bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fachinformationszentrum Chemie GmbH, Berlin — A Decade in the Service of Chemistry Information
Authors: Flambard Anthony R. , Weiske Christian M. 
Published: July 2007

AbstractWith the occurrence of the 10th anniversary of the foundation of FIZ CHEMIE in December 1991, a review is given of the historical events leading to the foundation of this government‐sponsored organization, followed by the company's aims and structure, developments during the last decade, and the printed and electronic chemical information and documentation services it offers to education, industry, and the public in general.
Synthese und Reaktionen der Metall‐Base [(C5Me4H)Co(PMe3)2]
Authors: Werner Helmut , Lippert Ferdinand , Peters Karl , Schnering Hans Georg Von 
Published: July 2007

Synthesis and Reactions of the Metal Base [(C5Me4H)Co(PMe3)2]The (tetramethylcyclopentadienyl)cobalt complex [(C5Me4H)Co(PMe3)2] (1), which is prepared from [CoCl(PMe3)3] and LiC5Me4H in 75% yield, behaves like a Lewis base and reacts with NH4PF6, CH3I, or CF3SO3CH3 by oxidative addition to give the cations [(C5Me4H)CoX(PMe3)2]+ (X = H, I, CH3; 2–4) isolated as PF6 salts. From 3 (X = I) and excess LiCH3 the dimethylcobalt(III) compound [(C5Me4H)Co(CH3)2(PMe3)] (5) is obtained. Treatment of the corresponding trifluoroacetato derivative [(C5Me4H)Co(PMe3)(OCOCF3)2] (6) with PMe3, P(OMe)3, and 1,2‐C6H4(PPh2)2 leads, in the presence of NH4PF6, to the formation of the cationic complexes 7–9. The displacement of the two PMe3 ligands in 1 by (Ph2P)2NMe gives the rather unstable chelate compound {(C5Me4H)Co[(Ph2P)2NMe]} (10), which on treatment with NH4PF6 is transformed into the stable complex {(C5Me4H)CoH[(Ph2P)2NMe]}PF6 (11). The structure of 11 has been determined by X‐ray diffraction methods.
Arsenosiloxane: Bildung und Zerfall von Trialkylsilyl‐arsenaten und ‐arseniten
Authors: Baier Michael , Bissinger Peter , Schmidbaur Hubert 
Published: July 2007

Arsenosiloxanes: Formation and Decomposition of Trialkylsilyl Arsenates and ArsenitesTris(trialkylsilyl) arsenates(V) are prepared from silver arsenate(V) and chlorotrialkylsilanes or from arsenic acid and hexaalkyldisilazanes. The triethylsilyl ester 1b is stable, but the trimethylsilyl ester 1a undergoes condensation at ambient temperature to give hexamethyldisiloxane and trimethylsilylpolyarsenates(V), including tetrakis(trimethylsilyl) diarsenate(V) (4a). According to an X‐ray crystal structure determination of 4a (triclinic, space group P1) centrosymmetrical dimers are present containing two edge‐sharing AsO6 octahedra with apex‐bridging by two AsO4 tetrahedra. 1a is converted into the salt [(Me3SiO)4As]+ CF3SO3− the cation of which is believed to be a component of the reaction chain. There is also evidence by mass spectrometry for the existence of (Me3SiO)5As (5). — Tris(trimethylsilyl) arsenite(III) (6) is prepared from AsCl3 and NaOSiMe3. With modified stoichiometry, side reactions give also the byproducts Cl2AsOSiMe3, ClAs(OSiMe3)2, Cl2AsOAsCl2, Cl2AsOAsCl(OSiMe3), O[AsCl(OSiMe3)]2, and cyclic chloroarsenosiloxanes (12, 13).
1,2,4‐Oxadithietane und ein 1,2,4‐Oxadithiet
Authors: Gerhardt Rolf , Kuschel Raimund , Seppelt Konrad 
Published: July 2007

1,2,4‐Oxadithietanes and a 1,2,4‐OxadithieteSO3 adds to (pentafluoro‐λ6‐sulfanyl)ethenes 2 with formation of 1,2‐oxathietane 1 and 1,2,4‐oxadithietanes 3. The latter class of compounds (examples 4a, b) can also be obtained from SO3 and alkylidenesulfur tetrafluorides F3C‐RC = SF4. HOSO2F elimination from 3 affords 3‐methylene‐1,2,4‐oxadithietanes 5. HF elimination from 4a occurs within the ring, resulting in the first oxadithiete 6. This isomerizes upon heating to an alkylidenesulfur difluoride oxide FSO2(F3C)CSF2O.
Reaktionen von Halogenthiazylen: Darstellung, Strukturen und Eigenschaften von perhalogenierten 1,2‐Thiazinen[1]
Authors: Boese Roland , Haas Alois , Heß Thomas 
Published: July 2007

Reactions of Halogeno Thiazyls: Preparation, Structures, and Properties of Perhalogenated 1,2‐ThiazinesReactions of (XSN)n(n= 1,3; X = F, Cl) with perfluorobutadiene provide the 1λ4,2‐thiazines1aand1b. The structure of1 bwas determined by single‐crystal X‐ray diffraction analysis. From the molecular structure it is evident that a formal [4 + 2] cycloaddition has occured. Fluorination with KF converts1 balmost quantitatively into1 a. The 1λ4,2‐thiazine1 adoes not exhibit fluorinating properties towards chloroalkanes but undergoes reaction with CH3OH and Me3SiNMe2to form1 cand1 d, respectively. 1,2‐Thiazine oxide3is obtained from1 aor1 band (Me3Si)2O. Treatment of1 bwith AgAsF6in SO2yields perfluoro‐1,2‐thiazin‐1‐ium hexafluoroarsenate (4) as the main product. No reaction is observed between FSN and hexa‐chlorobutadiene. The 1,2‐thiazines5, 6, and9are prepared from tetrachlorothiophene dioxide (7) and FSN. Fluorine abstraction reactions of5and6with formation of the expected 1,2‐thiazin‐1‐ium ions11and13, respectively, provide evidence for the structures of5and6. These cations are very sensitive to hydrolysis and are converted into the corresponding ketones12and14. The very unstable intermediate CF3SSN, formed on treating Me3SiSCF3or B(SCF3)3with FSN, decomposes to CF3SxCF3(X= 2–4), S4N4, S8, and N2. No addition product can be detected when CF3SSN prepared in situ is treated with dienes.
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 TritonmethanolateThe 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 CompoundsO‐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.
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 SaltsThe 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.
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 MetalsFor 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]. – TrisilacyclobutaniminesTreatment 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)pyridinesAn “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

AbstractOn 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 BondsGermanium 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‐phosphadiborolesCyclocondensation 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

AbstractThiohydrazide 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‐FrameworkMes(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

Abstracttrans‐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

AbstractIn 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.