Pyryliumolate. III. Synthese anellierter Benzotropolone

Pyryliumolates. III. Synthesis of Annulated Benzotropolones Dirhodiumtetraacetate catalyzed nitrogen extrusion from diazocarbonyl compounds ( 2a – f , 19c , 23d – f , 25b ) yields benzopyryliumolates (3) , which were trapped intramolecularly in situ to give tetracyclic adducts (4a, 5a–d, 20, 24a–c, 26) . Starting with 5a and 5d annulated benzotropolones ( 12a, d ) are accessible.     

Convenient preparation of aromatic aldehydes via DDQ oxidation. Application in the Synthesis of a Tripodand Containing Octahydroacridine Moieties

7-Methyloctahydroacridines 7a–d were obtained by a one-pot imine condensation/Lewis acid-catalyzed cyclization from aniline derivatives 5a–d and aldehyde 6 . Only those compounds 7 could be oxidized with DDQ to the corresponding octahydroacridine-7-carbaldehydes 9 , which bear a meta-chloro or bromo substituent (with respect to the methyl group) in addition to the para-amino group (i.e. 7c,d → 9c,d ). Aldehyde 9c was further converted to the novel tripodand 11 which was characterized by X-ray crystal structure analysis.     

Amphiphile und Mesogene Kohlenhydrate. 10. Mesophasenwechsel bie amphiphilen Tetradecyl-(N-acylamino)-2-desoxy-1-thio-β-D-glucopyranosiden durch Acylkettenvariation

Amphiphilic and Mesogenic Carbohydrates. 10. Change of the Type of the Mesophase by Variation of the Acyl Chain of Amphiphilic Tetradecyl (N-acylamino)-2-deoxy-1-thio-β-D -glucopyranosides The homologous amphiphilic tetradecyl-2-(N-alkanoylamino)-2-deoxy-1-thio-β-D -glucopyranosides 5a–f were synthesized from the 2-(N-alkanoylamino)-2-deoxy-D -glucopyranoses 1a–f via the glucosyl chlorides 2a–f , the glucosyl isothiuronium chlorides 3a–f , and the acetylated thioglucosides 4a–f . On heating the amphiphiles 5a–f form different types of liquid crystalline phases in dependence of the length of the acyl chain, i.e. 5a and 5b form smectic phases, 5d–f form columnar mesophases. Polarisation microscopy, DSC-measurements and contact preparations were used to characterise the liquid crystaline phases.     

Zirkonium-katalysierte Oxidation von primären aromatischen Aminen zu Nitroverbindungen mit tert-Butylhydroperoxid

Zirconium-catalysed Oxidation of Primary Aromatic Amines to Nitro Compounds Using tert-Butylhydroperoxide A broad range of primary aromatic amines ( 1a–x ) with electron donating and accepting substituents are oxidized in good to excellent yields to the nitro compounds 3a–x using tert-butylhydroperoxide as the oxidant and Zr(OtBu)₄ as the catalyst. The corresponding nitroso compounds 2m, 2n, 2s and 2u can be isolated in the conversion of electron-rich anilines 1m, 1n, 1s and 1u . The aminopyridines 5a–d are also converted to the corresponding nitropyridines 6a–d , but in lower yields (41–47%).     

Structure‐Based Insight into the Asymmetric Bioreduction of the CC Double Bond of α,β‐Unsaturated Nitroalkenes by Pentaerythritol Tetranitrate Reductase

Biocatalytic reduction of α‐ or β‐alkyl‐β‐arylnitroalkenes provides a convenient and efficient method to prepare chiral substituted nitroalkanes. Pentaerythritol tetranitrate reductase (PETN reductase) from Enterobacter cloacae st. PB2 catalyses the reduction of nitroolefins such as 1‐nitrocyclohexene ( 1 ) with steady state and rapid reaction kinetics comparable to other old yellow enzyme homologues. Furthermore, it reduces 2‐aryl‐1‐nitropropenes ( 4a–d ) to their equivalent (S)‐nitropropanes 9a–d . The enzyme shows a preference for the (Z)‐isomer of substrates 4a–d , providing almost pure enantiomeric products 9a–d (ees up to>99%) in quantitative yield, whereas the respective (E)‐isomers are reduced with lower enantioselectivity (63–89% ee) and lower product yields. 1‐Aryl‐2‐nitropropenes ( 5a , b ) are also reduced efficiently, but the products (R)‐ 10 have lower optical purities. The structure of the enzyme complex with 1‐nitrocyclohexene ( 1 ) was determined by X‐ray crystallography, revealing two substrate‐binding modes, with only one compatible with hydride transfer. Models of nitropropenes 4 and 5 in the active site of PETN reductase predicted that the enantioselectivity of the reaction was dependent on the orientation of binding of the (E)‐ and (Z)‐substrates. This work provides a structural basis for understanding the mechanism of asymmetric bioreduction of nitroalkenes by PETN reductase.     

Prolinamides versus Prolinethioamides as Recyclable Catalysts in the Enantioselective Solvent‐Free Inter‐ and Intramolecular Aldol Reactions

A solvent‐free asymmetric and direct anti‐aldol reaction of aliphatic ketones with aromatic aldehydes catalyzed by recyclable L ‐prolineamides and L ‐prolinethioamides 3 is studied. The L ‐prolinethioamide 3d (5 mol%), derived from L ‐Pro and (R)‐1‐aminoindane, is the most efficient catalyst for this process affording the anti‐aldol adducts in high yields with excellent diastereo‐ and enantioselectivities (up to >98/2 dr, up to 98% ee) at 0 °C or room temperature. Prolinethioamide 3d is an effective organocatalyst for the first asymmetric, solvent‐free, intramolecular Hajos–Parrish–Eder–Sauer–Wiechert reaction with comparable or higher levels of enantioselectivity (up to 88% ee) to reported catalysts in organic solvents. Moreover, organocatalyst 3d can be easily recovered and reused by a simple acid/base extraction.     

The viscoelastic properties of rubber–resin blends. III. The effect of resin concentration

The viscoelastic properties of a rubber–resin blend, which influences performance of the blend as a pressure-sensitive adhesive, depend upon the structure of the resin as well as its molecular weight. The effect of the concentration of a compatible resin in the blend was examined using a mechanical spectrometer. Four types of resins were used. These are the rosin esters, polyterpenes, pure monomer resins such as polystyrene and poly(vinyl cyclohexane), and petroleum stream resins. Each was examined in blends with both natural rubber and styrene–butadiene rubber over a range of concentrations. It is shown that the temperature of the tan δ peak for compatible systems can be predicted by the Fox equation, T = W₁T + W₂T, where W₁ and W₂ are the weight fractions of the resin and rubber, respectively, and the T_g's are the tan δ peak temperatures in K. The plateau modulus G for a blend can be identified as the G′ value in the rubbery plateau at the point where tan δ is at a minimum. The relationship between G and G, the plateau modulus for the undiluted elastomer, is shown to be proportional to the volume fraction of the elastomer raised to the 2.3–2.4 power for natural rubber with six different compatible resins. The exponent for styrene–butadiene rubber is 2.5–2.6 with four different resins. Using these relationships, both the tan δ peak temperature and plateau modulus can be predicted for a rubber–resin system from data on the unmodified elastomer and on one typical rubber–resin blend.     

Base-induced reactions of isothiazolium salts with active 5-methyl or 5-methylene groups

It is shown that N-phenyl-substituted isothiazolium salts 2/3a–e with active 5-methyl or 5-methylene groups can easily be obtained by reaction of β-thiocyanatovinylaldehydes 1 and substituted anilines. Based on a wide variety of isothiazolium salts accessible in that way, a study of their various reaction products, e.g. 1,6-diphenyl-substituted thiadiazapentalenes 4a–d , 5a–j and special spiro compounds 6 , and the influence of donor and acceptor substituents becomes possible. The structure of the basic skeleton of the thiadiazapentalenes was confirmed by X-ray analysis and ab initio MO calculations. Some mechanistic aspects are supported by the MO results.     

Transparent and organosoluble cardo polyimides with different trans/cis ratios of 1,4‐diaminocyclohexane via aromatic nucleophilic substitution polymerization

Two series of cardo polyimides were prepared from 1,4‐bis(4‐fluorophthalimide)cyclohexane with different trans/cis ratios and phenolphthalein/o‐cresolphthalein via aromatic nucleophilic substitution reaction. The inherent viscosities of the synthesized polymers were found to be 0.55–0.66 dL g^?1 in N,N′‐dimethylacetamide. The cardo polyimides showed excellent solubility in organic solvents, high glass transition temperatures (T_g) of 275–312 °C and moderate thermal stability with 5% weight loss temperatures (T_d5%) of 415–441 °C in nitrogen and 370–436 °C in air. The polyimide films exhibited high optical transparency with cut‐off wavelengths of 350–355 nm and moderate mechanical properties. The different properties of the polymers caused by trans and cis configurations of 1,4‐diaminocyclohexane were also investigated. It was found that with an increasing content of trans configuration of 1,4‐diaminocyclohexane in the polyimide backbone, T_g of the polyimides increased as well as T_d5%, while the solubility gradually decreased. The polyimide films had good optical transparency regardless of trans/cis configuration. © 2018 Society of Chemical Industry     

Optically Pure 1,2‐Bis[(o‐alkylphenyl)phenylphosphino]ethanes and Their Use in Rhodium‐Catalyzed Asymmetric Hydrogenations of α‐(Acylamino)acrylic Derivatives

Optically pure (S,S)‐1,2‐bis[(o‐alkylphenyl)phenylphosphino]ethanes 1a–d were prepared in four steps from phenyldichlorophosphine via phosphine‐boranes as the intermediates. The rhodium complexes 5a–d of these diphosphines were used for the asymmetric hydrogenations of α‐(acylamino)acrylic derivatives including β‐disubstituted derivatives. Markedly high enantioselectivity (78–>99%) was observed for the reduction of β‐monosubstituted derivatives. β‐Disubstituted derivatives were also reduced in considerably high enantioselectivity (up to 90%). The single crystal X‐ray analysis of the rhodium complex 5c of (S,S)‐1,2‐bis[phenyl(5′,6′,7′,8′‐tetrahydronaphthyl)phosphino]ethane ( 1c) revealed its δ‐type structure with face orientation of the two tetrahydronaphthyl groups and edge orientation of the two phenyl groups. This conformation corresponds to that of the rhodium complex of 1,2‐bis[(o‐methoxyphenyl)phenylphosphino]ethane (DIPAMP); the rhodium complex of (R,R)‐DIPAMP, whose chirality at phosphorus is opposite that of 5c , exhibits a λ‐type structure with the face orientation of the two o‐methoxyphenyl groups and the edge orientation of the two phenyl groups. The conformational similarity of these rhodium complexes as well as the stereochemical outcome in the asymmetric hydrogenations means that the coordinative interaction of the methoxy group of DIPAMP with rhodium metal is not the main factor that affects asymmetric induction.     

Several features of vinyl chloride–diallyl phthalate suspension copolymerization

Vinyl chloride–diallyl phthalate (VC–DAP) suspension copolymerization was carried out in a 5‐L autoclave and 200‐mL stainless steel vessel at 45°C. The apparent reactivity ratios of VC–DAP suspension copolymerization system were calculated as r_VC = 0.77 and r_DAP = 0.37. It shows that VC–DAP copolymer contains no gel when the feed concentration of DAP (f) is lower than a critical concentration (f_cr, inside the range of 0.466–0.493 mmol/mol VC at 80–85% conversion), the polymerization degree (DP) of copolymer increases with the increase of f and conversion. VC–DAP copolymer is composed of gel and sol fractions when f is larger than f_cr. The DP of sol fraction decreases as f increases, but the gel content and the crosslinking density of gel increase. The gel content also increases as conversion increases. The results also show that the index of polydispersity of molecular weight of sol changes with f, a maximum value appears when f is close to f_cr. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 156–162, 2000     

Quinoxalines. IX. Reaction of 2-(Halogenomethyl)-quinoxalines and -quinoline with hydroxybenzoic acids and their esters

In the presence of a base the title compounds react to products with ether structure ( 4, 6 ), or with ester structure ( 3 ), or to structure 5 containing both functionalities in dependence on the mole ratio of the starting substances, on reaction conditions and on the substituent patterns in the hydroxybenzoic acid component. Under the influence of alkali hydroxide the m- and p-substituted compounds ( 6e–g ) are saponified to the alkali salts of the carboxylic acid ( 4b, c ). The o-substituted compounds ( 6a–d ), however, are cyclized to the benzo[b]furanylquinoxalines ( 8 ). 8a, d are also obtained by thermal water elimination of the carboxylic acids 4a, d . The red-coloured benzofuranols 8 react with acetic anhydride and benzoyl-chloride/pyridine, resp., to the weakly yellow esters 9 . The stucture of the products 8 and 9 is studied by UVVIS derivative spectroscopy, by theoretical calculation of the dihedral angles and by ¹H and ¹³C NMR spectroscopy. The ¹H and ¹³C chemical shifts are completely assigned. The quinoxalines 8a–c and the quinoline 8d only exist in the hydroxy form.     

Strong Influences of Melting Time and Tm3+ Concentration on Blue Up-Conversion Photoluminescence for Tm3+/Yb3+ Co-Doped TeO2–TlO0.5–ZnO Glass

In this study, by a conventional melt quenching method, we synthesized novel up-conversion phosphors of 60TeO₂–30TlO_0.5–(9−x)ZnO–xTm₂O₃–1Yb₂O₃ (x = 0.1–0.5) glasses, whose system was recently developed in our collaborative group, and their blue up-conversion photoluminescence (UCPL) of Tm³⁺ ions via three-step energy transfer from near-infrared (NIR) sensitizer of Yb³⁺ ions was observed. In particular, the substantial rate of the energy transfer <γ_d5> in the third step from Yb³⁺ to Tm³⁺ under excitation at 975 nm, which determined the final blue UCPL intensity, was estimated as a function of the rare-earth concentration. With an aid of analytical methods of PL lifetime and Judd–Ofelt theory, it was revealed that the highest energy transfer rate <γ_d5> was achieved to be 2.07 × 10⁻¹⁷ cm³/s for x = 0.2, and further increasing Tm₂O₃ content x in the fixed Yb₂O₃ resulted in the decrease in the energy transfer rate <γ_d5>. One of the plausible causes was concentration quenching of Yb³⁺ ions. The other was back-transfer from Tm³⁺ to Yb³⁺ ions. The influence of the condition of glass synthesis and the melting time on <γ_d5> was also discussed.     

Reversible P(III)/P(V) Redox: Catalytic Aza‐Wittig Reaction for the Synthesis of 4(3H)‐Quinazolinones and the Natural Product Vasicinone

The catalytic aza‐Wittig reaction based on a phosphine/phosphine oxide catalytic cycle is reported. The by‐product triphenylphosphine oxide (Ph₃PO) was reduced in situ to triphenylphosphine (Ph₃P) with good chemselectivity so that the aza‐Wittig reaction can be accomplished by using merely a catalytic amount of triphenylphosphine. The reaction has been demonstrated in an efficient synthesis of 4(3H)‐quinazolinones and the natural product (S)‐vasicinone in high yields, by using a catalytic amount of triphenylphosphine (5%) and the tetramethyldisiloxane/titanium tetraisopropoxide [TMDS/Ti(O‐i‐Pr)₄] reductant system (81–95% yields and >99% ee).

     

Bimolecular formation of radicals by hydrogen transfer. 14. The uncatalyzed Transfer Hydrogenation of α-Methylstyrene by 2,6-disubstituted 9,10-Dihydroanthracenes

2,6-Dimethoxy-( 4a ), 2,6-bis(dimethylamino)-( 4b ), 2,6-dichloro- ( 4c ) and 2,6-dimethoxycarbonyl-9,10-dihydroanthracene ( 4d ) were prepared by conventional methods and used as hydrogen transfer donors to α-methylstyrene ( 5 ) between 290-350 °C. The mechanism followed second order kinetics and the rate constants were only slightly influenced by the solvent polarity and the type of substituents introduced. The activation parameters are also closely similar in the series with ΔS^≠ values between −21 and −28 cal/mol K. These results, together with the observation of a large isotope effect (k_H/k_D = 1.4–2.0 at 310–350 °C), suggest that the mechanism involves a primary kinetic H-atom-transfer from the donors to α-methylstyrene ( 5 ) in the rate determining step. The compounds 4a – 4d constitute a new probe for investigating polar effects on H-transfer reactions.     

Synthese und Reaktivität von tert-Butyl-(2-aryl-3-methyl-but-2-yl)-peroxiden

Synthesis and Reactivity of tert-Butyl-(2-aryl-3-methyl-but-2-yl) Peroxides tert-Butyl-(2-aryl-3-methyl-but-2-yl) peroxides (2a–d) were prepared from t-BuOOH and corresponding 2-aryl-methyl-butan-2-ols (1a–d) (Ar:p-MeO C₆H₄ (a) ; Ph (b) ; p-Cl C₆H₄ (c) ; m-CF₃ C₆H₄ (d) ) and characterized by NMR, MS and elemental analysis. Kinetic data for the thermolysis of 2a–d in cumene as the solvent were determined at 110–140 °C and the products analyzed. The rate constants satisfy the Hammett equation with σ giving a ρ-value of −0.73. Oxidation of 2a–d at 80 °C gives the corresponding acetophenones 4 , epoxides 6 and hydroperoxides 8 . The products of the oxidation of 2a–2d were analysed after reduction of the reaction mixtures with LiAlH₄. Relative reactivities of the tertiary C H bonds of peroxides 2 were determined by competitive oxidations. They amount to 0.115–0.275 (with respect to the tertiary C H bond of cumene)     

Phosphine‐Catalyzed Asymmetric Formal [4+2] Tandem Cyclization of Activated Dienes with Isatylidenemalononitriles: Enantioselective Synthesis of Multistereogenic Spirocyclic Oxindoles

The first highly enantioselective formal [4+2] tandem cyclizations between isatylidenemalononitriles and activated dienes catalyzed by bifunctional chiral phosphine catalysts have been developed, yielding multistereogenic spirocyclic oxindoles in high yields and excellent optical purity. This reaction is accomplished via a tandem Rauhut–Currier/Michael/Rauhut–Currier reaction sequence.

     

Evaluation of EVA–PVAc blend behavior by 1‐D and 2‐D solid‐state NMR

Ethylene‐co‐vinyl acetate and poly(vinyl acetate) blends were prepared in different proportions by melting in a HAAKE Rheomix mixer. The blends were prepared at a fixed temperature, rotation rate, and processing time. High‐resolution solid‐state nuclear magnetic resonance was chosen to characterize the blends with respect to structure–mobility–compatibility employing magic angle spinning with cross polarization and high‐power hydrogen decoupling and the measurements of the proton spin–lattice relaxation time in the rotating frame (Tρ). The miscibility between polymer chains was also studied by two‐dimensional ¹H–¹³C shift correlation (HETCOR). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 221–226, 1999     

Konformation und Rotationsbarrieren substituierter Glyoxylsäureamide

Conformation and Rotation Barriers of Substituted Glyoxylic Acid Amides Semiempirical calculations predict an orthogonal orientation of the carbonyl groups in tertiary glyoxylic acid amides, which is in good agreement with an X-ray structure analysis of 5 . Due to the influence of the α-carbonyl group, the rotation barrier in the substituted glyoxylic acid amides 2a–d, 3a, 3b , and 4–6 (ΔG^#_c = 84–92 kJ mol⁻¹) is about 10 kJ/mol higher than in simple acid amides, as was found by dynamic NMR line shape analysis.     

Preparation of cis‐1,4‐Polyisoprene Electrospun Microfibers

cis‐1,4‐Polyisoprene, a significant industrial elastomer, is electrospun into different nanostrucutures. Cis‐1,4‐polyisoprene electrospun fibers are prepared from cis‐1,4‐polyisoprene solutions in dichloromethane or chloroform and characterized by environmental scanning electron microscope and Fourier‐transform infrared spectroscopy. ESEM observation reveals that the cis‐1,4‐polyisoprene fibers show a bamboo‐like morphology with a nearly constant node distance, a diameter of 20–60 µm and a length of about 300 µm. In addition, within the individual nodes parallel grooves are clearly seen, which is very promising for their use in microprinting in the field of microelectronics. Smooth cis‐1,4‐polyisoprene fibers with a diameter of 5–8 µm can be obtained via electrospinning its chloroform solutions. In contrast to most polymers, the jet of cis‐1,4‐polyisoprene does not split during the electrospinning processes, which facilitates the collection of highly aligned fibers by using a rotating mandrel as a ground target.