bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoinduced electron transfer in porphyrin‐quinone cyclophanes, 6. Porphyrin‐quinone cyclophanes with gradually varied acceptor strength: Syntheses and characterizations
Authors: Staab Heinz A. , Weiser Jürgen , Futscher Michael , Voit Guido , Rückemann Andreas , Anders Christine
Published: July 2007

For studying intramolecular electron‐transfer reactions, three groups of double‐ and single‐bridged porphyrin‐quinone cyclophanes 1–4, 5–9, and 11–14, resp., with gradual variation of quinone acceptor strengths were synthesized. As key intermediates for building up the porphyrin‐cyclophane skeleton the correspondingly 3,6‐substituted 1,4‐bis[4‐(2‐formylphenyl)‐butyl]‐2,5‐dimethoxybenzenes 15–20 were synthesized. Condensation with pyrrole yielded the doubly bridged porphyrin cyclophanes 42–45; via the bis(dipyrrolylmethyl) derivatives 46–51 and 64–67 the single‐bridged porphyrin cyclophanes 58–63 and 72–75 were obtained by acidic condensation with triethyl formate. Cleavage of the methoxy groups and oxidation yielded the corresponding porphyrin‐quinone systems. Some magnesium and zinc complexes of these cyclophanes are described. Spectroscopic data (MS, 1H NMR) are reported in support of the proposed structures.
Siderophore, II. Tetrazolylenolat‐ und Semicorrinat‐Anionen als Chelatliganden für Eisen(II)‐und Kupfer(II)‐Ionen: Vom Molekül zum Kollektiv. Siderophores, II[1]. – Tetrazolyl Enolate and Semicorrinate Anions as Chelate Ligands for Iron(II) and Copper(II) Ion: From Molecular to Collective Structures
Authors: Saalfrank Rolf W. , Struck Oliver , Nunn Kurt , Lurz Claus‐Jürgen , Harbig Roland , Peters Karl , Schnering Hans Georg Von , Bill Eckhard , Trautweinc Alfred X.
Published: July 2007

Reaction of tetrazolyl enolate 2 (HL2) with Cu(II) acetate yields the 3D‐coordination polymer 4 ([CuL22]n). the structure of which is unequivocally established by single‐crystal X‐ray diffraction. The formation of 4 is understandable if 2 or its enolate is considered as tridentate chelate ligand and if an intermediate formation of the coordinatively unsaturated copper(II) building block 6 is assumed. The monomers 6 are bidentate coordinating by the two CN groups, which leads to linking of monomers and to coordinative saturation at the copper(II) center of 6 with formation of three‐dimensional 4. Semicorrin 8 (HL4), however, reacts with Fe(II) to give the exceptional mononuclear tetrahedral chelate complex 10 (X‐ray). EPR and Mössbauer spectra of 4 and 10 are discussed.
Phosphane – Tetrahalodiborane(4) Adducts: Formation of closo‐3,4,5,6‐Tetrabromo‐1,2‐diphosphahexaborane(4)
Authors: Keller Willi , Sneddon Larry G. , Einholz Wolfgang , Gemmler Armin
Published: July 2007

Tetrabromodiborane(4), B2Br4, forms a 1:2 adduct 1 with PBr3, which reacts at 350°C to closo‐1,2‐P2B4Br4 (4a) in 25% yield. Compound 4a neither rearranges to the 1,6‐isomer nor decomposes to an appreciable extent upon heating to 650°C. B2C14 reacts with equimolar amounts of either tris(trimethylsilyl)‐phosphane or 1,2‐bis(dichlorophosphanyl)ethane to give B2Cl4 · P(SiMe3)3 (2) and B2Cl4 · Cl2PCH2CH2PCl2 (3), respectively. Compound 2 represents the first phosphane – diborane(4) monoadduct with two boron atoms in different coordination environment.
Lanthanoiden‐Komplexe, II. Tris(tert‐butylcyclopentadienyl)neodym, ‐dysprosium und ‐thulium. Kristall‐ und Molekülstruktur von Bis(tert‐butylcyclopentadienyl)‐hydroxidoneodym und ‐dysprosium
Authors: Herrmann Wolfgang A. , Anwander Reiner , Kleine Matthias , Öfele Karl , Riede Jürgen , Scherer Wolfgang
Published: July 2007

Complexes of the Lanthanides, II[1]. – Tris(tert‐butylcyclopentadienyl)neodymium, ‐dysprosium, and ‐thulium. Crystal and Molecular Structure of Bis(tert‐butylcyclopentadienyl)hydroxidoneodymium and ‐dysprosium

NdCl3, DyCl3, and TmI3 (1a–c) react with the potassium salt K(tBuCp) (2) of tert‐butylcyclopentadiene in THF to yield the sublimable homoleptic tris(tert‐butylcyclopentadienyl) complexes of formula Ln(tBuCp)3 (3a–c). The thermal behavior makes these compounds potential precursors for chemical vapour deposition techniques (MOCVD).
Lanthanoiden‐Komplexe, III. Flüchtige Neodym‐ und Yttrium‐Alkoxide mit neuen sperrigen Chelatliganden
Authors: Herrmann Wolfgang A. , Anwander Reiner , Denk Michael
Published: July 2007

Complexes of the Lanthanides, III[1]. – Volatile Neodymium and Yttrium Alkoxides with New Bulky Chelating Ligands

The synthesis of a new type of lanthanide alkoxides is described. The “clinching alcohols” HOCHtBuCH2OEt (1a), HOCHtBuCH2NEt2 (1b), HOCtBu2CH2OEt (1c), and HOCH‐i Pr2CH2OEt (1d) react with Nd[N{Si(CH3)3}2]3 (2a) to form the corresponding homoleptic alkoxide complexes 3a–d. The same procedure is applied to obtain the novel yttrium alkoxide 4 from the amide precursor 2b and the alcohol 1d. The new complexes are all very soluble in aliphatic hydrocarbons and were characterized by means of analyses and spectroscopy. The interesting property of these complexes is their remarkable volatility, the highest so far achieved for lanthanide alkoxides.
Two‐Photon Chemistry in the Laser Jet: Photochemistry of the Diphenylhydroxymethyl Radical
Authors: Adam Waldemar , Oestrich Rolf Schulte
Published: July 2007

In the laser‐jet mode (argon ion laser) the excited hydroxy‐diphenylmethyl radical (3*) underwent H expulsion in inert solvents (benzene, acetonitrile) to produce benzophenone (two‐photon product), besides dimerization of its ground state 3 to benzpinacol (one‐photon product). In ethanol, the laser‐jet photolysis of benzophenone afforded as new products (two‐photon chemistry) benzhydrol, 4‐(1‐hydroxyethyl)benzophen‐one (1), together with benzpinacol and 1,1‐diphenyl‐1,2‐propandiol (4), which are also observed in low‐intensity photolyses (one‐photon chemistry). Benzhydrol is formed through H abstraction from the excited radical 3* and ketone 1 possibly by coupling of an excited radical 3* at its para position (highest spin density) with a transient 1‐hydroxyethyl radical. Photolysis of α‐phenylbenzoin (2) produced benzpinacol, benzophenone, pinacol 4, benzhydrol, ketone 1, and the benzoyl‐derived products benzil and benzaldehyde. Also benzhydrol was observed as a two‐photon product.
1,1,3,3‐Tetraalkoxy‐2‐azaallylium‐Salze: Darstellung und stereochemische Eigenschaften
Authors: Kupfer Rainer , Meier Stefan , Würthwein Ernst‐Ulrich
Published: July 2007

1,1,3,3‐Tetraalkoxy‐2‐azaallylium Salts: Synthesis and Stereochemical Properties The title salts 1 were synthesized in satisfactory yield by regioselective alkylation at the carboxyl oxygen atom of N‐(dialkoxymethylene)carbamates 7 with oxonium salts 8. According to IR, 1H‐ and 13C‐NMR spectra, in solution a bent 2‐azaallyl cation structure is strongly favored over a linear cumulenic form. Dynamic NMR spectra indicate a barrier of ca. 11.7 kcal/mol between these two valence isomers. – Quantum mechanical calculations (ab initio 3–21G optimizations) on the model compound 1,1,3,3‐tetrahydroxy‐2‐azaallylium (9) confirm the 2‐azaallyl structure as the global minimum on the energy hyperface. 2‐Azaallenium structures are calculated to be ca. 20 kcal/mol higher in energy. The conformations of the hydroxy groups depend on the C – N – C bond angle. The best isomeric N‐protonated N‐(dialkoxymethylene)carbamate 10a is predicted to be favored by ca. 3 kcal/mol over the energy lowest 2‐azaallylium structure 9a.
Neue Untersuchungen zur Reaktivität von Formaldehyd‐O‐oxid, Acetaldehyd‐O‐oxid und Propionaldehyd‐O‐oxid
Authors: Reiser Ralf , Süling Carsten , Schröder Gerhard
Published: July 2007

New Studies Concerning the Reactivity of Formaldehyde Oxide, Acetaldehyde Oxide, and Propionaldehyde Oxide

Reactivity and selectivity of formaldehyde oxide (1a), acetaldehyde oxide (1b), and propionaldehyde oxide (1c) is tested by adding a cooled solution of one or two dipolarophiles to a solution of the primary ozonides of the olefins 2a, 2b or the ketene acetals 7a–c, respectively. Different selectivities are observed for the different carbonyl oxides. Only 1a is able to react with non‐activated olefins like methylenecyclopentane (4a), norbornene (4b), 3‐methylstyrene (4c), and cyclopentadiene (4d) under these conditions. Activated olefins turn out to be good quenchers for 1a. Both 1a and 1b react with fulvene 4e in completely different ways. Contrary to 1a, the carbonyl oxides 1b and 1c clearly prefer carbonyl compounds to activated olefins.
Tricarbonylchrom‐Komplexe von chiralen [2.2]Metacyclophanen: Darstellung, Struktur und chiroptische Eigenschaften
Authors: Schulz Jürgen , Bartram Stefan , Nieger Martin , Vögtle Fritz
Published: July 2007

Tricarbonylchromium Complexes of Chiral [2.2]Metacyclophanes: Syntheses, Structures, and Chiroptical Properties

HPLC‐baseline separations of three racemic cyclophanes 3, 4, and 6 on cellulose tris(3,5‐dimethylphenyl)carbamate led to their enantiomers with high optical purity. Complexation of (‐)‐3 and (+)‐3 with triamminetricarbonylchromium yielded chiral Cr(CO)3 complexes (‐)‐(S)P‐(3S)M‐3a and (+)‐(R)P‐(3R)M‐3a stereoselectively. Derivatisation of the complexes by lithiation and reaction with electrophiles gave new substituted chiral Cr(CO)3 complexes of [2.2]metacyclophanes regio‐selectively. X‐ray structure analyses of one chiral chromium complex (‐)‐(R)P‐(5S)M‐14a and three chiral chromium‐free ligands (‐)‐(S)P‐3, (‐)‐(S)P‐4, and (‐)‐(S)P‐6 led to the assignment of the absolute configurations of all chiral compounds discussed here. The influences of substituents on the chiroptical properties are investigated. The helicity of [2.2]metacyclophanes is discussed. For the first time X‐ray structure analyses were performed of a bis‐Cr(CO)3 complex (9a) as well as of the first chromium complex 10a of a heteraphane. Dethioketalisation of (‐)‐(S)P‐3 with NBS gave (‐)‐(S)P‐18, the absolute chirality of which has been known, under retention of configuration.
Reversible [4 + 1]‐Selbstaddition von Alkyl(arylimino)phosphanen und regioselektive Cycloaddition mit (E)‐ und (Z)‐Azobenzol
Authors: Niecke Edgar , Link Manfred , Nieger Martin
Published: July 2007

Reversible [4 + 1] Selfaddition of Alkyl(arylimino)phosphanes and Regioselective Cycloaddition to (E)‐ and (Z)‐Azobenzene

Dehydrohalogenation of the amino(chloro)phosphanes RP(Cl)N(H)Aryl (1; RMe, Et; Aryl = 2,4,6‐Tri‐tert‐butylphenyl) affords the corresponding iminophosphanes RP NAryl (2) which undergo a reversible [4 + 1] selfaddition with participation of the aryl substituent to form 3,3a‐Dihydro‐2H‐1,2,3λ5‐benzoazadiphospholes 3. The regioselective cycloaddition of 2b towards (E)‐ and (Z)‐azobenzene (4a and b) has been demonstrated in the formation of two different phospholes 6 and 8 which are formed by a [2 + 1] and [4 + 1] cycloaddition reaction of the iminophosphane 2b. The structure of the fiveymembered ring systems 3, 6 and 8 has been elucidated by NMR spectroscopy and single‐crystal X‐ray studies of 3b and 6.
1,2,3,4–Diazadiboretidine: Reaktionen einer neuen Klasse ungesättigter Bor–Stickstoff–Vierringe
Authors: Thiele Björn , Paetzold Peter , Englert Ulli
Published: July 2007

1,2,3,4–Diazadiboretidines: Reactions of a Novel Class of Unsaturated Boron–Nitrogen Four–Membered Rings

1,2,3,4–Diazadiboretidines [B(tBu)–B(tBu)NR–NR] (REt, iPr: 2a, b) belong to the hitherto unknown class of head–head isomers of the known 1,3,2,4–diazadiboretidines (1). They are formed from the diborane(4) Cl–B(tBu)–B(tBu)–Cl and the hydrazines RHN–NHR in the presence of NEt3 via the partially unsaturated four–membered rings [–B(tBu)Cl–B(tBu)NR–NHR–] (4a, b), which are transformed into 2a, b by the abstraction of HCl by means of the base LiNC9H18. Whereas the pure products 2a, b are instable, solutions of 2a, b in alkanes can be handled at 0°C without considerable decomposition. Reaction of 2a, b with the amine oxide Me3NO leads to insertion of an O atom, reaction with diazoalkane tBuCR′N2 (R′  H, Me) to insertion of its β–N atom, and reaction with the azide PhCH2N3 to insertion of a nitrene N atom into the B–B bond of 2a, b with formation of five–membered rings 5a, b or 6a, b or 7a, b, respectively. Six–membered rings 8a, 9a, 10a, respectively, are the products of the insertion of the CC unit of 3–hexyne, the NN unit of EtO2C–NN–CO2Et, or the unsaturated C atoms of two molecules of CNtBu into the B–B bond of 2a. The condensation of the diaminodiborane(4) Cl–B(NMe2)–B(NMe2)–Cl with the hydrazine EtHN–NHEt in the presence of NEt3 yields the corresponding eight–membered ring [–B(NMe2)–B(NMe2)–NEt–NEt–]2 (11), which crystallizes in a twist conformation with symmetry group D2.
Beiträge zur Chemie des Bors, 213. Reaktionen eines Amino–imino–borans mit Triboran(7) und Decaboran(14)
Authors: Geisberger Gilbert , Linti Gerald , Nöth Heinrich
Published: July 2007

Contributions to the Chemistry of Boron, 213[1]. – Reactions of an Amino–imino–borane with Triborane(7) and Decaborane(14)

Triborane(7)‐THF hydroborates (tert‐butylimino)(tetramethylpiperidino)borane 1 slowly to form μ‐(tert‐butylamino)‐μ‐(tetramethylpiperidino)tetraborane(8) 5. This molecule shows fluxional behaviour at ambient temperature in solution. In the solid state, an X–ray structure analysis reveals the presence of the asymmetric 1104–styx valence tautomer. 1 does not react at ambient temperature with pentaborane(9) in dichloromethane/hexane solution. However, 1 reacts rapidly with decaborane(14) to produce a tetramethylpiperidine adduct of an 11‐(tert‐butylamino)undecaborane(14) as determined by an X–ray structure analysis. The same kind of reaction occurs between decaborane(14) and (2,6–diisopropylphenylimino)‐(2,2,6,6–tetramethylpiperidino)borane. Thus, decaborane(14) acts as a diprotic acid towards amino–imino–boranes.
Solid–State Structure of Tris(phenylsilyl)amine
Authors: Mitzel Norbert , Schier Annette , Schmidbaur Hubert
Published: July 2007

The solid–state structure of tris(phenylsilyl)amine (1) has been determined by single–crystal X–ray diffraction analysis. The compound crystallizes in the trigonal space group R3 with three formula units in the unit cell. The molecules, which display crystallographic C3 symmetry, contain almost completely planar NSi3 units with a propeller–like arrangement of the phenyl rings attached to them. By contrast, the carbon analogue tribenzylamine is strongly pyramidal at nitrogen, which – in the absence of steric effects – clearly demonstrates the planarization effect of silicon as a substituent to nitrogen in tertiary amines.
Dimethyldioxirane Oxidation of Enamines: First Spectral Evidence for Enamine Oxides by Stabilization through N‐Silylation
Authors: Adam Waldemar , Ahrweiler Michael , Paulini Klaus , Reißig Hans–Ulrich , Voerckel Volkmar
Published: July 2007

The oxygen transfer to the enamines 1a–f by dimethyldioxirane (DMD) in acetone solution leads to the α–amino epoxides 2a–f. The stability of the α–amino epoxides 2a–f depends only on the type of substitution at the nitrogen atom. Thus, while the epoxides 2a, b could be characterized spetroscopically, the epoxidation of the enamines 1c–f resulted in the corresponding α–amino ketone 3c (hydride shift) and the amides 4d–f (alkyl shift). The α‐[bis(trimethylsilyl)]amino epoxides 2a, b represent the first observable enamine oxides and emphasize the value of stabilizing such labile epoxides through disilylation of the enamine nitrogen atom.
Synthesis of Homobenzoctamine [9,10–Dihydro–9‐(1–methylaminomethyl)‐9,10–propanoanthracene] and Homomaprotiline [9,10–Dihydro–9‐(3–methylaminopropyl)‐9,10–propanoanthracene]
Authors: Karama Usama , Martin H. , Hoffmann R.
Published: July 2007

The synthesis of homobenzoctamine (10) and homomaprotiline (19) is described.
Fluorenylindate: Verbindungen mit schwachen In — C‐Bindungen
Authors: Neumüller Bernhard
Published: July 2007

Fluorenylindates: Compounds with Weak In — C Bonds

In diethyl ether, fluorenyllithium reacts with indium(III) chloride to yield a lithium tetrafluorenylindate (1). Recrystallisation from THF gives [Li(THF)4][In(C13H9)4] (2). If the reaction is carried out in THF, the chlorotrifluorenylindate [Li(THF)4]‐[ClIn(C13H9)3] (3) is isolated. According to crystal structure analyses 2 has long and weak In — C bonds [224.8(5) – 230.3(5) pm], while these distances in 3 are somewhat shorter [222.9 (5) – 226.7(4) pm].
Übergangsmetall‐Silyl‐Komplexe, 44. Darstellung der zweikernigen Silyl‐Komplexe (CO)3(R3Si)Fe(μ‐PR′R′′)Pt(PPh3)2 durch oxidative Addition von (CO)3(R′R′′HP)Fe(H)SiR3 an (C2H4)Pt(PPh3)2
Authors: Reinhard Georg , Knorr Michael , Braunstein Pierre , Schubert Ulrich , Khan Saeed , Strouse Charles E. , Kaesz Herbert D. , Zinn Alfred
Published: July 2007

Transition Metal Silyl Complexes, 44. — Preparation of the Binuclear Silyl Complexes (CO)3(R3Si)Fe(μ‐PR′R′′)Pt(PPh3)2 by Oxidative Addition of (CO)3(R′R′′HP)Fe(H)SiR3 to (C2H4)Pt(PPh3)2

The complexes (CO)3(R′R′′HP)Fe(H)SiR3 (1) [PHR′R′′ = PHPh2, PH2Ph, PH2Cy; SiR3 = SiPh3, SiPh2Me, SiPhMe2, Si(OMe)3] react with Pt(C2H4)(PPh3)2 to give the dinuclear, silyl‐substituted complexes (CO)3(R3Si)Fe(μ‐PR′R′′)Pt(PPh3)2 (2) in high yields. Upon reaction of 2 (R = R′ R′′ = Ph) with CO, the PPh3 ligand at Pt being trans to the PPh2 bridge is exchanged, and (CO)3(Ph3Si)Fe(μ‐PPh2)Pt(PPh3)CO (3) is formed. Complex 3 is characterized by an X‐ray structure analysis. The rather short Fe — Si distance [233.9(2) pm] and the infrared spectrum of 3 indicate that the Fe — Pt bond is quite polar.
Mehrfachbindungen zwischen Hauptgruppenelementen und Übergangsmetallen, CIX. Strukturchemische Aspekte der Fluorolefin‐;Chemie von Osmiumtetraoxid: Halogenierte Osmatester und Folgeprodukte
Authors: Herrmann Wolfgang A. , Eder Stefan J. , Scherer Wolfgang
Published: July 2007

Multiple Bonds Between Main Group Elements and Transition Metals, CIX. — Structural Aspects of Fluoroolefin Oxidation by Osmium Tetraoxide: Halogenated Osmate Esters and Their Products

The crystal and molecular structures of the first fluorinated osmate ester 1, the dioxoosmium(VI) dichloride 2, and the dioxoosmium(VI) oxalate 3 have been determined by single‐crystal X‐ray diffraction. They all contain the trans‐osmyl group {OsO2}2+ and cis‐oriented sets of ligands, typical of complexes (py)2OsO2X2 (py = pyridine). Increasing electron‐withdrawing power of the ligands X entails shortening of the OsN bonds, resulting in higher stability of these complexes against dissociation of pyridine.
Organomolybdän‐ und Organowolfram‐;Reagenzien, III. Chemoselektive, nichtbasische Carbonylmethylenierungs‐;Reagenzien aus MoOCl3(THF)2 und MoOCl4: Bildung, Thermolabilität, Struktur
Authors: Kauffmann Thomas , Fiegenbaum Petra , Papenberg Michael , Wieschollek Raphael , Wingbermühle Dorothea
Published: July 2007

Organomolybdenum and Organotungsten Reagents, III. — Selective, Nonbasic Carbonylmethylenation Reagents from MoOCl3(THF)2 and MoOCl4: Formation, Thermolability, Structure

From the family of more than 20 carbonylolefinating μ‐methylene molybdenum and tungsten complexes[1,2] the reagent “3”, obtained in solution by treatment of MoOCl3(THF)2 with two equivalents of methyllithium, is probably the most favorable one for chemoselective carbonylolefination reactions. As judged by the 13C‐ and 1H‐NMR spectra the reagent is not a single species, but a mixture of either isomeric 1,3‐dioxo‐1,3‐dimolybda(V)cyclobutane complexes 3, differing in the position of the ligands Cl, O, and THF at the molybdenum atoms, or of oligomers of 3. — Treatment of MoOCl4 with two equivalents of methyllithium gave a carbonylolefinating reagent “4” which, according to NMR data, consists of isomeric or oligomeric 1,3‐dioxo‐1,3‐dimolybda(VI)cyclobutane complexes 4. Both reagents are labile at room temperature, but differ from the classical carbonylolefinating reagents by an acidic rather than a basic character, resistance to hydroxy groups, and high selectivity.
Organomolybdän‐ und Organowolfram‐;Reagenzien, IV. über die Chemoselektivität des carbonylmethylenierenden Reagenzes aus 2 MoOCl3(THF)2 und 4 CH3Li
Authors: Kauffmann Thomas , Baune JüRgen , Fiegenbaum Petra , Hansmersmann Ursula , Neiteler Christel , Papenberg Michael , Wieschollek Raphael
Published: July 2007

Organomolybdenum and Organotungsten Reagents, IV. — About the Chemoselectivity of the Carbonylmethylenating Reagent from 2 MoOCl3(THF)2 and 4 CH3Li

From a series of carbonylolefinating Mo complexes the reagent “3”, obtained by low‐temperature methylation of two equivalents of MoOCl3(THF)2 with four equivalents of methyllithium and warming up, is especially favourable for chemoselective carbonylolefination reactions. It is readily accessible, reacts at low temperatures, exhibits high aldehydeversus‐ketone selectivity (Tables 1, 2; Scheme 2), high cheleselectivity (preference of a keto group in the α‐ or β‐ position to a hydroxy group before an isolated keto group: Table 4; Scheme 3), and in some cases anticheleselectivity (Table 6). It is nonbasic and tolerates hydroxy groups (even water in the solvent) as well as acyl chloride groups (Table 8). — The chemoselectivity of 3 is compared in several cases with other carbonylolefinating reagents.
„Dimerisierungsprodukte”︁ von 1,2‐Cyclooctadien?
Authors: Pietruszka JüRg , Künig Wilfried A. , Maelger Harald , Kopf JüRgen
Published: July 2007

“Dimerization Products” of 1,2‐Cyclooctadiene?

The conversion of 8,8‐dibromobicyclo[5.1.0]octane (2) with methyllithium is known to yield kinetically labile 1,2‐cyclooctadiene (1). This strained cyclic allene readily dimerizes at ambient temperature. The 1‐methyl derivative enjoys greater kinetic stability, but nevertheless only three [2 + 2]‐cycloaddition products can be isolated after workup. Whereas the dimerization products 17, 22, 23, 24 can be predicted from recent studies, the carbene adducts 15 and 16 were not yet reported. The stereochemistry of 17 and 22 is determined by X‐ray structure analysis of their Diels‐;Alder adducts with tetracyanoethylene.
Cyclophanes, XXXVIII. [2]Metacyclo[2]indenophanes: Synthesis, Anions and Iron Complexes
Authors: Bodwell Graham J. , Frim Ron , Hopf Henning , Rabinovitz Mordecai
Published: July 2007

[2.2]Metacyclophane can be directly formylated according to the Rieche method to give 4‐formyl[2.2]metacyclophane (12) in 44% yield. The synthesis of the [2]metacyclo[2]indenophane 8 from the aldehyde 12 by the pathway previously employed for the corresponding [2.2]paracyclophanes failed due to the harsh conditions of the cyclization step. An alternative synthesis of 8 and its isomer 9 involving the construction of the five‐membered ring prior to that of the cyclophane unit succeeded. Compounds 8 and 9 were obtained as an 82:18 mixture, deprotonation of which afforded the anion 10, which shows long‐term stability. The 1H‐NMR spectrum of this anion does not exhibit a through‐space charge transfer due to its structure. The 1H‐NMR parameters and molecular mechanics calculations are discussed. Both faces of 10 react in the presence of FeCl2 · 2 THF and a twentyfold excess of LiCp to give a 70:30 mixture of the ferrocene derivatives 7 and 35.
Trimethylsilylcyanid als Umpolungsreagens, XXII. Nucleophile Acylierung α,β‐ungesättigter Aldehyde durch umgepolte α,β‐ungesättigte Aldehyde
Authors: Hünig Siegfried , Schäfer Matthias , Schweeberg Walter
Published: July 2007

Trimethylsilyl Cyanide — A Reagent for Umpolung, XXII. — Nucleophilic Acylation of α,β‐Unsaturated Aldehydes by Umpolung of α,β‐Unsaturated Aldehydes

Ambident anions 1aA → 1dA, obtained from 1a — d by LDA, are treated with α,β‐unsaturated aldehydes 2a — c. In all cases the kinetically controlled 1,2/α adducts 3 are formed which in contrast to 1,2/α adducts with α,β‐unsaturated ketones do not rearrange to the thermodynamically stable 1,4/α‐ or 1,4/γ products 4a and 6. Adducts 4 are smoothly formed if imines of 2 are applied. A thermal oxy‐Cope rearrangement transforms adducts 3 into 6. Substantial proportions of 1,2/γ adducts 5 are produced from 1A and 2 in the presence of magnesium bromide.
(E/Z) Equilibria, 16. Lone Electron Pair Donor Quality of the Imino Function: Synthesis and Reactivity of Sterically Strongly Congested Iminocyclopentanes
Authors: Knorr Rudolf , Hintermeyer‐;Hilpert Monika , Mehlstäubl Johann , Hoang Thi Phung , Neuner Brigitte , Bührer Petra
Published: July 2007

2,6‐Dimethyl‐N‐(2,2,5,5‐tetramethylcyclopentylidene)aniline (4h) is obtained by permethylation; it forms salts (5) by N‐protonation. Its CN double bond is strongly shielded against nucleophilic attack and cannot be hydrolyzed. Nitration and bromination occur smoothly in the aromatic p‐position (12, 13), showing the directing power of the lone electron pair of the imino function. This π‐donor quality is assessed by probing weaker electrophiles and by qualitative competition experiments.
Light‐Induced [2 + 2] Cycloaddition of 2‐Morpholinoacrylonitrile to 1‐Naphthalenecarbonitrile
Authors: Düpp Dietrich , Erian Ayman Wahba , Henkel Gerald
Published: July 2007

Photoexcited 1‐naphthalenecarbonitrile (1) adds 2‐morpholinoacrylonitrile (2) in the [2 + 2] mode both at the C(1) – C(2) and C(7) – C(8) bond unidirectionally and with the formation of only one (3 and 4, respectively) of the two a priori possible stereoisomers in each case. The structure of 3 has been unambiguously confirmed by an X‐ray structural analysis.
Notizen/Notes Allenyl Enolates — A New Class of Chiral Ambident Nucleophiles, 2. Reaction with Iodine and Oxidizing Agents
Authors: Krause Norbert , Arndt Silke
Published: July 2007

The reaction of allenyl enolates, obtained by 1,6‐addition of lithium dimethylcuprate to 2‐en‐4‐ynoates 1a/b, with iodine is studied. Whereas the n‐butyl‐substituted enyne 1a gives a mixture of vinyl iodide 2a (48%) and methylated allene 3a (7%), the tert‐butyl‐substituted enyne 1b yields allene 3b (70%) exclusively. The products 2a and 3a are also obtained if Br2, O2, or CuCl2 are used to trap the allenyl enolate derived from 1a and Me2CuLi · LiI. These findings are discussed with the assumption that iodo‐allene 5 and the iodo‐containing Gilman cuprate [Me2Cu(I)Li2]2 are acting as intermediates.
Organometall‐Oxide — Höhervalente Derivate der d‐Metall‐Säuren, 6. Tris(3,5‐dimethyl‐1‐pyrazolyl)boranato‐substituierte Alkyl(dioxo)1‐, Methylenphosphoranyl(dioxo)1‐ und s̀1‐Allyl(dioxo)1‐Komplexe des Molybdäns und Wolframs
Authors: Sundermeyer Jörg , Putterlik Jürgen , Pritzkow Hans
Published: July 2007

Organometallic Oxo Complexes — Highervalent Derivatives of the d‐Metal Acids, 6. — Hydrotris(3,5‐dimethyl‐1‐pyrazolyl)borato‐Substituted Alkyl(dioxo)1‐, Methylenephosphoranyl(dioxo)1‐, and s̀1‐Allyl(dioxo) Complexes of Molybdenum and Tungsten

Tp*MoO2Cl (1) and Tp*WO2Cl (2) [Tp* = κ31‐HB(3,5‐Me2pz)3] react with trimethyl aluminium to form the corresponding dioxo(methyl) complexes Tp*MO2(CH3), MMo (3), W (4). An X‐ray crystal structure analysis of 3 is performed. The less oxidizing tungsten complex 2 is alkylated by Grignard reagents to yield alkyl complexes of the type Tp*WO2R 5–7 [RCH2SiMe3, CH2tBu and CH2C(Me)Ph2] and the s̀1‐2‐methallyl complex Tp*WO2(CH2CMeCH2) 8. Reactions of 2 with methylenephorphoranes R3PCH2 (RiPr, Ph) give transylidation products Tp*WO2(CHPiPr3) (9) and Tp*WO2(CH‐PPh3) (10). Hydrolysis of 10 leads to a trioxotungstate [Tp*WO3]– (11), stabilized by a hydroxyphosphonium cation.
Reaktionen von 1‐Phenyl‐3‐borolenen mit Aldehyden, Ketonen und Ketenen: Synthese von 1,2‐Oxaborolan‐Derivaten, 2,3‐anti‐1,3‐Diolen und ungesättigten β1‐Hydroxyalkylketonen
Authors: Herberich Gerhard E. , Englert Ulli , Wang Shaotian
Published: July 2007

1‐Phenyl‐3‐borolenes CH2CR1CR1CH2BPh) (1a: R1H; b: R1Me) react with aldehydes R2CHO to give cis‐1,2‐oxaborolanes CH2CR1[CR1(CH2)]CR2R3OBPh (2, R2 = e.g. Me, Ph, CHCH2, tBu, CCl3, R3 = H). Yields are nearly quantitative. Stereoselectivities usually are 100% (but only 95% for R2CHCH2, 97% for R2Me). Oxidation with NaOH/H2O2 in THF affords homoallylic anti‐1,3‐diols HOCR2R31‐CR1[CR1(CH2)]CH2OH (3). An X‐ray diffraction analysis of 3a (R2p1‐tolyl) proves the assigned stereochemistries. Ketones R2R3CO react analogously. Ketenes R2CCO form 5‐alkylidene‐4‐vinyl‐1,2‐oxaborolanes (4), which tend to undergo double‐bond migration. Oxidation produces two types of β1‐hydroxylalkyl ketones R22CHCOC[(E)CHMe]CH2OH (5) and R22CHCOCMe[CMeCH2]CH2OH (6).
Lanthanoiden‐Komplexe, IV. Alkyl‐und Donor‐substituierte Cyclopentadienyl‐Komplexe des Neodyms
Authors: Herrmann Wolfgang A. , Anwander Reiner , Munck Florian C. , Scherer Wolfgang
Published: July 2007

Complexes of the Lanthanides, IV[1]. — Alkyl‐and Donor‐substituted Cyclopentadienyl Complexes of Neodymium

Neodymium trichloride reacts with the potassium salt K(DoCH2CH2Cp) (2c, DoOMe; 2d, DoNMe2) of the functionalized cyclopentadienyls in THF to yield the sublimable homoleptic complexes Nd(DoCH2CH2Cp)3 (3c, d). Under the same conditions, K(iBuCp) (2a) yields the adduct Nd(i1‐BuCp)3(THF) (3a′), which is obtained free of THF by thermal treatment. The silylamide route is applied to synthesize the homoleptic neopentylcyclopentadienyl derivative Nd‐(NeopCp)3 (3b). The alkyl‐substituted complexes, particularly the isobutyl derivative, show a remarkable volatility. The first solvent‐free, monomeric complex of the type „LnCp2Cl”︁, namely Nd(Me2NCH2CH2Cp)2Cl (4), is obtained from NdCl3 and two equivalents of 2d.
Dreizentren‐oxidative Addition von Phosphor‐Yliden an Ru3(CO)12
Authors: Heineke Daniel , Scott Bohle D. , Vahrenkamp Heinrich
Published: July 2007

Three‐Centre Oxidative Addition of Phosphorus Ylides to Ru3(CO)12

Phosphorus ylides undergo oxidative addition to Ru3(CO)12 to yield a wide range of Ru3 clusters with triply bridging organic ligands derived from the ylides. Ph3PCH2 forms HRu3(CO)9(μ31‐Ph3P — CH — CO) (1) containing a phosphonio enolate. Ph3PCH — CHO yields a product mixture containing the phosphonio enolate‐bridged cluster and its PPh3 derivative 6, the phosphoniomethylidyne‐bridged compound H2Ru3(CO)9(μ31‐C — PPh3) (5), and the ketenylidene‐bridged compound H2Ru3(CO)8(PPh3)(μ31‐C — CO) (7). Thermal treatment converts the phosphonio enolate ligand (in 1) into the phosphoniomethylidyne ligand (in 5), and the latter into the ketenylidene ligand (in 7). With Ph3PCH — C(O)Me and Ru3(CO)12 ortho1‐metalated Ru3 derivatives 10, 11 of the phosphonio ketone R3P — C — C(O)Me are produced, and likewise with Ph3PCH — COOEt the ortho1‐metalated derivative 12 of the phosphonio ester R3P — C — CO2Et. Me3PCH — COOtBu is oxidatively added to form HRu3(CO)9(μ31‐Me3P — C — COOtBu) (13) bearing a phosphonio ester ligand. — The crystal structures of 6 and 13 are reported. The sequence of Ru3 clusters and the bonding modes of the μ3 ligands can be related to the surface reactions during Fischer‐Tropsch catalysis.
Rutheniumcluster‐vermittelter Aufbau von Kohlenstoff‐Ketten aus einem Phosphor‐Ylid und Alkinen
Authors: Heineke Daniel , Vahrenkamp Heinrich
Published: July 2007

Ruthenium cluster‐Mediated Formation of Carbon Chains from a Phosphorus Ylide and Alkynes

The phosphorus ylide Me3PCH — C(O)Ph induces fragmentation of Ru3(CO)12 with formation of the dinuclear complex Ru2(CO)7(μ21‐HC_… CPhCH — C(O)Ph) (1a) with a σ,π1‐bound allyl ligand, together with its PMe3 derivative 1b. The latter inserts PhCCPh into the Ru — C s̀ bond to yield two isomeric complexes Ru2(CO)5(PMe3)[μ1‐CPh \documentclass{article}\pagestyle{empty}\begin{document}$ \underline \cdots $\end{document} CPh \documentclass{article}\pagestyle{empty}\begin{document}$ \underline \cdots $\end{document} CH — CPhCH — C(O)Ph] (3a, b) with a (σ,π1‐allyl,π1‐olefin)1‐coordinated six‐carbon chain ligand. With HCCPh 1b undergoes double insertion with formation of the complex Ru2(CO)4(PMe3)(μ1‐CHCPhCH — CPhCH — CPhCH — C(O)Ph] (4) containing an eight‐carbon chain ligand with (σ,π1‐allyl,π1‐olefin,π1‐olefin) coordination. The structure of 3a (and thereby indirectly the constitution of 1 and 4) was proved by an X‐ray structure determination.
Metall‐π1‐Komplexe von Benzolderivaten, XLI. Bis(η61‐anilin)chrom: Synthese, Redoxverhalten und Brønsted‐Basizität
Authors: Elschenbroich Christoph , Hoppe Stefan , Metz Bernhard
Published: July 2007

Metal π Complexes of Benzene Derivatives, XLI[1]. — Bis(η61‐aniline)chromium: Synthesis, Redox Properties and Brønsted Basicity

Bis(η61‐aniline)chromium (6) has been prepared by protodesilylation of its N,N,N′,N′1‐tetrakis(trimethylsilyl) derivative 5, which is accessible by metal‐atom ligand‐vapor cocondensation (cc). Bis(η61‐dimethylaniline)chromium (3) is obtained directly from cc. The couples 3+/0 and 6+/0 feature the most negative redox potentials E1/2 ever reported for bis(arene)1‐metal complexes. According to EPR spectroscopy, applied to the radical cations 3+· and 6+· the site of oxidation is largely localized on the metal. The pH dependence of E1/2 is cast in Nerst‐Clark plots, whose breaks supply the pKs values of the mono‐and diprotonated forms of 3 and 6. η61‐Coordination to CrI increases the basicity of aniline by three pK units, whereas η61‐coordination to Cr1 effects a decrease by more than seven pK units. The first and second dissociation constants of the organometallic bis(ammonium) ions 3(H+)2 and 6(H+)2 differ by 2.7 pK units. This interval reflects the interaction of the two basic centers in 3 and 6 which approaches that of p1‐phenylenediamine. Thus, conjugation across the bis(η61‐arene)chromium unit is virtually uninhibited.
Reaktionen Pentafluorethyl‐substituierter Bicyclo[2.1.1]hexan‐Derivate
Authors: Kirmse Wolfgang , Wonner Aribert
Published: July 2007

Reactions of Pentafluoroethyl‐Substituted Bicyclo[2.1.1]hexane Derivatives

The effect of inductively electron‐withdrawing substituents on the generation of 2‐bicyclo[2.1.1]hexyl cations was probed by means of pentafluoroethyl groups. 2‐Pentafluoroethyl‐2‐bicyclo[2.1.1]hexyl brosylate (4a) and triflate (4b) were found to rearrange with formation of the analogous 1‐pentafluoroethyl‐2‐bicyclo[2.1.1]hexyl sulfonates 5a, b. Solvolytic displacement did not compete with the rearrangement but occurred on 5b at elevated temperatures. Deuterium labels revealed that the rearrangement proceeded stereospecifically, with the sulfonate departing and rebonding on the same side of the molecular plane. Complete inversion was observed during solvolysis of 5b in aqueous dioxane while some retention (16%) occurred in trifluoroacetic acid. Predominant inversion even with the analogous diazonium ion in water attests to the reluctant formation of 1‐pentafluoroethyl‐2‐bicyclo[2.1.1]hexyl cations. Solvolysis rates of 4a, b and 5b were in close agreement with those of the analogous cyano derivatives, thus confirming that the resonance interaction of α1‐cyano groups with carbocations is small.
syn1‐Periplanar Bisazo Skeletons — Syntheses and Reactions with Carbonylmetal Complexes
Authors: Bahr Nicolaus , Beckmann Eberhard , Mathauer Klemens , Hunkler Dieter , Keller Manfred , Prinzbach Horst , Vahrenkamp Heinrich
Published: July 2007

Preparatively useful synthesis for the novel, relatively mobile polycyclic syn1‐periplanar bisazo polycycles 4 and 5 are based on hydrazine condensation with readily available dienedione 6 and acid‐catalyzed rearrangement of bisurazole 12, respectively. In the preferred “closed” and “open” conformations of 4 and 5 the NN bonds are 314 and 496 pm, respectively, apart (MMX). From the reactions of 4 and 5 with carbonyliron and ‐ruthenium compounds, complexes are derived which are typical of monoazo ligands [4 · Fe(CO)4  20, 4 · Fe2(CO)721, 4 · Fe3(CO)922, 4[Fe2(CO)6]223, 4 · Ru3(CO)9 · 24, 5 · [Fe2(CO)6]2  25, 5 · Fe2(CO)6 · Fe3(CO)9  26]. For 21, 23 and 26 crystal structure analyses were performed, confirming i.a. in 26 the unique presence of a Fe2(CO)6 and a Fe3(CO)9 fragment attached to two azo units of the same molecule.
Azaazulene als Dienophile in der Diels‐Alder‐Cycloaddition mit 3,6‐Bis(trifluormethyl)1‐1,2,4,5‐tetrazin
Authors: Frenzen Gerlinde , Massa Werner , Reimers Uwe , Seitz Gunther
Published: July 2007

Azaazulenes as Dienophiles in the Diels‐Alder Cycloaddition with 3,6‐Bis(trifluoromethyl)1‐1,2,4,5‐tetrazine

The LUMO‐diene‐controlled [4 + 2] cycloaddition of the azaazulenes 6 and 17 with the tetrazine 1, one of the most reactive diazadienes “with inverse electron demand”, are described. Like azulene (2) the azaazulenes 6a, b react with 1 – probably by a two‐step mechanism via the dipolar species 7 – to yield the adduct 8; N2 elimination leads to 9, which rearranges to the pyridazo[4,5‐c]quinoline 13 and the azine‐substituted 1‐azaazulene 12. In a rather complex reaction sequence the 2‐azaazulene 17 forms the salt 18; the crystal structure of 18 has been determined by X‐ray diffraction methods.
Medium‐Sized Cyclophanes, 25. Bromination of [2.n]Metacyclophan‐1‐enes and Isolation of Two Isomers of 1‐Bromo[2.n]metacyclophan‐1‐enes
Authors: Yamato Takehiko , Matsumoto Jun‐Ichi , Ide Seiji , Suehiro Kazuaki , Kobayashi Kazumasa , Tashiro Masashi
Published: July 2007

Bromination of dimethyl[2.3]metacyclophan‐1‐ene (1b) with bromine affords the cis adduct 6b resulting from the addition to the bridging double bond; a similar reaction of dimethyl[2.4]metacyclophan‐1‐ene (1c) gives a mixture of the cis and trans adduct formed by the addition to the bridged double bond along with the products containing a brominated internal methyl group. On the other hand, bromination of dimethy1[2.n]metacyclophan‐1‐enes (1) with benzyltrimethylammonium tribromide affords exclusively the product of the cis addition 6 to the bridged double bond. Treatment of [3.2]metacyclophane 6b with potassium tert1‐butoxide in refluxing tBuOH for 1 h gives the dehydrobrominated product (E)‐8b in 95% yield; a similar reaction of [4.2]metacyclophane 6c furnishes two isomers, (E)‐8c and (Z)‐8c, of 1‐bromo[2.4]1‐metacyclophan‐1‐ene along with [2.4]metacyclophan‐1‐one 9c in 20% yield. The characterization and the reaction pathway of these products are discussed.
Multistep Redoxsystems, LX. 1,4,5,8‐Tetraoxo‐1,4,5,8‐tetrahydrothianthrene: Synthesis, Structure, and Spectroelectrochemical Properties
Authors: Hünig Siegfried , Sinzger Klaus , Bau Robert , Metzenthin Tobias , Salbeck Josef
Published: July 2007

The synthesis, structure, cyclovoltammetric and spectroelectrochemical data of 1,4,5,8‐tetraoxo‐1,4,5,8‐tetrahydrothianthrene (2a) are presented. A relation between the positive partial charge at the sulfur atom and the dihedral angle at the SS axis is discussed on the basis of semiempirical MO calculations.
Reaktivität von Cyclopentenyl‐Anion‐analogen Heterocyclen: Homophosphole — Synthese, 1,5‐Elektrocyclisierung, Inversion am Phosphor‐Atom
Authors: Klärner Frank‐Gerrit , Oebels Dirk , Sheldrick William S.
Published: July 2007

Reactivity of Cyclopentenyl‐Anion‐Analogous Heterocycles: Homophospholes — Synthesis, 1,5‐Electrocyclization, and Inversion at the Phosphorus Atom*[1]

The key step of a novel homophosphole synthesis is the reaction of phospholes 3a‐d with diazomethane in the presence of water leading to the oxidized 1,3‐dipolar cycloadducts anti‐7a‐d. The 1,5‐electrocyclization of homophosphole was observed by the temperature‐dependent rate of racemization of optically active anti‐8b (ΔH≠(31.24±0.59) kcal/mol; ΔS≠–(2.32±1.47) cal/mol K). In order to determine the activation parameters for the inversion at the phosphorus atom a (60:40) mixture of syn‐ and anti1‐homophosphole syn‐ and anti‐8b was prepared by H2O2 oxidation of anti‐8b complexed by CuCl and subsequent reduction with Cl3SiH. The enantiomerization [(+)‐anti‐8b → (–)‐anti‐8b] proceeds at 169.5°C 22 times faster than the inversion at the phosphorus atom (anti‐8b→syn‐8b). This shows unambiguously that the electrocyclic ring opening does not require a planar configuration at the phosphorus atom and can start from the nonplanar anti configuration due to a dihedral angle of ca. 0° between the orbital of the lone pair at the phosphorus atom and the cyclopropane Walsh orbitals favourable for a strong electronic interaction in this configuration. From the comparison of the activation parameters for the inversion at the phosphorus atom in the homophosphole (syn‐8b ⇆ anti‐8b) and the dihydrophosphole [(–)‐23 ⇆ (+)‐23] one can extrapolate, that the homoaromatic resonance stabilization in the planar homophosphole is small (ca. —2 kcal/mol) contrary to the surprisingly large aromatic stabilization in the planar phosphole (ca. —20 kcal/mol).
Reaktivität s̀1‐bishomoaromatischer Heterocyclen: Elektrocyclische Reaktionen und Cycloadditionen von syn‐ und anti1‐Bishomofuran und ‐Bishomothiophen
Authors: Golz Thomas , Hammes Susann , Klärner Frank‐Gerrit
Published: July 2007

Reactivity of s̀1‐Bishomoaromatic Heterocyles: Electrocyclic Reactions and Cycloadditions of syn‐ and anti1‐Bishomofuran and ‐Bishomothiophene

Professor William von E. Doering zum 75. Geburtstag gewidmet.

The title compounds syn‐4a, b and anti‐4a, b, synthesized by the CuCl‐catalyzed reaction of homofuran 1a or homothiophene 1b with diazomethane, are very different in their thermal stability. syn‐4a isomerizes to 2,3‐dihydrooxepine (7a) readily at 130°C whereas the rearrangement anti‐4a → 7a requires a temperature of about 370°C. A similar difference in thermal reactivity is observed between syn‐4b and anti‐4b. But syn‐4b undergoes in addition to the rearrangement to 2,3‐dihydrothiepine (7b) a dimerization (to 12?) on thermolysis in [D6]benzene solution at 140°C, whereas mainly isomerization to 9b, cis‐10b, and 11 (product of the elimination of sulfur from cis‐10b) occurs on thermolysis in the gas phase. The formation of 7a and 7b, respectively, is explained by the electrocyclic ring opening of syn‐4a or syn‐4b leading to the carbonyl ylide 5a or the thiocarbonyl ylide 5b followed by a sigmatropic 1,4 hydrogen shift. To rationalize the additional products in the thermolysis of syn‐4b an electrocyclic conrotatory ring closure in 5b leading to the highly strained episulfide trans‐10b is assumed to complete with the hydrogen shift. Under the reaction conditions trans‐10b is unstable and either dimerizes in solution or isomerizes in the gas phase. The formation of 9b in the thermolysis of syn‐4b indicates that a two‐step pathway may compete with the concerted process. syn‐4a, b react with various π acceptor‐substituted olefins to form cycloadducts of the general type 6a, b. The cycloaddition occurs stereospecifically cis with respect to the configuration of the starting olefin and non‐stereoselectively with respect to the endo/exo ratio. The kinetic analysis of the reaction of syn‐4a with fumaronitrile (FN), N1‐phenylmaleinimide (NPMI) or dimethyl dicyanofumarate (DCFM) shows unambiguously, that the adducts are formed by a 1,3‐dipolar cycloaddition of the intermediate carbonyl ylide 5a rather than a homo‐Diels‐Alder reaction of syn‐4a (in contrast to the cycloaddition of homofuran 1a). A comparison between the enthalpies of reactions syn‐4a → 5a (ΔHR ≤ 22.4 kcal/mol) and syn‐4d → 5d (ΔHR ≥ 47.5 kcal/mol) shows the carbonyl ylide to be a 1,3‐diradical, highly resonance‐stabilized by the heteroatom (resonance energy R.E. ≈︁ –25 kcal/mol).
Neue Beobachtungen zur Stereoselektivität von Monoiodcarben‐Additionen
Authors: Dehmlow Eckehard V. , Soufi Johanna , Stammler Hans‐Georg , Neumann Beate
Published: July 2007

New Observations Concerning the Stereoselectivity of Monoiodocarbene Additions

Contrary to our earlier claim, CHI gives endo/exo isomer mixtures with cyclooctene. However, only endo1‐iodo compounds 7, 8, 10–12 are obtained from COD and COT. Tricyclic compound 7 rearranges partially to bicyclic 9, X‐ray structure determinations of 7 and 9 were performed.
Synthese, NMR‐Spektren und Photoelektronen‐Spektren von cyclischen Keten‐N,X1‐acetalen (2‐Alkyliden‐N‐heterocyclen)
Authors: Quast Helmut , Ach Manfred , Kindermann Markus K. , Rademacher Paul , Schindler Michael
Published: July 2007

Synthesis, NMR Spectra, and Photoelectron Spectra of Cyclic Ketene N, X1‐Acetals (2‐Alkylidene‐N‐heterocycles)

Deprotonation by sodium hydride of the N1‐methyl‐2‐alkyl‐azolium salts 10c, 14–16 and 18 and of the perimidinium salt 20 as well affords the corresponding ketene N,X1‐acetals 1c, 3–5, 7, and 8 as air‐sensitive distillable oils or low‐melting crystals. The α1‐carbon atoms of cyclic ketene N,X1‐acetals resonate at very high field with the smallest chemical shift of no more than δ39 for the 5‐methylenedihydrotetrazol 2a. Geometries of 1a, b, 2a, and b were optimized on the Hartree‐Fock level with polarized double‐ζ basis sets, followed by IGLO calculations of the NMR chemical shifts. These are in excellent agreement with the unusual carbon‐13 shifts observed. The electronic structures of 1a, b, 2a, b, 3a, b, 4b, 5b, 6a, and b are investigated by photoelectron spectroscopy and semi‐empirical quantum chemical calculations. The observed ionization potentials are assigned to molecular orbitals on the basis of Koopmans' theorem. The order of reactivity in 1,3‐dipolar cycloaddition reactions of cyclic ketene N,X1‐acetals resembles that of the chemical shifts of their α1‐carbon atoms.
Induktiver Effekt, negative Hyperkonjugation und Gegenion sind nicht die Ursache der besonderen Eigenschaften des Bicyclo[3.2.1]octa‐3,6‐dien‐2‐yl‐Anions. — Eine NMR‐Studie mit phenylsubstituierten Modellen
Authors: Christl Manfred , Müller Heinrich
Published: July 2007

Inductive Effect, Negative Hyperconjugation, and Gegenion do not Cause the Unusual Properties of the Bicyclo[3.2.1]octa‐3,6‐dien‐2‐yl Anion. An NMR Study with Phenyl‐Substituted Models

The 13C‐NMR spectra of the phenyl‐substituted bicyclo[3.2.1]oct‐3‐en‐2‐yl anions of 41‐K and 61‐Li show that in the corresponding dienyl anions of 31‐K and 51‐Li not only C‐6,7 have unusual chemical shifts but also C‐2,3,4. The values of the phenyl groups prove the larger negative charge in the allyl system of 41‐K and 61‐Li as compared to that of 31‐K and 51‐Li, respectively. Thus, the C6–C7 π bond in 31‐K and 51‐Li causes the reduction of the negative charge in the allyl subunit. Different from the effect of the C6–C7 π bond in 31‐K, the anellated three‐membered ring in the tricyclo[3.3.1.02,4]1‐nonenyl anion of 71‐K has no influence on the chemical shifts of the phenyl‐substituted allyl anion moiety. Experiments aimed at the exchange of the metal cations of 31‐K, 51‐Li, and 61‐Li for a tetramethylammonium ion were successful only with 51‐Li. The NMR data of 51‐Li and 51‐NMe4 are virtually identical. In the case of 31‐Li and 61‐Li, the treatment with tetramethyl‐ammonium chloride caused an SN2 process with formation of the methylbicyclooctadienes 8a and 10, respectively. Also, 51‐Li underwent this reaction, however so slow that significant concentrations of 51‐NMe4 could be observed in solution. 7Li‐NMR spectra were taken from 51‐Li, 61‐Li, and the solution containing 51‐NMe4.
Über Substitutionsreaktionen an 1,3‐Dithietan‐1,1,3,3‐tetraoxid (Disulfen)
Authors: Frasch Markus , Sundermeyer Wolfgang
Published: July 2007

Substitution Reactions of 1,3‐Dithietane 1,1,3,3‐Tetraoxide (Disulfene)

Alkylation of 1,3‐dithietane 1,1,3,3‐tetraoxide (disulfene, 5) with alkyl iodides in the presence of NaH provides a mixture of cis/trans1‐isomers 4a‐c (Me, Et, iPr), which are further alkylated to 7a, b or brominated to 1a, b. Only by using the respective nonafluorobutanesulfonic acid esters (nonaflates, C4F9SO2OR) silylations, germylation, or stannylation of 5 is achieved with formation of the 2,4‐disilyl (6a, b, d, e), ‐digermyl (3f), and ‐distannyl (3g) compounds as well as the mixed alkyl/silyl species 2a, b. Attempts to synthesize compounds with a 2,4‐bridged structure by treatment of 5 with I–(CH2)3–I/NaH were unsuccessful, but yielded the unusual dispiro disulfene 8, whereas the dicyclic 2,4‐bridged compound 9 has been obtained from 5 and the respective 1,2‐disilyl ester of ethane. The first example of a 1λ6,3λ6‐1,3‐dithiete 10 is obtained by tetrasilylation of 5 accompanied by a rearrangement of two of the bulky Et3Si groups to the sulfone groups.