bluuebunny/crossref_metadata_2025 huggingface dataset:
Aryloxycarbonylcarbene Complexes of Bis(oxazolinyl)pyridineruthenium as Active Intermediates in Asymmetric Catalytic Cyclopropanations
Authors: Park Soon‐Bong , Sakata Naoya , Nishiyama Hisao
Published: July 2007

The reaction of [RuCl2(pybox)‐(C2H4)] (1) (pybox = 2,6‐bis[4′S)‐isopropyloxazolin‐2′‐yl]pyridine) and 2,6‐di‐tert‐butyltolyl diazoacetate (4) (DBT‐DA) in benzene at 50°C gave a stable 2,6‐di‐tert‐butyltolylcarbonylcarbene‐ruthenium complex 5 in 94% yield. The structure of 5 was characterized by NMR spectroscopy. 2,6‐Diisopropylphenyl diazoacetate (6) and 2,4,6‐trimethylphenyl diazoacetate (7) also gave the corresponding carbene complexes 9 and 10, respectively. Asymmetric carbene transfer from the carbene complexes to styrene resulted in formation of the trans isomer of phenylcyclopropanecarboxylates 2 with high enantioselectivity: 2 was obtained as the sole product in 80% yield (55% ee) from 5 at 80 °C and in 82% yield (97% ee) from 9 at 60°C; from 10 at 40°C, a mixture of 2 and 3 in a ratio of 97:3 was formed in 91% yield (97% ee for 2 and 99% ee for 3). After the carbene transfer reaction, the ethylene complex 1 could be regenerated and isolated by treatment of the reaction mixture under an ethylene atmosphere. The carbene complexes 9 and 10 (2 mol%) exhibited catalytic activity in the asymmetric cyclopropanation of styrene with the corresponding diazoacetates.
Heterosupramolecular Chemistry: An Approach to Modulating Function in Molecular Devices
Authors: Marguerettaz Xavier , Redmond Gareth , Nagaraja Rao S. , Fitzmaurice Donald
Published: July 2007

Linked viologen‐anthraquinone molecules are attached to TiO2 nanocrystallites supported on a conducting glass substrate. The resulting assembly is incorporated as the working electrode in an electrochemical cell. Under opencircuit conditions, band‐gap excitation of the semiconductor nanocrystallite results in viologen‐mediated electron transfer to anthraquinone. Prior application of a negative potential step, which results in 2e−/2H+ reduction of anthraquinone, permits electron transfer only to viologen. At positive applied potentials, electron transfer following band‐gap excitation is largely suppressed. Some implications of these findings for modulation of function in molecular devices are considered.
Supramolecular Motifs: Concerted Multiple Phenyl Embraces between Ph4P+ Cations Are Attractive and Ubiquitous
Authors: Dance Ian , Scudder Marcia
Published: July 2007

Examination of the Cambridge Structural Database reveals that Ph4P+ cations in crystals associate through phenyl‐phenyl nonbonded interactions which are attractive, concerted, and widespread. Intermolecular phenyl‐phenyl conformations, which are offset‐face‐to‐face (off), edge‐to‐face (ef) or vertex‐to face (vf), combine in five classes of supramolecular motifs for {Ph4P+}2 pairs, namely the sextuple phenyl embrace (SPE) with (ef)6 and offset sextuple phenyl embrace (OSPE) containing (off)1 (ef)2(ef/vf)2, the translational quadruple phenyl embrace (TQPE) with (ef)4, the parallel quadruple phenyl embrace (PQPE) with (off)1(vf)2, and the double phenyl embrace (DPE) with (off)1. Typical intermolecular attractive energies (kJ per mol of {Ph4P+}2) for these motifs are SPE 85, OSPE 57, TQPE 70, PQPE 41, DPE 34. There is strong interpenetration of the cations in these motifs: 489/770 structures in the CSD have P ⃛P≤7 Å (spherical Ph4P+ has a van der Waals diameter of 13.6 Å). Of the 812 instances of P ⃛P ≤7 Å, 86% are SPE, 10% are OSPE, 2% are TQPE, and only 2% are unclassified, Average P ⃛P separations in the PQPE and DPE are 8.3 Å. Centrosymmetry is prevalent in all except the TQPE, which has implications for the engineering of noncentric crystals.
Separation of Diastereomeric and Enantiomeric Alkyl Nitrates–Systematic Approach to Chiral Discrimination on Cyclodextrin LIPODEX‐D
Authors: Schneider Manfred , Ballschmiter Karlheinz
Published: July 2007

High‐resolution gas chromatographic separation of all diastereomeric monomethyl‐substituted cyclohexyl nitrates is shown on a nonpolar methylpolysiloxane stationary phase, and the first application of this procedure to the environmental diastereomeric analysis of alkyl nitrates is presented. Two characteristic signals in the achiral analysis of atmospheric samples could be assigned to the smallest alkyl nitrate containing two asymmetric carbon atoms, 3‐methyl‐2‐pentyl nitrate. Retention indices in the temperature‐programmed separation based on the n‐alkanes were determined. The homologous series of 1‐alkyl nitrates were found to be useful as ECD‐visible n‐alkanes. Enantiomeric separation of alkyl nitrates was achieved on heptakis(3‐O‐acetyl,‐2,6‐di‐O‐pentyl)‐β‐cyclodextrin (LIPODEX‐D). The influence of the nitrooxy group and the alkyl chain length on the chiral discrimination on LIPODEX‐D is discussed for 25 chiral alkyl nitrates. The absolute configurations of some alkyl nitrates were assigned by asymmetric synthesis of enantiomerically pure references. The complexity of the alkyl nitrate mixtures present in air samples does not allow a direct chiral separation as the alkyl nitrates partly coelute on the LIPODEX‐D column. Column coupling of LIPODEX‐D with a polar achiral stationary phase like polyalkylenglycol (PAG) was successfully applied to solve this problem, and the chiral alkyl nitrates present in a typical air sample were separated. A systematic nomenclature for alkyl nitrates is introduced to handle the steadily growing number of branched and long‐chain alkyl nitrates detected in environmental analysis.
Hydrogen, the First Alkali Metal
Authors: Hensel Friedrich , Edwards Peter P.
Published: July 2007

We examine the density‐dependent metal‐nonmetal transition (MNMT) for the Group 1 elements hydrogen, rubidium and caesium. Remarkably, the experimentally observed metallization densities agree closely with those predicted from the 1927 classical theory of K. F. Herzfeld, which outlines the critical conditions necessary for the metallization of any element of the periodic system. The metallization densities of the alkali metal elements are also consistent with the quantum mechanical theory of the MNMT, as first set out by Sir Nevill Mott.
Preparation, Characterization, and Reactivity of a Diamagnetic Vanadium Nitride
Authors: Song Jae‐Inh , Gambarotta Sandro
Published: July 2007

The reactions of (Ph2N)3V‐(THF) (1) with [(CH3)3Si]N3 and [(CH3)3Si]CHN2 proceed at room temperature to afford the corresponding derivatives (Ph2N)3V[N‐Si(CH3)3] (2a) and (Ph2N)3V[N2CHSi(CH3)3] (3). Reactions of both 2a and 3 with lithium isopropylamide provide the unprecedented anionic vanadium nitride species [(Ph2N)3V(μ‐N)Li(THF)3]·(THF)0.5 (4), which displays moderate nucleophilicity. It reacts with (CH3)3SiCl and Mel to reform the complex (Ph2N)3V(N‐R) [R = Si(CH3)3 (2a), Me (2b)]. Reactions with Cp2ZrCl2 and CpTiCl3 lead to the formation of the heterodinuclear bridged nitride complexes [(Ph2N)3V(μ‐N)ZrClCp]2] [Cp = Cp]=Cp (6a), CH3C5H4 (6b)] and [{(Ph2N)3V(μ‐N)}2TiClCp] (8).
Coordination Arrays: Synthesis and Characterisation of Rack‐Type Dinuclear Complexes
Authors: Hanan Garry S. , Arana Claudia R. , Lehn Jean‐Marie , Baum Gerhard , Fenske Dieter
Published: July 2007

A series of mono‐ and dimetallic complexes of rack type containing a dinucleating bis‐tridentate ligand and RuII‐2,2′:6′,2′‐terpyridyl (tpy) sites were synthesised and characterised. The 1H NMR spectra of the dimetallic complexes were correlated to structural features, and the crystal structures of the dimetallic complexes were determined. They provide information about the way in which the central substitutent affects the overall shape of the racks and the relative disposition of the metal centres, measured by the pinching angle of the bis‐tridentate ligand and the convergence angle of the ancillary tpy units. The latter demonstrates that a CH3 group yields the least bent complex and indicates how parallel the tpy units are. The dimetallic racks exhibit metal‐metal interactions mediated by the bis‐tridentate ligands as indicated by electrochemical and spectroscopic methods. The bridging‐ligand π* orbital and the dπ metal orbital are stabilised by complexation of a second metal. The results obtained provide guidelines for the design of extended racks bearing several metal centres in a linear arrangement, which also represent potential components of molecular electronic devices.
Cesium Fluoride–Bromine Intercalation Compounds
Authors: Drews Thomas , Marx Ruppert , Seppelt Konrad
Published: July 2007

CsF reacts with Br2 to form the two intercalation compounds CsF·Br2 and 2CsF·Br2. The former consists of layers of CsF squares separated by layers of Br2 molecules oriented perpendicular to the CsF layers. 2CsF·Br2 is a second‐stage compound, composed of two layers of CsF followed by one layer of bromine molecules. Iodine cannot replace bromine; instead, it reacts with CsF to form Cs2I8, and probably CsIF6 between 0° and 120 °C. Chlorine does not react at all with CsF. Bromine reacts with RbF only superficially, and after a long time some RbBr3 is observed; RbF and I2 give RbI3.
Anionic Glucophospholipids—A New Family of Tubule‐Forming Amphiphiles
Authors: Giulieri Françoise , Guillod Frédéric , Greiner Jacques , Krafft Marie‐Pierre , Riess Jean G.
Published: July 2007

A new family of amphiphiles that form tubules (i.e., hollow cylindrical bilayer‐based microstructures) by self‐aggregation has been identified, namely, anionic glucophospholipids of type 1, in which a double‐tailed hydrophobe is grafted through a phosphate linkage to the O‐6 position of a polar glucose head group. Compounds 1a‐c self‐assemble into stable, hollow tubular microstructures when dispersed in water and cooled below the temperature at which the transition between crystal and liquid‐crystal phases takes place (estimated from change in turbidity). The diameter of the microstructures appears to depend on the nature of the hydrophobic tail, significantly smaller diameters being obtained for fluorinated tails. No tubules were obtained when galactose (2a‐c, pH<11) or mannose (3a‐c) derivatives were used instead of glucose derivatives, or when glucose was derivatized at the O‐3 (4b) rather than O‐6 position; in these cases only vesicles were formed. Tubules made of 1 converted rapidly into giant vesicles when heated; they spontaneously formed again upon cooling. The presence of a fluorinated chain, as in 1b and 1c, increased the temperature at which the tubule‐vesicle interconversion occurred to above room temperature. Because the amphiphiles are negatively charged, the formation of tubules is pH‐dependent and is favored at higher pH. These findings support the view that hydration of and hydrogen bonds between polar heads play a major role in tubule formation. Hydration of the sugar‐derived head groups decreases as the number of intermolecular hydrogen bonds increases; this favors membrane crystallization and tubule formation.
Investigation of the Self‐Assembly Pathway of Pentanuclear Helicates by Electrospray Mass Spectrometry
Authors: Marquis‐Rigault Annie , Dupont‐Gervais Annick , Van Dorsselaer Alain , Lehn Jean‐Marie
Published: July 2007

The self‐assembly of the pentanuclear double helicates Hh, Ha and He from the corresponding oligobipyridine strands Lh, La and Le and Cu1 ions has been investigated by NMR and electrospray mass spectrometry (ESMS). Where as Hh is assembled rapidly (in less than 20 min), He (about 20 h) and especially Ha (about 60 h) form much more slowly. The rate decreases strongly with increasing steric bulk of the substituents in the 4,4′‐positions on the bipyridine units; this indicates that the search processes (wrapping, unwrapping) that lead to the final helicate are strongly hindered by the size of the substituents. The ESMS data give information about the species present in solution under different conditions and allow the formulation of possible formation pathways, which may involve, in particular, helicates of hairpin type.
A Novel Type of Resonance‐Stabilised Dicobalt Complex with a Cyclopentadienylidene Bridge—Synthesis, Structure and Electronic Properties of [(C5R5)Co(μ‐C5H4)Co(L)(C5R5)'] (L = C2H4, CO, CNtBu, PR3, P(OMe)3; R = H, Me)
Authors: Wadepohl Hubert , Galm Wolfgang , Pritzkow Hans , Wolf Andreas
Published: July 2007

The dinuclear μ‐cyclopentadienylidene complexes [(C5R5)Co(μ‐C5H4)‐Co(C2H4)(C5R'5)] (5) [5aa (R = R' = H), 5ab (R = H, R' = Me), 5ac (R = H, R'5 = H4Me), 5ba (R = Me, R' = H), 5bb (R = R' = Me) and 5da (R5 = Me4Et, R' = H)] were synthesised from [(C5R5)Co(η4‐C5H6)] (4) [4a (R = H), 4b (R = Me), 4d (R5 = Me4Et)] and [(C5R'5)Co(C2H4)2] (1) [1a (R' = H), 1b (R' = Me) and 1c (R'5 = H4Me)]. In these reactions, both CH bonds of the methylene group of coordinated cyclopentadiene are activated under mild conditions. Substitution of the ethylene ligand in 5 by L leads to the carbonyl, isocyanide, phosphine, and phosphite derivatives [(C5R5)Co(μ‐C5H4)Co(L)‐(C5R'5)] [6aa, 6ab, 6ba, 6bb (L = CO), 7aa (L = tBuNC), 8aa, 8ab (L = PMe3), 9aa (L = PMe2Ph), 10aa (L = PMePh2) and 11aa (L = P(OMe)3)]. The crystal structures of 5aa, 5ab, 5ba, 6aa and 8aa have been determined. The experimental geometry is rationalised in terms of two limiting structures with μ‐η4:η1 and μ‐η5:η1 coordination of the bridging cyclopentadienylidene ligand. On the basis of the 18 valence electron rule, zwitterionic character is assigned to latter. This structure is preferred when L is an acceptor ligand, as in 6. In solution, 5–11 are fluxional with rapid rotation about the very short cobalt–carbene C bond. In addition the hindered rotation of the ethylene ligand in 5ab was studied by DNMR spectroscopy. In solution, a singlet‐triplet equilibrium was established by variable‐temperature NMR spectroscopy for 8aa. The temperature‐dependent 1H NMR line shifts were analysed by means of an isotropic shift model to give 24≤ΔH° ≤ 32 kJ mol‐1 and 45≤ΔS° ≤74 J mol‐1 K‐1 with the triplet state being preferred by entropy at higher temperatures.
Regiochemistry of Twofold Additions to [6,6] Bonds in C60: Influence of the Addend‐Independent Cage Distortion in 1,2‐Monoadducts
Authors: Djojo Francis , Herzog Andrea , Lamparth Iris , Hampel Frank , Hirsch Andreas
Published: July 2007

Three series of regioisomeric bisadducts of C60, namely, C62(anisyl)4 and the mixed systems C62(anisyl)2‐(COOEt)2, and C61(COOEt)2(NCOOEt), were synthesized starting from the 1,2‐monoadducts C61(COOEt)2 (1), C61‐(anisyl)2 (2), and C60(NCOOEt) (4) by using the Bingel and Bamford‐Stevens reactions, and nitrene additions. In the case of C61(COOEt)2(NCOOEt) the complete series of nine possible regioisomers were isolated for the first time. For steric reasons the cis‐1 isomers of C62(anisyl)4 and C62(anisyl)2(COOEt)2 were not formed. The transannular [6,6] bonds in the cis‐1 isomer 42 of C61(COOEt)2(NCOOEt) are closed. The properties and regioselectivities of formation of these bisadducts and their monoadduct precursors were compared with those of the series C62‐(COOEt)4 and C60(NCOOEt)2, which we synthesized previously. In the additions to 1, 2, and 4 the preferred positions of attack are e and trans‐3 for sterically demanding addends (e.g., combinations of C(anisyl)2 and C(COOEt)2) and cis‐1, e, and trans‐3 for sterically less demanding addends (e.g., combinations of N(COOEt) and C(COOEt)2). A detailed analysis of the MO structures, the experimental and calculated geometries of monoadduct precursors, and the stabilities of reaction products leads to the conclusion that the addend‐independent cage distortion itself is responsible for the observed regioselectivities of bisadduct formations.
Ab Initio Models for the Nitroaldol (Henry) Reaction
Authors: Lecea Begoña , Arrieta Ana , Morao Iñaki , Cossío Fernando P.
Published: July 2007

Ab initio calculations (up to MP4SDQ/6‐31+G*//MP2(FU)/6‐31+G*+ δZPVE) on several model nitroaldol (Henry) reactions have been performed. It is found that the free nitronate anions react with aldehydes via transition states in which the nitro and carbonyl dipoles are antiperiplanar to each other. This kind of reaction yieldsanti (erythro)nitroalcohols as major products. The Henry reaction between lithium nitronates and aldehydes is predicted to occur via cyclic transition structures yieldingsynnitroalcohols as major products. The stereocontrol in these model reactions is low. The factors affecting the stereoselectivity in the reaction between dilithiated nitronates and aldehydes are also discussed.
Novel inorganic cage structures based on ass ligands and cyclopentadienylruthenium groups
Authors: Brunner Henri , Nuber Bernhard , Poll Ludwig , Roidl Gaby , Wachter Joachim
Published: July 2007

The reaction of [Cp(*)2Ru2‐(CO)4] [a: Cp(*) = Cp* (η5‐C5Me5); b: Cp(*) = Cpx (η5‐C5Me4Et)] with β‐realgar in boiling n‐decane gives [Cp(*)2Ru2‐As4S4] (1a,b). in good yields along with some [Cp(*)2Ru2‐As4S2] (2a,b). According to X‐ray diffraction analyses of 1b and 2a, their structures belong to two different types of inorganic clusters. Whereas 1b has a cage structure in which the [Cp(*)2Ru2 unit is inserted into the As4S4] cradle, 2a has a sandwich structure in which two coplanar η2‐As4S ligands and the Cp* ligands are oriented parallel to one another. Analysis of the As‐S connectivity in the core of 1 b reveals a structural relationship to the extremely rare form of arsenic sulfide As4S4(II), and not to the metastable high‐temperature form β‐As4S4 used in the synthesis. At lower temperatures (60, 115°C) formation of CO‐containing products is observed.
The Vinylketene‐Acylallene Rearrangement: Theory and Experiment
Authors: Bibas Hervé , Wong Ming Wah , Wentrup Curt
Published: July 2007

Alkoxyvinylketenes4are generated by flash vacuum thermolysis (FVT) or photolysis of 3‐alkoxycyclobutenones3. The thermal interconversion of4and allene carboxylic acid esters5under FVT conditions is demonstrated by Ar matrix FTIR spectroscopy. In addition, ethoxy‐vinylketene4bundergoes thermal elimination of ethene with formation ofs‐cis‐ands‐trans‐acetylketene(8). An analogous aminovinylketene‐to‐allenecarbox‐amide conversion is observed on FVT of 3‐dimethylaminocyclobutenone3c. A facile 1, 3‐chlorine migration in 2, 3‐buta‐dienoyl chloride(5d)is also reported. Consistent with the experimental observations, 1, 3‐methoxy, 1, 3‐chloro, and 1, 3‐dimethylamino migrations in vinylketene are calculated (G2(MP2, SVP) level) to have moderate barriers of 169, 157, and 129 kJ mol−1, respectively, significantly less than the corresponding 1, 3‐H shift barrier (273 kJ mol−1). The stabilization of the four‐center transition structures is rationalized in terms of the donor‐acceptor interaction between the lone pair electrons of the migrating donor substituent and the vacant central carbon p orbital of the ketene LUMO. The predicted migratory aptitude in the series of substituted vinylketenes, R‐C(CH2)‐CHCO, is in the order N(CH3)2>SCH3>SH>Cl>NH2>OCH3>OH>F>H>CH3, and correlates well with the electron‐donating ability of the R group.
Nitridosilicates‐A Significant Extension of Silicate Chemistry
Authors: Schnick Wolfgang , Huppertz Hubert
Published: July 2007

Because of its low chemical reactivity Si3N4 has hardly been used as a starting material for the preparation of multinary silicon nitrides or nitridosilicates, but has gained increasing importance as a nonoxidic material for high‐performance applications. A novel synthetic approach is presented, which starts from silicon diimide (Si(NH)2) and makes available a large variety of novel nitridosilicates. The structures of these nitridosilicates represent a significant extension from those found in the family of oxosilicates. Because of their outstanding chemical and physical stability, nitridosilicates might be of particular interest for the development of novel inorganic nitridic materials.
Synthesis of 1,2,3,4‐Bisiminofullerene and 1,2,3,4‐Bis(triazolino)fullerene—on the Mechanism of the Addition Reactions of Organic Azides to [60]Fullerene
Authors: Shen Clifton K.‐F. , Yu Hsiao‐Hua , Juo Chiun‐Gung , Chien Kuo‐Ming , Her Guor‐Rong , Luh Tien‐Yau
Published: July 2007

The reactions of organic azides with [60]fullerene have paved the way for the synthesis of adducts with a variety of structures. Treatment of [60]fullerene with 2,2‐dibenzyl‐1,3‐diazidopropane (10) in refluxing chlorobenzene afforded three products, namely, 8, 9, and 11 in 18, 25, and 11% yields, respectively. Thermolysis of 9a in refluxing chlorobenzene gave a 40:54:6 mixture of 8, 11, and C60 in quantitative yield. No interconversion between 8 and 11 was observed. Whereas 11 was stable towards thermolysis, 8 decomposed to C60 (35% yield) on refluxing in chlorobenzene for 24 h, but it did not produce any 11. This indicates that 9a is an intermediate in the formation of 8 and 11. A general mechanism for the addition of azides to C60 is proposed. A similar mechanistic pathway is suggested for the thermolysis of 9a.
Stereoselective Umpolung Reactions with MetalatedP‐Chiral Cyanohydrin Phosphates—Enantioselective Synthesis of Tertiary Cyanohydrins
Authors: Schrader Thomas
Published: July 2007

We present the first cyanohydrin derivative4that allows diastereoselective umpolung reactions. In4the OH group of the cyanohydrin is linked with a chiral phosphate, which can be removed hydrolytically after asymmetric synthesis. Cyclization of pseudoephedrine1dwith POCl3gave2d. This was followed by addition of racemic benzaldehyde cyanohydrin3to give the key intermediate4dwith complete retention of the configuration at phosphorus. Deprotonation of4d, followed by addition of a wide variety of electrophiles afforded the crystalline products5with high diastereomeric excesses (deup to 94%). High asymmetric induction was also achieved for the reaction of4−Li+with acyl halides, α‐bromoacetates, 2‐cycloalkenones, α,β‐unsaturated esters, and γ‐bromoacetates. Lewis acid assisted hydrolysis proceeded without racemization and gave high yields of ketone cyanohydrins6. From the ring‐opened chiral auxiliary7, optically pure pseudoephedrine1was readily recovered by acid hydrolysis. Optically pure (R) and (S) ketone cyanohydrins are now accessible in a very general strategy, which circumvents the substrate limitations of enzymatic synthesis.
Self‐Assembly of Dinuclear CH2‐bridged Titanium(IV)/Catecholate Complexes: Influence of the Counterions and of Methyl Substituents in the Ligand
Authors: Albrecht Markus
Published: July 2007

The spontaneous self‐assembly of methylene‐bridged dinuclear TiIV complexes M4[L3Ti2] (L = 1–3) from CH2‐bridged di(catechol) ligands (1‐H4–3‐H4) was found to proceed in the presence of lithium or sodium carbonate acting as a base (M = Li, Na). In contrast, only an unspecific mixture of coordination compounds was obtained in the presence of potassium carbonate. This difference in behavior is due to the ability of Li+ or Na+ to stabilize the triple‐stranded dinuclear titanium(IV) species [L3Ti2]4‐. In the solid state, Li4[(1)3Ti2] exhibits a highly symmetric structure with three lithium cations bound to the meso‐helicate tetraanion. 6Li NMR together with 1H NMR studies at variable temperature revealed that, in solution, an unsymmetrical „bowl‐shaped”︁ species is formed with only two Li+ bound to the anion. A methyl substituent on the methylene spacer of the di(catechol) ligand (ligand 2) led to supramolecular systems with new stereocenters and thus a higher content of information. However, only one of the four possible diastereoisomeric metal complexes of [(2)3Ti2]4‐ was observed. A third type of ligand, with a methyl group attached to one terminus of the linear ligand, was also investigated. The synthesis of such an unsymmetrical ligand, 3‐H4, was readily achieved starting from 2,3‐dimethoxyben‐zyl alcohol (4) and 2,3‐dimethoxybenz‐aldehyde (6). Upon complexation, the ligand 3‐H4 led to a statistical mixture of the two possible isomers of the dinuclear titanium(IV) complex [(3)3Ti2]4‐.
Poly(triacetylene) Oligomers: Synthesis, Characterization, and Estimation of the Effective Conjugation Length by Electrochemical, UV/Vis, and Nonlinear Optical Methods
Authors: Martin Rainer E. , Günter Peter , Bosshard Christian , Gubler Ulrich , Gramlich Volker , Gross Maurice , Boudon Corinne , Gisselbrecht Jean‐Paul , Diederich François
Published: July 2007

Poly(triacetylene)s [PTAs, (CCCRCRCC)n–] are a new class of linearly conjugated polymers with a nonaromatic all‐carbon backbone. To explore structure–property relationships in PTAs, we prepared a series of monodisperse oligomers ranging from monomer to hexamer by oxidative Glaser–Hay coupling of a bifunctional („chain‐forming”︁) (E)‐hex‐3‐ene‐1,5‐diyne in the presence of an endcapping unit. All six oligomers are amazingly stable towards exposure to light, air, and temperatures beyond their melting points. They have been fully characterized and are readily soluble in a wide range of solvents. The conjugated rods are reversibly reduced in one‐electron transfer steps and cannot be oxidized below +1.23 V vs. Fc/Fc+. The effective conjugation length in PTAs was estimated from the electronic absorption (UV/Vis) data, and various evaluation methods yielded convergence of the optical properties in the range of 7 to 10 monomer units. The nonresonant second‐order molecular hyperpolarizability γ was measured in CHCl3 by means of the third harmonic generation (THG) at Δ = 1.907 μm. A plot of γ/n vs. n revealed a power law γ ≈ na for γ with a fitted exponent a = 2.5 ∓ 0.1. From the THG measurements, an effective conjugation length of about 10 monomer units was found, in surprisingly good agreement with the value obtained from UV/Vis spectroscopy data.
The Stable (Phosphino)(Silyl)Carbene As A Useful Building Block: Synthesis And Reactivity of 2‐Phosphorus‐Substituted 2H‐Azirines
Authors: Piquet Valérie , Baceiredo Antoine , Gornitzka Heinz , Dahan Françoise , Bertrand Guy
Published: July 2007

[Bis(dicyclohexylamino)phosphino]trimethylsilylcarbene (1) reacts with benzonitrile leading to the corresponding 2‐phosphino‐2H‐azirine 3 in 85% yield. Treatment of 3 with trifluoro‐methanesulfonic acid, methyl trifluoro‐methanesulfonate, or elemental sulfur leads to the P‐hydrogeno‐2‐phosphonio‐,P‐methyl‐2‐phosphonio‐, or 2‐thioxo‐phosphoranyl‐2H‐azirine (4, 5, and 7) in 77, 87, and 91% yields, respectively. Irradiation of 3 gives rise to the 1,2λ5‐azaphosphete 8 (98% yield). Treatment of 3 with BF3·OEt2, BH3·SMe2, Lawesson's reagent, or methyl isothiocyanate gives heterocycles 9 (90% yield), 10 (76% yield), 12 (83% yield), or 13 (80% yield), while under the same experimental conditions, heterocycle 8 reacts with the same reagents to give 9 (82% yield), 11 (83% yield), 12 (86% yield), and 15 (56% yield), respectively. Thermolysis of the P‐hydrogeno‐2‐phosphonio‐2H‐azirine 4 at 55°C leads to the cationic, four‐membered heterocycle 17 (96% yield), while photolysis of the P‐methylazirine analogue 5 in the presence of dimethyl acetylenedicarboxylate affords pyrrole 19 (64% yield). Irradiation of the thiox‐ophosphoranyl azirine 7 gives the 1,3,5λ5‐thiazaphosphole 20 in 79% yield. The influence of the coordination state of phosphorus on the reactivity of 2‐phosphorus‐substituted 2H‐azirines is studied.
Aggregation, Reaggregation and Degradation of a Trifunctional Thallium(I) Amide Induced by Weak TlI ⃛ TlI Attraction
Authors: Hellmann Konrad W. , Gade Lutz H. , Fleischer Roland , Kottke Thomas
Published: July 2007

Metal exchange of the solvated tripodal lithium amide [H3CC{CH2N(Li‐solv)SiMe3}3] (1, solv = ether solvent) with thallium(I) chloride leads to the previously reported pentametallated dimeric thallium amide [{H3CC(CH2NSiMe3)3}2(H)Tl5] (2) in high yield. That the redox‐induced partial demetallation of the amide presumably occurs at an intermediate stage of the metal exchange is inferred from the isolation and structural characterization of the mixed Tl‐Li amide [H3CC{CH3N(Tl) SiMe3}3][H3CC{CH2NSiMe3}3(H)(Tl)(Li‐thf)]·(toluene) (3), which has a crystal structure closely related to that of 2. In both cases the central structural motif, defined by weakly attractive Tl ⃛ Tl contacts, is a tetrahedral metal array in which a triangular thallium triamide unit is capped by an exposed Tl atom of a second building block. Compound 3 may be converted to 2 by metal exchange with TlCl. The two supramolecular components of 2 reaggregate upon recrystallization in a nonpolar solvent such as pentane to yield the dimeric aggregate of the fully metallated thallium amide [H3CC{CH2N(Tl)‐SiMe3}3]2 (4). An X‐ray crystallographic study of 4 established the existence of dimeric aggregation through Tl ⃛ Tl interactions leading to a more open dimeric form than 2 and 3, which is interpreted as being due to a structural mismatch of the building blocks. Compound 4 may be thermally degraded by prolonged stirring in toluene at ambient temperature to yield the previously reported mixed‐valence TlITlII amide [H3CC(CH2NSiMe3)3Tl2] (5).
Structure and Properties of Ba6Ni25S27
Authors: Gelabert M. C. , Ho M. H. , Malik A.‐S. , Disalvo F. J. , Deniard P. , Brec R.
Published: July 2007

Ba6Ni25S27, synthesized by solid‐state reaction of BaS, NiS, and Ni at 675°C, is cubic (Pm3m, a = 10.057(1) Å). The structure was refined by using powder X‐ray diffraction and Rietveld methods with Rp = 6.28%, Rwp = 8.13%, χ2 = 3.120. The structure, isotypic with Ba6Co25S27, consists of an extended network of Ni8S14 pseudo‐cube clusters, NiS6 octahedra, and Ba6S octahedra. Extended Hückel calculations of this compound indicate the band structure near the Fermi level to be composed mostly of d‐character orbitals of tetrahedral Ni, and reveal a peak in the density of states slightly below the Fermi level. The temperature dependence of the electrical resistivity exhibits a local maximum with thermal hysteresis at around 230 K. Above and below this transition, the slope of the resistivity is positive, with a room‐temperature resistivity (ρ = 0.23 mωcm) in the range for that of a poor metal conductor. Magnetic susceptibility measurements from 4 to 900 K indicate a sharp change in slope at around 225 K, with a steadily increasing susceptibility up to 900 K. The susceptibility below 225 K suggests Pauli paramagnetic behavior. Low‐temperature powder X‐ray diffraction and subsequent structure refinement shows that the lattice parameter, a, undergoes a slight change in slope at temperatures of around 235 K.
The Role of Fluorine in the Stereoselective Tandem Aza‐Michael Addition to Acrylamide Acceptors: An Experimental and Theoretical Mechanistic Study
Authors: Fustero Santos , Chiva Gema , Piera Julio , Volonterio Alessandro , Zanda Matteo , González Javier , Ramallal Antonio Morán
Published: July 2007

Aza‐Michael additions of α‐amino esters to fluorinated acceptors take place in a highly stereoselective manner, to give partially modified Ψ[NHCH2]retropeptides incorporating a hydrolytically stable trifluoroalanine mimic. The reaction mechanism has been investigated experimentally and theoretically, in order to explain the effect of the trifluoromethyl group on the reactivity and the origins of the experimentally observed stereocontrol. The reaction is a two‐step process, involving a tandem aza‐Michael addition followed by a stereoselective hydrogen transfer. Both steps are base‐catalyzed. The high level of stereocontrol is the result of a combination of electrostatic interactions and steric effects.
Improved glioblastoma treatment with Ad5/35 fiber chimeric conditionally replicating adenoviruses
Authors: Hoffmann Dennis , Meyer Bernhard , Wildner Oliver
Published: July 2007

Adenovirus type 5 (Ad5)‐based vectors have been used in clinical trials for glioblastoma treatment, but the capacity of Ad5 to infect human glioma cells was questioned. Seeking to improve the adenovirus transduction, we tested four Ad5‐based vectors differing only in their fiber gene on permanent and short‐term cultures of glioblastoma cells. A wild‐type fiber Ad5 vector (Ad5.Luc) was compared to an RGD integrin‐binding motif‐containing fiber adenovirus (AdlucRGD) and the two fiber chimeras Ad5/3 and Ad5/35, with vector binding redirected to the Ad3 or Ad35 receptor, respectively. Compared to Ad5, the transduction of the tested short‐term glioblastoma cultures with the vector Ad5/35.Luc, AdlucRGD and Ad5/3.Luc was enhanced by ∼72%, ∼13% and ∼2%, respectively. To limit adenovirus spread, we aimed to develop conditionally replicative Ad5/35 vectors by targeting the expression of the essential E1 and E4 genes; in addition, some vectors had the E1Δ24 deletion. We analyzed eleven promoters for their activity in glioblastoma cells and determined the specificity of eight replicative adenovirus vectors in vitro. We evaluated the most promising vectors with E1/E4 under the control of the GFAP/Ki67 or E2F‐1/COX‐2 promoters, and the native Ad5 or the chimeric Ad5/35 fiber for their antineoplastic activity in a subcutaneous and intracranial glioblastoma xenograft model. Animals treated with the Ad5/35‐based vectors showed significantly smaller tumors and longer survival than those treated with the homologous Ad5 vectors; no significant toxicity was observed in the intracranial model. Our data suggest that Ad5/35‐based vectors are promising tools for glioblastoma treatment. Copyright © 2007 John Wiley & Sons, Ltd.
Offender and crime characteristics of female serial arsonists in Japan
Authors: Wachi Taeko , Watanabe Kazumi , Yokota Kaeko , Suzuki Mamoru , Hoshino Maki , Sato Atsushi , Fujita Goro
Published: July 2007

This study of Japanese female serial arsonists examined their crimes and background characteristics. The data were a sample from the national police register containing arson cases resulting in charges in Japan between 1982 and 2005. Serial arsonists were 6% of the arson offenders and 12% of these were female, resulting in 83 female serial arsonist data sets. The mean age was 37.6 years and 43% were unemployed. Nearly half were married. Only 28% had a documented history of mental problems and 22% had a prior arrest, usually for theft (19%). Female serial arsonists are characterised by going to a place near their home with a lighter and setting fire directly to combustible materials. Non‐metric multidimensional scaling was used to analyse 33 variables related to the offences. The arsons could be differentiated in terms of either expressive or instrumental sources of action. Expressive arsons were opportunistic and impulsive acts, motivated by emotional distress. The fires were mostly set close to home. Expressive arsons were characteristic of 66% of the females. Instrumental arsons were often motivated by revenge and involved planned and goal‐directed behaviours. They were committed by 13% of the females. Instrumental arsonists tended to travel further from home. Copyright © 2007 John Wiley & Sons, Ltd.
Inter‐ and intramolecular hetero Diels‐Alder reactions, 51. Intermolecular hetero Diels‐Alder reactions of enamino ketones. Effect of high pressure on the kinetics and diastereoselectivity
Authors: Tietze Lutz F. , Hübsch Thomas , Ott Christian , Kuchta Gabriele , Buback Michael
Published: July 2007

The hetero Diels‐Alder reaction of the enamino ketones 1b and 1c with ethyl vinyl ether (2) in dichloromethane to give the dihydropyrans 3b/4b and 3c/4c is studied at high pressure up to 5 kbar. The kinetics is measured by on‐line FT‐IR spectroscopy up to 3 kbar. The cycloadditions show a relatively high pressure‐dependent increase in diastereoselectivity in favor of the trans adducts 4b and 4c, respectively. The activation volumes at atmospheric pressure, ΔV, are determined to be −(43.3 ± 2.1) and −(43.9 ± 2.9) cm3 mol−1 for the reactions of 1b and 1c at 100°C in dichloromethane solution. The activation enthalpies, ΔH≠ for the two cycloadditions at 1500 bar are (64.4 ± 0.4) kJ mol−1 and (64.0 ± 0.6) kJ mol−1. The ΔΔV values are (3.8 ± 0.3) and (4.6 ± 0.3) cm3 mol−1 and the ΔΔH≠ values (1.5 ± 0.2) and (2.1 ± 0.3) kJ mol−1, respectively.
Substituenteneffekte auf die CC‐Bindungsstärke, 16. Thermische Stabilität und Bildungsenthalpie von β‐Dicarbonylverbindungen. — Stabilisierung von α,α′‐Diketoalkyl‐Radikalen
Authors: Nölke Margot , Verevkin Sergej P. , Beckhaus Hans‐Dieter , Rüchardt Christoph
Published: July 2007

Substituent Effects on the CC Bond Strength, 16. — Thermal Stability and Enthalpies of Formation of β‐Dicarbonyl Compounds. — Stabilisation Enthalpies of α,α′‐Diketoalkyl Radicals

The geminal interactions of the two carbonyl groups in seven β‐diketones of the type 8–9 and 11–13 were estimated from their enthalpies of formation, which were deduced from their heats of combustion and enthalpies of vaporization. The radical stabilisation enthalpies RSE of the α,α′‐diketoalkyl radicals 9–13 were obtained from the enthalpies of activation ΔH≠ of thermal CC bond cleavage of eight model compounds of the type 9–13 by their comparison with ΔH≠ of comparable hydrocarbons of similar strain. For non‐cyclic α,α′‐diacyl‐alkyl radicals and six‐membered cyclic ones RSE = 54.8 ± 1.3 kJ mol−1 was determined, which indicates an additive stabilisation by two carbonyl groups.
Strukturen und Moleküleigenschaften ladungsgestörter Moleküle, 54. Pyridinium‐tetraphenylcyclopentadienid‐Betain und die Einelektronen‐Oxidation zu seinem Radikalkation
Authors: Bock Hans , Nick Sabine , Näther Christian , Göbel Ilka , John Andreas , Kleine Markus
Published: July 2007

Structures and Molecular Properties of Charge‐Perturbed Molecules, 54. — Pyridinium‐Tetraphenylcyclopentadienide Betaine and the Single‐Electron Oxidation to Its Radical Cation

The single‐crystal structure of the dark‐blue pyridinium‐tetraphenylcyclopentadienide betaine shows the pyridine ring and the phenyl substituents twisted between 37 and 55°, indicating reduced π interactions between cos2 ω = 0.6 and 0.4. According to AM1 calculations based on the structure coordinates, the total charges of the pyridinium cation acceptor and the cyclopentadienyl anion donor amount to +0.62 and −0.53. This pronounced betaine zwitterionic character causes a 0.5 eV (!) bathochromic shift from 22000 cm−1 in aqueous to 18000 cm−1 in n‐heptane solution, which can be correlated with the respective ET solvent parameters. Cyclovoltammetry in H2CCl2/0.1 M R4N⊕ClO yields an irreversible reduction potential at −1.5 V and two oxidation potentials at +0.36 and +1.28 V, of which the lower one is reversible. With F3CCOO⊖Ag⊕, therefore, a radical cation can be generated and is characterized by ESR/ENDOR spectra. The coupling constants are satisfactorily reproduced by McLachlan calculations, which also suggest that most of the spin population should be localized within the five‐membered ring.
Kleine Ringe, 85. Versuche zur Darstellung von Alkyltri‐tert‐butyltetrahedranen auf dem Cyclopentadienon‐Weg; Synthese der Cyclopentadienone
Authors: Maier Günther , Franz Lothar Hermann
Published: July 2007

Small Rings, 85. — Attempts to Synthesize Alkyltri‐tert‐butyltetrahedranes by the Cyclopentadienone Route; Synthesis of the Cyclopentadienones

Starting from 2‐bromotri‐tert‐butylcyclopentadienone (1) a series of highly substituted cyclopentadienones has been prepared, hoping that they might be suitable candidates for the synthesis of a variety of tetrahedranes with different sterically demanding substituents.
Kleine Ringe, 89. Eine alternative Synthese von Tetra‐tert‐butyltetrahedran
Authors: Maier Günther , Fleischer Frank
Published: July 2007

Small Rings, 89. – An Alternative Synthesis of Tetra‐tert‐butyltetrahedrane

Cyclopropenyldiazomethane 3 is an ideal precursor for tetra‐tert‐butyltetrahedrane (6). Both, photochemical and thermal decomposition of 3 lead to cyclobutadiene 7, which can be photoisomerized to tetrahedrane 6. Tetra‐tert‐butyltetrahedrane (6) is also formed directly by a cheletropic cycloaddition of the carbenic center to the cyclopropene double bond in carbene 4. This is the first example for the synthesis of a tetrahedrane, which does not occur via the corresponding cyclobutadiene. The formation of pyridazine 10 dominates the thermolysis of 3. Azete 12 is obtained both by photolysis as well as by thermolysis of Dewar‐pyridazine 11, the irradiation product of 10.
Synthesis of fluorenylidene‐ and 9‐alkylidene‐3,6‐dimethyl‐4,5‐diazafluorene compounds from 2,2′‐biarene‐3,3′‐diyl bis(triflate) by a palladium‐catalyzed domino process
Authors: König Burkhard , Bubenitschek Peter , Jones Peter G.
Published: July 2007

A convenient synthesis of the fluorenylidene and the 4,5‐diazafluorenylidene moiety is described. The palladium‐catalyzed coupling of 6,6′‐dimethyl‐2,2′‐bipyrdine‐3,3′‐diyl bis(triflate) (2) with phenylacetylene leads to the 4,5‐diazafluorenylidene compound 4 as the major reaction product by an intramolecular cyclization. Under the same conditions biphenyl‐2,2′‐diyl bis(triflate) (6) gives the threefold coupling product 7. The connectivity of 4 and 7 is confirmed by crystal structure analysis.
α,ω‐Dialkyl‐substituted polyenes by palladium‐catalyzed coupling reactions of vinyltin compounds with vinyl halides
Authors: Kiehl Alfried , Eberhardt Anke , Müllen Klaus
Published: July 2007

α,ω‐Dialkyl‐substituted linear polyenes are synthesized in good yields by the palladium‐catalyzed coupling reaction of trialkyltin‐ and iodo‐substituted olefinic precursors. Central building blocks are the distannylated butadiene 8 and vinyl iodide 3. Our synthetic strategy was successfully applied to the preparation of the tert‐butyl polyenes 13, 14, and 15 as well as polyenes 25 and 26 with longer α,ω‐dialkyl chains.
Sterically congested molecules, 14. Imine protonation in toluene solution: A problem akin to the N‐protonation in rhodopsin
Authors: Knorr Rudolf , Ferchland Kathrin
Published: July 2007

The protonation state of N‐(1,1,3,3‐tetramethyl‐2‐indanylidene)methylamine (5/6) is assessed on the basis of fully assigned 1H‐ and 13C‐NMR spectra in [D8]toluene and in CDCl3. In either solvent the basicity of 5 remains intermediate between those of pyridine (weaker) and triethylamine (stronger). Nearly complete proton transfer to 5 in toluene occurs with trifluoroacetic and dichloroacetic acids, whereas partial protonation is achieved by chloroacetic acid or acetic acid and even by biphenyl‐2,2′‐diol (7). As a possible model for imine protonation in the hydrophobic region of proteins like the rhodopsins, the sterically shielded iminium cation 6 (or 2) does not require solvation by a polar solvent; rather it can be stabilized in toluene solution by a counteranion whose proton affinity is diminished by an assisting hydrogen bond.
Sterically congested molecules, 15. Estimation of the ion‐pair NH‐acidity constant of the imino function
Authors: Knorr Rudolf , Ferchland Kathrin
Published: July 2007

The lithium imide 3 is slightly more basic than lithium bis(tri‐methylsilyl)amide (5c) in THF solution. Based on a reported pKa value for hexamethyldisilazane (4c) and assuming the simplest form of ion‐pair equilibration in eq. 1, the apparent pKa = 26.5 was determined for the imine 6.
Ein einfacher Weg zu 3′‐Desoxy‐α‐L‐ und 3′‐Desoxy‐β‐D‐apionucleosiden
Authors: Hammerschmidt Friedrich , Öhler Elisabeth , Polsterer Johann‐Peter , Zbiral Erich , Balzarini Jan , Declercq Erik
Published: July 2007

A Convenient Route to 3′‐Deoxy‐α‐L‐ and 3′‐Deoxy‐β‐D‐apionucleosides

The cyclic thionocarbonate 3, easily available in three steps from 3′‐O‐benzoyl‐2,3‐O‐isopropylidene‐D‐apio‐β‐D‐furanose (1), is deoxygenated with n‐Bu3SnH to yield the 3′‐deoxy epimers 4 [methyl 3‐C‐(benzoyloxymethyl)‐3‐deoxy‐α‐L‐threo‐tetrofuranoside] and 6 [methyl 3‐C‐(benzoyloxymethyl)‐3‐deoxy‐β‐D‐erythro‐tetrofuranoside]. These are separated by chromatography and further converted to the 3′‐deoxy‐α‐L‐apionucleosides 11–13, and the 3′‐deoxy‐β‐D‐apionucleosides 17–19, respectively.
Convenient Synthesis of Biologically Important Retinoids
Authors: Biesalski Hans‐K. , Doepner Gudrun , Kunz Horst , Paust Joachim , John Michael
Published: July 2007

The toxic and teratogenic effects caused by the highly biologically active (all‐E)‐retinoic acid and its derivatives prompted us to synthesize a number of retinoids. We developed synthetic approaches to (all‐E)‐retinyl β‐D‐glucuronide 3, methyl (retinoyl β‐D‐glucopyranoside)uronate 5, (all‐E)‐retinoic acid β‐D‐glucopyranosyl ester 8 and (all‐E)‐retinoyl β‐D‐glucuronide 6 in high purity and yield. Compound 3 was synthesized under Koenigs‐Knorr conditions from (all‐E)‐retinol and an α‐halogenose. Compounds 5 and 8 were prepared by esterification of a silver salt of (all‐E)‐retinoic acid with an α‐glycosyl halide in pyridine. (all‐E)‐Retinoyl β‐D‐glucuronide 6 was prepared by reaction of (all‐E)‐retinoyl fluoride with underivatized β‐D‐glucuronic acid. Compounds 5, 6 and 8 show biological effects similiar to those of retinoic acid.
Synthesis of (4E,7S)‐(−)‐7‐Methoxy‐4‐tetradecenoic Acid, a Major Constituent of the Marine Cyanophyte Lyngbya Majuscula
Authors: Müller Claudia , Voss Gundula , Gerlach Hans
Published: July 2007

The metabolite of the marine cyanophyte Lyngbya majuscula (4E,7S)‐(−)‐7‐methoxy‐4‐tetradecenoic acid (1) has been synthesized for the first time in optically active form in eight steps in 20% overall yield, Heptyloxirane (3) and the alkyne 4 containing the carboxyl group masked as a tricyclic orthoester were prepared by known methods from 5 and 6 as starting materials. Reaction of lithiated 4 with 3 afforded in 74% yield the alkyne 2 which could easily be transformed into the target molecule. Hydrogenation with Lindlar catalyst produced 7 which could be isomerized to 8 with (E) configuration. Methylation of the 7‐hydroxy group in 8 gave 9 which could be transformed into the methyl ester 10 and the (4E,7S)‐acid 1 in high yield.
A reinvestigation of the Meerwein‐Ponndorf‐Verley reduction A highly efficient variation using zirconium catalysts
Authors: Knauer Birgit , Krohn Karsten
Published: July 2007

A new variation of the Meerwein‐Ponndorf‐Verley reduction based on mechanistic considerations is presented. Under optimized conditions 1‐(4‐dimethylaminophenyl)ethanol was used as the reducing alcohol (2–4 equiv.), Zr(O‐tBu)4 as the catalyst (0.2 equiv.), and toluene or cyclohexane as the solvent. Aldehydes and ketones (if not extremely sterically hindered) were reduced to the corresponding alcohols at room temperature mostly within 2–4 h in essentially quantitative yield. α,β‐Unsaturated carbonyl compounds cleanly react in a 1,2‐mode to afford the corresponding allylic alcohols.
Eine neue Synthesestrategie zur Darstellung chiraler, polysubstituierter, an Pyranosen anellierter Tetrahydrofurane
Authors: Al‐Tel Taleb H. , Meisenbach Mark , Voelter Wolfgang
Published: July 2007

A New Synthetic Strategy for the Synthesis of Chiral Polysubstituted Tetrahydrofurans Annulated to Pyranoses

An efficient strategy for the regio‐ and stereoselective synthesis of the chiral tetrahydrofurans 2, 3, 5, 6, 10–16, fused to the pyranose skeleton, from the anhydro sugars 1 and 4 and 1,3‐dicarbonyl compounds via 5‐enol‐exo‐exo‐tet ring closure is described. Furthermore, the syntheses of the regioisomeric tetrahydrofuran 9, the γ‐hydroxy‐tetrahydrofulan 19 and the branched‐chain sugar 20 were successfully achieved.
Template synthesis of the first amide‐based rotaxanes
Authors: Vögtle Fritz , Händel Mirko , Meier Stephan , Ottens‐Hildebrandt Stephan , Ott Frank , Schmidt Thomas
Published: July 2007

The first rotaxanes 6a, 6b and 11 with an amide structure are described. Their (supramolecular template) syntheses are strikingly simple. The central part of the „axle”︁ is added to the „wheel”︁ and subsequently capped. The macromonocycle („wheel”︁) provides the receptor cavity for the „axle”︁ and the triphenylmethane stoppers confirm the mechanical bond between „wheel”︁ and „axle”︁.