bluuebunny/crossref_metadata_2025_split huggingface dataset:
Formal [4 + 3], [4 + 2], [4 + 1] cycloadditions and acid‐base reaction of 2‐methyl‐1,3‐dimorpholino‐1,3‐butadiene with Fischer carbene complexes
Authors: Barluenga José , Aznar Fernando , Fernández Mónica 
Published: July 2007

Abstract2‐Methyl‐1,3‐dimorpholino‐1,3‐butadiene 1 reacted with α,β‐unsaturated Fischer carbene complexes to give a wide range of different products depending on the substitution pattern. Thus, sevenmembered rings (4, 5 and 6) could be obtained from chromium complexes 2 with aromatic or vinylic groups at the β position. Similar results were observed when α‐methyl‐substituted carbene complex 7 a was used. Six‐membered carbocycles (derivatives of cycloadducts 12 and 13) were isolated after reaction with both chromium and tungsten complexes bearing one or two alkyl groups at the β position (10 and 11). Moreover, cyclopentenones 20 were the main products when the starting carbene complexes were alkyl‐substituted at both α and β positions (19a, b) or when aromatic (19c, d) instead of vinylic complexes were used. A bicyclo[4.1.0]heptene system 18 has also been obtained in the special case of reaction with β,β‐dimethylvinylchromium complex 13b; its formation could be explained as a formal carbene insertion into a C–H bond. The behaviour of diene 1 towards alkoxymethylcarbene complexes 22 was unusual. The different reaction products (cyclopentadienes 23, bicyclo[3.1.0]hexenes 24, aromatic amine 25 and metallatrienes 26) imply a mechanism in which the deprotonation of the carbene complex by the diene is followed by Michael addition to the iminium salt formed.
Zinc(II)‐Catalyzed Disproportionation in Rubber: The mechanism of Sulfur Vulcanization Revisited
Authors: Nieuwenhuizen Peter J. , Timal Sandjai , Haasnoot Jaap G. , Spek Anthony L. , Reedijk Jan 
Published: July 2007

AbstractModel studies have shown that cross‐link precursors, that is, intermediates in the sulfur vulcanization of rubber, are transformed into cross‐links by a nonsymmetric but regioselective disproportionation mechanism. Thus, two equivalents of the crosslink precursor of the type RSSX are transformed into XSX and the actual cross‐link RSSSR. Exchange of sulfur atoms is a prerequisite. A mechanism involving an SNi′ reaction with an allylic moiety, suggested in the literature, has not been observed. The disproportionation reaction is catalyzed by rubber‐soluble zinc‐dithiocarbamate complexes, an important class of vulcanization accelerators. By virtue of ligand‐functional‐group exchange reactions these complexes serve to transport and exchange sulfur atoms.
Controlling Self‐Assembly
Authors: Gillard Richard E. , Raymo FrançIsco M. , Stoddart J. Fraser 
Published: July 2007

AbstractAs a result of cooperative noncovalent bonding interactions (namely, π–π stacking, [CH…︁O] hydrogen bonding, and [CH…︁π] interactions) supramolecular complexes and mechanically interlocked molecular compounds—in particular pseudorotaxanes (precatenanes) and catenanes—self‐assemble spontaneously from appropriate complementary components under thermodynamic and kinetic control, respectively. The stereoelectronic information imprinted in the components is crucial in controlling the extent of the formation of the complexes and compounds in the first place; moreover, it has a very significant influence on the relative orientations and motions of the components. In other words, the noncovalent bonding interactions—that is, the driving forces responsible for the self‐assembly processes—live on inside the final superstructures and structures, governing both their thermodynamic and kinetic behavior in solution. In an unsymmetrical [2]catenane, for example, changing the constitutions of the aromatic rings or altering the nature of substituents attached to them can drive an equilibrium associated with translational isomerism in the direction of one of two or more possible isomers both in solution and in the solid state. Generally speaking, the slower the components in mechanically interlocked compounds like catenanes and rotaxanes move with respect to each other, the easier it is for them to self‐assemble.
Regulation of ACh receptor clustering by the tyrosine phosphatase Shp2
Authors: Zhao Xiaotao T. , Qian Yueping K. , Chan Ariel W.S. , Madhavan Raghavan , Peng H. Benjamin 
Published: July 2007

AbstractAt the vertebrate neuromuscular junction (NMJ), postsynaptic aggregation of muscle acetylcholine receptors (AChRs) depends on the activation of MuSK, a muscle‐specific tyrosine kinase that is stimulated by neural agrin and regulated by muscle‐intrinsic tyrosine kinases and phosphatases. We recently reported that Shp2, a tyrosine phosphatase containing src homology two domains, suppressed MuSK‐dependent AChR clustering in cultured myotubes, but how this effect of Shp2 is controlled has remained unclear. In this study, biochemical assays showed that agrin‐treatment of C2 mouse myotubes enhanced the tyrosine phosphorylation of signal regulatory protein α1 (SIRPα1), a known activator of Shp2, and promoted SIRPα1's interaction with Shp2. Moreover, in situ experiments revealed that treatment of myotubes with the Shp2‐selective inhibitor NSC‐87877 increased spontaneous and agrin‐induced AChR clustering, and that AChR clustering was also enhanced in myotubes ectopically expressing inactive (dominant‐negative) Shp2; in contrast, AChR clustering was reduced in myotubes expressing constitutively active Shp2. Significantly, expression of truncated (nonShp2‐binding) and full‐length (Shp2‐binding) forms of SIRPα1 in myotubes also increased and decreased AChR clustering, respectively, and coexpression of truncated SIRPα1 with active Shp2 and full‐length SIRPα1 with inactive Shp2 reversed the actions of the exogenous Shp2 proteins on AChR clustering. These results suggest that SIRPα1 is a novel downstream target of MuSK that activates Shp2, which, in turn, suppresses AChR clustering. We propose that an inhibitory loop involving both tyrosine kinases and phosphatases sets the level of agrin/MuSK signaling and constrains it spatially to help generate high‐density AChR clusters selectively at NMJs. © 2007 Wiley Periodicals, Inc. Develop Neurobiol, 2007
Reaktionen von Diaminen mit Fulleren C60
Authors: Kampe Klaus‐Dieter , Egger Norbert 
Published: July 2007

Reactions of Diamines with Fullerene C60Reactions of 1,2‐ and 1,3‐diamines 2a‐i, including diamines containing primary amino groups, with C60 (1) in toluene are described, leading to mono‐ and bisadducts 3–16. In this way fullerene derivatives carrying NH as a nucleophilic functional group have been synthesized. Yields and ratios of mono‐ and bisadducts formed depend on reaction conditions and on the structure of the diamine. The scope of this reaction leading to defined mono‐ and bisadducts in appreciable yields has been investigated. Mono‐ and bisadducts formed can be separated by column chromatography on SiO2. Mass and NMR spectra reveal that the isolated basic fullerene derivatives are dehydro adducts. NMR spectra show that the monoadducts have a symmetrical structure. In all cases investigated the addition forming the mono‐ and bisadducts of 1 occurs across a 6–6 bond. Likewise analogous additions take place with C70. Remarkably, tertiary diamines such as 2p and q react with 1 forming the monoadduct 8 in small yields by loss of an alkyl group. Proposed structures of some regioisomeric bisadducts are discussed.
Synthesis and conformational studies of pentahydroxy[2.1.2.1.1]‐ and hexahydroxy [2.1.1.1.1.1]metacyclophanes
Authors: Yamato Takehiko , Yasumatsu Masashi , Doamekpor Louis Korbla , Nagayama Souichiro 
Published: July 2007

AbstractBase‐catalyzed condensation of 1,2‐bis[5‐tert‐butyl‐3‐(5‐tert‐butylsalicyl)‐2‐hydroxyphenyl]ethane (8) with formaldehyde in xylene affords a novel ethylene‐bridged calixarene‐analogous macrocyclic metacyclophane. However, not the desired 2 has been obtained. Instead, the novel macrocyclic compounds pentahydroxy[2.1.2.1.1]‐ (9) and hexahydroxy‐[2.1.1.1.1.1]metacyclophane (10) have been isolated in 35 and 25% yields, respectively. The mechanism for the above disproportionation occurring during the base‐catalyzed condensation of 8 to afford these macrocyclic metacyclophanes and their 1H‐NMR spectral behavior are discussed.
Deamination Reactions, 56. Cyclopropane Participation in Norbornyl Cations
Authors: Herrmann Roland , Kirmse Wolfgang 
Published: July 2007

AbstractNitrous acid deamination of spiro[bicyclo[2.2.1]heptane‐7,1′‐cyclopropan]‐endo‐2‐amine (13) affords 74% of the analogous endo alcohol 24‐OH and 26% of the rearranged exo alcohol 25‐OH. The exceptional preference for endo attack of the nucleophile is attributed to intervention of the bridged norpinyl cation 21 which is stabilized by the spiroannellated cyclopropane ring. The spiro[bicyclo[2.2.1]heptane‐3,1′‐cyclopropan]‐2‐yl cations 23 arising from Wagner‐Meerwein rearrangement are captured by water to give high exo:endo product ratios.
Synthesis and Solvolysis of Bicyclo[3.1.1]hept‐3‐en‐2‐yl, Bicyclo[3.1.1]hept‐2‐yl, and 2‐Halogenocyclohex‐2‐en‐1‐yl Methanesulfonates and p‐Nitrobenzoates
Authors: Bentley T. William , Norman Simon J. , Kemmer Ralf , Christl Manfred 
Published: July 2007

AbstractAs an extension of previous work bicyclo[3.1.1]hept‐3‐en‐2‐ol (5) was synthesised in four steps from benzvalene and is now much more accessible than by former routes. The 3‐bromo derivative 9 of 5 was obtained from bicyclo[2.1.1]hexene by addition of dibromocarbene and hydrolysis of the resulting dibromide 8. – Methanesulfonates were prepared from 5, 9, 2‐norpinanol (7) as well as from 2‐bromo‐ (11a) and 2‐chlorocyclohex‐2‐en‐1‐ol (11b). Due to its high reactivity, the bicycloheptenyl mesylate 12 could only be characterised by low‐temperature NMR spectra. At 20°C, 2‐norpinyl mesylate (16) rearranged slowly to endo‐ (endo‐17) and exo‐2‐norbornyl mesylate (exo‐17) in the ratio 2:1. The formation of endo‐17 was also the major process on treatment of 16 with aqueous ethanol or acetone. – Solvolyses of bicyclo[3.1.1]‐heptenyl mesylates 12 and 20 proceed 4–5 times more slowly than solvolyses of corresponding cyclohexenyl mesylates 21c and 21a. The β‐bromine substituent deactivates solvolyses of 21a compared with 21c, and 20 compared with 12, by a factor of 2 · 103. The allylic double bond accelerates solvolyses of 21c compared with cyclohexyl mesylate by a factor of 107. However, 12 solvolyses only 100 times faster than norpinyl mesylate 16, showing a 105‐fold effect due to cyclobutylcarbinyl ring expansion. From solvolysis data the energy difference between the 2‐norpinyl and 2‐norbornyl cation is estimated to be 16 kcal mol−1, in fair agreement with a recent ab initio calculation.
A Novel Cycloocta[d]‐/Barreleno[d]pyridazine Rearrangement
Authors: Baumann Luzian , Folkerts Andree , Imming Peter , Klindert Thilo , Massa Werner , Seitz Gunther , Wocadlo Sigrid 
Published: July 2007

AbstractAs part of the valence tautomeric system cyclooctatetraene (2) bicyclo[4.2.0]octa‐2,4,7‐triene (3), the monocyclic polyene (2) reacts as a dienophile with the diazadiene 3,6‐bis(trifluoromethyl)‐1,2,4,5‐tetrazine (1) to form after N2‐elimination two products: The 1 : 1‐adduct 6, a cycloocta[d]pyridazine, and the tetracyclic bis‐Diels‐Alder cycloadduct 9. Depending on solvent polarity and temperature, compound 6 displays interesting novel rearrangements. On refluxing in nonpolar solvents like toluene, compound 6 yields the barreleno[d]pyridazine 13 in high yield. Compound 13 can be oxidized with 4‐phenyltriazolinedione 14 to the barreleno[d]pyridazine 15. When the more polar nitromethane is used as a solvent, heating of 6 at 90° 2°C surprisingly leads to the dihydrocycloocta[d]pyridazine 18 in a multistep reaction including proton‐shift tautomerism and [1, 5]‐sigmatropic rearrangement. The structures of the compounds 15 and 18 were assigned by the spectral data and verified by X‐ray crystallography.
Crystal and molecular structure of newly synthesized 2,3,2′,3′‐Bis{8″,11″‐dioxa[4.3.3]propella(3″,4″)}biphenyl
Authors: Grochowski Jacek , Jamrozik Janusz , Serda Paweł , Zesławski Wojciech 
Published: July 2007

AbstractThe title compound 5 was obtained from 2,2′,3,3′‐tetramethylbiphenyl in a multi‐step reaction sequence leading to the bis(propellane). X‐ray structure analysis proved the identity of bis(propellane). In the solid state the molecule possesses roughly a twofold symmetry axis perpendicular to the biphenyl bond. The conformation of the molecule is determined by a 53.5(1)° torsional angle between the biphenyl planes. The propellane bond is parallel to the phenyl plane in both symmetric parts of the molecule, what implies a boat conformation of the fused six‐membered rings.
Substituent effects on the CC bond strength, 19. Geminal substituent effects, 10. Radical stabilization enthalpies of α,α‐bis(methoxycarbonyl)alkyl and tris(methoxycarbonyl)methyl radicals
Authors: Rakufs Klaus , Verevkin Sergey P. , Keller Manfred , Beckhaus Hans‐Dieter , Rüchardt Christoph 
Published: July 2007

AbstractHeats of formation ΔH(g) were determined from enthalpies of combustion ΔH(c) and enthalpies of vaporization ΔH or enthalpies of sublimation ΔH for the eight substituted methanetricarboxylates 2a‐h. From these data and from previously determined enthalpies of formation Δ of substituted malonic esters new thermochemical group increments were derived. From these increments and from the recently published improved increments for carboxylic acid esters the gem. interaction enthalpies of two and three COOR groups were calculated. The radical stabilization enthalpies RSE of α,α‐bis(methoxycarbonyl)alkyl (18.2 kJ mol−1, 1a) and tris‐(methoxycarbonyl)methyl radicals (5.2 kJ mol−1, 1b) were derived from kinetic data obtained by means of our previously developed protocol. They were corrected for the gem. interaction energies of the ester groups in the ground state and are satisfactorily explained by an additive stabilizing effect of the ester substituents and by dipolar substituent interactions in the radicals. The dipolar energies were taken from MM2 calculations.
Photochemistry of a benzofuro‐annulated oxanorbornadiene formation of propellanes by trapping of an intermediate carbonyl ylide with CN and CC dipolarophiles
Authors: Bussenius Jörg , Keller Manfred , Eberbach Wolfgang 
Published: July 2007

AbstractOn photochemical excitation of the benzofuro‐annulated oxanorbornadiene 10 in the presence of dipolarophiles the 1:1 addition compounds 11, 22, 23a,b, and 24, respectively, are formed as the only monomeric products. The mechanistic interpretation is based on a reaction sequence which involves [2 + 2] photocycloaddition to the oxaquadricyclane 12, 1,3‐dipolar cycloreversion to the carbonyl ylide 13 and subsequent face‐selective trapping by the corresponding dipolarophile. No indication of the transformation of 13 to the highly strained [3]3,6‐oxepinophane 14 was obtained. With the formation of 11 one of the rare examples of the cycloaddition of a nitrile dipolarophile (i.e. acetonitrile) was uncovered.
Carbon–oxygen bond insertion in the reaction of dialkoxycarbenes with anhydrides
Authors: Pole David L. , Warkentin John 
Published: July 2007

AbstractDimethoxycarbene (1a) and methoxy(2,2,2‐trifluoroethoxy)‐carbene (1b) were generated in benzene solution by thermolysis of the corresponding 2,2‐dialkoxyoxadiazolines 7. The carbenes were trapped by intermolecular reaction with a variety of cyclic anhydrides 8. The products 9 are formally the result of carbene insertion into the bond between the carbonyl carbon and the ring oxygen atoms. The results of a competition between dimethylmaleic and dichloromaleic anhydrides for dimethoxycarbene suggests that this reaction proceeds by nucleophilic attack of dialkoxycarbene onto the carbonyl carbon atom of the anhydride.
Photoactive cyclophanes, I. Synthesis, photophysical and photochemical properties of cinnamophanes
Authors: Greiving Helmut , Hopf Henning , Jones Peter G. , Bubenitschek Peter , Desvergne Jean‐Pierre , Bouas‐Laurent Henri 
Published: July 2007

AbstractIn order to transfer the so‐called topochemical control established by Schmidt and coworkers to fluid solutions, the [2.2]paracyclophane framework was substituted with two acryloyl substituents, one on each of the two decks. The 4 products thus formed are termed cinnamophanes. The pseudo‐gem derivative, 1, was shown to undergo a very efficient stereospecific [2 + 2] photocycloaddition to form 5 with the highest quantum yield (0.8) ever observed for such a reaction. Whereas 2, 3 and 4, the regioisomers of 1, undergo a trans‐cis photoisomerisation, compound 1 leads to the photocycloadduct as the sole photoproduct. This unusually fast cycloaddition reaction is not sensitive to oxygen and is largely unaffected by temperature variations. It is believed to be a singlet state reaction. The synthesis and a spectroscopic (absorption and fluorescence emission) study of 1–4 and 5 are described.
Pheromone synthesis, CLXX. A new synthesis of faranal [(3S,4R,6E,10Z)‐3,4,7,11‐tetramethyl‐6,10‐tridecadienal], the trail pheromone of the pharaoh's ant, Monomorium pharaonis
Authors: Mori Kenji , Murata Noriaki 
Published: July 2007

AbstractFaranal (1), the trail‐following pheromone of the worker of Pharaoh's ant (Monomorium pharaonis), was synthesized by the coupling reaction of the iododiene 3 with the chiral building block 8 as the key step. The geometrically pure iododiene 3 was prepared by the zirconocene‐mediated carboalumination reaction of 2 followed by treatment with iodine.
Theoretical Study of Pericyclic Reactions of Nitrosoethylene and (Thionitroso)ethylene
Authors: Sperling Dirk , Mehlhorn Achim , Reißig Hans‐Ulrich , Fabian Jürgen 
Published: July 2007

AbstractStructure and reactivity of the title compounds 1 were examined by ab initio methods at the post Hartree‐Fock level of theory. Both compounds are expected to undergo electrocyclic ring closure to 4H‐1,2‐oxazete (4O) and 4H‐1,2‐thiazete (4S), respectively. The alternative electrocyclic reaction affording 2H‐azirine 1‐oxide (3O) and 2H‐azirine 1‐thioxide (3S) is definitely less favoured. (Thionitroso)ethylene (1S) is more reactive than the oxygen‐containing congener. The same holds for the cycloaddition reaction with ethylene. [4 + 2] Hetero Diels‐Alder reactions furnishing 4H‐1,2‐oxazine (5O) or 4H‐1,2‐thiazine (5S) are favoured over the [3 + 2] cycloaddition reactions providing 2H‐pyrrole 1‐oxide (2O) and 2H‐pyrrole 1‐thioxide (2S). The results of RMP2/6‐31G* calculations and results obtained at lower levels of theory (RHF, PM3) are compared and discussed with respect to the experimental material available. Some additional single‐point calculations at the computationally more demanding QC1SD/6‐31G* level confirmed conclusions drawn from RMP2 calculations. Some test calculations also showed that the theoretical results are less affected by consideration of the temperature by statistic thermodynamics and by inclusion of solvent effects by a self‐consistent reaction‐field method.
Sauerstoff‐Abfang von Radikalen in überkritischem Kohlendioxid; Bildungsenthalpie und Rekombinationsbarriere des Cycloheptatrienyl‐Radikals
Authors: Roth Wolfgang R. , Hunold Frank , Neumann Martin , Bauer Frank 
Published: July 2007

Oxygen Trapping of Radicals in Supercritical Carbon Dioxide; Heat of Formation and Recombination Barrier of the Cycloheptatrienyl RadicalThe homolytic thermal cleavage of bitropenyl (1) in supercritical carbon dioxide has been measured in the presence of 1 to 180 bar oxygen between 120 and 170°C. From these data the activation parameters of the dissociation and recombination reaction are derived, which lead to a heat of formation for the tropenyl radical (2) of ΔHfo = 64.7 kcal · mol−1. By using this value a radical stabilization energy (RSE) or 31.5 kcal · mol−1 is obtained, which differs by 1.7 kcal · mol−1 from the planar, acyclic isomer (trans,trans‐1,3,6‐trien‐5‐yl: RSE = 29.8 kcal · mol−1), which is practically equivalent to the relief of ring strain due to the formation of the radical. In agreement with the observed stability of 2 the equilibrium constant for its reaction with oxygen at 143°C is Keq = 727.7 mol−1, which corresponds to a bond strengths of 31.5 kcal ˙ mol−1 for R–O2·. The equipment and the method used for these experiments are described in detail.
Regioselectivity of Multiple Cyclopropanations of C60 and Introduction of a General Bond‐Labeling Algorithm for Fullerenes and Their Derivatives
Authors: Hirsch Andreas , Lamparth Irs , Schick Georg 
Published: July 2007

AbstractA computational (AM1) analysis is presented which shows that the observed regioselectivities of multiple cyclopropanations of C60 are due to orbital‐allowed processes. Next to the coefficients of frontier orbitals the characteristic cage distortions of the oligomethanofullerenes are discussed. For further experimental corroboration the synthesis and characterization of an unsymmetrical trisadduct with a I, eI, III*‐addition pattern are described. Moreover, since a systematic and descriptive assignment of addition patterns in derivatives of C60 and higher fullerenes becomes more and more important, a simple and general algorithm is introduced, which enables unambiguous bond labeling of both [6,6]‐ and [5,6]‐bonds as well as the assignment of the absolute configuration of any fullerene derivative.
Supramolecular Chemistry, 62. Ligand and Cosubstrate Effects on the Hydrolysis of Phosphate Esters and DNA with Lanthanoids
Authors: Rammo Jörg , Schneider Hans‐Jörg 
Published: July 2007

AbstractAttempts are described to enhance the catalytic activity of lanthanide ions by providing cosubstrates with an increasing number of nucleophilic groups or by attaching corresponding polyols covalently to stronger metal‐binding centers like diazacrown ethers. Although the kinetic effects on the hydrolysis of bis(4‐nitrophenyl) phosphate (BNPP) and of super‐coiled plasmid DNA are only moderate, their dependence on cosubstrate structure and polyol configuration unambiguously demonstrates that these are involved in the slow step of the reactions. Thus, addition of gluconic acid to a LaCl3solution leads to a marked increase of DNA cleavage from 20 to 71%. Naphthyl units covalently bound to the diazacrown show little effect onBNPPhydrolysis, but enhance DNA hydrolysis again from e.g. 38% (RF II) to 60%. Preliminary affinity measurements with calf thymus DNA, using a fluorimetric assay with ethidium bromide, show for polyamines a dependence on the number of ligand charges as observed earlier. The naphthyl compound is characterized by a high affinity; preliminary NMR data indicate that the naphthyl units intercalate into DNA.
Studies Related to Fatty Acid Desaturation, III. Preparation and Use of Thiaoleic Acids
Authors: Poulain S. , Noiret N. , Nugier‐Chauvin C. , Patin H. 
Published: July 2007

AbstractNew thiaoleic acid methyl esters 1 have been prepared as models for studies on Δ12‐saturation, Convergent synthetic pathways to those acids from the 10‐(tetrahydropyranyloxy)‐dec‐1‐yne 2 are described. After saponification, their inhibitory effect on the in vivo desaturation of [1‐14C] oleic acid into [1‐14C] linoleic acid has been evaluated using green algae, Chlorella sorokiniana, as a biological model. This result may indicate that the oleyl‐desaturase initiates dehydrogenation of a normal substrate by hydrogen atom abstraction at C‐13.
Pheromone Synthesis, CLXXV.– Synthesis of Koiganal I and II, the Sex Pheromone Components of the Webbing Clothes Moth
Authors: Takikawa Hirosato , Takenaka Motonobu , Mori Kenji 
Published: July 2007

AbstractKoiganal I [(E)‐2‐octadecenal (1)] and II [(2E,13Z)‐2,13‐octadecadienal (2)], the female‐produced pheromone components of the webbing clothes moth (Tineola bisselliella), were synthesized.