycloaddition. The conclusion is drawn for our case that there are more arguments against than arguments for the CT complex being a preorientation complex in the [4 + 2] cycloaddition.
Reductive Transformations, 19(2) Electron‐Transfer‐Induced Dimerization of β‐Alkylstyrenes and the Structures of the Resulting 1,4‐Dilithiobutanes(1)
Authors: Schade Peter , Schäfer Thomas , Müllen Klaus , Bender Dietmar , Knoll Konrad , Bronstert Klaus
Published: July 2007

Upon reaction with lithium β‐alkylstyrenes undergo dimerization of the resulting radical anions with the formation of 2,3‐dialkyl‐1,4‐dilithio‐1,4‐diphenyl butanes 1–8. The structure and the dynamic behavior of these dilithium organyls are investigated by cryoscopic measurements and 1H‐, 13C‐, and 6Li‐NMR spectroscopy at different temperatures. The butane chain adopts a cisoid conformation; the two benzyl subunits chelate one lithium cation while the other is solvent‐separated from the hydrocarbon frame. Depending on the size of the alkyl substituents and the reaction temperature, the dimerization of the radical anions with the formation of two stereogenic centers can proceed diastereoselectively.
Small and Medium Rings, 771) Nonconjugated π,π Interactions Approaching Classical π,π Conjugation – PE‐Spectroscopical Investigation of the 7,8;12,19‐Diseco‐1,16‐dodecahedradiene System
Authors: Elsässer Dominik , Hassenrück Karin , Martin Hans‐Dieter , Mayer Bernhard , Lutz Georg , Prinzbach Horst
Published: July 2007

Transannular (orbital) interactions in compounds 1–9 are studied by means of He(Iα)‐PE spectroscopy. Unusually strong through‐space‐dominated π,π interaction is found to be operative in the nonconjugated 1,6‐dienes 1, 2, 7, and 8. The π,π splitting of 1.9 eV for disecododecahedradiene 1 is even surpassed by the record value of 2.2 eV for disecodienedione 2, which almost equals that in 1,3‐butadiene (2.46 eV). The experimental results are explained by computational methods, especially by analyses of the precanonical MOs.
Neue Wege zum Aza‐nido‐decaboran‐Gerüst
Authors: Müller Jens , Paetzold Peter , Englert Ulli , Runsink Jan
Published: July 2007

Novel Syntheses of the Aza‐nido‐decaborane Skeleton

The known nido‐NB9H12 (3) can be synthesized by thermolysis of either arachno‐B9H13(NH3) (4) in xylene (11%) or arachno‐B10H12(N3)(NH2) (5) in diglyme (100%). The deprotonation of 5 yields the anion arachno‐[NB10H13(N3)]− (6), whose skeleton is derived from the closed 13‐vertex deltahedron. On protonation, a degradation of 6 is observed to give nido‐NB9H11(N3) (7), which crystallizes in the monoclinic space group P21/c. The borane 3 is attacked by Et3N · BH3 with evolution of H2 and formation of the 6‐BH2 — NEt3 derivative of 3 (8). Both nido‐species 8 and 7 add the isonitrile CNtBu at the position 9 to yield the arachno‐products 9 and 10, respectively. The adduct 11 is formed from 7 and the azadiboriridine (‐ tBuB — BtBu — NtBu —).
7‐Substituierte Cycloheptatriene als Dienophile in der Diels‐Alder‐Cycloaddition mit inversem Elektronenbedarf
Authors: Baumann Luzian , Kämpchen Thomas , Seitz Gunther
Published: July 2007

7‐Substituted Cycloheptatrienes as Dienophiles in the Diels‐Alder Cycloaddition With Inverse Electron Demand

A series of 7‐substituted cycloheptatrienes 1, including CN, CO2CH3, C6H5, C(CH3)3, CH3, CH(OCH3)2, H, N(CH3)2 groups has been submitted to inverse [4 + 2] cycloaddition with 3,6‐bis(trifluoromethyl)‐1,2,4,5‐tetrazine (5). Reaction of 5 with π‐acceptor‐substituted cycloheptatrienes such as 1a–c leads exclusively to cyclopropa[f]phthalazines 8 and 9, whereas 7‐alkylcycloheptatrienes 1d–f give mixtures of cyclopropa[f]phthalazines 10 and 12 and 7H‐cyclohepta[d]pyridazines 11 and 13. Moreover, 7‐methylcycloheptatriene (1e) yields three further products 19, 20, 21, derived from heptafulvene 16, formed intermediately by dehydrogenation of 1e. In contrast to 1a—f, reaction of 5 with cycloheptatriene (1g) yields the corresponding 5H‐cyclohepta[d]pyridazine 22 quantitatively. Surprisingly, no [4 + 2] cycloadducts are observed with the π‐donor‐substituted cycloheptatriene 1h. Instead, the indazol 27 and the triazoles 25 and 28 are formed.
Collisionally Activated Dissociation of Some Bulkily Substituted Pyridinium Cations, II. Substituent Effect on Appearance Potential
Authors: Anders Ernst , Koch Rainer , Katritzky Alan R. , Malhotra N. , Eyler John R. , Zimmerman Jeffrey A.
Published: July 2007

Collisionally activated dissociations (CADs) of various pyridine‐ring substituted N‐benzylpyridinium cations in the gas phase form the substituted pyridine and benzyl carbocation. Appearance energies (AEs) are estimated quantitatively from the appearance thresholds of the corresponding fragment ion from the laser‐desorbed pyridinium cations. MO calculations predict that such unimolecular dissociation processes lead initially to ion‐molecule pairs (IMPs): some such IMPs are of significantly lower energy than the fully dissociated products. The AEs have also been compared with the energy differences [ΔΔHf=ΔHf(Py) + ΔHf(R+) — ΔHf(Py+R)] determined by AM1 calculations: in many cases these are quite close to the calculated energy differences; discrepancies are discussed.
Aminobenzole, 22. Darstellung, physikalische Eigenschaften und Kristallstrukturen von Mono‐, Di‐ und Trichlor‐2,4,6‐tris(dialkylamino)benzolen
Authors: Effenberger Franz , Mündl Gabriele
Published: July 2007

Aminobenzenes, 22. — Synthesis, Physical Properties, and Crystal Structures of Mono‐, Di‐, and Trichloro‐2,4,6‐tris‐(dialkylamino)benzenes

Mono‐, di‐ and trichlorotris(dialkylamino)benzenes 2,3, and 4 are prepared selectively by chlorination of triaminobenzenes 1 with one, two, or three equivalents of N‐chlorosuccinimide, resp., in tetrachloromethane. From spectroscopic data it is deduced that the introduction of chloro substituents into symmetrical triaminobenzenes 1 causes a severe steric hindrance for the dialkylamino groups without disturbing the aromatic π system. X‐ray structural analyses of the trichlorotriamino compounds 4a and 4c confirm the spectroscopic interpretation. Among the trichloro compounds 4a—d only for 4c the anodic oxidation is reversible.
Regiocontrol in Pd(0)‐Mediated Couplings of a Bis(enol triflate) with Alkynes — Stereoselective Syntheses of Monocyclic Dienediynes Related to the Neocarzinostatin Chromophore
Authors: Scheuplein Stefan W. , Harms Klaus , Brückner Reinhard , Suffert Jean
Published: July 2007

The stereoselective synthesis of (Z)‐dienediynes 2 related to the neocarzinostatin chromophore 1 is described. (Z)‐Bis(enol triflate) 3, accessible stereoselectively from 2‐formylcyclopentanone in 2 steps, serves as the key intermediate. It is subjected to consecutive Pd(0)‐catalyzed couplings with two different alkynes and furnishes 2 via monocoupling products 8.
Struktur und Reaktivität von Bis(π‐pentamethylcyclopentadienyl)‐(2‐methyliden)titanacyclobutan
Authors: Beckhaus Rüdiger , Flatau Sabine , Trojanov Sergej , Hofmann Peter
Published: July 2007

Structure and Reactivity of Bis(π‐pentamethylcyclopentadienyl)(2‐methylidene)titanacyclobutane

The reaction of vinyllithium with bis(π‐pentamethylcyclopentadienyl)titanium dichloride in a molar ratio of 2:1 quantitatively yields the unexpected titanacyclobutane derivative(2) (Cp* = [C5(CH3)5]). The isolated complex2has been characterized by spectroscopic methods and by elemental analysis, and its structure has been confirmed by an X‐ray structure determination. The chemical reactivity of2is characterized by the splitting of the four‐membered ring at higher temperatures, forming a titanocene vinylidene fragment {Cp2*Ti = C = CH2} and ethylene. This cycloreversion is confirmed by the fragmentation behavior in the mass spectrometer, and some aspects of it have been studied by Extended Hückel Model calculations.
Kristallstruktur, Festkörperpolymerisation und Ionenleitung in Alkalisalzen ungesättigter Carbonsäuren, 1. Untersuchungen an wasserfreiem Lithiumacrylat, Lithiumacrylat‐tetartoshydrat und ‐hektonmethanolat
Authors: Beck Horst P. , Trübenbach Peter
Published: July 2007

Crystal Structure, Solid‐State Polymerization and Ionic Conductivity of Alkali Salts of Unsaturated Carboxylic Acids, 1. — Investigations on Lithium Acrylate, Lithium Acrylate Tetartoshydrate and Lithium Acrylate Hektonmethanolate

The structures of lithium acrylate tetartoshydrate C3H3LiO2 · 1/4 H2O (1) and the corresponding hektonmethanolate C3H3LiO2 · 1/6 CH3OH (2) have been determined by single‐crystal X‐ray diffraction. They both consist of a framework of corner‐ and edge‐shared LiO4 tetrahedra. The vinyl groups extend into channels running through the inorganic framework in all three main directions, where they are stacked in a zipper‐like manner. However, the distances between these functional groups are too large for a diffusionless topochemical polymerization. Polymerization takes place thermally at temperatures between 180 and 280°C after loss of solvate molecules. The amorphous polymer is an ionic conductor above 238 °C with an activation energy of 0.57 eV.
Synthese und Struktur von Bis(trimethylstannyl)‐ und Bis(dimethylhalogenstannyl)aminen: zur Rolle des Stickstoff‐Elektronenpaares
Authors: Diemer Stefan , Noth Heinrich , Polborn Kurt , Storch Wolfgang
Published: July 2007

Synthesis and Structure of Bis(trimethylstannyl) and Bis(dimethylhalostannyl) Amines: The Role of the Nitrogen Lone Pair

Monoaminostannanes RNH— SnMe3 (1) with substituents R = tBu, Mes, 2,6‐iPr2C6H3 are obtained by transmetallation from Me3SnX and RNH—Li, the distannylamines RN(SnMe3)2 (2) by transamination of Et2N —SnMe3 with RNH2, and bis(dimethylhalostannyl)amines R—N(SnMe2X)2 (8) by stannazane cleavage of 2 with Me2SnX2 or by SnC cleavage with BX3 (8n, o). Me2Sn(NtBuH)2, prepared from tBuNHLi and Me2SnBr2, decomposes with tBuNH2 elimination into the diazadistannetidine 4 already below room temperature. Information from multinuclear NMR spectra of type 2, 4, and 8 compounds ascertain the proposed relation between the value of the geminal coupling constant 2J(119Sn117Sn) of distannazanes and the Sn—N—Sn bond angle as determined by the X‐ray structure analysis of 2c and of (8a)2 as well as the participation of the electron pair at the nitrogen atom in bonding. 2c has C2 symmetry, contains a planar nitrogen atom with SnN bond lengths of 2.044 Å and an Sn—N—Sn bond angle of 125.0°. The aryl group stands perpendicular to the Sn2N plane. These data exclude any π interaction between the N atom and the substituents. 2c, therefore, represents an example of a tertiary amine with the lone electron pair at the nitrogen atom in a p‐type orbital. The supposed distannylamine (ClMe2Sn)2NMe (8a) is actually a dimer, whose unexpected structure contains a diazadistannetidine unit bearing two Me2SnCl2 groups at its nitrogen atoms in cis‐configuration. This arrangement allows the formation of weak intramolecular SnCl bonds.
Beiträge zur Chemie des Bors, 211. Zum Aufbau von Bor‐Germanium‐Bindungen mit Dimethylgermylen
Authors: Mayer Erwin P. , Nöth Heinrich , Rattay Winfried , Wietelmann Ulrich
Published: July 2007

Contributions to the Chemistry of Boron, 211[1]. — On the Formation of Boron‐Germanium Bonds with Dimethylgermylene

2‐(Dimethylgermyl)‐1,3,2‐benzodioxaborole (3) is formed by insertion of dimethylgermylene into the BH bond of catechol borane (2). According to the same principle, the trigermylborane 5 is obtained by insertion of three Me2Ge units into the BCl bond of chloro(2,2,6,6‐tetramethylpiperidino)borane (4). Me2Ge reacts with 9‐fluorenylidene(tetramethylpiperidino)‐borane 8 to yield the trigermaborolane 10, which is characterized by an X‐ray structure analysis.
Das Koordinationsverhalten der Stickstoffbasen R—CN (R = H, Cl, I, CH3) und des Pyridins gegenüber AsF5 in Lösung
Authors: Tornieporth‐Oetting Inis C. , Klapötke Thomas M.
Published: July 2007

The Coordination Behaviour of the Nitrogen Bases R—CN (R = H, Cl, I, CH3) and Pyridine towards AsF5 in Solution

The coordination behaviour of the nitriles R—CN (R = H, Cl, I, CH3) and of pyridine towards the strong Lewis acid AsF5 in solution is investigated and discussed on the basis of the hardsoft acid‐base (HSAB) principle. Solution equilibria are studied by means of 1H‐NMR spectroscopy. For the equilibrium of HCN, ICN, and AsF5 with the corresponding coordinated Lewis acid—Lewis base adducts the estimated value for the equilibrium constant is in good agreement with the experimental data.
Strukturaufklärung eines doppelsträngigen Polymers mittels Modellstudien
Authors: Godt Adelheid , Enkelmann Volker , Schlüter Arnulf‐Dieter
Published: July 2007

Structure Elucidation of a Double‐Stranded Polymer by Using Model Studies

Syntheses and complete structural characterization (including constitution, configuration, conformation) of the double‐stranded compounds Ua‐5b, Ss‐5b, U‐7b, S‐7b, UUa‐8, SUs‐8, UUUaa‐9, USUas‐9, SUUsa‐9, and SSuss‐9 are described. These compounds contain up to three repeating units of the ladder polymer 3 and are therefore used as model compounds to elucidate interesting structural aspects of this polymer. A model for the spherical shape of 3 is presented. The molecular structures in the crystals of S‐7b, SUs‐8, Ua‐5b have been determined.
Synthesis of a Novel Optically Active C2‐Symmetric 2,2′‐Bipyridine
Authors: Bolm Carsten , Ewald Martina , Zehnder Margareta , Neuburger Markus A.
Published: July 2007

Optically active 2,2′‐bipyridine (S,S)‐1 was synthesized by radical cyclization and a nickel(0)‐mediated coupling of enantiomerically pure bromopyridine (S)‐8. Palladium, copper, and cobalt complexes of 1 were prepared. The solid‐state structures of meso‐1 and 11 were determined by X‐ray crystal structure analysis.
Synthesis, Fluorescence, and Photostabilities of 3‐(Perfluoroalkyl)coumarins
Authors: Matsui Masaki , Shibata Katsuyoshi , Muramatsu Hiroshige , Sawada Hideo , Nakayama Masaharu
Published: July 2007

The regioselective reaction of coumarins 1 with bis(perfluo‐roalkanoyl) peroxides affords 3‐(perfluoroalkyl)coumarins 2 in moderate yields. The absorption and emission maxima of coumarins 2 show bathochromic shifts compared with the 3‐unsubstituted coumarins. The fluorescence intensities of 3‐(perfluoroalkyl)coumarins 2 are smaller than those of the 3‐unsubstituted ones. However, the photostabilities of coumarins 2 are higher than those of the 3‐unsubstituted ones.
Zur Kenntnis der thermischen Umlagerung des Bicyclo[1.1.0]butan‐Systems. Eine kinetische Studie des Übergangs von Tricyclo[4.1.0.02,7]heptanen in Bicyclo[3.2.0]hept‐6‐ene
Authors: Christl Manfred , Stangl Roland , Jelinek‐Fink Hans
Published: July 2007

On the Thermal Rearrangement of the Bicyclo[1.1.0]butane System. A Kinetic Investigation of the Conversion of Tricyclo[4.1.0.02,7]heptanes into Bicyclo[3.2.0]hept‐6‐enes

Tricyclo[4.1.0.02,7]heptane (7), its 1‐ (20) and 2‐phenyl derivatives (22), tetracyclo[5.1.0.02,4.03,5]octane (17), 1,2,3,4‐tetrahydro‐1,2,3‐methenonaphthalene (25) as well as its 1‐ (35), 2‐ (32), and 3‐phenyl derivatives (27) have been thermolyzed in solution in the temperature range between 110 and 230° C. The activation parameters of these reactions have been determined. The parent hydrocarbon 7 is converted into bicyclo[3.2.0]hept‐6‐ene (11) in high yield, and the other substrates behave analogously, i.e. the cyclobutene derivatives 18, 21, 23, 26, 28, 33, 34, and 36 are formed. Arising from 27, the cyclobutene 28 is observed as intermediate, which is transformed rapidly to a mixture of the benzocycloheptenes 29 and 31. To undergo this ring enlargement, the other cyclobutenes require more severe conditions. The thermal rearrangements of 20, 22, and 27 are accompanied by parallel reactions, which have been identified as acid‐catalized processes in the case of 22 and 27 giving rise to the norcarene derivatives 24 and 30, respectively. In 2‐phenylmethenonanpthalene 32 two pathways to a cyclobutene derivative exist; they are found to be followed in a 82:18 ratio. The relative reaction rates of all substrates investigated can be interpreted in terms of a consistent mechanistic model. Accordingly, the tricyclo[4.1.0.02,7]heptane system is transformed in a concerted but highly asynchronous process to an (E,Z)‐1,3‐cycloheptadiene, which then undergoes a rapid conrotatory ring closure to yield the corresponding bicyclo[3.2.0]hept‐6‐ene.
2,3‐(Ethylenedisulfonyl)‐1,3‐butadiene, à Versatile Diels‐Alder Diene and Dienophile
Authors: Lee Shwu‐Jiuan , Peng Man‐Li , Lee Jui‐Chen , Chou Ta‐Shue
Published: July 2007

2,3‐(Ethylenedisulfonyl)‐1,3‐butadiene (1) may be readily prepared from its stable 3‐sulfolene precursor 10. Compound 1 undergoes Diels‐Alder reactions with a number of dienophiles ranging from electron‐deficient to electron‐rich alkenes as well as an aldimine. It also reacts as both the diene and the dienophile in some [4 + 2] cycloadditions.
Reductive Transformations, 16[1] Electron Transfer and Regioselectivity in the Alkylation of a Hydrocarbon Mono‐ and Dianion
Authors: Müllen Klaus , Alexander Jürgen , Klabunde Kay‐Uwe , Klärner Frank‐Gerrit , Lund Henning , Lund Torben
Published: July 2007

The reductive alkylation of the pyrene isomer 1 affords bridged [14]annulenes (2) and 2a,3‐dihydro‐2a,3‐dialkyldicyclopenta[ef,kl]heptalenes (3). The involvement of an electron transfer (ET) in this reaction is demonstrated by optically pure electrophiles. Supporting evidence for ET processes is provided by cyclic voltammetric measurement of rate constants for both the ET process and the SN2 reaction. The choice of the electrophile is relevant not only for the importance of electron transfer, but also for the regioselectivity of the alkylation reaction.
Fluor‐ und Fluoroxodithietane
Authors: Viets Detlef , Waterfeld Alfred , Mews Rüdiger , Weiss Ilse , Oberhammer Heinz
Published: July 2007

Fluoro‐ and Fluorooxodithietanes

(1) was isolated from the reaction of 2,2,4,4‐tetrafluoro‐1,3‐dithietane (3) with CIF in an unpassivated monelcylinder. The hydrolysis of 1 gives (2): the trans derivative (2b) and the cis isomer (2a) are formed in a 4:1 ratio. (7) is oxidized by CIF at room temperature to give the known (8) in 87% yield. At 50°C from 8 and (9) is formed besides the ring cleavage products CF3SO2CF2SF4Cl (10) and CF3SO2CF2SF5 (11). The gasphase structure of 9 (e.d.) is described. (5) and (13) coordinate by the oxygen of the SO group to AsF5, with an unstable sulfonium salt is formed, while from the reaction of AsF5 and SbF5 with 8 (15 a, b, M = As, Sb) are isolated.
η1‐P‐ und η2‐OP‐gebundene (Ether‐phosphan)osmium(II)‐Komplexe und ihre gegenseitige Umwandlung
Authors: Lindner Ekkehard , Rothfuß Helmut , Fawzi Riad , Hiller Wolfgang
Published: July 2007

η1‐P‐ and η2‐OP‐Bonded (Ether‐Phosphane)Osmium(II) Complexes and their Mutual Conversion

Reactions of cis‐Br2Os(CO)4 with the (ether‐phosphane) ligands 2a–f results in the formation of the cis,cis,trans‐complexes Br2Os(CO)2(P ∼ O)2 (3a–f). 3b crystallizes in the mono‐clinic space group P21/c with Z = 4. Irradiation of 3a–f leads to the cleavage of a further CO group and the formation of an OsO bond to give the mono(chelate) complexes Br2Os(CO)‐(PO) PO (5a–f), with one of the O,P ligands being bidentate. 5a–f exist as mixtures of different trans‐P (A,B) and cis‐P isomers (C–G). Dependent on the fact that a reversible cis/trans equilibrium or an irreversible trans → cis transformation is possible or that no trans‐P isomers are present at any temperature, 5a–f may be classified in three categories. Inter‐conversion of the isomers A–G results from dissociation of the η1‐P coordinated ether‐phosphane and concomitant occurrence of the 16e− species Br2Os(CO)(PO) (8). From temperature‐dependent 31P{1H}‐NMR spectroscopic investigations the temperature for the reversible opening of the metal‐oxygen contact is determined. The reversible opening leads to the complexes Br2Os(CO)(PO)2 (9) with a vacant coordination site depending on the Os–O bonding strength. 5a–f react with CO to give all‐trans‐Br2Os(CO)2(PO)2 (4a–f). The action of the ether‐phosphanes 2a–f on OsBr2(PPh3)4 (7) affords the bis(chelate) complexes Br2Os(PO)2 (6a–f) which add carbon monoxide to form all‐trans‐4a–f.
Tantaloxide durch Gasphasenhydrolyse, Druckhydrolyse und Transportreaktion aus 2H‐TaS2: Synthesen von TT‐Ta2O5 und T‐Ta2O5 und Kristallstruktur von T‐Ta2O5
Authors: Hummel Hans‐U. , Fackler Richard , Remmert Peter
Published: July 2007

Tantalum Oxides by Gasphase Hydrolysis, Pressure Digestion, and Chemical Transport of 2H‐TaS2: Synthesis of TT‐Ta2O5, T‐Ta2O5 and X‐ray Structure Determination of T‐Ta2O5

TT‐Ta2O5 is obtained by pressure digestion in water using 2H‐TaS2 as starting material at a temperature of 200°C followed by a dehydratization procedure of initially formed amorphous HTaO3. The X‐ray powder diagram of TT‐Ta2O5 revealed a hexagonal unit cell with space group P6/mmm and lattice constants a = 3.639, c = 3.901 Å. This material undergoes a phase transition during heating from 20 to 900°C. The resulting product is crystallizing orthorhombic with space group Pmm2 and lattice constants a = 43.997(8), b = 3.894(1), c = 6.209(3) Å and Z = 12. Single crystals of this phase (T‐Ta2O5) have been prepared by chemical transport reaction using TT‐Ta2O5 as starting material and NH4Cl as transport agent. The structure of T‐Ta2O5 consists of pentagonal‐bipyramidal coordinated tantalum atoms connected with distorted TaO6 octahedra. The Ta–O distances vary between 1.84 and 3.09 Å and the mean Ta–O distance is 1.99 Å.
Organoborierung von Tetrakis(trimethylsilylethinyl)stannan – Röntgenstrukturanalyse eines 5‐Stannaspiro[4.4]nona‐1,3,6,8‐tetraen‐Derivates[1]
Authors: Wrackmeyer Bernd , Kehr Gerald , Boese Roland
Published: July 2007

Organoboration of Tetrakis(trimethylsilylethynyl)stannane – X‐ray Structure of a 5‐Stannaspiro[4.4]nona‐1,3,6,8‐tetraene Derivative

Tetrakis(trimethylsilylethynyl)stannane (1) reacts with non‐cyclic trialkylboranes BR3 [2, R = Me (a), Et (b), Pr (c), iPr (d)] and 9‐alkyl‐9‐borabicyclo[3.3.1]nonanes[2e (alkyl = Et), 2f (alkyl = neopentyl)] to give the 3,8‐dialkyl‐2,7‐bis(dialkylboryl)‐1,4,6,9‐tetrakis(trimethylsilyl)‐5‐stannaspiro[4.4]nona‐1,3,6,8‐tetraenes 5a to f in high yield. The reaction proceeds stepwise, and intermediates as well as final products were characterized by 1H, 11B, 13C, 29Si, 119Sn NMR spectroscopy. According to an X‐ray structure analysis of 5f · 0.5 CH2Cl2 (space group P2/c) the endocyclic CSnC bond angles are small [84.9(2) and 84.2(2)°] and the two five‐membered rings are not exactly planar. Steric crowding causes a strong twist of the skeleton of the other ring systems. The agreement between solid‐state and liquid‐phase NMR data shows that main structural features are retained in solution.
Reaktionen an Silicium‐Silicium‐Bindungen, 2[1] Trichlorsilylierung von tert‐Butyldichlorphosphan und tert‐Butylbis(trimethylsilyl)phosphan mit Hexachlordisilan: Ein Weg zu neuen bifunktionellen (Trichlorsilyl)phosphanen
Authors: Martens Rainer , Mont Wolf‐Walther Du
Published: July 2007

Reactions of Silicon‐Silicon Bonds, 2[1]. – Trichlorosilylations of tert‐Butyldichlorophosphane and tert‐Butylbis(trimethylsilyl)phosphane with Hexachlorodisilane: Synthesis of New Bifunctional (Trichlorosilyl)phosphanes

Di‐tert‐butyl(trimethylsilyl)phosphane (1) and tert‐butylbis(trimethylsilyl)phosphane (3) react with one equivalent of hexachlorodisilane with exchange of one trimethylsilyl group by a trichlorosilyl group under mild conditions to give di‐tert‐butyl(trichlorosilyl)phosphane (2) and tert‐butyl(trichlorosilyl)(trimethylsilyl)phosphane (4) in fair yields. tert‐Butylbis(trichlorosilyl)phosphane (5) is available from tert‐butyldichlorophosphane without organometallic reagents and solvents by simple reductive trichlorosilylation with the help of two equivalents of hexachlorodisilane. 5 is a useful precursor for phosphaalkane synthesis: with pivaloyl chloride, 5 leads to tert‐butyl‐[tert‐butyl(trichlorosilyloxy)methylene]phosphane (6). From 4 with pivaloyl chloride mainly 6 and some known tert‐butyl[tert‐butyl(trimethylsilyloxy)methylene]phosphane (7) are formed.
„2,2′‐Bisdimedonyliden” – ein neues elektrophiles Olefin
Authors: Schank Kurt , Fünfrocken Michael
Published: July 2007

„2,2′‐Bisdimedonylidene‘ – a Novel Electrophilic Olefin

Herrn Professor Michael Hanack zum 60. Geburtstag gewidmet.

The title compound has been prepared unambiguously by dehydrogenation of known „2,2′‐bisdimedonyl’ (8). Its typical electrophilic character leads to additions of various nucleophiles which prove the molecular structure. Physical data are in disagreement with those mentioned in the literature.
Thermal Rearrangements, XX[1] The Kinetics of Thermal Isomerisation of 4‐Methyl‐1,2,5‐hexatriene in the Gas Phase
Authors: Hopf Henning , Wachholz Gerhard , Walsh Robin
Published: July 2007

4‐Methyl‐1,2,5‐hexatriene (13) has been prepared and subjected to gas‐phase pyrolysis. Above 220°C, 13 rearranges reversibly to both trans‐5‐hepten‐1‐yne (14) and its cis‐isomer 15. Formation of 14 is faster than that of 15. These isomerisations are accompanied by a slower irreversible rearrangement to 1‐methyl‐4‐methylene‐1‐cyclopentene (16) and 1‐methyl‐3‐methylene‐1‐cyclopentene (17). Rate constants and Arrhenius parameters have been obtained for all these reactions which were shown to be homogeneous and unimolecular. For the processes 13 ⇄ 14 and 13 ⇄ 15 the data are consistent with [3,3] Cope‐type sigmatropic rearrangements. For the process 13 → 16 + 17, a rate‐determining formation of the 1‐methyl‐3‐methylenecyclopentane‐2,5‐diyl diradical is proposed. The rearrangements form a consistent pattern with other known examples. – The equilibrium data are shown to be in good agreement with thermodynamic estimates based on Group Additivity. The additivity scheme of Benson required extension to provide values for two new group contributions.
Crystal and Molecular Structure of (Tri‐tert‐butyl‐η5‐cyclopentadienyl)‐(1,2,4‐tri‐tert‐butyl‐η3‐cyclopentenyl)nickel
Authors: Schneider JöRg J. , Krüger Carl
Published: July 2007

(Tri‐tert‐butyl‐η5‐cyclopentadienyl)(1,2,4‐tri‐tert‐butyl‐η3‐cyclopentenyl)nickel (1) is accessible by the metal vapor route. The molecule adopts a slipped sandwich structure in the solid state with the nickel atom η5‐η3‐coordinated to the five‐membered rings. Its 13C‐NMR data are reported together with data on (tert‐butyl‐η5‐cyclopentadienyl)(tert‐butyl‐η3‐cyclo‐pentenyl)nickel 2 and (di‐tert‐butyl‐η5‐cyclopentadienyl)(di‐tert‐butyl‐η3‐cyclopentenyl)nickel 3.
Helical Phenanthrenes, 3[1] Syntheses, Enrichment of Enantiomers, and Barriers to Racemization of Twisted 9, 10‐Phenanthrenequinones
Authors: Fritsch Rainer , Hartmann Erwin , Andert Doris , Mannschreck Albrecht
Published: July 2007

The known syntheses of the 9, 10‐phenanthrenequinones 10a – c were improved by the chlorotrimethylsilane modification of the acyloin condensation of biaryl diesters. The novel quinones 4a, 4b, and 12 were prepared. For the first time, enantiomers (M and P) of this class of compounds were enriched semipreparatively by liquid chromatography on optically active sorbents. The barriers to thermal racemization amount to 90 – 130 kJ mol‐1 (Table 2) and are thus higher than the barriers for the corresponding phenanthrene hydrocarbons by roughly 20 kJ mol‐1. The reasons for this increase are discussed in terms of repulsive interactions in the transition state of helix inversion.
A New Versatile Synthesis of Ring‐Substituted 2‐Cyclopropylglycines and Related Amino Acids
Authors: Wessjohann Ludger , Krass Norbert , Yu Dahai , Meijere Armin De
Published: July 2007

Alkyl 2‐chloro‐2‐cyclopropylideneacetates 2 serve as universal starting materials for a new general synthesis of cyclopro‐pylglycines by a simple three‐ to four‐step methodology. 1,4‐Addition of nucleophiles, substitution with azide ion, and mild catalytic deprotection lead to a variety of salt‐free cyclopropyl‐substituted amino acids in good yields, including the natural products 2‐(1‐methylcyclopropyl)glycine (4) and cleonin (5).
Synthesen mit dem Reagenz Pentamethylcyclopentadienylbromid/Silbertetrafluoroborat: Das Pentamethylcyclopentadienyl‐Kation als reaktive Zwischenstufe
Authors: Jutzi Peter , Mix Andreas
Published: July 2007

Syntheses with the Reagent Pentamethylcyclopentadienyl Bromide/Silver Tetrafluoroborate: The Pentamethylcyclopentadienyl Cation as Reactive Intermediate

Pentamethylcyclopentadienyl bromide 1 reacts with silver tetrafluoroborate with abstraction of the halide ion to form pentamethylcyclopentadienylium tetrafluoroborate (2). The 4π‐antiaromatic cation in 2 can be trapped with different nucleophiles. Thus, 2 reacts with methanol to give 5‐methoxy‐1,2,3,4,5‐pentamethyl‐1,3‐cyclopentadiene (4). In the presence of methylamine, dimethylamine, or diethylamine, the corresponding pentamethylcyclopentadienyl‐substituted amines 5, 6, and 9 are formed. Trapping of 1 with pyridine or dimethyl sulfide leads to the ionic compounds 7 and 8, respectively. The reaction of 2 with sterically crowded amines leads to tetramethylfulvene (3).
Synthesis and X‐Ray Diffraction Analysis of Bis(phenylsulphonyl)semibullvalenes. Lifting of the Degeneracy of Semibullvalenes in the Crystal Lattice[1]
Authors: Quast Helmut , Carlsen Jurgen , Janiak Rolf , Peters Eva‐Maria , Peters Karl , Schnering Hans Georg Von
Published: July 2007

The bicyclo[3.3.0]octanediones 4 and 9a, b and the [n.3.3]‐propellanediones 9c, d, f, h react with thiophenol in the presence of titanium(IV) chloride and triethylamine to afford high yields of the vinyl sulphides 5 and mixtures of the vinyl sulphides 10/11. Sodium perborate oxidizes the vinyl sulphides 5 and 10/11 to the corresponding vinyl sulphones 6 and 12/13. N‐Bromosuccinimide converts 6 into the dibromodisulfones 7. The exo,exo configuration of 7b is established by X‐ray crystallography. The mixtures of disulphones 12/13 are brominated by N‐bromosuccinimide to yield complex mixtures of uncharacterized dibromodisulphones 14. Debromination of the dibromodisulphones 7, and the mixtures of 14 as well, by the zinc‐copper couple results in the formation of crystalline semibullvalenes 8 and 15 in moderate to high yields. – X‐ray diffraction analyses of 8a, b and 15a–d reveal large variations of the apparent atomic distances in the cyclopropane rings (C2–C8) and at the open ends of the molecules (C4…C6). This result is interpreted in terms of equilibrating, non‐degenerate valence tautomers resulting in averaged atomic distances. The equilibrium constants are calculated from the atomic distances on the basis of a limiting value of 157.8 pm for the C2–C8 bonds of the non‐rearranging valence tautomers. The results are compared to those obtained from X‐ray diffraction analyses of other substituted semibullvalenes. The lifting of the degeneracy of semibullvalenes in the solid state is attributed to subtle intermolecular interactions.
Chiral Organometallic Reagents, V[1] A Test on the Configurational Stability of Chiral Organolithium Compounds Based on Kinetic Resolution; Scope and Limitations
Authors: Hirsch Reinhard , Hoffmann Reinhard W.
Published: July 2007

The test on the configurational stability of chiral organolithium compounds is based on the kinetic resolution of the racemic organolithium compound on reaction with an enantiomerically pure electrophile. The limits of this test have been evaluated by model calculations. The factors that have been considered are: Optimum values for the kinetic resolution; effects of < 100% enantiomeric purity of the chiral electrophile; parallel side reactions of the organolithium compounds with the electrophile.
Oxidative Addition von Aldehyden und Schiffbasen an Ru3(CO)12
Authors: Scott Bohle D. , Breidt Verena F. , Powell Anne K. , Vahrenkamp Heinrich
Published: July 2007

Oxidative Addition of Aldehydes and Schiff Bases to Ru3(CO)12

Aldehydes show a wide variation of their reactive behaviour towards Ru3(CO)12. Aliphatic and simple aromatic aldehydes form simple oxidative addition products Ru3(CO)10(μ‐H)(μ‐RC = O) (1) either not at all or in low yields as impure compounds, while under forcing conditions dinuclear ruthenium μ‐carboxylate complexes or the hydride H2Ru4(CO)13 are formed. Electron‐rich aldehydes give good yields of cluster type 1 (R = p‐MeOC6H4, p‐Me2NC6H4, ferrocenyl). Schiff bases behave similarly, their oxidative addition products being Ru3(CO)10(μ‐H)(μ‐RC = NR′) (10, R = C6H5, p‐MeOC6H4, p‐Me2NC6H4, R′ = C6H5, p‐MeC6H4). Of the ortho‐substituted benzaldehydes, the methoxy compound produces clusters 6 and 7 resulting from aldehyde oxidative addition and aromatic ortho metalation. Salicylaldehyde and its p‐tolylimine give the compounds Ru3(CO)8(μ‐η2‐OC6H4CH = X)2 (9, 11, X = O, NC6H4Me) with a bridging phenolate and a terminally bound aldehydic O or Schiff base NR function. 3‐Pyridinecarbaldehyde reacts quickly with Ru3(CO)12 to give products 8 derived from pyridine CH rather than aldehyde CH oxidative addition. The crystal structures of 9 and 11 were determined.
Organische Synthesen mit Übergangsmetall‐Komplexen, 58. Heptafulvenylcarben‐Komplexe von Chrom und Wolfram. – Azaspiro[4]‐Anellierung an 1‐Metalla‐1,3‐diene mit Isocyaniden; Liganden‐Abspaltung mit Pyridin oder durch Thermolyse
Authors: Aumann Rudolf
Published: July 2007

Organic Syntheses via Transition Metal Complexes, 58[1]. – Heptafulvenylcarbene Complexes of Chromium and Tungsten. – Azaspiro[4] Anellation to 1‐Metalla‐1,3‐dienes with Isocyanides; Displacement of Ligands by Pyridine or by Thermolysis*

(Cycloheptatrien‐1‐ylmethyl)carbene complexes LnM = C(OEt)CH2‐c‐C7H7 3 [LnM = Cr(CO)5 (a), W(CO)5 (b)] are transformed into heptafulven‐8‐ylcarbene complexes LnM = C(OEt)CH = c‐C7H7 5 in two steps. The first step involves the formation of (tropyliummethyl)carbene complexes [LnM = C(OEt)CH2‐c‐C7H6]+ [BF4]‐ 4 by a hydride abstraction from the cycloheptatriene ring of 3 with [Ph3C]+ [BF4]‐ (4a, 4b: 70%). 4 is deprotonated with Et3N to give 5 (5a: 89%; 5b: 92%). 5 adds one equivalent of cyclohexyl isocyanide (6) to the LnM = C – C = C unit via the intermediate ketenimine complexes LnM[c‐C6H11N = C = C(OEt) – CH = c‐C7H6] 7, which cyclize spontaneously and form the (thermolabile) azaspiro[4.6]undecatetraene complexes 8 (8a: 91%; 8b: 93%). The reaction of 8a, b with pyridine leads to the disengagement of a pyrrole 10 in almost quantitative yields. Thermolysis of 8a, b in the absence of pyridine gives an azulene 12.
Catalytic Enantioselective Conjugate Addition of Dialkylzinc Compounds to Chalcones
Authors: Bolm Carsten , Ewald Martina , Felder Marcel
Published: July 2007

Conjugate addition of diethylzinc to enones is catalyzed by a complex derived from Ni(acac)2 and C2‐symmetric 2,2′‐bipyridine 3 or chiral pyridines 5–12. The products are obtained with optical purities up to 89% ee. A strong positive nonlinear relationship between the enantiomeric excess of the ligand and the ee of the product has been observed. The factors which govern catalyst activity and enantioselectivity have been investigated.
Substituierte 2,5‐Dihydro‐1,2,5‐oxoniadiboratole, cis‐1,2‐Diborylalkene und 1,2,5‐Oxadiborolane – Herstellung und Charakterisierung
Authors: Köster Roland , Seidel Günter
Published: July 2007

Substituted 2,5‐Dihydro‐1,2,5‐oxoniadiboratoles, cis‐1,2‐Diborylalkenes, and 1,2,5‐Oxadiborolanes – Preparation and Characterization

The potassium salts magnified image (A: R = R′ = Et; B: R2 = C8H14, R′ = Me; C: R2 = C8H14, R′ = Et) react with various electrophiles (H+, R+, Me3ElIV+) to form substituted 1,3,2‐diboroxanes (1, iso8b) including 1,2,5‐oxadiborolanes (2, 4, 6, 9, 10), dialkylvinylboranes (1'), 2,5‐dihydro‐1,2,5‐oxoniadiboratoles (3, 5) and cis‐1,2‐diborylalkenes (7, 8). In particular, A–C react with HCl (as Me3NHCl/THF or HCl/Et2O) to give O[B(Et)C(Et) = CHR]2 (1a: R = Me; 1b: R = Et), R2BCR′ = CHEt (1'a: R = R′ = Et; 1'b: R2 = C8H14, R′ = Me; 1'c: R2 = C8H14, R′ = Et) and magnified image (2a: R,R′ = Et; 2b: R2 = C8H14, R′ = Me; 2c: R2 = C8H14, R′ = Et). With MeI in THF the cyclic compounds magnified image (3a) or magnified image (4b/4'b: R = Me; 4c/4'c: R = Et) and with Et3O · BF4 in CH2Cl2 the heterocycle magnified image‐ (5a) and cis‐EtOB(C8H14)C(Et) = C(Et)BEt (5c) and/or magnified image (6b: R = Me; 6c: R = Et) are obtained. The reactions of A with ClElIVMe3 (ElIV = Si, Ge, Sn) lead to cis‐Et2BC(Et) = CB(Et)OE1IVMe3 [ElIV=Si(7a), Ge (8a)] and to cyclic magnified image (9a). The salts B and C react with ClElIVMe3 (ElIV = Si, Ge) to form cis‐C8H14BC(R) = C(Et)B(Et)OElIVMe3 (ElIV = Si: 7b: R = Me; 7c: R = Et; ElIV = Ge: 8b: R = Me, 8c: R = Et). On heating 8b isomerizes to cis‐Me3GeC(Me) = C(Et)B(Et)OBC8H14 (iso8b). From B and C with ClSnMe3 the substituted 1,2,5‐oxadiborolanes magnified image (10b/10'b: R = Me; 10c: R = Et) are obtained together with (C8H14B)2O.
Synthese, Kristallstruktur und fluktuierendes Verhalten von cis‐Cl2Ru(CO)(P∽O)(PˆO) mit cis‐ständigen (Ether‐Phosphan)‐Liganden
Authors: Lindner Ekkehard , Möckel Andrea , Mayer Hermann August , Fawzi Riad
Published: July 2007

Synthesis, Crystal Structure, and Fluxional Behavior of cis‐Cl2Ru(CO)(P∽O)(PˆO) with cis‐Positioned (Ether‐Phosphane) Ligands

Reaction of the ether‐phosphane ligands 2a–c with Cl2Ru‐(PPh3)3 (1) results in the formation of the bis(chelate) complexes trans‐Cl2Ru(PˆO)2 (3a–c) (P∽O = η1‐P‐coordinated; Pb̂O = η2‐O,P‐coordinated). With CO both Ru–O bonds are cleaved to give all‐trans‐Cl2Ru(CO)2(P∽O)2 (4a–c). The mono(chelate) complexes 5a–c are obtained from stoichiometric amounts of 3a–c and 4a–c. Upon heating the kinetically controlled products 5a–c are transformed into the thermodynamically more stable isomers cis‐Cl2Ru(CO)(P∽O)(PˆO) (6a–c). Both 5a–c and 6a–c show fluxional behavior. The higher coalescence temperatures and estimated ΔG≠ values of 6a–c (75, 67, and 70°C, respectively) compared to 5a–c (55, 0, and ‐10°C, respectively) indicate different exchange mechanisms for 5 and 6. According to an X‐ray structure analysis, 6b crystallizes in the monoclinic space group P21/c with Z = 4. The action of CO on 6a–c affords the cis,cis,trans complexes 7a–c.