bluuebunny/crossref_metadata_2025_split huggingface dataset:
Methylenphosphanyl‐Komplexe von Chrom, Molybdän, Wolfram, Eisen und Nickel: Synthese und Reaktionen
Authors: Niecke Edgar , Metternich Hans‐Jürgen , Nieger Martin , Gudat Dietrich , Wenderoth Peter , Malisch Wolfgang , Hahner Christoph , Reich Wolfgang 
Published: July 2007

Methylenephosphanyl Complexes of Chromium, Molybdenum, Tungsten, Iron and Nickel – Synthesis and ReactivityHerrn Professor Heinrich Nöth zum 65. Geburtstag gewidmet.
The reaction of the functionalized P/C double bond systems X – PC(R)SiMe3 [RSiMe3 and XCl (1a), Cp* (5a) or RPh and XBr (1b), Cp* (5b)] with alkali carbonylmetallates or carbonyl complexes of group 6, 8, and 10 metals leads to the formation of the transition metal‐substituted phosphaalkenes [{M} – PC(R)SiMe3 3a – j and 4a – i], in which the P – C fragment acts as a one‐electron donor. Depending on the nucleophilicity of the transition metal anion used, but also on the methylene carbon substituents [1a: (SiMe3)2: 1b: (Ph)1‐SiMe3], a different stability of the (methylenephosphanyl)1‐metal complexes is observed, which results in a broad spectrum of reactivities. As demonstrated by the reactions of the (methylenephosphanyl)metal complexes with sulfonic acid derivatives (10a – c), diverse transition metal complexes (11a – c), as well as chalcogenes (14a – c, 15), a change in the reactivity is observed, indicating a transition from an olefinic to a carbenic character of the methylenephosphane. In comparison to the phenyl‐substituted derivatives 4a – i the bis(trimethyl)1‐substituted species 3a – j exhibit an increased reactivity. This is reflected in the easy decarbonylation of 3a – d to the phosphavinylidene complexes 12a – d.
Ein einfacher Weg zur Herstellung von Alkylpalladium‐Verbindungen durch PdO‐Bindungs‐Spaltung in kationischen Bis(ether‐phosphan)palladium(II)1‐Komplexen mit Grignard‐Reagenzien
Authors: Lindner Ekkehard , Dettinger Johannes , Fawzi Riad , Steimann Manfred 
Published: July 2007

A Simple Method for the Preparation of Alkylpalladium Compounds by PdO Bond Cleavage in Cationic Bis(etherphosphane)palladium(II) Complexes with Grignard ReagentsHerrn Professor Heinrich Nöth zum 65. Geburtstag gewidmet.
The bis(chelate) complexes [Pd(P∩O)2][ClO4]2 (3a – e) react with methylmagnesium chloride with a concomitant cleavage of two weak PdO bonds to give the methyl complexes trans1‐ClPd(P∼O)2(CH3) (4a – e) (P ∼ O; η1‐P1‐coordinated; P∩O: η21‐O, P1‐chelated; Scheme 1). Diffusion of pentane into the reaction mixture of 4a–e in the presence of the formed magnesium salts yields the cationic complexes trans‐[Ch3Pd(P∼O)1‐(P∩O)][ClO4] (6a, c). The reaction of 3a–e with benzylmagnesium chloride affords the cationic benzyl complexes cis‐[PhCh2Pd(P∼O)(P∩O)][ClO4] (8a–e) in which only one PdO bond has been cleaved. In the presence of carbon monoxide 4a–e adn 6a, c are transformed into the corresponding acyl complexes CH3C(O)Pd(P∼O)2Cl (5a–e and [CH3C(O)Pd‐(P∼O)(P∩O)][ClO4] (7a, c). Whereas at 183 K variable‐temperature 31P{1H}1‐NMR measurements of 6a, c, 7a, c indicate a non‐rigid behavior of the two differently bound ether‐phosphanes, the dynamic process is frozen out for 8a–e. By a lineshape analysis of the spectra the thermodynamic parameters ΔG≢, ΔH≢, and ΔS≢ are obtained. According to a crystal structure analysis 3d and 6c crystallize in the monoclinic space group P21/c with Z4.
Carben‐analoge Amidoosmium‐Komplexe mit OsN‐Doppelbindung: Synthese, Struktur und Reaktivität von [(Mes)Os(=NHR)(PiPr3)]PF6
Authors: Daniel Thomas , Mahr Norbert , Werner Helmut 
Published: July 2007

Carbene‐Type Amidoosmium Complexes with an OsN Double Bond: Synthesis, Structure and Reactivity of [(Mes)Os(=NHR)(PiPr3)]PF6*The reaction of [(Mes)Os(PiPr3)Cl2] (1) (Mes1,3,5‐C6H3Me3) with primary amines RNH2 (RPh, Me, Et) in acetone/water (1:1) gives, after addition of KPF6, the amidoosmium(II) complexes [(Mes)Os(=NHR)(PiPr3)]PF6 (2–4) in 60–80% yield. From 1 and Et2NH, the chloro(hydrido)compound [(Mes)1‐OsH(PiPr3)Cl] (5) is formed. The X‐ray structural analysis of 2 reveals that the geometry around the osmium atom is trigonalplanar (with the midpoint of the mesitylene ring as one coordination site) and that the OsN distance of 1.923(4) Å is in agreement with an OsN double bond. Thermolysis of 4 (REt) at 165°C leads to the formation of the aldimino(hydrido)osmium complex [(Mes)OsH(NHCHMe)(PiPr3)]PF6 (6) by β1‐hydride migration from the NCH2 carbon atom to the metal atom. Protonation of 3 (RMe) with HCl gives the amine complex [(Mes)Os(NH2Me)(PiPr3)Cl]PF6 (7), whereas on treatment of 3 and 4 with CD3NO2 the deuterated derivatives [(Mes)Os(=NDR)(PiPr3)]PF6 ([D1]‐3, [D1]‐4) are almost quantitatively formed. Compound 2 (RPh) reacts with KOtBu by proton abstraction and phosphane elimination to give the dinuclear imidoosmium complex [(Mes)2Os2(μ1‐NPh)2] (8).
Synthese und Struktur von [Rh2(μ1‐NO)(μ1‐H)(PiPr3)4]: Ein chiraler, NO‐und Hydrid‐verbrückter Rhodium(0)1‐Zweikernkomplex
Authors: Wolf Justin , Nürnberg Oliver , Werner Helmut 
Published: July 2007

Synthesis and Structure of [Rh2(μ1‐NO)(μ1‐H)(PiPr3)4]: A Chiral, NO‐and Hydride‐Bridged Binuclear Rhodium(0) ComplexThe reaction of RhCl3 · 3 H2O, PiPr3, iPrONa / iPrOH and N1‐methyl‐N1‐nitroso‐4‐tosylamide (diazald) yields the binuclear rhodium complex [Rh2(μ1‐NO)(μ1‐H)(PiPr3)4] (3) in 67% yield. 3 is probably formed via [RhH(PiPr3)3] (4) for which an improved preparative procedure is given. The X‐ray structural analysis of 3 proves that two pairs of inequivalent phosphane ligands are present. In solution, 3 shows a fluctional behavior which is reminiscent to that of molecules possessing axial chirality.
Synthesis of 2,6‐Diphenylbarbarlane by Oxidation of Dipotassium 2,6‐Diphenylbicyclo[3.3.1]nonadienediide with 1,2‐Dibromoethane. – Preparative Reversed‐Phase Liquid Chromatography of Hydrocarbons
Authors: Quast Helmut , Carlsen Jürgen , Janiak Rolf 
Published: July 2007

AbstractThe diphenylbicyclo[3.3.1]nonadiene 11 is deprotonated by butylpotassium to afford the black‐red crystalline dipotassium diphenylbicyclo[3.3.1]nonadienediide 12. At low temperatures, 12 is oxidized in tetrahydrofuran solution by 1,2‐dibromo‐ethane yielding the diphenylbarbaralane 13 which is isolated in 57% yield on a 20‐mmol scale after cyclic liquid chromatography on C18 reversed‐phase silica gel with methanol. The packing procedure for suitable columns is also detailed.
A Methyl Group Effect on the Conformation of Methylated [3.2]Metacyclophan‐10‐enes
Authors: Grützmacher Hans‐Friedrich , Neumann Ekkehard 
Published: July 2007

AbstractThe syntheses of 7,13‐dimethyl[3.2]metacyclophan‐10‐ene (5) and 7,10,11,13‐tetramethyl[3.2]metacyclophan‐10‐ene (6) starting from 1,3‐bis(4‐methylphenyl)propane (1) are reported. 5 exists in the anti conformation typical of [3.2]metacyclophan‐enes while 6 prefers the syn conformation because of steric repulsion between the methyl groups at the etheno bridge and at the aromatic rings.
[n + 2]‐Cycloadditionsreaktionen des (Arylimino)phosphenium‐Ions, [P≡NAr]+–kationische PN‐Heterocyclen mit ungewöhnlicher Struktur und Bindungssituation
Authors: David Gabriele , Niecke Edgar , Nieger Martin , Gönna Volker Von Der , Schoeller Wolfgang W. 
Published: July 2007

[n + 2] Cycloaddition Reactions of the (Arylimino)phosphenium Ion, [P≡NAr]+–Kationic PN Heterocycles with Unusual Structure and Bonding SituationThe iminophosphenium ion [P≡NAr]+ (Ar=2,4,6‐tBu3C6H2) (1) reacts with aminoiminophosphanes R2N–P=NtBu (R=iPr, Me3Si) (2) and alkyl azides RN3 (R=tBu, Et3C) (6) to yield the corresponding [n + 2] cycloadducts [R2NP (NAr)P(NtBu)+ (3) and [PN(Ar)NNN(R)]+ (7), respectively. Single‐crystal X‐ray diffraction studies show that 3a can be considered as an intramolecular donor‐acceptor complex while 7 can be regarded as a cyclic diaminophosphenium cation coupled to a diimine fragment, which is in accordance with results of ab initio calculations.
Weitere Reaktionen der Iminoborane RB≡NR′ mit Neopentylidentantal‐Komplexen
Authors: Braunschweig Holger , Paetzold Peter , Boese Roland 
Published: July 2007

Further Reactions of Iminoboranes RB≡NR' with Neopentylidenetantalum ComplexesThe azaboratantalacyclobutanes [–NR≡–BR–CH(tBu)–Ta‐CpCl2–] (3b, d, f, h–1; R/R′=Pr/tBu, iPr/tBu, iPr/iPr, tBuCH2/tBuCH2, Me3SiCH2/Me3SiCH2, tBu/Me, tBu/iPr, tBu/SiMe3) are formed from the corresponding iminoboranes RB≡NR′ and the neopentylidenetantalum complex [tBuHC=TaCpCl2] (2a) by [2 + 2] cycloaddition. The elimination of HCl from 3b, d, f, h and from the four known azaboratantalacyclobutanes 3a, c, e, g [R/R'equals;Et/tBu, Bu/tBu, Ph/tBu, iBu/iBu] gives the azaboratantalacyclobutenes [–NR′–BR–C(tBu)TaCpCl–] (4a–h). X‐Ray structural analyses of 4e, f show these cyclic carbenetantalum complexes to contain short Ta–C and Ta–N bonds and perhaps some transannular Ta–B interaction. The complex [tBuHC=TaCl3(THF)2] (2b) adds iminoboranes RB≡NtBu with unbranched alkyl groups (R=Et, Pr, Bu) in a 1:2 molar ratio to yield the diazoniadiboratatantalacyclohexadienes 5a–c; the product 5a adopts a non‐planar ring structure in the crystal. The 1:2 reaction of 2b with tBuB≡NMes, instead, results in the cyclobutane [–N(Mes)–B(tBu)–N(Mes)–TaCl3(THF)–] (7m).
[ω‐(Phosphanyl)alkyl]cyclopentadienyl Complexes
Authors: Kettenbach Ralf T. , Bonrath Werner , Butenschön Holger 
Published: July 2007

AbstractThe syntheses and characterisation of the [ω‐(phosphanyl)alkyl]cyclopentadienyl anions 2, 3, 6–8, 10, and 11 are described. These anions form metallocenes 12–15 and 17–19 with FeCl2 · 2 THF and with ZrCl4 · 2 THF, respectively. With ICo(CO)4 chelated carbonbyl complexes 23–25, 28, and 29 are formed. The unchelated intermediate 20 has been detected by IR spectroscopy. The carbonyl chelate complexes are thermally stable. Under photochemical conditions, ligand exchange reactions are possible which in the case of 1,5‐cyclooctadiene proceed with decomplexation of the phosphane arm. This does not prevent a reaction at the cobalt(I) atom; treatment of 35 with diphenylethyne gives the corresponding tetraphenylcyclobutadiene complex 36 in good yield, the phosphane arm remaining uncoordinated.
Chemie des η1‐Rhenium‐koordinierten Triphenylcyclopropenyl‐Liganden
Authors: Löwe Christiane , Shklover Valery , William Bosch H. , Berke Heinz 
Published: July 2007

Chemistry of the η1‐Rhenium‐Coordinated Triphenylcyclopropenyl LigandThe s̀‐coordinated pentacarbonyl[η1‐1,2,3‐triphenylcyclopropenyl)rhenium complex 1 is transformed into the green tetracarbonyl(η2‐1,2,3‐triphenylpropenetriyl)rhenium compound 2 with loss of CO by heating or irradiation. In addition, tetracarbonyl(η3‐4‐oxo‐1,2,3‐triphenylcyclobutenyl)rhenium (3a) and Tricarbonyl(η5‐1,2,3,4,5,6‐hexaphenylcyclohexadienyl)‐rhenium (4) were obtained from this reaction. Treatment of 1 with trimethylamine N‐oxide leads under oxygen transfer to tetracarbonyl(η2‐3‐oxo‐1,2,3‐triphenyl‐1‐propenyl)rhenium (5) and tricarbonyl(trimethylamine)(η2‐3‐oxo‐1,2,3‐triphenyl‐1‐propenyl)rhenium (6). The NMe3 ligand in 6 can be substituted either by CO or trimethyl phosphite to yield 5 or tricarbonyl‐(trimethyl phosphite)(η2‐oxo‐1,2,3‐triphenyl‐1‐propenyl)‐rhenium (7), respectively. Complex 1 reacts with trimethyl‐phosphane or trimethyl phosphite to give tetracarbonyl(phosphorus donor)(η1‐4‐oxo‐1,2,3‐triphenyl‐2‐cyclobuten‐1‐yl)rhenium 8b [L = PMe3] or 8c [L = P(OMe)3]. The derivatives Re(CO)3L2‐η1‐C3Ph3CO [L = CO, 8a; L = PMe3, 8d; L = P(O‐Me)3 8e] were obtained by treatment of 3a with CO or two equivalents of PMe3 or P(OMe)3. The formation of 8d and 8e proceeded via the tricarbonyl(phosphorus donor)(η3‐4‐oxo‐1,2,3‐triphenylcyclobutenyl)rhenium compounds 3b and 3c. The unusual η1‐coordination of the cyclobutenone system in 8 was established by an X‐ray structure analysis of 8c. Furthermore, 4 and 5 were characterized by single‐crystal X‐ray diffraction. Reactions of 2 with alkynes led to substituted tricarbonyl(cyclopentadienyl)rhenium derivatives Re(η5‐C5Ph3RR')(CO)3 9 (R = R' = Ph, 9a; R = R' = CO2Me, 9b; R = R' = CO2Et, 9c; R = Ph, R' = H, 9d).
Beiträge zur Chemie des Imidazols, III. 2‐Telluroimidazoline — stabile Tellurocarbonyl‐Verbindungen
Authors: Kuhn Norbert , Henkel Gerald , Kratz Thomas 
Published: July 2007

Imidazole Chemistry, III[1]. — 2‐Telluroimidazolines — Stable Tellurocarbonyl Compounds2‐Telluroimidazolines 6 are obtained as stable solids from the imidazol‐2‐ylidenes 4 and tellurium in good yields. The X‐ray structure of 6c reveals the relevance of the mesomeric structure 5 [d(C1—Te) = 2.087(4) Å] which is confirmed by the upfield shift in the 125Te NMR spectra (dL < —150).
ω‐Hydroxy‐ortho‐quinodimethane: trapping with trifluoroacetone and photocyclization
Authors: Griesbeck Axel G. , Stadtmüller Stefan 
Published: July 2007

Abstractω‐Hydroxy‐ortho‐quinodimethane (2), generated by photoenolization of 2‐methylbenzaldehyde (1) in benzene, is quantitatively trapped with trifluoroacetone to give the bicyclic hemiacetal 6 and the hydroxy aldehyde 7. A less effective trapping reaction is observed with benzaldehyde with the formation of the bicyclic hemiacetal 5. The formation of benzocyclobutenol 4 is probable due to a two‐photon process involving electronically excited 2.
Synthesis, Structure, and Antitumour Testing of Platinum(II) and Palladium(II) Complexes of 1,6‐Diaminotetrahydropyrrolo[2,3‐b]pyrrole‐2,5(1H,4H)‐dione
Authors: Borrell José I. , Beti Carlos , Ventosa Nora , García‐Puig Eduard , Planas Carles , Alvarez‐Larena Angel , Piniella Juan F. 
Published: July 2007

AbstractThe syntheses of the platinum(II) and palladium(II) complexes of 1,6‐diaminotetrahydropyrrolo[2,3‐b]pyrrole‐2,5(1H,4H)‐dione (3) are described. These compounds contain a six‐membered chelate ring with four nitrogen atoms. An X‐ray diffraction study of the palladium(II) complex [Pd(3)Cl2] shows a distorted “sofa” conformation for this chelate ring. Both complexes exhibited in the 1H‐NMR spectrum an ABgem system for the amino protons. In vitro ICL50 and ICT50 and in vivo antitumour activities have been determined for these products. The corresponding dicarboxylato complexes have been obtained by the reaction of the platinum(II) complex [Pt(3)Cl2] with silver sulfate followed by the addition of barium hydroxide and oxalic, malonic, hydroxymalonic, and 1,1‐cyclobutanedicarboxylic acid.
Silaheterocyclen, XXV. (Me3SiO)2SiCHCH2tBu: Ein Siloxy‐funktionalisiertes Syntheseäquivalent für Dichlorneopentylsilaethen
Authors: Auner Norbert , Heikenwälder Claus‐Rüdiger , Ziche Wolfgang 
Published: July 2007

AbstractSilaheterocycles, XXV[1]. — (Me3SiO)2SiCHCH2tBu: A Siloxy‐Functionalized Synthetic Equivalent for Dichloroneopentylsilene(Me3SiO)2SiCHCH2tBu (4) is obtained by the reaction of (Me3SiO)2Si(Cl)CHCH2 (2) with LitBu. The reaction proceeds via the α‐lithiated species 3, which can be intercepted by trimethylsilyl triflate to give 5. Silaethene 4 dimerizes to the E/Z‐isomers of disilacyclobutane 7 and adds to Me3SiOMe to give 6. The reactivity of 4 resembles that of Cl2SiCHCH2tBu (1): A [4 + 2] cycloadduct is obtained from the reaction with anthracene, and with 1,3‐cyclohexadiene and 1,3‐cycloheptadiene mixtures of monosilacyclobutanes (10 and 12) and bicyclic Diels‐Alder adducts (9 and 11) are available. Exclusive [2 + 2] cycloaddition reactions take place with styrene (formation of 13), 2,3‐dimethyl‐1,3‐butadiene (→19), and 1,3‐butadiene (→21). With quadricyclane only the product (14) originating from a [2 + 2 + 2] cycloaddition is formed, while with 2,5‐norbornadiene the [2 + 2] and [2 + 2 + 2] cycloadducts (14 and 15) are formed. In addition the ene products (16, 18, 20, 22) are isolated in some cases from side reactions. — The tendency of 1 and 4 to preferably participate in [2 + 2] cycloaddition reactions is ascribed to the polarity of the SiC bond and the additional influence of the π donor ligands at silicon. These factors enable a stepwise [2 + 2] reaction in which the primary zwitterionic intermediates B are cyclized to yield the SiC four‐membered ring compounds.
Neue Wege zu Bis[(cyclopentadienyl)cobalt]‐μ‐(η5‐2,3‐dihydro‐1,3‐diborolyl)‐Tripeldeckerkomplexen über Wasserstoff‐Verschiebungsreaktionen in Derivaten des 4,5‐Diisopropyliden‐1,3‐diborolans, des 2,4,5‐Triisopropyliden‐1,3‐diborolans und des Benzo‐1,3‐diborafulvens
Authors: Enders Markus , Gangnus Bernd , Hettrich Ralph , Magos‐Martin Zsuzsanna , Stephan Martin , Pritzkow Hans , Siebert Walter , Zenneck Ulrich 
Published: July 2007

New Routes to Bis[(cyclopentadienyl)cobalt]‐μ‐(η5‐2,3‐dihydro‐1,3‐diborolyl) Triple‐Decker Complexes by Hydrogen Shift Reactions in Derivatives of 4,5‐Diisopropylidene‐1,3‐diborolane, 2,4,5‐Triisopropylidene‐1,3‐diborolane, and Benzo‐1,3‐diborafulveneThe 31 VE dicobalt triple‐decker complexes 6, 7a, 7b, c, 8a, b, and 9a, b with bridging 2,3‐dihydro‐1,3‐diborolyl ligands are prepared. The reaction of the 1,3‐diborole 1 with [(C5Me5)‐Co(C2H4)2] leads to the sandwich complex 5, which is treated with [(C5H5)Co(C2H4)2] to yield unsymmetrical 6. The 4,5‐diisopropylidenetrimethyl‐1,3‐diborolane 3 undergoes a metal‐induced 1,5‐hydrogen shift and reacts with [(C5H5)Co(C2H4)2] to form the triple‐decker 7a. The reaction of the 2,4,5‐triisopropylidene‐1,3‐diborolane 4 with [(C5H5)Co(C2H4)2] leads to a mixture of the triple‐deckers 7b/c, formed by intermolecular hydrogen shift. The benzo‐1,3‐diborafulvene derivatives 2b and 2c also react with [(C5H5)Co(C2H4)2] to give the triple‐decker 8b and a mixture of 9a, b. In addition, the trinuclear complex 8c is obtained in low yield. The new paramagnetic triple‐decker complexes have been analyzed by NMR and ESR spectroscopic measurements as well as by electochemistry. The constitutions of 7b/c, 8b, 8c, and 9a/b have been confirmed by X‐ray structure analyses. The complexes are iso‐structural, the Co—Co distances range from 3.277(1) (7b/c) to 3.316(1) Å for 8c.
Chemie der Isoblausäure, 9. Dreikomponenten‐Cycloadditionen mit Cyanokomplexen
Authors: Fehlhammer Wolf Peter , Rieger Dirk , Lotz Sabine , Kernbach Ulrich , Fuchs Joachim 
Published: July 2007

Chemistry of Hydrogen Isocyanide, 9[1]. — Three‐Component Cycloadditions with Cyano ComplexesA novel and obviously general reaction of the coordinated cyano ligand in [M(CN)(CO)5]— (M = Cr, W) is reported, viz. its high‐yield one‐step [2 + 1 + 2] cycloaddition with a great variety of isocyanides and ketones resulting in carbenoid metal complexes of five‐membered N,O heterocycles. The structure of the product 1a from [W(CN)(CO)5]—, tert‐butyl isocyanide, and diethyl ketone has been elucidated by X‐ray diffraction and found to contain a C‐bound non‐aromatic 4‐aminooxazoline with an unprecedented π‐delocalization along the magnified imageexo chain which is also evident from severe low‐field shifts of the C‐2 and C‐4 signals in the 13C‐NMR spectra. The heterocycles are cleaved off the metal by oxidative decomposition with KMnO4/Fe(NO3)3 to give the corresponding oxazolinones, e.g. 4, with a high potential for biological activity. The general validity of this reactivity pattern for metal cyanides is further demonstrated by the successful incorporation of cyanoiron(II) and ‐cobalt(III) species in these three‐component cycloaddition reactions.
Verkronte‐Fullerene
Authors: Osterodt Jens , Windscheif Paul‐Michael , Vögtle Fritz , Nieger Martin 
Published: July 2007

Crowned FullerenesC60 reacts with [15]crown‐5‐substituted diphenylcarbene precursors to give the corresponding benzo‐crowned methano‐fullerenes 7, which were isolated preparatively and characterized. Two isomers 7a and 7b, which equilibrate to 7a upon heating, were detected by HPCL and separated. The [15]crown‐5‐, [18]crown‐6‐, and bis[15]crown‐5‐substituted hydrazones 3b—d have been prepared. The X‐ray structure analysis of the crowned hydrazone 3b shows distinct hydrogen bonding patterns between NH‐ and crown oxygen atoms in dimer‐type arrangements.
Diastereomerically Pure 3‐(Silyloxy)oxetanes by a Selective Paternò‐Büchi Reaction
Authors: Bach Thorsten , Jödicke Kai 
Published: July 2007

AbstractDiastereomerically pure 3‐[(trimethylsilyl)oxy]oxetanes 3 were prepared in moderate to good yields (45–72%) by the Paternò‐Büchi reaction of silyl enol ethers 2 with benzaldehyde. The photocycloaddition exhibits a high degree of regio‐ and diastereoselectivity. The substituents R in the silyl enol ether have been varied [R = Me, Et, iPr, tBu, Ph, CH(OMe)2, CH(OCH2)2, C(OCH2)2Me], and it was found that steric bulk is mainly responsible for enhanced selectivity (diastereoselectivity from 70:30 up to 95:5). The regiochemical control is perfect (regioselectivity >95:5) except for silyl enol ether 2a (R = Me) in the case of which a 90:10 ratio of regioisomers was observed. Irradiation of the reaction mixture at lower temperature (–25°C) led to a further improvement of diastereoselectivity. The relative configuration of the products obtained was elucidated both by 1H‐NMR spectroscopy and by chemical degradation. As a mechanistic hypothesis to explain the high observed diastereoselectivity we propose that the steric environment in the intermediate diradical 11 determines the selectivity according to two possible reaction pathways, i.e. bond formation and retrocleavage.
Preparation and Conformational Studies of Ethylene‐Bridged Calixarene‐Analogous Macrocyclic Metacyclophanes
Authors: Yamato Takehiko , Saruwatari Yoshiyuki , Doamekpor Louis Korbla , Hasegawa Ken‐Ichi , Koike Masanori 
Published: July 2007

AbstractThe novel macrocyclic compounds hexahydroxy[2.1.2.1.2.1]‐ (7b) and octahydroxy[2.1.2.1.2.1.2.1]metacyclophane (7c) have been prepared from anisole in six steps by using the tert‐butyl function as a positional protective group on the aromatic ring. Base‐catalyzed condensation of 1,2‐bis(5‐tert‐butyl‐2‐hydroxy‐phenyl)ethane (5) with formaldehyde in refluxing xylene does not afford the dimeric product, tetrahydroxy[2.1.2.1]metacyclophane 6a, but furnishes the larger macrocycles 6b and 6c in 70–90% yield. AlCl3/MeNO2‐catalyzed trans‐tert‐butylation of 6b and 6c in toluene gives the desired metacyclophanes 7b and 7c in 60 and 80% yields, respectively, along with tert‐butyltoluene 8b. The conformations of the systems such as trimer 6b and tetramers 6c, 7c have been evaluated from their dynamic 1H‐NMR spectra. The tetramer 6c is fixed to form a “pleated‐loop” conformation like the calix[8]arenes due to the much more stronger intramolecular hydrogen bonding among the hydroxyl groups than in the trimer 6b.
(Ethyl‐, Ethenyl‐ and Ethynylsilyloxy)aluminum Compounds Generated by Heterolytic Cleavage of 1,3‐Disubstituted Disiloxanes
Authors: Bissinger Peter , Paul Martin , Riede Jürgen , Schmidbaur Hubert 
Published: July 2007

Abstractsym‐Diorganodisiloxanes RH2SiOSiH2R (R = C2H5, 7; C2H3, 8; C2H, 9) are prepared by hydrolysis of organo(bromo)silanes which are available in high yields by the reaction of organo‐(phenyl)silanes with liquid HBr. Asymmetrical cleavage of these disiloxanes with AlCl3 leads to the formation of organo‐(chloro)silanes and aluminosiloxane dimers [RH2SiOAlCl2]2 (R = C2H5, 10; C2H3, 11; C2H, 12). Crystal structure determinations of 11 and 12 reveal a planar centrosymmetrical SiOAl2OSi skeleton with three‐coordinate oxygen atoms and tetrahedral four‐coordinate aluminum atoms. Treatment of 7–9 with Me2AlCl yields volatile dimethylaluminumorganosilyl oxides [RH2SiOAlMe2]x (R = C2H5, 13; C2H3, 14; C2H, 15; x = 2, 3, 4). NMR studies confirm the presence of more than one oligomer in solutions of these compounds. The asymmetrical compound (HC‐CSiH2O)2Me3Al2Cl (16), resulting from small amounts of MeAlCl2 in the Me2AlCl used, is isolated as a byproduct in the synthesis of 15. The crystal structure of 16 shows a disorder of the molecules leading to pseudosymmetry with a center of inversion.