Transition-metal-promoted reactions of boron hydrides. 17. Titanium-catalyzed decaborane-olefin hydroborations.

The titanium-catalyzed hydroboration reactions of decaborane with a variety of terminal olefins have been found to result in the exclusive, high-yield formation of monosubstituted decaborane 6-R-B(10)H(13) products, arising from anti-Markovnikov addition of the cage B6-H to the olefin. The titanium-catalyzed reactions are slow, often less than one turnover per hour; however, their high selectivities and yields coupled with the fact that they are simple, one-pot reactions give them significant advantages over the previously reported routes to 6-R-B(10)H(13) compounds. The catalyst also has extended activity with reactions carried out for as long as 13 days, showing little decrease in reactivity, thereby allowing for the production of large amounts of 6-R-B(10)H(13). The titanium-catalyzed reactions of decaborane with the nonconjugated diolefins, 1,5-hexadiene and diallylsilane, were found to give, depending upon reaction conditions and stoichiometries, high yields of either alkenyl-substituted 6-(CH(2)=CH(CH(2))(4))-B(10)H(13) (4) and 6-(CH(2)=CHCH(2)SiMe(2)(CH(2))(3))-B(10)H(13) (5) or linked-cage 6,6'-(CH(2))(6)-(B(10)H(13))(2) (6) and Me(2)Si(6-(CH(2))(3)-B(10)H(13))(2) (7) compounds, respectively. The unique tetra-cage product, Si(6-(CH(2))(3)-B(10)H(13))(4) (8), was obtained by the catalyzed reaction of 4 equiv of decaborane with tetraallylsilane. Sequential use of the titanium catalyst and previously reported platinum catalysts (PtBr(2) or H(2)PtCl(6).6H(2)O with an initiator) provides an efficient pathway to asymmetrically substituted 6-R-9-R'-B(10)H(12) species. The structures of compounds 5, 6, and 8, as well as a platinum derivative, (PSH(+))(2)-commo-Pt-[nido-7-Pt-8-(n-C(8)H(17))B(10)H(11)](2)(2-), of 6-(n-octyl)decaborane have been established by single-crystal crystallographic determinations.     

Photochemische Reaktionen. 107. Mitteilung. Zur Photochemie offenkettiger 2,6-bzw. 2,7-Dien-Carbonylverbindungen

The Photochemistry of Open-Chained 2,6- or 2,7-Dien-Carbonyl Compounds On ¹n, π*-excitation (λ > 347 nm) citral (5) and the methyl ketone 10 isomerize to compounds A (7, 19) and B (6, 20) , whereas the phenyl ketone 11 changes into the isomer 24 of type E. Evidence is given that the conversions to A and B may arise from the ³n, π*-state of the 2,6-diene-carbonyl compounds. On ¹n, π*-excitation (λ = 254 nm) 5 and 10 yield the isomers A (7, 19) and D (18, 22) , but no products of type B. Furthermore, conversion of 10 to the isomer 21 of type C is observed. Selective ¹n, π*-excitation (λ = 254 nm) as well as selective ¹n, π*-excitation (λ > 347 nm) of the 2,7-diene-carbonyl compounds 12 and 13 give rise to isomerization to the compounds F (25, 28) , exclusively. The intramolecular [2 + 2]-photocycloadditions are shown to be triplet processes. UV.-irradiation (λ > 280 nm) of compounds F (25, 28) furnishes the isomeric products G (26, 29) which photoisomerize to oxetanes of type H (27, 30).     

Azole. 44.

The structure analyses of racemic 3‐chloro‐1‐(4‐morpholino‐5‐nitro­imidazol‐1‐yl)­propan‐2‐ol, C₁₀H₁₅ClN₄O₄, (II), and 3‐chloro‐1‐(5‐morpholino‐4‐nitro­imidazol‐1‐yl)­propan‐2‐ol, C₁₀H₁₅ClN₄O₄, (III), have been undertaken in order to determine the position of the morpholine residue in these two isomers. The morpholine residue in (II) is connected at the 4‐position, while in (III), it is connected at the 5‐position of the imidazole ring. The morpholine mean planes and nitro groups in the two compounds deviate from the imidazole planes to different extents. The nitro groups in (II) and (III) take part in the conjugation system of the imidazole rings. In consequence, the exocyclic C—N bonds are significantly shorter than the normal single Csp²—NO₂ bond and the nitro groups in (II) and (III) show an extraordinary stability on treatment with morpholine and piperidine [Gzella, Wrzeciono & Pöppel (1999). Acta Cryst. C 55 , 1562–1565]. In the crystal lattice, the mol­ecules of both compounds are linked by O—H?N and C—H?O intermolecular hydrogen bonds.     

Synthesen von Heterocyclen. 19. Mitt.

Zusammenfassung Bei der Kondensation von o-Hydroxy-acetophenonen (I–VI) mit Benzylmalonsäure-bis-(2,4-dichlorphenol)-ester VII entstehen über Derivate des 4-Hydroxy-6-phenyl-2-pyrons (z. B. IX) solche des 5,8-Dioxo-2,3-benzo-1,4,7-dipyranopyrans (XI–XVII). Mit unsubstituiertem Malonsäure-bis-(2,4-dichlorphenol)-ester XXI reagieren diese (I, V und VI) vermutlich zu Estern der Cumarin-3-carbonsäuren XXII–XXIV.Aus o-Hydroxy-propiophenonen und dem Ester XXI bilden sich dagegen Verbindungen von Typ des Pyrono-pyrons (XXV und XXVI).Herrn Prof. Dr.M. Rebek in Freundschaft und Verehrung zum 70. Geburtstag gewidmet.     

珠子参化学成分分析

从珠子参根茎中分离得到7个化合物. 利用核磁共振、 质谱和红外等手段, 并结合其理化性质, 鉴定了其结构, 它们分别是24(R)-珠子参苷R1, 6-O-[β-D-吡喃葡萄糖基(1→2)-β-D-吡喃葡萄糖基]-20-O-[β-D-吡喃葡萄糖基(1→4)-β-D-吡喃葡萄糖基]-20(S)-原人参三醇、 6″-乙酰基-人参皂苷Rd、 人参皂苷Rf、 竹节参皂苷Ⅳa、 人参皂苷Rd和竹节参皂苷Ⅴ. 其中, 24(R)-珠子参苷R1和6-O-[β-D-吡喃葡萄糖基(1→2)-β-D-吡喃葡萄糖基]-20-O-[β-D-吡喃葡萄糖基(1→4)-β-D-吡喃葡萄糖基]-20(S)-原人参三醇为2个新化合物, 6″-乙酰基-人参皂苷Rd 和人参皂苷Rf为首次从珠子参根茎中得到.     

Azinyl Sulfides. LXVII.

The title compound, C₆H₇NS, is planar, with endo‐C—N—C bond angles of 118.7 (2) and 118.8 (2)°, and C—S bond lengths of 1.697 (2) and 1.692 (2) Å for the two symmetrically independent mol­ecules. 1‐Methylpyridinium‐4‐thiol­ate is the major contributor to the molecular structure in the solid state.     

Triterpenoid saponins from Ilex mamillata C.Y. Wu ex C.J. Tseng

Two new triterpenoid saponins, ilemaminosides A and B (1 and 2) along with six known saponins (3-8) were isolated from 70% ethanolic extract of the leaves of Ilex mamillata C.Y. Wu ex C.J. Tseng. The new saponins were characterised as 3-O-α-L-arabinopyranosyl-ilexgenin B (1) and 3-O-β-D-glucopyranosyl-(1?→?3)-α-L-arabinopyranosyl-ilexgenin B (2). The structures of compounds 1 and 2 were elucidated on the basis of the chemical and spectroscopic methods, and the structures of known compounds were identified by comparison of their spectroscopic data with those reported in the literature. The compounds showed inhibitory activities in anti-inflammatory assay in?vitro with IC(50) values in the range 25.37-38.33?μg?mL(-1).     

Irreversible enzyme inhibitors. LXXXIII. Candidate active-site-directed irreversible inhibitors of dihydrofolic reductase. VIII. Derivatives of 2,4-diaminopyrimidine. II

2,4-Diamino-6-(p-aminophenethyl)pyrimidines with a 5-phenylbutyl (XIX) and 5-(p-chlorophenyl) (VIII) substituent were synthesized by condensation of the corresponding pyrimidine-6-carboxaldehydes (XVI, X) with the Wittig reagent derived from p-nitro-benzyl bromide, followed by catalytic hydrogenation. Selective bromoacetylation of VIII and XIX afforded the candidate active-site-directed irreversible inhibitors of dihydrofolic reductase, namely, 6-(p-bromoacetamidophenethyl)-2,4-diaminopyrimidine with a 5-(p-chlorophenyl)- (IV) and 5-phenylbutyl- (III) substituents. Although III and IV were excellent reversible inhibitors of dihydrofolic reductase, neither showed any inactivation of the enzyme; in contrast, the corresponding 2-amino-6-(p-bromoacetamidophenethyl)-5-phenylbutyl-4-pyrimidinol (II) - which differs from III only in the 4-substituent (NH₂ vs. OH) - was an excellent active-site-directed irreversible inhibitor of dihydrofolic reductase, but II was a poor reversible inhibitor. Thus the conformations of II and III are most probably different when complexed to dihydrofolic reductase.     

Ferrocene compounds. XXXIX.

In the title compound, [Fe(C₅H₅)(C₁₄H₁₃O)], the plane of the heterocyclic ring is almost perpendicular to the plane of the substituted cyclo­penta­dienyl ring, and the heterocyclic ring adopts a half‐chair conformation. The conformation of the nearly parallel cyclo­penta­dienyl (Cp) rings [the dihedral angle between their planes is 2.7 (1)°] is almost halfway between eclipsed and staggered, and the rings are mutually twisted by about 19.4 (2)° (mean value). The mean lengths of the C—C bonds in the substituted and unsubstituted cyclo­penta­dienyl ring are 1.420 (2) and 1.406 (3) Å, respectively, and the Fe—C distances range from 2.029 (2) to 2.051 (2) Å. The phenyl and unsubstituted cyclo­penta­dienyl rings are involved in C—H⃛π interactions, with intermolecular H⃛centroid distances of 2.85 and 3.14 Å for C—H⃛π(Ph), and 2.88 Å for C—H⃛π(Cp). In two of these interactions, the C—H bond points towards one of the ring bonds rather than towards the ring centroid. In the crystal structure, the C—H⃛π interactions connect the mol­ecules into a three‐dimensional framework.     

Cover Picture: Angew. Chem. Int. Ed. 12/2002

The cover picture shows the thermally induced shape‐memory effect for a covalently cross‐linked polymer network. The polymer in its temporary shape (cube, picture on top) is heated from room temperature up to 70°C. Within 60 seconds the sample recovers its memorized, permanent shape of a nearly planar foil (picture on top left). The visual change of the material from opaque to transparent is caused by the melting of crystallites of the switching segments. The scheme in the center of the picture illustrates the molecular mechanism of the shape‐memory effect. The shown polymer network, which is synthesized from poly(ε‐caprolactone)dimethacrylate as macromonomer, is one of the first polymer systems that have specifically been developed for applications in the biomedical field. The net points (black) determine the permanent shape while the crystallites (blue) stabilize the temporary shape. More on the current state and the potential of this technology can be found in the review by A. Lendlein and S. Kelch on p. 2034 ff.     

云南重楼中的新甾体皂苷

从云南重楼Paris polyphylla Sm. var. yunnanensis(France. )Hand.-Mazz.的干燥根茎中分离鉴定了4个甾体皂苷(1~4), 其中化合物1是新化合物, 采用波谱技术鉴定其结构为24-O-β-D-吡喃半乳糖基-(23S,24S)-螺甾-5, 25(27)-二烯-1β,3β,23,24-四醇-1-O-β-D-吡喃木糖基(1→6)-β-D-吡喃葡萄糖基(1→3)[α-L-吡喃鼠李糖基(1→2)]-β-D-吡喃葡萄糖苷.     

Photophysics of fluorinated benzene. III. Hexafluorobenzene

A theoretical study of the photoabsorption spectroscopy of hexafluorobenzene (HFBz) is presented in this paper. The chemical effect due to fluorine atom substitution on the electronic structure of benzene (Bz) saturates in HFBz. State- of-the-art quantum chemistry calculations are carried out to establish potential energy surfaces and coupling surfaces of five energetically low-lying electronic (two of them are orbitally degenerate) states of HFBz. Coupling of these electronic states caused by the Jahn-Teller (JT) and pseudo-Jahn-Teller (PJT) type of interactions are examined. The impact of these couplings on the nuclear dynamics of the participating electronic states is thoroughly investigated by quantum mechanical methods and the results are compared with those observed in the experiments. The complex structure of the S(1) ← S(0) absorption band is found to originate from a very strong nonadiabatic coupling of the S(2) (of πσ* origin) and S(1) (of ππ* origin) state. While S(2) state is orbitally degenerate and JT active, the S(1) state is nondegenerate. These states form energetically low-lying conical intersections (CIs) in HFBz. These CIs are found to be the mechanistic bottleneck of the observed low quantum yield of fluorescence emission, non overlapping absorption, and emission bands of HFBz and contribute to the spectral width. Justification is also provided for the observed two peaks in the second absorption (the unassigned "c band") band of HFBz. The peaks observed in the third, fourth, and fifth absorption bands are also identified and assigned.     

Bildung siliciumorganischer Verbindungen. XXXXVI. Si-fluorierte Carbosilane

Formation of organosilicon compounds. XXXXVI. Si-fluorinated carbosilanes Compounds (1)–(7) (see “Inhaltsübersicht”) are obtained by reaction of carbosilanes containing Si? Cl groups with ZnF₂. The linear compounds (8) and (9) are prepared from ZnF₂ and (Cl₃Si)₂CCl₂, and (Cl₃Si? CCl₂)SiCl₂, respectively, whereas the cyclic compounds are formed by photochemical chlorination. Photochemical chlorination of (3) goes via compounds (13) and (14) (isolation is possible); both of them can be prepared too by reaction of Si? Cl derivatives with ZnF₂. Compounds (16) and (17) are obtained from the corresponding Si? Cl derivatives.     

Solvent-induced crystallization. I. Crystallization kinetics

The kinetics of crystallization of quenched poly(ethylene terephthalate) (PET) films during the imbibition of methylene chloride (MeCl₂) vapor is studied by density measurements. The effects of film thickness (0.0025–0.086 cm) and temperature (0–38°C) were examined. The data suggest that MeCl₂ transport controls the crystallization in thick films and at elevated temperatures, but that spherulite growth controls in thin films and at reduced temperatures. The application of a mathematical model developed previously supports this mechanistic interpretation of the data.     

Microbial metabolism. Part 5. Dihydrokawain

Preparative scale fermentation of (6S)-dihydrokawain (1) with Rhizopus arrhizus (ATCC 11145) gave 3'-hydroxydihydrokawain (2) and (8S)-hydroxydihydrokawain (3). Structure elucidation of the metabolites was based on spectroscopic data. The C-8 absolute configuration of (3) was assessed via its Mosher's esters.     

Thermal analysis graphite intercalation compounds with dichlorides of some d-elements: A.S. Skoropanov,G.S. Petrov,A.A. Vecher,Yu.N. Novikov and M.E. Vol'pin,Thermochim. Acta, 90 (1985) 339-342

Kinetic and thermodynamic aspects of the axial base dissociation of solid Co(salen) (X-py) complexes, X = H (1), 3-Me (2), 4-Me (3), 3,4-Me₂ (4), 3,5-Me₂ (5), 3-NH₂ (6), 3-Cl (7), 3-CN (8), 4-CN (9), have been investigated by means of TG-DSC and isothermal weight-loss measurements. These adducts endothermically dissociate the axial base giving rise to the oxygen-active Co(salen) complex. The axial base dissociation reactions fit the contracting disc equation and the kinetic compensation effect is observed for all the adducts excepting Adducts 4–6. For the remaining adducts the kinetic and thermodynamic stabilities of the Co-(X-py) bond are found to increase linearly with increasing Hammett's substitution constants of X except for Adducts 3 and 9. These results are discussed in terms of the σ and π interactions between cobalt(II) and substituted pyridine. Factors dominating the kinetic bond stability are briefly discussed.     

Pneumatochemical impedance spectroscopy. 1. Principles

Pneumatochemical impedance spectroscopy (PIS) is the indirect transposition of electrochemical impedance spectroscopy (EIS) to solid-gas reactions. In PIS analysis, an analogy is made between pressure and electrical potential on one hand and gas flow and electric current on the other hand, and pneumatochemical transfer functions are derived from gas-phase measurements. Potentially, this spectroscopy can be used to analyze the dynamics of any solid-gas system including adsorption (surface) and absorption (bulk) phenomena, gas (H2) permeation across metallic membranes, and electrocatalysis in gaseous fuel cells. Hydrogen absorption by intermetallic compounds (IMCs), a process of great practical interest for hydrogen storage applications, is more specifically considered in this paper, and the kinetic equations derived in this work pertain only to this case. Whereas classical electrochemical impedance measurements are performed using an harmonic analyzer and monochromatic potential (potentiostatic mode) or current (intentiostatic mode) perturbations, PIS investigation of the dynamics of IMC-H2(g) systems is more conveniently performed using Sievert's-type gas distribution apparatus (SGDA) and polychromatic pressure perturbation signals. This is first because monochromatic isothermal pressure modulations cannot be easily obtained experimentally over the frequency domain of interest and, second, because most IMC-H2(g) systems exhibit strongly nonlinear behaviors in two-phase domains (hysteresis), and this proscribes harmonic analysis. A further benefit of using SGDA and nonharmonic perturbations is that kinetic and thermodynamic information are collected simultaneously during the same experiment. The measurement and modeling of the pneumatochemical transfer functions associated with IMC-H2(g) systems, both in solid solution and two-phase domains, are discussed in this paper which is organized in two parts. The principles of PIS analysis, based on the theory of linear and time-invariant systems, are presented in the first part. The dynamics of hydrogen sorption by metals and IMCs is analyzed in the second part, where a detailed analysis of the multistep reaction paths involved in sorption mechanisms is proposed.     

Solvent-induced crystallization. II. Morphology

The Morphology of quenched poly(ethylene terephthalate) (PET) films crystallized by low-molecular-weight organic penetrants is studied by scanning electron microscopy. Films with thicknesses from ca. 1 mil (0.0025 cm) to ca. 35 mil (0.1 cm) were exposed to methylene chloride (MeCl₂) and N,N-dimethylformamide (DMF) in the temperature ranges 0–38°C and 22–70°C, respectively. The effects on the surface and internal structures of contact with liquids and saturated vapors were examined. Severe porosity at the surface results from contact with the liquids, but only minor surface roughness appears following contact with vapors. Internal porosity developed in the thinnest films (ca. 1 mil) during crystallization in liquid environments. Here, the internal void fraction is greatest along the film centerline and decreases with increasing crystallization temperature. A mathematical model discussed previously accounts for the observed behavior.     

Structural characterisation of a water-soluble polysaccharide from tissue-cultured Dendrobium huoshanense C.Z. Tang et S.J. Cheng

A water-soluble polysaccharide TC-DHPA4 with a molecular weight of 8.0 × 10⁵ Da was isolated from tissue-cultured Dendrobium huoshanense by anion exchange and gel permeation chromatography. Monosaccharide analysis revealed that the homogeneous polysaccharide was made up of rhamnose, arabinose, mannose, glucose, galactose and glucuronic acid with a molar ratio of 1.28:1:1.67:4.71:10.43:1.42. The sugar residue sequence analysis based on the GC-MS files and NMR spectra indicated that the backbone of TC-DHPA4 consisted of the repeated units:→6)-β-Galp-(1→6)-β-Galp-(1→4)-β-GlcpA-(1→6)-β-Glcp-(1→6)-β-Glcp-(→. The sugar residue sequences β-Glcp-(1→)-α-Rhap-(1→3)-β-Galp-(1→, β-Glcp-(1→4)-α-Rhap-(1→3)-β-Galp-(1→, β-Galp-(1→6)-β-Manp-(1→3)-β-Galp-(1→, and α-l-Araf-(1→2)-β-Manp-(1→3)-β-Galp-(1→ were identified as the branches attached to the C-3 position of (1→6)-linked galactose in the backbone.     

Pseudochalkogenverbindungen. XXIV. Cyanamido-trimetaphosphimate

Pseudochalcogeno Compounds. XXIV. Cyanamido Trimetaphosphimates Synthesis and properties of sodium cyanamido trimetaphosphimates Na₃[P₃(NH)₃O_6?n(NCN)_n] (n:2,4) are reported. This compounds may be obtained by cautious hydrolysis of the corresponding hydrocyanamido-chloro-trimetaphosphimates, P₃N₃Cl_6?n(NHCN)_n. For sodium trimetaphosphimate, Na₃[P₃(NH)₃O₆] a simple, modified synthetic route is described. Possibilities of the formation of pseudochalcogeno-trimetaphosphimates of the type [P₃(NH) ₃O_6?n{C(CN)₂}_n]^3? (n = 2, 4) are discussed.