bluuebunny/crossref_metadata_2025 huggingface dataset:
Kristallstruktur, Festkörperpolymerisation und Ionenleitung in Alkalisalzen ungesättigter Carbonsäuren, 2[1] Untersuchungen an Lithiummethacrylat und Lithiummethacrylattritonmethanolat
Authors: Beck Horst P. , Trübenbach Peter
Published: July 2007

Crystal Structure, Solid‐State Polymerization, and Ionic Conductivity of Alkali Salts of Unsaturated Carboxylic Acids, 2[1]. — Investigations on Lithium Methacrylate and Lithium Methacrylate Tritonmethanolate

The structures of lithium methacrylate C4H5O2Li (1) and the corresponding lithium methacrylate tritonmethanolate C4H5O2Li · 1/3 CH3OH (2) have been determined by singlecrystal X‐ray diffraction. Compound 1 is built up by inorganic layers – a two‐dimensional network of corner‐ and edge‐shared LiO4 tetrahedra – and organic double layers with a hydrophobic interaction of zipper‐like arranged methacrylate groups. The crystal structure of compound 2 can also be envisaged as a layered structure where „inorganic” and „organic” blocks alternate. Here edge‐ and cornershared LiO4 tetrahedra extend in zig‐zag chains along [010] which are bridged by carboxyl groups. The compound is an ionic conductor. – In both compounds the distances between the functional groups are too large for a diffusionless topochemical polymerisation. Polymerisation takes place thermally between 200 and 290°C. It can also be induced by UV irradiation in the presence of benzoin.
[(BH2)5S4]−: ein neues Chalcogenoborwasserstoff‐Anion mit Noradamantan‐Struktur – Theoretische Untersuchung der Molekülstruktur[1]
Authors: Binder Herbert , Wolfer Klaus , Ehmann Wolfgang , Pfeffer Wolf‐Peter , Peters Karl , Horn Hans , Ahlrichs Reinhart
Published: July 2007

[(BH2)5S4]−: A New Chalcogeno Boron Hydride Anion with Noradamantane Structure – Theoretical Investigation of the Structure[1]

The reaction of NaBH4/THF · BH3 with elemental sulfur produces Na[(BH2)5S4] (4a) with hydrogen evolution. These nucleophilic degradation reactions proceed via [H3B –μ2‐S(B2H5)]− (1) and the intermediate 3 by loss of BH4− and cyclization. 4 can also be obtained by addition of 1 to 1,2,4,3,5‐trithiadiborolane (5). 4 builds up a noradamantane‐like skeleton B5S4. An X‐ray structure determination of [(C6H5)4P] · 4 failed because of disordering of the anion. 1H‐, 11B‐NMR shifts and 1J(11B1H) coupling constants convey further structural information. Structural data have been calculated by SCF methods.
Kationische Umlagerungen bei 2‐Azabicyclo[3.2.0]heptan‐Systemen Zur NMR‐Analytik von 17O‐ oder 18O‐markierten Substanzen
Authors: Franzisket Ludwig , Heesing Albert
Published: July 2007

Cationic Rearrangements of 2‐Azabicyclo[3.2.0]heptane Systems. – NMR and MS Methods for the Analysis of 17O‐ or 18O‐Labelled Compounds

O‐Tosylation of 2‐hydroxy‐2‐azabicyclo[3.2.0]hept‐6‐ene and ‐heptane results in rearrangements to 1‐aza‐[2.2.1] systems. The regioselectivity is caused by kinetic control. High stereose‐lectivity, partial scrambling of the O‐label and low yields in cross‐over experiments agree with the intermediacy of tight ion pairs. – For the quantitative analysis of labelling, 17O‐NMR, 13C‐NMR and mass spectrometry are optimized and their efficiencies compared.
Kurzmitteilung/Short Communication Solvent‐Free [1.1.1]Propellane from 1,3‐Diiodobicyclo[1.1.1]pentane
Authors: Alber Frank , Szeimies Günter
Published: July 2007

[1.1.1]Propellane (1) could be prepared free of solvent by reaction of 1,3‐diiodobicyclo[1.1.1]pentane (3) with sodium cyanide in dimethyl sulfoxide (DMSO). Highly pure 1 was obtained in an overall yield of more than 50% related to the propellane precursor 1,1‐dibromo‐2,2‐bis(chloromethyl)cyclopropane (2).
o‐Benzochinon‐Addukte, Umlagerungs‐ und Eliminierungs‐Reaktionen von 1,1,3‐Trimethyl‐1,3,2‐diazaphospholidin‐1‐ium‐Salzen[1]
Authors: Becker W. , Schmutzler R. , Schiebel H. M.
Published: July 2007

o‐Benzoquinone Adducts, Rearrangement and Elimination Reactions of 1,1,3‐Trimethyl‐1,3,2‐diazaphospholidin‐1‐ium Salts

The 1,1,3‐Trimethyl‐1,3,2‐diazaphospholidin‐1‐ium Salts X− [1 (X = [Br, Y = NEt2), 2 (X = [BPh4], Y = Me), 3 (X = [BPh4], Y = Ph), 4 (X = [BPh4], Y = NEt2), 5 (X = [BPh4], Y = tBu)] were treated with o‐benzoquinones. The reaction of 1 with tetrachloro‐o‐benzoquinone furnished the spirophosphorane 6 with an intact N → λ5P donor‐acceptor interaction. The reaction of 2, 3, and 4 with 3,5‐di‐tert‐butyl‐o‐benzoquinone furnished [BPh4]− [8 (Y = Me), 9 (Y = Ph), 10 (Y = NEt2)]. The reaction of 5 with 3,5‐di‐tert‐butyl‐o‐benzoquinone yielded 7 which exhibited no significant N →λ5P donor‐acceptor interaction. The rearrangement product 11 was formed in small amounts during the reaction of 5 with tetrachloro‐o‐benzoquinone; 11 was also prepared by an alternative route. Thermolysis of the 1,1,3‐trimethyl‐1,3,2‐diazaphospholidin‐1‐ium salts X− [14 (X = Br), 15 (X = I)] in vacuo led, with elimination of methyl halide, to the 1,3,2‐diazaphospholidines 16 (X = Br) and 17 (X = I). The salts were characterized by FAB‐MS.
Stereoelectronic and Steric Effects in the Synthesis and Recognition of Diastereomeric Ethers by NMR and EPR Spectroscopy
Authors: Mäurer Manfred , Stegmann Hartmut B. , Hiller Wolfgang , Müller Bernd
Published: July 2007

(2,6‐Di‐tert‐butyl‐4‐hydroxyphenyl)‐alkyl‐carbinols I are easily dehydrated in the presence of catalytic amounts of a mineral acid to form the corresponding phenyl‐alkyl‐carbocations Ia. These cations can be reversibly deprotonated to the quinone methides Ib, therefore, an equilibrium between both reactive compounds is assumed. In the absence of nucleophiles a reaction of these intermediates with the starting carbinol is observed leading to symmetrical ethers Id. In alcoholic solution the solvent acts as a nucleophilic compound and the formation of an unsymmetrical ether Ie is observed predominantly. If the nucleophile contains a chiral carbon atom diastereomers are formed in this reaction which are observed in variable concentrations depending on the reaction time. The assignment of these isomers to the meso and racemic compound has been achieved by NMR investigations in solution in combination with their solid‐state structures determined by X‐ray crystallography. These results indicate a remarkable thermodynamic stabilization of the symmetrical ethers in the racemic form whereas the meso compounds are favored if the products are formed under kinetic control. In both cases the diastereomer ratio is determined by steric repulsion and the generalized anomeric effect. – A bonding interaction of lone pairs of the ether oxygen with the π system of the corresponding phenoxyl ring was also observed by EPR investigations. This electron delocalization contributes remarkably to the mechanism responsible for the distinction of the diastereomeric radicals by different β‐proton coupling constants.
Alkyleisen‐ und Alkylcobalt‐Reagenzien, IV[1] Aldehydselektive Cyanoalkylierungen mit Cyanoalkyl‐Derivaten von Eisen(II) und anderen Übergangsmetallen
Authors: Kauffmann Thomas , Kieper Hansjörg , Pieper Hans
Published: July 2007

Alkyliron and Alkylcobalt Reagents, IV[1]. – Aldehyde‐Selective Cyanoalkylation with Cyanoalkyl Derivatives of Iron(II) and Other Transition Metals

For the transfer of the cyanomethyl residue with high aldehyde vs. ketone selectivity, the Fe reagent 3 a is a good alternative to the known Ti reagent 1a[2], whereas analogous reagents with the metals Mn, Co, Ni or Cu are unfavorable. For the aldehyde‐ vs. ketone‐selective transfer of the branched residues 1‐cyanoethyl and cyanoisopropyl, the Fe reagents 3b and 3c are distinctly better than the Ti reagents 1b and 1c.
Bis(cyclopentadienyl)methan‐verbrückte Zweikernkomplexe, V. Heteronukleare Co/Rh‐, Co/Ir‐, Rh/Ir‐ und Ti/Ir‐Komplexe mit dem Bis(cyclopentadienyl)methan‐Dianion als Brückenliganden
Authors: Werner Helmut , Schneider Dirk , Schulz Michael
Published: July 2007

Bis(cyclopentadienyl)methane‐bridged Dinuclear Complexes, V[1]. – Heteronuclear Co/Rh‐, Co/Ir‐, Rh/Ir‐, and Ti/Ir Complexes with the Bis(cyclopentadienyl)methane Dianion as Bridging Ligand*

The lithium and sodium salts of the [C5H5CH2C5H4]‐ anion, 1 and 2, react with [Co(CO)4I], [Rh(CO)2Cl]2, and [Ir(CO)3Cl]n to give predominantly the mononuclear complexes [(C5H5‐CH2C5H4)M(CO)2] (3, 5, 7) together with small amounts of the dinuclear compounds [CH2(C5H4)2][M(CO)2]2 (4, 6, 8). The 1H‐ and 13C‐NMR spectra of 3, 5, and 7 prove that the CH2C5H5 substituent is linked to the π‐bonded ring in two isomeric forms. Metalation of 5 and 7 with nBuLi affords the lithiated derivatives 9 and 10 from which on reaction with [Co(CO)4I], [Rh(CO)2Cl]2, and [C5H5TiCl3] the heteronuclear complexes [CH2(C5H4)2][M(CO)2][M′(CO)2] (11–13) and [CH2(C5H4)2]‐[Ir(CO)2][C5H5TiCl2] (17) are obtained. Photolysis of 11 and 12 leads almost quantitatively to the formation of the CO‐bridged compounds [CH2(C5H4)2][M(CO)(μ‐CO)M′(CO)] (14, 15). According to an X‐ray crystal structure analysis the Co/Rh complex 14 is isostructural to [CH2(C5H4)2][Rh2(CO)2(μ‐CO)] (16).
Siliciumverbindungen mit starken intramolekularen sterischen Wechselwirkungen, 47. Trisilacyclobutanimine
Authors: Weidenbruch Manfred , Hamann Jörg , Pohl Siegfried , Saak Wolfgang
Published: July 2007

Silicon Compounds with Strong Intramolecular Steric Interactions, 47[1]. – Trisilacyclobutanimines

Treatment of hexa‐tert‐butylcyclotrisilane (4) with aryl isocyanides leads to the trisilacyclobutanimines 5–8. Reaction of the 1,4‐diisocyanobenzene derivative 7 with two molecules of 4 leads to the double insertion product 9, the X‐ray structure analysis of which shows the Si3CN framework atoms to be almost exactly coplanar. The planes of the two four‐membered rings are strictly parallel whereas the linking phenylene group forms a 71.67° angle with these planes. The most striking features of these and of related compounds are their dark colours with longest wavelength absorptions between 500 and 540 nm.
Zum Mechanismus der Carbodesilylierung 4‐ bzw. 5‐substituierter 2‐(Trimethylsilyl)pyridine mit Benzaldehyd
Authors: Effenberger Franz , Krebs Andreas , Willrett Peter
Published: July 2007

On the Mechanism of the Carbodesilylation of 4‐ or 5‐Substituted 2‐(Trimethylsilyl)pyridines

An “ylide mechanism” is proposed for the carbodesilylation of 2‐(trimethylsilyl)pyridines with benzaldehyde. In contrast, 3‐and 4‐(trimethylsilyl)pyridines, react only in the presence of a base catalyst via pyridyl anions with electrophiles. The rates of the uncatalyzed carbodesilylation reactions of 4‐substituted 2‐(trimethylsilyl)pyridines 2 with benzaldehyde correlate very well with the resonance parameters of the substituents ρRO, whereas the rates of 5‐substituted 2‐(trimethylsilyl)pyridines 7 correlate with the inductive substituent parameters ρI in the Taft equation. This is to our knowledge the first direct determination of the resonance parameters ρRO.
Bis(methylene)phosphorane and Related Compounds: Electrocyclization to Ring Systems
Authors: Schoeller Wolfgang W. , Busch Thilo
Published: July 2007

On the bais of ab initio calculations of double‐ζ quality at a SCF and MCSCF level, bonding in bis‐ylenephosphoranes is compared with the one in phosphoranes. The investigations include the series H3PX, HPX2, HPX (X = CH2, NH, O, SiH2, PH, S). The bis‐ylenephosphorane formation becomes more favorable with increasing electronegativity of X. An extreme case is the electropositive group X = SiH2. The resulting π‐system suffers from the Jahn‐Teller distortion, causing reduction from C2v to lower C2 symmetry in the corresponding bis‐ylenephosphorane. Energetically, the corresponding ring systems are more stable than their bis‐ylenephoshorane counterparts (for X = CH2 and PH). The electronic hypersurface of the hitherto unknown bis(phosphinylidene)phosphorane is explored in detail and compared in regard to bonding with its analog bis(methylene)phosphorane. For both cases π‐push‐pull substitution is important for stabilization of the planar allylic geometry.
Ringerweiterung in spirocyclischen Germanium(II)‐di(phosphanyl)methanid‐Verbindungen durch Einschiebung von Schwefel und Selen in Germanium‐Phosphor‐Bindungen
Authors: Karsch Hans H. , Baumgartner Gustav , Gamper Siegfried , Lachmann Joachim , Müller Gerhard
Published: July 2007

Ring Expansion of Spirocyclic Germanium(II) Di(phosphanyl)methanide Complexes by Insertion of Sulfur and Selenium into Germanium‐Phosphorus Bonds

Germanium in the intermolecularly stabilized germylene derivative Ge[C(PMe2)2(SiMe3)]2 (2a) is not oxidized by sulfur but the latter inserts 1 to 4 chalcogenide atoms into the Ge–P bonds of the four‐membered chelate (4/4‐) rings to give 4/5‐, 5/5‐, 5/6, and 6/6‐membered spirocycles Ge[C2(SPMe2)n(PMe2)4‐n(SiMe3)2] (n = 1–4: 4, 5a, 6, 7). Only 5a and 7 could be obtained in pure form, whereas compounds 4 and 6 with odd‐numbered chalcogenide atoms are only characterized in solution, where they exist in equilibrium with 2a and 5a or 5a and 7, respectively. All these molecules are fluctional in solution. 7 is also obtained from GeCl2 · dioxane and Li[C(SPMe2)2(SiMe3)]. The selenium compound Ge[C(SePMe2)(PMe2)(SiMe3)]2 (5b) is obtained from 2a and grey selenium in toluene. An X‐ray structure determination of 5b shows a distorted sphenoidal arrangement [approximate C2 symmetry of a spirocyclic germanium center within two five‐membered rings containing a nearly linear Se–Ge–Se unit (Ge–Se 2.712/2.769(1) Å)]. The angle PGeP is 95.9(1)°. A bonding model with a stereochemically non‐active electron lone pair at the formal germanium(II) center may account for this geometry. As byproducts in the sulfurization reactions, bis‐(phosphanyl)methane disulfides are also observed in certain cases, from which H2C(SPMe2)2 has been isolated in pure form and characterized structurally.
Synthesen, Strukturen und Eigenschaften von 2,5‐Dihydro‐1H‐1,2,5‐phosphadiborolen
Authors: Frankhauser Pascal , Drieß Matthias , Pritzkow Hans , Siebert Walter
Published: July 2007

Syntheses, Structures, and Properties of 2,5‐Dihydro‐1H‐1,2,5‐phosphadiboroles

Cyclocondensation of the (Z)‐1,2‐bis[chloro(dialkylamino)boryl]ethenes 6a–c and 1,2‐bis[chloro(diisopropylamino)‐boryl]benzene (8a) with the lithium phosphides Li2P–C6H5, Li2P–C6F5, Li2P–C6H2(tBu)3, [LiPH2 · dme], and P(SiMe3)3, yields the 2,5‐dihydro‐1H‐1,2,5‐phosphadiboroles 1a–c, 2b, c, 3a–c, 4c, 5c, 9a. Compounds 4c, 5c, 9a are characterized by an X‐ray structure analysis. Due to the B–N π bond, these derivatives are monomeric with little contribution of B–P π interaction. However, low‐temperature 1H‐NMR studies show that the P‐inversion barrier is distinct lower (10–15 kcal mol‐1) than for PH3 and organophosphanes (ca. 35 kcal mol‐1). This may be a result of favorable B–P π interaction in the transition state of the inversion at phosphorus. Reaction of the B‐methyl‐substituted 1,2‐bis(chloromethylboryl)benzene (8b) with P(SiMe3)3 gives the 1,2‐dihydro‐1H‐1,2,5‐benzophosphadiborole 9b which forms the dimer (9b)2 below 40°C by an intermolecular B–P acceptor‐donor bond. The structure of (9b)2 is confirmed by an X‐ray crystal structure analysis. Treatment of 1c with oxygen, sulfur, or selenium leads to the corresponding 1,2,5‐chalcogenadiborole derivatives 10, 11 and 12. By this process, the phenylphosphorus group is eliminated as the pentamer (C6H5‐P)5 in 25% yield. Reaction of 1c with Me2BBr gives the Lewis acid‐base adduct 13 bearing an λ3σ4‐coordinated phosphorus and one four‐coordinated boron atom. π complexation of 1c with the (CO)3Fe fragment leads to the iron complex 15 (X‐ray diffraction analysis). Deprotonation of 3c with MeLi gives the P‐Li‐substituted phosphadiborole [3c‐H]Li which reacts with MeI, Me2SiCl2, Me3SiCl to form the P‐methylated and ‐silylated derivatives 14a, 14b, 2c. Reaction of 2b with one equivalent of MeOH at ‐78°C in pentane does not give the expected P‐unsubstituted compound 3b. Instead, B–P ring cleavage is observed with formation of H2P–SiMe3 and (Z)‐1,2‐bis[(diethylamino)methoxyboryl]ethene.
Ring‐chain transformations, IX[1] Synthesis and ring‐chain tautomerism of 2‐(ω‐aminoalkyl)‐1,3,4‐thiadiazoles
Authors: Radics Ute , Liebscher Jürgen , Ziemer Burkhard , Rybakov Viktor
Published: July 2007

Thiohydrazide compounds 1 react with lactam acetals 2 or lactim ethers 3 by condensation giving unusual zwitterionic tautomers 5 of lactam thioacylhydrazones 4. These compounds 5 form mixtures of tautomers in neutral solution. In acidic solution, however, most of them undergo a reversible ringchain transformation to novel 2‐(ω‐aminoalkyl)‐1,3,4‐thiadiazole salts 9. Alkylation of zwitterionic thioacylamidrazones 5 gives S‐alkylation products 6.
Synthese und Struktur von neuen Germanium‐Phosphor‐Heterocyclen mit einem Ge2P2‐Ringgerüst
Authors: Drieß Matthias , Pritzkow Hans , Winkler Uwe
Published: July 2007

Synthesis and Structure of New Germanium‐Phosphorus Heterocycles Containing a Ge2P2‐Framework

Mes(tBu)GeF2 (Mes = 2,4,6‐trimethylphenyl) reacts with two equivalents of [LiPH2 · dme] (dme = dimethoxyethane) to give the 1,3,2,4‐diphosphadigermetane 1 which was characterized by an X‐ray structure analysis. Surprisingly, only the trans‐configurated isomer (with regard to the tBu groups at germanium) is formed. In solution at 25°C the latter compound exists as a 1:1 mixture of cis and trans isomers (with regard to the H atoms at phosphorus). Lithiation at phosphorus with tBuLi gives the corresponding 1,3‐dilithio derivative which reacts with tBuHgCl to form the 1,3‐dimercurio derivative 2. Photolysis of 2 with visible light leads to 3, the first derivative of a 1,3‐diphospha‐2,4‐digermabicyclo[1.1.0]butane with tBu/tBu‐exo,exo configuration. As another product of the photolysis the trimercurio compound 5 is isolated and characterized by an X‐ray structure analysis.
A Stopped‐Flow Kinetic Study of the Reaction of trans‐1‐(Dimethylamino)‐1,3‐butadiene with Dimethyl Dicyanofumarate
Authors: Sustmann Reiner , Rogge Monika , Nüchter Ursula , Harvey Jeremy
Published: July 2007

trans‐1‐(Dimethylamino)‐1,3‐butadiene and dimethyl dicyanofumarate react in acetonitrile and dichloromethane at –40°C with a second‐order rate constant of 107 to 108 l mol‐1 s‐1. This was determined by following the decay of the UV absorption of diene and dienophile with a stopped‐flow spectrofluorimeter. After disapperance of the reagents a new absorption (λmax = 400 nm, lgϵ = 2.514) is recorded which decays by a first‐order process. The analysis of the kinetic data (Ea = 14.5 ± 0.1 kcal mol‐1, lgA = 14.71 ± 0.05, ΔH# = 14.1 ± 0.1 kcal mol‐1, δS# = 7.2 ± 0.2 cal mol‐1 K‐1, ΔG# = 11.95 ± 0.01 kcal mol‐1) in combination with stereochemical studies on the cycloaddition of the E/Z isomeric dienophiles dimethyl dicyanofumarate and dicyanomaleate leads to the interpretation that the new species is a zwitterion.
The Pagodane Route to Dodecahedranes Unsaturated (Hyperstable) and Saturated Bissecododecahedranes
Authors: Murty Bulusu A. R. C. , Pinkos Rolf , Spurr Paul R. , Fessner Wolf‐Dieter , Lutz Georg , Fritz Hans , Hunkler Dieter , Prinzbach Horst
Published: July 2007

In bissecododecahedra‐1,10(11)‐dienes, the syn‐periplanar and unusually proximate arrangement of the π bonds is responsible for extraordinary physical properties such as strong throughspace homoconjugation, low oxidation potentials, and a special reactivity pattern. In pursuit of route B to dodecahedranes[1], the hyperstability predicted (MM2) for these bissecodienes and the related monoenes has been experimentally verified only for the latter in their resistance towards catalytic hydrogenation. Non‐hydrogenative saturation of (3,8‐difunctionalized) bissecodienes (3, 8, 13) and monoenes (4, 9, 14) becomes increasingly hampered due to the increased steric congestion on the more spherical molecular surfaces but can be achieved in „high‐driving‐force” reactions [cis‐hydroxylation (26, 27, 41, 42), epoxidation (38, 54, 57, 58, 60, 63, 80, 83), cyclopropanation (55, 59, 61, 64]. In contrast, cycloadditive four‐, five‐ (73), and six‐membered (76) ring annulation again is limited to monoadditions. The half‐cages in the bissecododecahedrane structures provide for remarkable steric steering and protection [e.g. anti‐selective protonation (alkylation) of carbanions 57a (84a)2‐, lack of hydrazone formation from ketones 58, 89, resistance of syn‐bis(acid chloride) 86 towards hydrolysis.
Struktur von α‐(Dimethylamino)benzyllithium in Lösung: Dynamisches Gleichgewicht zwischen einer η1‐ und einer η3‐Spezies
Authors: Ahlbrecht Hubertus , Harbach Jürgen , Hauck Tim , Kalinowski Hans‐Otto
Published: July 2007

Structure of α‐(Dimethylamino)benzyllithium in Solution: Dynamic Equilibrium between an η1 and an η3 Species

Temperature‐dependent 1H‐ and 13C‐NMR‐spektroscopic shifts observed in tetrahydrofuran are indicative of an equilibrium between a high‐temperature η3 and a low‐temperature η1 species. MNDO calculations are in accord with this view, and HOESY experiments proof it, too. The equilibrium is controled by solvation or complexation, low Lewis basicity of the solvent or bidentate ligands favoring the η3, high Lewis basicity or tridentate ligands the η1 species. Equilibrium as well as rate constants have been estimated, and from their temperature dependence the thermodynamics of the equilibrium and the activation barriers were calculated.
Conformation in the Solid State and in Solution of 3,3′(4H,4′H)‐Spirobi[2H‐1,5‐benzodioxepin]
Authors: Grochowski Jacek , Rutkowska Maria , Rys Barbara , Serda Pavel , Snatzke Günther
Published: July 2007

The “spiro‐coplanar” conformation of 6,6′‐methoxycarbonyl‐3,3′(4H,4′H)‐spirobi[2H‐1,5‐benzodioxepin] (1b) and the 3P configuration of the corresponding menthol ester 1c have been determined from chiroptical data by application of the exciton theory. The solid‐state conformation of the central part of the menthol ester molecule is “spiro‐coplanar”, too, with nearly D2 symmetry. The menthol moieties have chair conformations, and the absolute configurations at their chiral centers have been assigned using enantiomer‐sensitive Bijvoet pairs; they are in agreement with the known absolute configuration of menthol.
Von vierfach funktionalisierten Cyclophanen zu rohrförmigen Molekülen
Authors: Schröder Axel , Karbach Detlef , Güther Ralf , Vögtle Fritz
Published: July 2007

From Fourfold Functionalized Cyclophanes to Tube‐Shaped Molecules

A series of fourfold functionalized 2,11‐dithia‐ and 2,11‐diaza[3.3]cyclophanes 15–17 and 18–22, resp., is prepared by using a new multistep‐strategy starting from 7 or m‐xylene, respectively. The cyclophanes are used to construct tube‐shaped molecules of type 24 by macrocyclization reactions of e. g. 21 and 22. Macrocycle 24 turns out to be conformationally flexible.
Stereochemie der Denitrogenierung von optisch aktivem 9,10‐Dihydro‐5,6‐diazalumibullvalen zu optisch aktivem 3,4‐Dihydrosemibullvalen
Authors: Askani Rainer , Andermann Thomas , Müller Karl Michael
Published: July 2007

Stereochemical Course of the Denitrogenation of Optically Active 9,10‐Dihydro‐5,6‐diazalumibullvalene to Optically Active 3,4‐Dihydrosemibullvalene

Thermal decomposition of optical active diazalumibullvalene derivative (+)‐6 gives optical active dihydrosemibullvalene (+)‐5. The absolute configurations of optical active 6 and 5 were determined by correlation to tricyclooctanone 9 and 2‐cyclopentene‐1‐acetic acid (21), respectively. From these results it is concluded that thermal denitrogenation of 6 occurs by concerted six‐electron cycloreversion competing most likely to a multi‐step N2 elimination via the symmetrical diradical intermediates 8 and 7.
Ein neuartiger Einstieg in Wittig‐Umlagerungen – Eine stereoselektive [1,2]‐Wittig‐Umlagerung mit Konfigurationsumkehr am Carbanion‐Zentrum
Authors: Hoffmann Rolf , Brückner Reinhard
Published: July 2007

A Novel Entry into Wittig Rearrangements – A Stereoselective [1,2]‐Wittig Rearrangement with Inversion of Configuration at the Carbanion Center

The O,Se‐ketal 10, through lithium naphthalenide induced reductive cleavage of its C–Se bond, was converted into the α‐lithio ether 11a with an equatorially oriented CO bond. At ‐78°C, 11a undergoes a rapid [1,2]‐Wittig rearrangement to provide stereoselectively the homoallylic alcohol 12a with an axial OH group. Thus, the rearrangement proceeds with inversion of configuration at the carbanion center.
Highly Selective High‐Pressure Cycloadditions
Authors: Winterfeldt Ekkehard , Wray Victor
Published: July 2007

High‐pressure cycloadditions of the nonsymmetric dienophiles itaconic anhydride (6) and citraconic anhydride (7) to the homochiral cyclopentadiene 1 can be exercised with excellent regioselectivity (100%) and face selectivity
Metallkomplexe von Farbstoffen, III. Übergangsmetall‐Komplexe mit Pyrrolindigo
Authors: Schmidt Christoph , Wagner Hans‐Ulrich , Beck Wolfgang
Published: July 2007

Metal Complexes of Dyes, III[1,2]. – Transition Metal Complexes of Pyrrole Indigo The dianions of octahydroindigo and 4,4′‐dibutyl‐5,5′‐dimethylpyrrole indigo (L) react with metal salts and chloro‐bridged complexes [(μ‐Cl)M(Cl)PR3]2 (M = Pd, Pt; R = nBu, Et), [(μ‐Cl)M(Cl)(η5‐C5Me5)]2 (M = Rh, Ir) to give the bis‐N,O chelate complexes [M(L – 2H+)]n (M = Cu, Zn), (L – 2H+)[M(Cl)(PR3)]2 (M = Pd, Pt), and (L – 2H+)[M(Cl)(η5‐C5Me5)]2 (M = Rh, Ir). The electronic spectra of the soluble complexes with phosphane or C5Me5 ligands show a large bathochromic shift of the absorptions in the visible region compared to the free neutral ligands which is in accordance with PPP calculations of model compounds.
Derivate des Borols, XIX. (Borol)dicarbonylcobaltat‐Ionen: Synthese, Struktur und Reaktivität
Authors: Herberich Gerhard E. , Carstensen Tobias , Englert Ulli
Published: July 2007

Derivatives of Borole, XIX[1]. – (Borole)dicarbonylcobaltate Ions: Synthesis, Structure, and Reactivity[3]

Reduction of the dinuclear (borole)carbonylcobalt complexes [(3,4‐R2C4H2BPh)Co(CO)2]2 (3a: R = H, b: R = Me) with Na/Hg in THF at –30°C affords the anions [(3,4‐R2C4H2BPh)‐Co(CO)2]− (2a,b−) which can be isolated as [Na([15]crown‐5)]+ salts. The structural data of PPh4 · 2a indicate a strong Co – C(CO) interaction and relatively weak cobalt‐to‐boron bonding. Methylation of the anions 2a,b− gives labile metal alkyl complexes (3,4‐R2C4H2BPh)Co(CO)2Me while protonation and subsequent addition of phosphanes afford boracyclopentenyl complexes as e.g. (C4H5BPh)Co(CO)2(PMe3) (5a). The latter reacts with Ph3CBF4 to give the salt [(C4H4BPh)Co(CO)2‐(PMe3)]BF4 (6 · BF4). At –80CC cation 6+ undergoes hydride addition at the carbonyl carbon to give the formyl species (C4H4BPh)Co(CO)(CHO)(PMe3) (7) which transforms to the hydride (C4H4BPh)CoH(CO)(PMe3) (8). At room temperature the same reaction produces 5a. Deuteration studies show that the oxidative formation of 6+ from 5a and the formation of 5a by addition of hydride to 6+ are nonstereospecific processes.
Thiiran als Schwefelquelle für das 3z4e‐Bindungssystem im Komplex {(η5‐C5H5)(CO)2Mn}2S
Authors: Beuter Georg , Drobnik Stefan , Lorenz Ingo‐Peter , Lubik Alfred
Published: July 2007

Thiirane as Sulfur Source for the 3c4e Bonding System in the Complex {(η5‐C5H5)(CO)2Mn}2S

Thiirane (2) is used as source for the directed formation of the symmetrically bridged complex { (3) by its reaction with (η5‐C5H5)(CO)2MnTHF (1). Compound 3 can be oxidized, protonated, or methylated to give the {(η5‐C5H5)(CO)2Mn}2SSO complex {SO (4) or the SR+ cations [{(η5‐C5H5)(CO)2Mn}2SR]+ (R = H, CH3) (5, 6). Compounds 5 and 6 show an equilibrium between the open and closed form in solution at room temperature. According to an X‐ray structural analysis 3 crystallizes in the triclinic space group Pη1 and shows the open form IIa with a 3c4e bonding system which is isolobal to SO2, whereas the analogous rhenium complex has the isomeric closed form IIb with a metal – metal bond which is isolobal to thiirane.
Phosphoniothiolat–Komplexe: Darstellung und Umlagerung in Phosphan–Komplexe
Authors: Fischer Helmut , Fluck Klaus H. , Troll Carsten
Published: July 2007

Phosphoniothiolate Complexes: Synthesis and Rearrangement to Phosphane Complexes

Pentacarbonyl(thiobenzaldehyde)tungsten (1) reacts with phosphanes PR3 to give the phosphoniothiolate / complexes (CO)5W[SC(H)Ph(PR3)] (2) (RMe, Et, Ph, 4–MeC6H4). Similarly, the thiobenzophenone complex (CO)5W[SCPh2] (3) affords (CO)5W[SC(Ph)2PMe3] (4). The phosphoniothiolate complexes obtained from 1 and PPh2H or P(2,4,6–Me3C6H2)H2 rapidly rearrange by formal S,P migration of (CO)5W and P,C migration of H to form the phosphate complexes (CO)5W{P‐(Ph)2[C(Ph)H(SH)]} (5) and (CO)5W{P(2,4,6–Me3C6H2)H‐[C(Ph)H(SH)]} (6/6′).
Die hypothetischen Phosphor–Cluster P6 und P8 – welche Isomeren wären die stabilsten?
Authors: Janoschek Rudolf
Published: July 2007

The Hypothetic Phosphorus Clusters P6 and P8 – Which Isomers Would Be the Most Stable Ones?

The hexaphosphabenzvalene 3 turned out to be the most stable P6 isomer applying ab initio MP4(SDQ)/CEP–DZ* calculations, and therefore plays a favorite role for synthesis. The cubic P8 is replaced by a polycyclic structure 8 which is more stable by 49 kcal mol‐1, but still thermodynamically unstable with respect to 2 P4.
On the Reactions of Fe(CH2)+ with 1,7–Octadiene in the Gas Phase
Authors: Stöckigt Detlef , Schwarz Helmut
Published: July 2007

In contrast to the reactions of “bare” Fe+ with 1,7–octadiene (1), the chemistry of Fe(CH2)+ with 1 represents a “textbook” example for a gas–phase metathesis process to generate in a clean fashion Fe(C2H4)+. Similarly, for the formation of Fe(C6H6)+ a mechanism is suggested which is in keeping with the experimental findings. In contrast, the reactions of Fe(CH2)+ with 1 leading to Fe(C3H4)+ and Fe(C4H6)+ are so complex that a coherent description is not yet possible.
Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen, CXIV. Organorhenium(VII)‐oxide
Authors: Herrmann Wolfgang A. , Kühn Fritz E. , Romão Carlos C. , Huy Hoa Tran , Wang Mei , Fischer Richard W. , Kiprof Paul , Scherer Wolfgang
Published: July 2007

Multiple Bonds between Main Group Elements and Transition Metals, CXIV. — Organorhenium(VII) Oxides

Alkylrhenium(VII) oxides of formulae RReO3 and RReO3 · L (L = quinuclidine) result from dirhenium heptaoxide and dialkylzinc compounds at low temperatures in THF solution. Unbranched, noncyclic organorhenium oxides prove to be less thermolabile than branched‐chain derivatives, with the thermal stability decreasing with increasing chain length. Complexes with branched carbon chains normally can be isolated as 1:1 adducts of a nitrogen base, e.g. quinuclidine. A first chiral alkylmetal oxide and base‐stabilized cyclopropyltrioxorhenium(VII) are also described.
Pyridinium N‐Phenoxide Betaines and Their Application to the Characterization of Solvent Polarities, XIX. The Halochromism of Pyridinium N‐Phenoxide Betaine Dyes in Acetonitrile Solution
Authors: Reichardt Christian , Asharin‐;Fard Siamak , Schäfer Gerhard
Published: July 2007

The halochromism of the negatively solvatochromic pyridinium N‐phenoxide betaine dye 1 has been measured in acetonitrile solution and linearly correlated with the effective charge of the cations of the added alkaline and alkaline earth salts. The observed negative halochromism of betaine dye 1 constitutes a new type of true halochromism, in contrast to the trivial halochromism found for the first time by Baeyer and Villiger in 1902.
Trimethylsilylcyanid als Umpolungsreagens, XX. Zur Regioselektivität der Addition von Carbonyl‐;Verbindungen an umgepolte α,β‐ungesättigte Aldehyde
Authors: Hünig Siegfried , Schäfer Matthias
Published: July 2007

Trimethylsilyl Cyanide — A Reagent for Umpolung, XX. — On the Regioselectivity of the Addition of Carbonyl Compounds to α,β‐Unsaturated Aldehydes after Umpolung

By addition totBuMe2SiCN to α,β‐unsaturated aldehydes5the silylated cyanohydrins6are produced. Deprotonation of6provides allylic anions which can be attached to aldehydes and ketones in α‐position (kinetic control) (→8) or γ‐position (thermodynamic control) (→9). In contrast to the Me3Si group which has been applied so far thetBuMe2Si group is stable under the reaction conditions. Therefore, the ratio of α/γ adducts can be tuned from >95:5 to <5:95 depending on the substitution pattern of6, the aldehydes and ketones, the reaction time and temperature, and even by some additives. The γ adducts9are easily transformed into γ‐butyrolactones27by acidic hydrolysis.
Darstellung und Charakterisierung von Anthrylenmagnesium‐Innerkomplexen
Authors: Benn Reinhard , Bogdanović Borislav , Brüning Martin , Grondey Hiltrud , Herrmann Wolfram , Kinzelmann Hans‐;Georg , Seevogel Klaus
Published: July 2007

Preparation and Characterization of Inner Complexes of Anthrylenemagnesium

Anthracene derivatives containing ether or amino groups in 9‐ or 9,10‐position (1 – 10) react with magnesium to form new magnesium anthracene inner complexes (11 – 20). These complexes as well as their organic starting materials have been extensively characterized by spectroscopy and chemical means. It was found that solvent ligands which are present in all magnesium anthracene complexes known to date can be partially or totally replaced by inner complexation. For some of the new magnesium anthracene inner complexes the complex formation rates have been determined.
Crystal Structure of the Explosive Parent Benzyne Precursor: 2‐Diazoniobenzenecarboxylate Hydrate
Authors: Horan Christopher J. , Barnes Charles L. , Glaser Rainer
Published: July 2007

The structure of the highly unstable benzyne precursor 2‐diazoniobenzenecarboxylate (3) has been determined by single‐crystal X‐ray diffraction. The structure is discussed in comparison to ab initio results for several conformers of 3, related aromatic diazonium ions, and phenyl cation and also to crystal structures of simple diazonium ion salts and of benzoates. Structural features and characteristic distortions are related to the electron density distributions and to intra‐ and intermolecular interactions between the neighboring functional groups.
Allenyl Enolates — A New Class of Chiral Ambident Nucleophiles, 1. Reaction with C and Si Electrophiles
Authors: Arndt Silke , Handke Gabriele , Krause Norbert
Published: July 2007

The regio‐ and stereoselectivity of the reaction of allenyl enolates obtained by 1,6‐addition of lithium dimethylcuprate to acceptor‐substituted enynes 1 with C and Si electrophiles is examined. It is found that allyl bromide reacts at C‐4 to give 4‐substituted 2,4‐dienoates 2; in contrast, methyl triflate and carbonyl compounds react at C‐2 to yield 2‐substituted β‐allenic esters 3–12. The hard electrophile chlorotrimethylsilane reacts at the enolate oxygen atom to provide allenyl enol ether 14. The regioselectivity of these trapping reactions depends only on the nature of the electrophile; the stereoselectivities, on the other hand, are a function of both the steric properties of the allenyl enolate and the type of electrophile. The regio‐and stereoselectivities are rationalized in terms of charge control and frontier‐orbital control, of kinetic and thermodynamic control, and of steric interactions in intermediates and transition states.
Preparation and Some Reactions of (Acylamino)diorganoboranes
Authors: Yalpani Mohamed , Köster Roland , Boese Roland
Published: July 2007

The carboxamides RCONH2 [RPh (1), tBu (2)] react with BEt3 and with (9H‐9‐BBN)2 to give the (acylamino)diethylboranes 3, 4 and the 9‐acylamino‐9‐BBN 5, 6, respectively. Compounds 3 and 4 are largely monomeric (NMR) in solution and dimeric as crystalline solids [X‐ray structure of (4)2]. The 9‐BBN derivatives 5 and 6 are associated and probably polymeric in solution (NMR). The 1:1 adducts 7 and 8 containing the ring (X‐ray structure of 7) are formed on the reaction of 3 and 4 with (9H‐9‐BBN)2 by borane exchange. The former is also obtained directly by treating compound 1 or 2 with (9H‐9‐BBN)2. Compound 7 reacts at 140–150°C to give the air‐stable heterocycle 11 (X‐ray structure).
Synthese und Struktur des ersten Tellur‐haltigen Borazin‐Derivats und einer Tellur‐haltigen Bor – Stickstoff‐Spiro‐Verbindung
Authors: Koch Hans‐Joachim , Roesky Herbert W. , Besser Susanne , Herbst‐Irmer Regine
Published: July 2007

Synthesis and Structure of the First Tellurium‐Containing Borazine Derivative and a Tellurium‐Containing Boron – Nitrogen Spirocyclic Compound

We describe the synthesis of the first tellurium‐containing borazine derivative MeN[PhBN(Me)]2TeCl2 (2). Compound 2 has been prepared by the reaction of MeN[PhBN(Me)SiMe3]2 and TeCl4. The spirocyclic compound [PhB(tBuN)2]2Te (4) has been synthesized by the reaction of PhB(tBuNLi)2 (3) with TeCl4 in a molar ratio of 2:1. The single‐crystal X‐ray structures of 2 and 4 are reported.
Monofunktionelle tetraedrische Zink‐Komplexe L3ZnX [L3Tris(pyrazolyl)borat]
Authors: Alsfasser Ralf , Powell Anne K. , Vahrenkamp Heinrich , Trofimenko Swiatoslaw
Published: July 2007

Monofunctional Tetrahedral Zinc Complexes L3ZnX [L3Tris(pyrazolyl)borate]

The pyrazolyl borates K[HBpz3*] (abbreviated KL3, pz*3‐phenyl‐, 3‐tolyl‐, 3‐anisyl‐3,5‐diphenyl pyrazolyl) react with zinc salts ZnX2 (XCl, Br, I, NO3) to form the mononuclear neutral tetrahedral zinc complexes L3ZnX (1 – 4). The corresponding alkylzinc complexes L3ZnR (5 – 8; RMe, Et, tBu, Ph) result either from L3ZnCl and LiR or from ZnEt2 and KL3. These alkylzinc compounds are remarkably stable towards oxidation and hydrolysis. For specific cases the reaction of L3ZnR with carboxylic acids is found to yield the carboxylates L3ZnOCOR (9, 10), and likewise with thioacetic acid to yield the thioacetates L3ZnSCOMe (11). Facile cleavage of L3ZnR with thiols and selenophenol produces the thiolates L3ZnSR (12, 13) and the selenolates L3ZnSePh (14). The complexes L3ZntBu which are the most reactive of the alkylzinc compounds are cleaved by H2O, H2S, NH3 and various OH and NH compounds with formation of the bis(ligand) complexes Zn(L3)2 (15). Crystal structure determinations of one L3ZnX complex each for XNO3 (4a), CH3 (5a), SCOMe (11a), and SEt (12a) confirm the nature of the compounds and the relation of 4a and 12a to the active centers of zinc‐containing enzymes.
Cycloadditionen von Benzothiet und aromatischen Nitroso‐Verbindungen
Authors: Saul Klaus , Eckes Heinz‐Ludwig , Meier Herbert , Jacob Dominic
Published: July 2007

Cycloaddition Reactions of Benzothiete and Aromatic Nitroso Compounds

The new heterocyclic ring systems 4H‐3,1,2‐benzoxathiazines 4 and 2,3‐dihydro‐1,2‐benzothiazol 1‐oxides 6 can be synthesized by cycloaddition of benzothiete (1) and aromatic nitroso compounds 3. The regioselectivity of the primary step and the secondary thermal or acid‐catalyzed rearrangements are discussed.
Reactivity of Dithiazinanes towards BH3, BD3 and BF3. New Heterocycles: 5,5‐Dimethyl‐1,3‐dithia‐5‐azonia‐4‐boratacyclohexane and 6,6‐Dideuterio‐5‐methyl‐5[D1]methyl‐1,3‐dithia‐5azonia‐4‐boratacyclohexane. A Method for the Dimethylation and Monodeuteriomethylation of Primary Amines
Authors: Flores‐Parra Angelina , Cadenas‐Pliego Gregorio , Martínez‐Aguilera Luz Maria R. , Lourdes García‐Nares M. , Contreas Rosalinda
Published: July 2007

5‐Methyl‐and 5‐tert1‐butyl‐1,3,5‐dithiazinane (1 and 7) react with BH3·THF, and Et2O·BF3 to yield the N1‐coordinated adducts 2 – 4 (with BH3, BD3, and BF3, respectively). The conformations and spectroscopic properties of the adducts are discussed. The reactions of 1 and 7 with BY3·THF lead to the six‐membered boron heterocycles 5,5‐dimethyl‐1,3‐dithia‐5‐azonia‐4‐boratacyclohexane (5), 4,4‐dideuterio‐5‐methyl‐5[D1]methyl‐1,3‐dithia‐5‐azonia‐4‐boratacyclohexane (6), and 5‐tert1‐butyl‐5‐methyl‐1,3‐dithia‐5‐azonia‐4‐boratacy‐clohexane (8). Compounds 2 and 5 are isolobal isomers. The reaction of BH3 or BD3 with 7 affords, after heating, tert1‐butyldimethylamine – borane (9) and tert1‐butyldi([D1]methyl)1‐amine – trideuterioborane (11), respectively. The dithiazinane derivatives may be used in organic synthesis for the dimethylation of primary amines and the preparation of alkyldimethylamines with monodeuterated methyl groups.
(Ether‐phosphan)eisen(II)1‐Komplexe mit den Koordinationszahlen Vier, Fünf und Sechs
Authors: Lindner Ekkehard , Geprägs Michael , Fawzi Riad , Steimann Manfred
Published: July 2007

(Ether‐phosphane)iron(II) Complexes with the Coordination Numbers Four, Five, and Six

Photolysis of cis,cis,trans1‐Br2(OC)2 Fe(P∑O)2 (1a, b) [O,PPh2PCH2CH2OCH3 (a), Ph2PCH2C4H7O (b)] results in the formation of the iron(II) complexes Br2Fe(P∼O)2 (2a), [BrFe‐(P∩O)(μ1‐Br)]2 (4b), and [trans1‐Br2Fe(P∩O)(μ1‐CO)]2 (5a) with the coordination numbers four, five, and six, respectively. 2a crystallizes in the triclinic space group P\documentclass{article}\pagestyle{empty}\begin{document}$\bar{1}$\end{document} with Z2 and has two monodentated O,P functions (P∼O: η1‐P1‐coordinated; P∩O:η2‐O,P1‐coordinated). The dimeric complex 4b with two O∩P‐chelated ligands crystallizes in the orthorhombic space group Pbca with Z4. 2a and 4b, which react under CO pressure to give the starting complexes 1a, b, are also accessible from the ether‐phosphanes 3a, b and anhydrous FeBr2.
Darstellung und Struktur von 1‐Oxa‐3,5‐diaza‐1,3,5‐hexatrienen. Die 1‐Oxa‐3,5‐diaza‐1,3,5‐hexatrien/2H‐1,3,5‐Oxadiazin‐Tautomerie
Authors: Buhmann Martin , Würthwein Ernst‐Ulrich , Möller Manfred H.
Published: July 2007

Synthesis and Structures of 1‐Oxa‐3,5‐diaza‐1,3,5‐hexatrienes. The 1‐Oxa‐3,5‐diaza‐1,3,5‐hexatriene/2H‐1,3,5‐Oxadiazine Tautomerism

Reaction of N1‐lithio‐or N1‐trimethylsilyl‐substituted imines 1 with N1‐acylimidic acid derivatives 2 provides 1‐oxa‐3,5‐diaza‐1,3,5‐hexatrienes 3 in fair to good yields. Depending on the substitution pattern, the acyclic compounds 3 form an equilibrium with their cyclic tautomers, e.g. 2H‐1,3,5‐oxadiazines 4. Aromatic substituents at C‐6 favor the acyclic form 3, whereas aliphatic groups (e.g. tert1‐butyl) lead to the exclusive formation of the ring tautomer 4. For a typical example (3d/4d) the free enthalpy of activation for the ring/chain tautomerism was determined to be ca. 12.5 kcal/mol. Detailed spectroscopic data (1H‐, 13C‐NMR, IR, UV) for both tautomers are given. The X‐Ray analysis of the acyclic compound 3a shows a central CN bond with Z configuration and with s‐gauche conformations of the adjacent CO and CN systems. According to quantum mechanical ab initio calculations (MP2/6‐31G*/6‐31G*) for the C3H4N2O model compounds, the ring tautomer 6 is by ca. 6 kcal/mol lower in energy than the acyclic forms 7. Within the series of open‐chain tautomers 7, gauche forms are lower in energy than s‐trans conformers, indicating that amide resonance is more important for these systems than polyene delocalization, s‐cis Forms were found to be transition states. The acyclic conformers 7 are rather flexible; barriers of rotation for both C – N bonds are calculated to 4 – 5 kcal/mol only (RHF/ 3‐21G/3‐21G).
Substituenteneffekte auf die CC‐Bindungsstärke, 13. Kinetische und thermodynamische Stabilität von α1‐alkylierten α1‐Amino‐carbonsäureestern – Stabilisierungsenergie von α1‐Amino‐α1‐(ethoxycarbonyl)alkyl‐Radikalen
Authors: Schulze Rainer , Beckhaus Hans‐Dieter , Rüchardt Christoph
Published: July 2007

Substituent Effects on the Strength of CC Bonds, 13[1]. – Kinetic and Thermodynamic Stability of α1‐alkylated α1‐Amino Acid Esters – Energy of Stabilization of α1‐Amino‐α1‐(ethoxycarbonyl)alkyl Radicals

Thermolytic cleavage of 1a–c and 2a–c into radicals in solution are clean first‐order processes. The activation parameters for CC bond homolysis were determined. Compared with the corresponding data for hydrocarbons of equal strain a decrease of bond strength of 14.4 kcal/mol results by the combined interaction of the amino and the ethoxycarbonyl substituents. The heat of formation of 5 was determined by combustion calorimetry [δHco (1)– 1207.75 ± 0.20 kcal/mol] combined with the heat of vaporization (δHvo13.31 ± 0.10 kcal/mol). Compared with the additive behaviour of group increments the resulting heat of formation (δHfo (g)– 112.02 ± 0.24 kcal/mol] suggests a synergetic, geminal destabilization of Hsyn1.9 ± 1.4 kcal/mol. Combination of the kinetic data of bond homolysis of 1a–c and 2a–c with the synergetic ground‐state destabilization leads to a synergetic, capto‐dative radical stabilization of Hsyn (rad)6.7 kcal/mol.
2,4,6,8‐Tetraphenylbarbaralan – ein orangeroter, thermochromer Kohlenwasserstoff ohne Chromophor[1,2]
Authors: Quast Helmut , Knoll Katja , Peters Eva‐Maria , Peters Karl , Schnering Hans Georg Von
Published: July 2007

2,4,6,8‐Tetraphenylbarbaralane – an Orange‐Red, Thermochromic Hydrocarbon Devoid of a Chromophore[1,2]

The diphenylbicyclo[3.3.1]nonanedione 6 adds phenylcerium‐(III) dichloride to afford a high yield of the triphenyl‐2‐oxa‐twistanol 8. In contrast, phenyllithium yields a mixture of tri‐phenylhydroxyketone exo‐7, tetraphenylbicyclo[3.3.1]nona‐nediol 9, and 8. The latter is dehydrated by sulfuric acid in acetic acid to produce the triphenylbicyclo[3.3.1]nonenone 10 in almost quantitative yield. Addition of phenylcerium(III) dichloride to 10 affords a 3:2 mixture of the tetraphenylbicy‐clo[3.3.1]nonenols exo‐ and endo‐11 which may be separated by chromatography. Dehydration of the mixture yields quantitatively the tetraphenyldiene 12. On treatment with an excess of butylpotassium in pentane, 12 is converted to the deep violet, crystalline dipotassium salt 17 which may be purified by reprecipitation from its tetrahydrofuran solution with pentane. When the solution of 17 in tetrahydrofuran is slowly added to an excess of 1,2‐dibromoethane at –60°C, the dianion is immediately oxidized to produce the tetraphenylbarbara‐lane 4 which is isolated in 30% yield as orange‐red crystals after chromatography. – The structures of the new compounds are based on spectroscopic evidence and X‐ray diffraction analyses of 4, 8, exo‐11, and 12. The conformations in solution are inferred on the basis of vicinal proton coupling constants and a comparison with coupling constants calculated with the aid of the Karplus equation from torsional angles obtained by X‐ray diffraction analyses. The conformation of exo‐11 in solution closely resembles that present in the crystal. – While the barbaralane 4 exists as a pair of very rapidly rearranging degenerate valence tautomers in solution, the degeneracy is lifted in the crystal lattice. As a result, the crystal consists of two rapidly rearranging but non‐equivalent valence tautomers in a ratio of 9:1 as estimated from the apparent atomic distance C2–C8 of 4 and the C2–C8 bond length of the model barbaralane 18. – The orange‐red colour of 4 in the crystal and in solution results from a pronounced shoulder in the UV/Vis spectrum at 430 nm, the intensity of which strongly depends on the temperature. Thus, 4 is the first barbaralane which exhibits colour though it is lacking a classical long‐wavelength chromophore.
[2,3]1‐Thia‐Wittig Rearrangements Proceeding with Complete Inversion or with Partial Loss of Configuration at the Carbanionic Center
Authors: Brickmann Kay , Brückner Reinhard
Published: July 2007

Two pairs of diastereomeric γ1‐(benzyloxy)1‐α1‐(tributylstannyl) sulfides (anti‐ and syn‐13, anti‐ and syn‐30) were prepared, nBuLi induced tin/lithium exchange in each of these compounds furnished α1‐lithiated sulfides which underwent [2,3]1‐thia‐Wittig rearrangements in THF at – 78°C within 30 min. Competing [1,2]1‐thia‐Wittig rearrangements were not observed, not even starting from stannyl sulfides 30 where the [2,3] shift requires the intermediacy of lithium thiolates 32 in which the aromaticity of a benzene ring is given up. The homoallyl thiols syn‐ and anti‐19 were formed stereoselectively starting from the allylthio stannanes anti‐ and syn‐13, respectively. This implies that the underlying thia‐Wittig rearrangements are stereospecific and proceed with inversion of configuration at the carbanionic center, and that the lithio sulfides anti‐ and syn‐18 formed in the course of these reactions are configurationally stable until they rearrange. The benzylthio stannanes anti‐ and syn‐30 rearranged with low stereoselectivity. They furnished the benzyl thiols 33 as 71:29 and 28:72 mixtures of diastereomers, respectively. This means that the lithio sulfide intermediates involved in the latter rearrangements suffer some epimerization anti‐31 ⇄ syn‐31 prior to the sigmatropic bond shift.