bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Pyrazole)silver(I) and ‐gold(I) Complexes with Strong and Weak Hydrogen‐Bonding Interactions as the Basis of One‐ or Two‐Dimensional Structures
Authors: Gallego M. Luz , Ovejero Paloma , Cano Mercedes , Heras José V. , Campo José A. , Pinilla Elena , Torres M. Rosario 
Published: June 2004

AbstractNew AuI/AgI complexes containing one or two substituted pyrazole ligands [Au(Hpzbp2)(PPh3)](p‐CH3C6H4SO3) [Hpzbp2 = 3,5‐bis(4‐n‐butoxyphenyl)pyrazole] (1) and [M(HpzR2)2]nX [HpzR2 = Hpzbp2, M = Au, n = 1, X = p‐CH3C6H4SO3 (2), NO3− (3); n = 2, X = 1,5‐naphthalenedisulfonate (1,5nds) (4); HpzR2 = Hpzbp2, M = Ag, n = 1, X = BF4− (5), CF3SO3− (6); HpzR2 = HpzNO2 (3,5‐dimethyl‐4‐nitropyrazole), M = Ag, n = 1, X = BF4− (7), CF3SO3− (8)], have been prepared and characterized. Compounds 1, 2, 5 and 8 have been proved to be useful for supramolecular assembly from their single X‐ray diffraction analysis. In all cases strong hydrogen bonds maintain the cationic units bonded to their corresponding counterions. The crystal packing arrangement of 1, 2 and 5 is, however, determined by weak C−H···O/F hydrogen‐bonding interactions involving the remaining O/F atoms of the counterion. By contrast, for 8 a two‐dimensional layer‐type polymeric network is formed by π···π (NO2···NO2) and coordinative Ag···O interactions in which the NO2 substituent on the pyrazole is implicated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
An Attempt to Programme the Orientation of Bis(heterocyclic) Azine Heterotopic Sequences around AgI, CuI and ZnII Metal Centres
Authors: Mathieu Julien , Ghermani Noureddine , Bouhmaida Nouzha , Fenet Bernard , Marsura Alain 
Published: June 2004

AbstractFour novel bis(heterocyclic) sequences, which incorporate a 2,2′‐bipyridine system with the 2,2′‐bithiazole, 4,4′‐bithiazole, 2,2′‐bipyrazine or 4,4′‐bipyrimidine units, have been synthesized. In the presence of stoichiometric amounts of CuI, AgI or ZnII cations, fully oriented discrete head‐to‐head (H‐H) or head‐to‐tail (H‐T) species have been observed by NMR and X‐ray crystallography. The orientation of the ligands in the AgI, CuI or Zn II dinuclear complexes during the self‐assembly process appears to be under the control of electronic factors relating to the electronic configuration of the different bis(heterocyclic) sequences. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
A Study of the Electronic Spin‐State Crossover in {Fe[HC(3,4,5‐Me3pz)3]2}(BF4)2
Authors: Reger Daniel L. , Elgin J. Derek , Smith Mark D. , Grandjean Fernande , Rebbouh Leila , Long Gary J. 
Published: June 2004

AbstractThe synthesis, structural, magnetic, and Mössbauer spectroscopic properties of {Fe[HC(3,4,5‐Me3pz)3]2}(BF4)2 are reported. The single‐crystal X‐ray structure results indicate that at 150 K {Fe[HC(3,4,5‐Me3pz)3]2}(BF4)2 has a structure which is very similar to that observed at 220 K for the trigonally distorted octahedral, high‐spin {Fe[HC(3,5‐Me2pz)3]2}(BF4)2 complex. Both the magnetic and Mössbauer spectroscopic results indicate that {Fe[HC(3,4,5‐Me3pz)3]2}(BF4)2 is high spin between 160 and 296 K. Upon cooling, {Fe[HC(3,4,5‐Me3pz)3]2}(BF4)2 exhibits a complete electronic spin‐state crossover from the high‐spin to the low‐spin state at approximately 110 K and remains completely low spin down to 4.2 K; upon subsequent warming from 4.2 K, the transition from the low‐spin to the high‐spin state occurs at 148 to 150 K. {Fe[HC(3,4,5‐Me3pz)3]2}(BF4)2 exhibits a rather large thermal hysteresis of 38 K in its spin‐state crossover. Thus, {Fe[HC(3,4,5‐Me3pz)3]2}(BF4)2 behaves differently from both {Fe[HC(3,5‐Me2pz)3]2}(BF4)2, which is known to show a unique spin‐state crossover of one‐half of its iron(II) ions associated with a phase transition, and Fe[HB(3,4,5‐Me3pz)3]2, which is known to remain high‐spin even upon cooling to 1.7 K. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis and Theoretical Studies of a Double Helical Complex with the Ligand 4′,4′′′‐Bis(ferrocenyl)‐2,2′:6′,2′′:6′′,2′′′:6′′′,2′′′′‐quinquepyridine
Authors: Aguado Javier E. , Calhorda Maria José , Costa Paulo J. , Crespo Olga , Félix Vitor , Gimeno M. Concepción , Jones Peter G. , Laguna Antonio 
Published: June 2004

Abstract4′,4′′′‐Bis(ferrocenyl)‐2,2′:6′,2′′:6′′,2′′′:6′′′,2′′′′‐quinquepyridine (Fc2qpy) reacts with AgOTf (OTf = trifluoromethylsulfonate) to give a complex of stoichiometry [Ag(Fc2qpy)]OTf. The crystal structure reveals a dinuclear arrangement among the cations with an Ag···Ag close contact of 3.089(2) Å. The ligands are wrapped around the silver atoms in a double helical array. Further hydrogen bonding between triflate units and the protons of the ferrocene or pyridine moieties results in a supramolecular structure. Theoretical studies confirm the existence of a weak Ag−Ag bond, and show that the dinuclear form can be more stable than the mononuclear one, when there is a favorable balance between the reorganization energy of the two quinquepyridine chains and the energy released by the formation of stronger Ag−N bonds and the new Ag−Ag interaction in the helix. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Homolysis of the Ln−N (Ln = Yb, Eu) Bond − Synthesis, Structure, and Catalytic Activity of Ytterbium(II) and Europium(II) Complexes Having (Dimethylamino)propyl‐ and (Dimethylamino)ethyl‐Functionalized Indenyl Ligands
Authors: Sheng Enhong , Zhou Shuangliu , Wang Shaowu , Yang Gaosheng , Wu Yongyong , Feng Yan , Mao Lili , Huang Zixiang 
Published: June 2004

AbstractWe have synthesized a new series of ytterbium(II) and europium(II) complexes by tandem silylamine elimination/homolysis of Ln−N (Ln = Yb, Eu) bonds. The interaction of 2 equiv. of C9H7CH2CH2CH2NMe2 (1) with [(Me3Si)2N]3Ln(μ‐Cl)Li(THF)3 (Ln = Yb, Eu) in toluene under reflux produced lanthanide(II) complexes [(η5:η1‐C9H6CH2CH2CH2NMe2)2Ln] [Ln = Yb (2), Eu(3)] in 67 and 74% yields, respectively. Treatment of 2 equiv. of Me2Si(Me2NCH2CH2C9H6)(NHtBu) with [(Me3Si)2N]3Eu(μ‐Cl)Li(THF)3 in toluene at 80 °C afforded a europium(II) complex [η5:η1‐Me2Si(Me2NCH2CH2C9H5)(NHtBu)]2Eu·(OC4H8)0.5 (4) in 46% yield. The interaction of 2 equiv. of Me2NCH2CH2C9H6SiMe3 with [(Me3Si)2N]3Eu(μ‐Cl)Li(THF)3 produced a europium(II) compound [η5:η1‐(Me2NCH2CH2C9H5SiMe3)]2Eu (5) in 49% yield. Treatment of 2 equiv. of Me2NCH2CH2C9H7 with [(Me3Si)2N]3Eu(μ‐Cl)Li(THF)3 in toluene gave a europium(II) complex (η5:η1‐Me2NCH2CH2C9H6)2Eu (6) in 57% yield. All the compounds were fully characterized by spectroscopic methods and elemental analyses. The structures of the complexes 4, 5, and 6 were determined by single‐crystal X‐ray analyses. The catalytic activities of organometallic complexes were examined; we found that all of the complexes can function as single‐component MMA polymerization catalysts with good activity. We studied the effects of solvent and temperature on the catalytic activities and the stereochemistries of the polymers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis and Characterization of Cubane‐Like Cr4E4 (E = S, Se) Clusters − Molecular Structures of (η5‐RC5H4)4Cr4E4 (E = S, R = MeCO, MeO2C, EtO2C; E = Se, R = H)
Authors: Song Li‐Cheng , Cheng Hua‐Wei , Chen Xin , Hu Qing‐Mei 
Published: June 2004

AbstractTreatment of the Cr−Cr singly‐bonded dimers [η5‐RC5H4Cr(CO)3]2 (1, R = MeCO; 2, R = MeO2C; 3, R = EtO2C) with excess sulfur in refluxing THF gave the cubane Cr4S4 clusters (η5‐RC5H4)4Cr4S4 (4, R = MeCO; 5, R = MeO2C; 6, R = EtO2C). The cubane Cr4S4 cluster 4 reacted with excess 2,4‐dinitrophenylhydrazine to produce the hydrazone derivative [η5−2,4‐(NO2)2C6H3NHN=C(Me)C5H4]4Cr4S4 (7). The singly‐bonded dimers of [η5‐RC5H4Cr(CO)3]2 (8, R = Me; 9, R = EtO2C), in the presence of excess selenium, reacted similarly to the linear Cr2Se complexes [η5‐RC5H4Cr(CO)2]2Se (10, R = Me; 11, R = EtO2C), which reacted with an equimolar quantity of selenium to afford the cubane Cr4Se4 clusters (η5‐RC5H4)4Cr4Se4 (12, R = Me; 13, R = EtO2C). A particularly interesting phenomenon is the cross‐assembled reaction of the linear Cr2Se complexes [η5‐MeC(O)C5H4Cr(CO)2]2Se (14) and [CpCr(CO)2]2Se (15) in the presence of excess selenium in THF that gave rise to a series of cubane Cr4Se4 clusters [η5‐MeC(O)C5H4]nCp4−nCr4Se4 (16, n = 0; 17, n = 1; 18, n = 2; 19, n = 3; 20, n = 4). The possible pathway for the cross‐assembled reaction is suggested. Furthermore the new clusters were characterized by elemental analysis and spectroscopy, and in the case of 4−6 and 16 also by X‐ray diffraction techniques. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Syntheses and Molecular Structures of Novel Alkali Metal Tetraorganylcyclopentaphosphanides and Tetraorganyltetraphosphane‐1,4‐diides
Authors: Wolf Robert , Schisler Andrea , Lönnecke Peter , Jones Cameron , Hey‐Hawkins Evamarie 
Published: June 2004

AbstractThe reaction of sodium with RPCl2 and PCl3 (12:4:1) in THF gives Na[cyclo‐(P5R4)] [R = iPr (1), Ph (2)], while four equivalents of RPCl2 [R = Ph, 2,4,6‐Me3C6H2 (Mes), tBu] react with ten equivalents of sodium sand or elemental potassium in refluxing THF to yield the compounds [Na2(THF)5(P4Ph4)] (3), [Na2(THF)4(P4Mes4)] (4), and [Na2(THF)4(P4tBu4)] (5), or the potassium salt [K2(THF)6(P4Mes4)] (6). Recrystallizing 6 from 1,4‐dioxane/pentane (1:3) also led to [{K(L)2}2{K(L)}6(P4Mes4)4·0.5THF]∞ (L = 1,4‐dioxane) (7). In the solid state, compounds 3−6 exist as isolated ion‐contact complexes, in which the P4 chain of the (P4R4)2− ligand has a syn arrangement, while a polymeric helical arrangement was observed for 7. A minor product, [{K(pmdeta)(HP3Mes3)}2{K2(P4Mes4)}]·0.25hexane (8), was isolated from the reaction of MesPCl2 and K (1:2.5). Compound 8 contains the first structurally characterized example of a triphosphanide anion, (HP3Mes3)−, besides K2(P4Mes4). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Lithium and Potassium Amides of Sterically Demanding Aminopyridines
Authors: Scott Natalie M. , Schareina Thomas , Tok Oleg , Kempe Rhett 
Published: June 2004

AbstractThe reaction of Grignard compounds of 1‐bromo‐2,4,6‐diisopropylbenzene (1) or 1‐bromo‐2,6‐dimethylbenzene (2), formed in situ, with 2,6‐dibromopyridine in the presence of a catalytic amount of [(dme)NiBr2] (dme = 1,2‐dimethoxyethane) and tricyclohexylphosphane (1:2 ratio) leads to the corresponding monoarylated bromopyridines. These bromopyridines undergo Pd‐catalysed aryl amination (Buchwald−Hartwig amination) with 2,6‐diisopropylaniline giving rise to (2,6‐diisopropylphenyl)[6‐(2,4,6‐triisopropylphenyl)pyridin‐2‐yl]amine (Ap*H) and (2,6‐diisopropylphenyl)[6‐(2,6‐dimethylphenyl)pyridin‐2‐yl]amine (Ap′H) (Ap = aminopyridinate). Deprotonation of Ap*H in diethyl ether using BuLi results (after workup in hexane) in a colourless crystalline material. X‐ray structural analysis reveals it to be a monomeric three‐coordinate lithium aminopyridinate. In toluene solution, an equilibrium between [(Ap*Li)2] (in excess at room temperature) and [Ap*Li(OEt2)] (prominent at low temperature) is observed. Reaction of Ap′H with BuLi in diethyl ether gives rise to [Ap*LiAp*Li(OEt2)]. Deprotonation of Ap*H and Ap′H using KH leads to [Ap*K]n and [Ap′K]∞, respectively. [Ap′K]∞ is a rare example of a crystalline organometallic polymer, as determined by X‐ray analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
NMR Evidence for Major Groove Binding of Both Λ‐ and Δ‐[Ru(bpy)2(pqx)](PF6)2 to the Oligonucleotide d(CGCGAATTCGCG)2
Authors: Garoufis Achilleas , Malandrinos Gerasimos , Hadjiliadis Nick 
Published: June 2004

AbstractThe enantiomeric complexes Λ‐ and Δ‐[Ru(bpy)2(pqx)](PF6)2 [pqx = 2‐(2′‐pyridyl)quinoxaline] were synthesized and characterized by various spectroscopic techniques. Their binding properties to the oligonucleotide duplex d(CGCGAATTCGCG)2 were subsequently studied by NMR spectroscopy. 1D and 2D NMR techniques provided evidence for major‐groove binding of both enantiomers with the oligonucleotide. The Δ‐[Ru(bpy)2(pqx)](PF6)2 enantiomer binds more deeply enantiomer to the oligonucleotide than the Λone. The quinoxalinic moiety of the pqx ligand faces the major groove in the Δ complex and is oriented at the external side of the adduct in the Λ complex. Both complexes show some affinity for the T8C9 base sequence of the dodecanucleotide helix. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
3,7‐Dioxa‐1‐azabicyclo[3.3.0]octanes Substituted at the C‐5 Position − From Local to Global Stereochemistry
Authors: Darabantu Mircea , Maiereanu Carmen , Silaghi‐Dumitrescu Ioan , Toupet Loïc , Condamine Eric , Ramondenc Yvan , Berghian Camelia , Plé Gérard , Plé Nelly 
Published: June 2004

AbstractMultiple approaches are described for the elucidation of the stereochemistry in solution (high‐resolution NMR spectroscopy) and in the solid state (X‐ray diffractometry) that are based on ab initio calculations (level RHF/6‐31G*) of some representative 3,7‐dioxa‐1‐azabicyclo[3.3.0]octanes. The results are presented in terms of conformational analysis, anomeric effects, chelating properties and aggregation phenomena. The significance of these findings with respect to diastereoselective synthesis is discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
First Generation Cysteine‐ and Methionine‐Derived Oxazolidine and Thiazolidine Ligands for Palladium‐Catalyzed Asymmetric Allylations
Authors: Schneider Paulo H. , Schrekker Henri S. , Silveira Claudio C. , Wessjohann Ludger A. , Braga Antonio L. 
Published: June 2004

AbstractA new series of enantiopure oxazolidine‐thioether and thiazolidine‐alcohol ligands have been synthesized from L‐cysteine, S‐methyl‐L‐cysteine, and L‐methionine in a straightforward manner that allows numerous structural variations to be formed. These types of ligands have not previously been used in asymmetric palladium‐catalyzed allylations and their efficacy was explored in the reaction of rac‐1,3‐diphenyl‐2‐propenyl acetate with dimethyl malonate. The reaction proceeds in excellent yield and with good enantioselectivity. The palladium catalyst derived from N‐benzyl‐2,2‐dimethyl‐4‐(2‐thiapropyl)oxazolidine (12) provides the allylation product in a quantitative yield and with an enantiomeric excess of 94%. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
The Convenient Synthesis of Hydrogen‐Bonded Ureidopyrimidinones
Authors: Keizer Henk M. , Sijbesma Rint P. , Meijer E. W. 
Published: June 2004

AbstractBlocked isocytosine isocyanates are conveniently obtained by the reaction of 1,1′‐carbonyldiimidazole (CDI) with isocytosines. The resulting precursors for quadruple hydrogen‐bonded structures can be isolated and stored for further use. Reaction with either aliphatic or aromatic amines gives the corresponding mono‐, bi‐, or trifunctional ureidopyrimidinone derivatives in good to excellent isolated yields. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
An Expeditious Library Synthesis of N‐Monoalkylated Aminopiperidines and ‐pyrrolidines
Authors: Ayesa Susana , Argyropoulos Dimitris , Maltseva Tatiana , Sund Christian , Samuelsson Bertil 
Published: June 2004

AbstractN‐Monosubstituted aminopiperidines and ‐pyrrolidines are important building blocks for the synthesis of small‐molecule compound libraries. We have developed a practical solid‐phase route to N‐monosubstituted aminopiperidines and ‐pyrrolidines utilizing a selective reductive alkylation of primary or secondary amines attached to a Merrifield or Wang resin. Purification is achieved by simple filtration after each reaction step. The synthetic route developed can be readily applied to an extensive pool of commercially available aromatic and aliphatic aldehydes for conversion into the corresponding N‐monoalkylated diamino templates. Solid‐phase NMR spectroscopy was used to monitor the reactions. The new pulse sequences described in this report have further extended the usefulness of this nondestructive analytical methodology. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Tuning Second‐Order Optical Nonlinearities in Push‐Pull Benzimidazoles
Authors: Carella Antonio , Centore Roberto , Fort Alain , Peluso Andrea , Sirigu Augusto , Tuzi Angela 
Published: June 2004

AbstractThe synthesis and full characterization of new chromophores with second order optical nonlinearities containing the 2‐phenyl‐(5,6)‐nitrobenzimidazole group is reported. Starting from 2‐{4‐[(4‐N,N‐dihydroxyethylamino)phenylazo]phenyl}‐5(6)‐nitrobenzimidazole, a combined theoretical and experimental approach, including theoretical computations of second order nonlinear optical activity (MNDO/AM1), X‐ray structural analysis and synthetic strategies, has led to a significant optimization (more than 50%) of the NLO activity of related chromophores. The results indicate that 6‐nitro‐substituted compounds are more active than 5‐nitro‐substituted ones and that a further increase of NLO activity can be achieved by insertion of a carbon−carbon double bond between the benzimidazole and 2‐phenyl rings. Calculations also suggest that an additional improvement of the nonlinearity should be expected upon functionalization of the N1 atom of the 6‐nitrobenzimidazole with electron‐withdrawing groups. Experimental nonlinearities (EFISH technique, μβ/10−48esu, λ = 1.907 μm, DMF solution) between 940 and 1550 were measured. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of Terpenoid Lactones with the p‐Menthane System
Authors: Dams Iwona , Białońska Agata , Ciunik Zbigniew , Wawrzeńczyk Czesław 
Published: June 2004

AbstractStarting from (R)‐(+)‐ and (S)‐(−)‐pulegone enantiomeric pairs of hydroxy lactones and keto lactones were obtained by Claisen rearrangement of cis‐pulegols and lactonization of epoxy esters. The hydroxy lactones were reduced with LiAlH4 in order to assign the configuration of the chiral centers. The structures of the synthesized compounds were established on the basis of spectroscopic and crystallographic data. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
New, Sesquiterpenoid‐Type Bicyclic Compounds from the Buds of Betulapubescens − Ring‐Contracted Products of β‐Caryophyllene?
Authors: Klika Karel D. , Demirci Betül , Salminen Juha‐Pekka , Ovcharenko Vladimir V. , Vuorela Satu , Can Başer K. Hüsnü , Pihlaja Kalevi 
Published: June 2004

AbstractThe essential oils obtained from the buds of Betula pubescens ssp. pubescens and B. pubescens ssp. czerepanovii were analyzed both by GC and GC/MS and, of the 31 compounds identified, 14‐acetoxy‐β‐caryophyllene was determined to be the main component in both oils in addition to 25 other previously known compounds. Three of the compounds were isolated from the oils and further characterized by NMR spectroscopy and mass spectrometry, including a new bicyclic aldehyde (4,8,8‐trimethyl‐2‐methylenebicyclo[5.2.0]nonane‐4‐carbaldehyde, birkenal), a new tricyclic lactone (1,4,4,8‐tetramethyl‐10‐oxatricyclo[6.2.1.02,5]undecan‐9‐one, hushinone), and the recently described 6‐hydroxycaryophyllene. The isolation of birkenal also enabled identification of its corresponding alcohol {(4,8,8‐trimethyl‐2‐methylenebicyclo[5.2.0]non‐4‐yl)methanol, birkenol} and the acetate of this alcohol {(4,8,8‐trimethyl‐2‐methylenebicyclo[5.2.0]non‐4‐yl)methyl acetate, birkenyl acetate}, both of which are also novel compounds and are present in the two essential oils. These new compounds, bearing evident sesquiterpenoid traits, potentially arise biosynthetically as ring‐contracted products of β‐caryophyllene or a derivative thereof. The fifth novel compound present in the oils was determined to be the acetate of 6‐hydroxycaryophyllene. The preferred conformations of the seven‐ or nine‐membered rings in these structures were also determined. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Syntheses of 7‐(2‐Hydroxy‐1‐phenylethyl)‐ and 7‐(2‐Hydroxy‐2‐phenylethyl)guanine, DNA Adducts Derived from Styrene 7,8‐Oxide
Authors: Novák Jan , Linhart Igor , Dvorˇáková Hana 
Published: June 2004

Abstract7‐(2‐Hydroxy‐1‐phenylethyl)‐ and 7‐(2‐hydroxy‐2‐phenylethyl)guanines are important DNA adducts which can be used as markers of exposure to styrene. Two synthetic routes leading to these compounds are presented using allyl‐protected bromohydrins as synthetic equivalents of styrene oxide to alkylate 2‐amino‐6‐chloropurine or 7‐methyl‐10‐oxo‐9,10‐dihydropyrimido[1,2‐a]purine as precursors to guanine. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
New Perfluoroalkyl‐Substituted Bisoxazolines as Chiral Ligands in Asymmetric CuII‐Catalyzed Reactions
Authors: Simonelli Barbara , Orlandi Simonetta , Benaglia Maurizio , Pozzi Gianluca 
Published: June 2004

AbstractTwo new enantiomerically pure perfluoroalkyl‐substituted bisoxazolines (F‐Box) have been prepared by a reaction sequence that involves formation of the properly functionalized Box followed by introduction of one or two n‐C8F17 residues. These ligands were employed for the first time in the Mukaiyama aldol addition of silylketene thioacetals to methylpyruvate promoted by Cu(OTf)2 (up to 85% ee) and in the ene reaction between α‐methylstyrene and ethylglyoxalate in the presence of Cu(OTf)2 (up to 74% ee). We compared the reactivities of the new ligands with those of two other chiral fluorous bisoxazolines that we have reported previously. In both cases, the F‐Box that has the lower fluorine content performed better, in terms of chemical yield and enantioselectivity, than the more‐fluorinated one. The recovery and recycling of the ligands is realized either by phase separation of the reaction solvents or by filtration through a short plug of fluorous silica gel. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Organic Bases as Additives to Improve the Radiochemical Yields of [11C]Ketones Prepared by the Suzuki Coupling Reaction
Authors: Rahman Obaidur , Llop Jordi , Långström Bengt 
Published: June 2004

AbstractThe Suzuki cross‐coupling reaction was employed in the syntheses of eight new [11C‐carbonyl]ketones. The reactions between the corresponding boronic acids and the corresponding triflates were performed in the presence of [11C]carbon monoxide and a palladium(0) complex as the catalyst. Lithium bromide was added to facilitate the reactions, and different bases were tested to improve the radiochemical yields. All the ketones were synthesised, with the achievement of isolated radiochemical yields (decay‐corrected) of between 14 and 74%. Important improvements in the radiochemical yield were achieved by use of tetrabutylammonium fluoride in the synthesis of ketones incorporating alkyl groups, while potassium tert‐butoxide was the best base among those tested for improving the radiochemical yields in the syntheses of biaryl ketones. The optimal amount of base was determined in all cases. Only for compounds 3e and 3h were better radiochemical yields obtained when no base was used. No radiochemical impurities were detected after isolation of the compounds. The specific radioactivity for compound 3a was determined, and a value of 200 GBq/μmol was obtained. Compound 3b was labelled simultaneously with [11C] and (13C)carbon monoxide and the position of the labelled atom was determined and confirmed by 13C NMR spectrometry. Tetrabutylammonium fluoride and potassium tert‐butoxide are reported as useful bases for Suzuki carbonylation with [11C]/(13C)carbon monoxide. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Dialkylation of Various Butane‐2,3‐diacetals Using Allylsilane and 1,8‐Bis(trimethylsilyl)‐2,6‐octadiene
Authors: Mariet Natacha , Pellissier Hélène , Ibrahim‐Ouali Malika , Santelli Maurice 
Published: June 2004

AbstractWe report in this paper a greatly improved procedure for the formation of a range of 1‐acetyl‐1‐methyl‐2,5‐divinylcyclopentanes from 1,8‐bis(trimethylsilyl)octa‐2,6‐diene (BISTRO) and 1,2‐diacetals prepared directly from biacetyl. These 1‐acetyl‐1‐methyl‐2,5‐divinylcyclopentanes are building blocks for the synthesis of 2‐ and 3‐methoxy‐12‐oxo‐17β‐vinylestranes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)