1,5-Stereocontrol in tin(IV) halide mediated reactions between N- and S-substituted pent-2-enylstannanes and aldehydes or imines

Following transmetalation of (4S)-4-(dibenzylamino)pent-2-enyl(tributyl)stannane with tin(IV) bromide, reactions of the resulting allyltin tribromide with aldehydes gave (3Z)-1,5-syn-5-(dibenzylamino)hex-3-en-1-ols with excellent, ca. 98:2, stereocontrol. (4R)-5-Benzylthio-4-methylpent-2-enyl(tributyl)stannane similarly reacted with aldehydes to give (3Z)-1,5-anti-6-benzylthio-5-methylhex-3-en-1-ols with 87:13 stereocontrol. Although the analogous reaction of (4R)-4-benzylthiopent-2-enyl(tributyl)stannane with benzaldehyde proceeded with some stereoselectivity, 80–90:20–10, in favour of the (3Z)-1,5-syn-diastereoisomer, the yield was low due to a competing Lewis acid catalysed 1,4-elimination. N-Acylamino- and S-acylthio-pent-2-enylstannanes reacted with aldehydes with variable syn/anti-stereoselectivities. Tin(IV) chloride promoted reactions of the 4-(dibenzylamino)pent-2-enylstannane with 1-alkoxycarbonylimines gave (E)-alk-4-enoates with a modest preference for the 2,6-anti-products, 2,6-anti/2,6-syn=75:25.     

Vertical excitation as a transient phenomenon

For a particular model with two electronic states, each with two vibrations, the dipole correlation function governing electronic absorption is e ^?iωOt cosγt with spectrum ω ₀±γ. The function starts as e ^?iωOt (γ?ω ₀), with Fourier transform peaking around ω ₀ instead of ω ₀±γ, and this is associated with vertical excitation. After a time t～2/γ the spectrum goes over into the normal one. As a generalization, a procedure is outlined for characterizing the state reached first after interaction with light is initiated. Finally it is suggested that one can understand aspects of internal conversion by analogy with the case of vertical excitation.     

Synthesis of 2-methyl-N-(2,2,2-trichloroethylidene)- and 2-methyl-N-(2,2,2-trichloroethyl)benzenesulfonamides from N,N-dichloro-2-methylbenzenesulfonamide and trichloroethylene

The reaction of N,N-dichloro-2-methylbenzenesulfonamide with trichloroethylene gave a new representative of highly electrophilic N-sulfonyl polyhaloaldehyde imines, 2-methyl-N-(2,2,2-trichloroethylidene) benzenesulfonamide. High reactivity of the product was demonstrated in the addition of water and 2-methylbenzenesulfonamide and reactions with benzene, toluene, anisole, thiophene, and 2-chlorothiophene. N,N-Dichlorobenzenesulfonamides and N,N-dichlorotrifluoromethanesulfonamide failed to react with 1,1,3,3,4,4-hexachlorobut-1-ene and 1,1,2,3,4-pentachlorobuta-1,3-diene under the conditions ensuring formation of N-(2,2,2-trichloroethylidene)arenesulfonamides from N,N-dichloroarenesulfonamides and trichloroethylene.     

Über die Si3-N-bindung: XXXV. Darstellung von N-β-halogenäthyl-N,N-bis(trimethylsilyl)aminen

N-β-Haloethyl-N,N-bis(trimethylsilyl)amines, which can be used for the introduction of aminoethyl groups into organic or organosilicon compounds, are prepared in good yields from N-trimethylsilylaziridine and trimethylhalosilanes. This reaction is spontaneous with trimethylbromo- and -iodosilane, whereas it is necessary to run the reactions with trimethylchlorosilane in the presence of dipolar aprotic solvents and at higher temperatures.N-β-Bromoethyl-N,N-bis(trimethylsilyl)amine (II) is also obtained by silylation of N-β-bromoethylamine hydrobromide with trimethylsilyldiethylamine or with N-trimethylsilyl-N-methyl acetamide. Furthermore N-β-iodoethyl-N,N- bis(trimethylsilyl)amine is prepared by the reaction of II with MgI₂ or of aziridine and N-trimethylsilylaziridine respectively, with trimethylchlorosilane and MgI₂.From the silylation of N-β-bromoethylamine hydrobromide with trimethylsilyldiethylamine N,N-bis(trimethylsilyl)-N′,N′-diethylethylenediamine is isolated as a side product or, at higher temperatures, as the main product.     

Elastic behavior of non-Gaussian polymethylene chains

In this paper, elastic behaviors of non-Gaussian polymethylene (PM) chains with chain length N=100 are investigated by rotational isomeric state model. Here the tetrahedral lattice of PM chain and the non-local interaction of Sutherland potential are adopted. In the metropolis movement of PM chain, a four-bond movement model is used. The average energy and average Helmholtz free energy with various elongation ratios λ are calculated by Monte Carlo simulation method. The average energy increases with elongation ratio λ and the average Helmholtz free energy decreases with elongation ratio λ. The elastic force f and the energy contribution to elastic force f_u can be obtained from f=∂〈A〉/∂r and f=∂〈U〉/∂r. We find that the elastic force f increases with elongation ratio λ and the energy contribution f_u decreases with elongation ratio λ, and f_u is less than zero. The ratio f_u/f is close to −0.21 for λ?1.25, and −0.04 to −0.35 for λ>1.25 at T=364 K. In our calculation, the rubber elasticity may be discussed in terms of the chemical structure of polymer chains.     

Trans-selective γ-arylation of macrocyclic N-picolinoylcycloalkylamines through palladium-catalyzed methylene sp3 carbon–hydrogen bond activation

While numerous stereoselective methylene β- and γ-carbon–hydrogen activation reactions are reported, there are no examples of trans-selective γ-carbon–hydrogen activation of cyclic compounds. Herein I report the first trans-selective palladium-catalyzed γ-arylation of N-picolinoylcycloalkylamine with aryl iodides. Trans-arylation of macrocyclic N-picolinoylcyclododecylamine proceeded to give trans-3-aryl-N-picolinoylcyclododecylamine as a sole mono-arylated product in up to 85% yield. Other, larger substrates were also applicable to trans-arylation, albeit with lower efficiency. The picolinoyl group of the trans-arylated product was easily removed with zinc and diluted hydrochloric acid.     

Synergistic Effect of Lithocholic Acid with Gentamicin against Gram-Positive Bacteria but Not against Gram-Negative Bacteria

Listeria monocytogenes (L. monocytogenes) is an important Gram-positive food-borne pathogen that severely threatens public health. A checkerboard microdilution method was performed to evaluate the synergistic effect of lithocholic acid (LCA) with Gentamicin (Genta) against L. monocytogenes. BacLight LIVE/DEAD staining, scanning electron microscopy and biofilm inhibition assays were further used to explore the bactericidal effect and antibiofilm effect of this combination on L. monocytogenes. Additionally, the synergistic effects of LCA derivatives with Genta were also evaluated against L. monocytogenes, S. aureus and S. suis. The results indicated that a synergistic bactericidal effect was observed for the combined therapy of LCA at the concentration without affecting bacteria viability, with Genta. Additionally, LCA in combination with Genta had a synergistic effect against Gram-positive bacteria (L. monocytogenes, S. aureus and S. suis) but not against Gram-negative bacteria (E. coli, A. baumannii and Salmonella). BacLight LIVE/DEAD staining and scanning electron microscopy analysis revealed that the combination of LCA with Genta caused L. monocytogenes membrane injury, leading to bacteria death. We found that 8 μg/mL LCA treatment effectively improved the ability of Genta to eradicate L. monocytogenes biofilms. In addition, we found that chenodeoxycholic acid, as a cholic acid derivative, also improved the bactericidal effect of Genta against Gram-positive bacteria. Our results indicate that LCA represents a broad-spectrum adjuvant with Genta for infection caused by L. monocytogenes and other Gram-positive pathogens.     

Crystal structure and magnetic structure of TbOOH

The monoclinic modification of terbium oxide hydroxide, TbOOH, was prepared using hydrothermal technique. The crystal structure was investigated by three-dimensional single-crystal X-ray analysis and was refined to a conventional R-value of 8.1%. The space group is $\text{P2}{}_1\text{m}$, No. 11, with a = 6.04 Å, b = 3.69 Å, c = 4.33 Å, and β = 109.0°. The terbium atom is seven coordinated with oxygen atoms, and the structure is not hydrogen bonded.The compound is antiferromagnetic with a Néel temperature of 10°K. Neutron diffraction powder patterns were measured at 300°K and 4.2°K. The magnetic super lattice reflections were indexed on the basis of a monoclinic unit cell with the dimensions a_M = 2a, b_M = b, c_M = c, and β_M = β, where a, b, c, and β are the dimensions of the chemical unit cell. The structure contains two independent magnetic atoms. A nonclinear antiferromagnetic arrangement of the spins describes the magnetic structure. The spin at one atom has an angle of 43° with the ac plane and the projection of the spin on the ac plane has an angle of 59° with the a axis. The spin on the other atom has an angle of ?43° with the ac plane, the projection having the same angle of 59° with the a axis.     

Enhanced Oxytetracycline Production by Streptomyces rimosus in Submerged Co-Cultures with Streptomyces noursei

In the present study, Streptomyces rimosus was confronted with Streptomyces noursei, Penicillium rubens, Aspergillus niger, Chaetomium globosum, or Mucor racemosus in two-species submerged co-cultures in shake flasks with the goal of evaluating the oxytetracycline production and morphological development. The co-culture of S. rimosus with S. noursei exhibited stimulation in oxytetracycline biosynthesis compared with the S. rimosus monoculture, whereas the presence of M. racemosus resulted in a delay in antibiotic production. Different strategies of initiating the “S. rimosus + S. noursei” co-cultures were tested. The improvement in terms of oxytetracycline titers was recorded in the cases where S. noursei was co-inoculated with S. rimosus in the form of spores. As the observed morphological changes were not unique to the co-culture involving S. noursei, there was no evidence that the improvement of oxytetracycline levels could be attributed mainly to morphology-related characteristics.     

Ultrasonic speed in compressed liquid by a sing-around method

A new apparatus for the measurement of ultrasonic speed in compressed liquid was constructed. The reliability of this instrument was confirmed by measuring the speeds in pure benzene in the ranges from 283.15 to 323.15 K and pressures up to near freezing pressure, and by comparing the results with literature values. The isentropic compressibilities κ_S were also determined using the experimental speeds and densities, and the results κ_S(u) were compared with those observed directly elsewhere κ_S(d) and those calculated thermodynamically κ_S(c) from (p, V_m, T). At atmospheric pressure, the present results, while agreeing with κ_S(u) reported in the literature, show differences from κ_S(d) and κ_S(c), while those for higher pressures close on a simple curve with κ_S(c).     

Alkylation and aldol reactions of acyl derivatives of N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine: asymmetric synthesis of α-alkoxy-, α-substituted-β-alkoxy- and α,β-dialkoxyaldehydes

Treatment of a range of O-protected glycolate derivatives of the chiral auxiliary N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine with KHMDS in the presence of 18-crown-6 followed by addition of an alkyl halide generates α-substituted derivatives with very high levels of diastereoselectivity. Alternatively, reaction of the potassium enolate of a propanoate or O-protected glycolate derivative of N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine with a range of aldehydes gives syn-aldol products with high levels of diastereoselectivity. These adducts may be reductively cleaved with LiAlH₄ to give enantiopure α-alkoxy-, α-substituted-β-alkoxy- and α,β-dialkoxyaldehydes in good yield.     

Chelating behavior of new chelating resins derived from n-(o-hydroxybenzyl)iminodiacetic acid

The chelating behavior of a new resin prepared by polycondensation of N-(o-hydroxybenzyl) iminodiacetic acid (o-HDA) with phenol and formaldehyde, is compared with that of the monomer, with p-HDA resin and p-HDA monomer, and with Chelex-100. The order of chelate stability for the o-HDA resin is Cu(II) > Ni(II) > Zn(II) > Co(II). An unusually high stability of the o-HDA and o-HDA resin iron(III) chelates in acidic solution is attributed to the participation of the o-hydroxyl group in the coordination process.     

Regio- and stereo-selectivities of the ortho and meta photocycloaddition reactions of ethylenes to benzene and its simple derivatives

The photoreactions of benzene, toluene, anisole, and benzonitrile with acrylonitrile, methacrylonitrile, and vinyl acetate, and of toluene and o- and p-xylene with maleic anhydride are described. The acrylonitriles do not react with benzonitrile but yield mixtures of ortho photocycloadducts with the other arenes. Contrary to previous findings both exo and endo stereoisomers of the ortho cycloadducts of benzene and acryloitrile are formed: the reaction is selective towards the exo isomer but the stereoisomers from methacrylonitrite and benzene are formed with approximately equal efficiencies. Complex mixtures of regio- and stereoisomers of the ortho cycloadducts are formed between toluene and the acrylonitriles but their addition to anisole is more selective and in acetonitrile essentially only 1,2-attack of the ethylene on the arene is observed. The 2:1 photoadducts of maleic anhydride with toluene and o- and p-xylene reflect formation of two regio ortho photocycloadducts in each case. The variation in the ratios of these isomers with temperature and light intensity is interpreted in terms of the differing photolabilities of the 1:1 adducts and their reactivities towards the thermal addition of the second molecule of maleic anhydride. Vinyl acetate undergoes 1,2-cycloaddition to benzonitrile but with the other arenes, meta cycloadducts are favoured. These latter additions are specifically 2,6- with respect to toluene and anisole but there is little regioselectivity with respect to the ethylene although the 7-endo acetate of the meta cycloadduct with benzene does constitute 60% of the reaction mixture.     

Michael addition of phenylacetonitrile to the acrylonitrile group leading to diphenylpentanedinitrile. Structural data and theoretical calculations

Knoevenagel condensation of phenylacetonitrile with 4-diphenylaminophenylacetonitrile in the presence of piperidine was carried out to obtain a novel conjugated compound. In addition to the expected compound 2-(phenyl)-3-(4-diphenylaminophenyl)acrylonitrile (I), the 3-((4-diphenylamino)phenyl)-2,4-diphenylpentanedinitrile (II) was also obtained with a good yield. Compound II was obtained as a result of the Michael addition of phenylacetonitrile with 2-(phenyl)-3-(4-diphenylaminophenyl)acrylonitrile (I). Conversely, when the same reaction was performed in the presence of KOH as catalyst, only the α,β-unsaturated nitrile (I) was afforded with a 92 % yield. The structures were confirmed with IR, EI-MS and NMR spectroscopy. Single crystals I and II were formed and their structures were determined by X-ray single-crystal diffraction analysis. Crystal I belongs to the monoclinic system with space group P2₁/n having unit cell parameters of a = 16.8589(5) Å, b = 6.68223(17) Å, c = 19.8289(7) Å, β = 111.133(4)○ and Z = 4. Crystal II belongs to the same monoclinic system with space group P2₁/c, having unit cell parameters of a = 10.8597(4) Å, b = 24.7533(10) Å, c = 9.7832(4) Å, β = 91.297(3)○ and Z = 4. In addition to the structural data analysis, some theoretical calculations that reveal the nature of relevant structure-property relationships are also reported.     

Reactivity of 1-phenylsulfinyl-2-phenylsulfanylethylene (SOSE) with O-nucleophiles generated by potassium tert-butoxide

E-1-Phenylsulfinyl-2-phenylsulfanylethylene (E-SOSE) reacts with O-nucleophiles generated by means of t-BuOK via an addition-elimination mechanism, thus affording the product of substitution of the phenylsulfanyl group in a stereo-conservative process. When used alone, the strongly basic and hindered tert-butoxide brings about elimination of either the phenylthiolate or phenylsulfinate groups. Z-SOSE is much more prone to elimination: either with t-BuOK alone or with other O-nucleophiles generated by t-BuOK, it always leads to products derived from elimination. Other alkaline tert-butoxides or other bases appear not as effective in generating species nucleophilic enough to react with E-SOSE.     

Direct N- and C-alkenylation of nitrogen-containing heterocycles with magnesium alkylidene carbenoids

Treatment of magnesium alkylidene carbenoids, which were generated from 1-chlorovinyl p-tolyl sulfoxides with isopropylmagnesium chloride at −78 °C in toluene, with N-lithio nitrogen-containing heterocycles gave N-alkenylated products in moderate to good yields. Also, the reaction of C-lithio indoles, which were generated from N-protected indoles, with magnesium alkylidene carbenoids gave C-2 or C-3 alkenylated products, corresponding to the protective group. The intermediate of these reactions were found to be the alkenyl anion, which could be trapped with electrophiles to give the heterocycles having fully substituted alkenes.     

Asymmetric synthesis of α-mercapto-β-amino acid derivatives: application to the synthesis of polysubstituted thiomorpholines

Tandem conjugate addition of homochiral lithium N-benzyl-N-(α-methyl-p-methoxybenzyl)amide to tert-butyl cinnamate and enolate trapping with TsS^tBu proceeds with high diastereoselectivity to give a homochiral anti-α-tert-butylthio-β-amino ester. Stepwise deprotection gives the corresponding free α-tert-butylthio-β-amino acid without epimerisation. Tandem conjugate addition of homochiral lithium N-allyl-N-(α-methylbenzyl)amide to tert-butyl cinnamate and enolate trapping with TsS^tBu followed by conversion of the S-tert-butyl group to a disulphide, and reduction with Lalancette’s reagent generates polysubstituted thiomorpholine derivatives.     

Asymmetric ortho-lithiation of 1,n-dioxa[n]paracyclophane derivatives for the generation of planar chirality

The asymmetric induction of planar chirality in 1,n-dioxa[n]paracyclophane derivatives via asymmetric ortho-lithiation is described. Enantioselective ortho-lithiation of unflippable 1,n-dioxa[n]paracyclophanes (n≤11) using sec-BuLi-(?)-sparteine at ?78 °C and subsequent treatment with electrophiles gave the corresponding planar-chiral monosubstituted paracyclophanes with excellent ee. Further lithiation of these compounds and treatment with electrophiles gave planar-chiral paracyclophanes with two different substituents. Dilithiation of unflippable 1,n-dioxa[n]paracyclophanes gave the corresponding C₂-symmetrical disubstituted products with almost perfect ee. In the case of flippable 1,n-dioxa[n]paracyclophanes (n≥12), a stepwise reaction was required for the highly enantioselective formation of disubstituted products.     

Highly stereoselective anti-aldol reactions catalyzed by simple chiral diamines and their unique application in configuration switch of aldol products

Chiral derivatives of trans-1,2-diaminocyclohexane with different N,N-dialkyl groups in well-defined orientations have been synthesized, and applied as catalysts for the asymmetric aldol reaction between a variety of aldehydes and ketones. Enantiomeric catalyst 1j catalyzed the reaction in ethanol and provided excellent diastereoselectivity and enantioselectivity. Significantly, simple replacement of organic solvents with water switched the products of the aldol reactions from anti to syn configuration. Such catalytic reactions led to the products with anti to syn diastereoselectivity up to 99:1 in ethanol, while in water gave the products with syn to anti diastereoselectivity up to 99:1.     

State-selected molecular-beam reaction dynamics of K with HF (υ = 1, j = 5, 6 and 7)

The crossed-molecular-beam method has been used to measure relative integral cross sections σ_r (υ = 1, j; E) of the endothermic (0.75 eV) reaction K + HF (υ = 1, j) → KF + H as a function of both the rotational quantum number j (j = 5, 6 and 7) and the translational energy E (0.55 ? E ? 1.32 eV) of the reagents. The vibrational-rotational (υ, j) states of HF were populated by infrared pumping with the radiation of a properly tuned pulsed chemical HF laser. In addition, relative cross sections with υ = 0 but averaged with respect to the initial rotational-state distribution of the HF molecules were also determined. The results exhibit three remarkable features: (a) σ_r (υ = 1, j; E) rises with increasing j, (b) the steepness of the ascent roughly decreases with increasing E, (c) at E = 0.98 eV reagent vibrational energy is about a factor of 200 more efficient in promoting the reaction than reagent translational energy. An intuitive dynamical model suggests that observations (a) and (b) are to be expected for a reaction governed by a potential-energy surface with a late barrier. This is consistent with the well-known interpretation of large vibrational effects as indicated by result (c).