Regio- and stereoselective (3 + 2)-cycloaddition reactions of nitrones with cyclic allenes

An effective approach to access functionalized 2H-cyclonona(deca)[d]isoxazoles and 15-oxo-3,10-methanobenzo[b][1]azacyclododecines has been developed by the reaction of N-aryl-C,C-bis(methoxycarbonyl)nitrones with cyclonona(deca)-1,2-dienes in a one-pot fashion. The reaction of N-aryl-C-(phenylcarbamoyl)nitrones with these allenes proceeds strictly regioselectively giving the mixtures of diastereomeric isoxazolidines containing a double bond at the C⁴-position of the isoxazolidine ring. The quantum chemical calculations show that the regioselectivity of these reactions is in good agreement with the reactivity indices of the considered compounds.

Selective and reversible 1,3-dipolar cycloaddition of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones under microwave irradiation

The first example of the cycloaddition of in situ-generated azomethine imine under microwave conditions is described. The reaction of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones proceeds regio- and stereoselectively giving mostly good yields of the corresponding perhydropyrazolopyrazoles. The products of the reaction undergo cycloreversion under the reaction conditions.

The Forest Observation System, building a global reference dataset for remote sensing of forest biomass

Forest biomass is an essential indicator for monitoring the Earth's ecosystems and climate. It is a critical input to greenhouse gas accounting, estimation of carbon losses and forest degradation, assessment of renewable energy potential, and for developing climate change mitigation policies such as REDD+, among others. Wall-to-wall mapping of aboveground biomass (AGB) is now possible with satellite remote sensing (RS). However, RS methods require extant, up-to-date, reliable, representative and comparable in situ data for calibration and validation. Here, we present the Forest Observation System (FOS) initiative, an international cooperation to establish and maintain a global in situ forest biomass database. AGB and canopy height estimates with their associated uncertainties are derived at a 0.25 ha scale from field measurements made in permanent research plots across the world's forests. All plot estimates are geolocated and have a size that allows for direct comparison with many RS measurements. The FOS offers the potential to improve the accuracy of RS-based biomass products while developing new synergies between the RS and ground-based ecosystem research communities.

Cyclization of ortho-ethynylbiaryls as an emerging versatile tool for the construction of polycyclic arenes

Cyclization and cycloisomerization of ortho-aryl(ethynyl)arenes provide an easy direct access to fused polycyclic aromatic carbo- and heterocycles. This methodology has demonstrated an impressive progress in the recent years. The goal of this review is to give a comprehensive outlook on the synthetic potential, scope, limitations, and mechanistic aspects of the cyclization reactions. The material is arranged according to the activation method that can be used to induce cyclization: pyrolysis, metal catalysis, electrophilic activation, radical induction, base catalysis. Particular attention is paid to the specificity of ortho-ethynylbiaryls with a heterocyclic central core.

The bibliography includes 257 references.

Thiazol-4-one derivatives from the reaction of monosubstituted thioureas with maleimides: structures and factors determining the selectivity and tautomeric equilibrium in solution

2-(Alkyl(aryl)amino)thiazol-4(5H)-ones can regioselectively be prepared from monoalkyl(aryl)thioureas and maleimides. In solution, the former heterocycles exist in a tautomeric equilibrium with 2-(alkyl(aryl)imino)thiazolidin-4-ones and the substituent on the exocyclic nitrogen atom governs the ratio of these tautomers. Isomers with the alkyl group in the endocyclic position can be obtained from N-methyl(ethyl)thioureas. 2D NMR spectroscopy and DFT calculations rationalize experimental results.

Regioselective Synthesis of 7-(Trimethylsilylethynyl)pyrazolo[1,5-a]pyrimidines via Reaction of Pyrazolamines with Enynones

Condensation of enynones readily available from cheap starting material with pyrazolamines provides easy access to fluorescent 7-(trimethylsilylethynyl)pyrazolo[1,5-a]pyrimidines. The reaction is straightforward, does not require the use of any additional reagents or catalysts, and can be performed without inert atmosphere. Various substituents and functional groups in both enynone and pyrazolamine are tolerated. The presented method features full regioselectivity, high isolated yields, and simplicity of both setup and product purification. Fluorescent properties of the obtained pyrazolopyrimidines were studied.

Synthesis of di-, tri- and tetracyclopropylhydrazines

Previously unknown 1,1-dicyclopropylhydrazine was obtained in two steps starting from dicyclopropylamine. It serves as a convenient starting material to tri- and tetracyclopropylhydrazines, which have not been described in the literature either. Tricyclopropylhydrazine was prepared in an overall four-step sequence featuring the de Meijere-Chaplinski modification of the Kulinkovich reaction as a key step. Tetracyclopropylhydrazine was obtained by the reductive amination of the cyclopropanone ethyl trimethylsilyl acetal with 1,1-dicyclopropylhydrazine or with the parent hydrazine. Synthetic utility of these cyclopropylhydrazine building blocks is presented as well.

Synthesis of thiazolidines via regioselective addition of unsymmetric thioureas to maleic acid derivatives

The regioselectivity of the reaction between unsymmetric thioureas and maleic acid derivatives has been studied, and general regularities have been established.

Chromatographic enantioseparation of amino acids using a new chiral stationary phase based on a macrocyclic glycopeptide antibiotic

The separation of the enantiomers of several a-amino acids was studied on a new chiral stationary phase (CSP) which is based on the macrocyclic glycopeptide antibiotic eremomycin attached to silica particles. Retention and separation factors were determined under analytical conditions at ambient temperature for different mobile phase compositions. In order to evaluate the potential with respect to preparative separations the adsorption isotherms of D- and L-methionine were determined for one mobile phase composition applying the elution by characteristic point method. The isotherms were validated by comparing experimentally determined elution profiles with predictions based on the equilibrium dispersive model. Finally, the performance of the eremomycin CSP was compared with a commercially available CSP based on the macrocyclic antibiotic teicoplanin. After determining the isotherms of D- and L-methionine also for the teicoplanin phase, the equilibrium dispersive model was used for both CSP to identify optimal operating conditions. For the separation and conditions considered the new eremomycin CSP revealed a better performance compared to the teicoplanin CSP.

Application of an eremomycin-chiral stationary phase for the separation of DL-methionine using simulated moving bed technology

Recently a new chiral stationary phase (CSP) was introduced, based on the immobilization of the macrocyclic glycopeptide eremomycin to epoxy-activated silica. The application of this new CSP to preparative enantioseparation using simulated moving bed (SMB) chromatography will be presented. MeOH-H(2)O (0.1M NaH(2)PO(4))=20/80 (v/v) was used as the mobile phase to separate the enantiomers of methionine. Successful separation was realized providing productivities around 15 g(product)/l(stat)/h for both l and d-methionine under nonlinear conditions. In such delicate continuous chromatographic separation processes, besides productivity, the long-term stability of the applied stationary phases is of importance. Column to column fluctuations were negligible and long-term stability of the preparative stationary phase was satisfactory according to the results of perturbation experiments performed before and after long-term SMB runs.

[Sorbents with immobilized glycopeptide antibiotics for separating optical isomers by high-performance liquid chromatography]

Chiral sorbents for HPLC separation of optical isomers carrying glycopeptide antibiotics (eremomycin or its eremosaminyl aglycon, ristomycin, or vancomycin) fixed onto the surface of silica gel have been synthesized. The patterns of the retention and separation of profen isomers and their dependence on the nature of the chiral selector and the eluant composition have been studied. The sorbents were shown to be highly enantiospecific in separating the isomers of alpha-amino-, alpha-hydroxy-, and alpha-methylphenylcarboxylic acids (profens).

New chiral stationary phase with macrocyclic glycopeptide antibiotic eremomycin chemically bonded to silica

A new chiral stationary phase (CSP) was prepared by attachment of macrocyclic glycopeptide antibiotic eremomycin to the epoxy-activated silica under mild conditions. In contrast to CSP with immobilized vancomycin, which is a close structural analogue of eremomycin, the prepared CSP reveals high enantioselectivity for separation of amino acids enantiomers. It was demonstrated by the example of ristocetin A CSP that method of the immobilization of macrocyclic glycopeptide antibiotics affects remarkably the resulting enantioselectivity.

Preparation and Reactivity of [D3d]-Octahedrane: The Most Stable (CH)12 Hydrocarbon

The synthesis of the (CH)12 hydrocarbon [D(3d)]-octahedrane (heptacyclo[6.4.0.0(2,4).0(3,7).0(5,12).0(6,10).0(9,11)]dodecane) 1 and its selective functionalization retaining the hydrocarbon cage is described. The B3LYP/6-311+G* strain energy of 1 is 83.7 kcal mol(-1) (4.7 kcal mol(-1) per C-C bond) which is significantly higher than that of the structurally related (CH)16 [D(4d)]-decahedrane 2 (75.4 kcal mol(-1); 3.1 kcal mol(-1) per C-C bond) and (CH)20 [I(h)]-dodecahedrane 3 (51.5 kcal mol(-1); 1.7 kcal mol(-1) per C-C bond); the heats of formation for 1-3 computed according to homodesmotic equations are 52, 35, and 4 kcal mol(-1). Catalytic hydrogenation of 1 leads to consecutive opening of the two cyclopropane rings to give C2-bisseco-octahedrane (pentacyclo[6.4.0.0(2,6).0(3,11).0(4,9)]dodecane) 16 as the major product. Although 1 is highly strained, its carbon skeleton is kinetically quite stable: Upon heating, 1 does not decompose until above 180 degrees C. The B3LYP/6-31G* barriers for the S(R)2 attack of the tBuO. and Br3C. radicals on a carbon atom of one of the cyclopropane fragments (Delta(298) = 27-28 kcal mol(-1)) are higher than those for hydrogen atom abstraction. The latter barriers are virtually identical for the abstraction from the C1-H and C2-H positions with the tBuO. radical (DeltaG(298) = 17.4 and 17.9 kcal mol(-1), respectively), but significantly different for the reaction at these positions with the Br3C. radical (DeltaG(298) = 18.8 and 21.0 kcal mol(-1)). These computational results agree well with experiments, in which the chlorination of 1 with tert-butyl hypochlorite gave a mixture of 1- and 2-chlorooctahedranes (ratio 3:2). The bromination with carbon tetrabromide under phase-transfer catalytic (PTC) conditions (nBu4NBr/NaOH) selectively gave 1-bromooctahedrane in 43 % isolated yield. For comparison, the PTC bromination was also applied to 2,4-dehydroadamantane yielding 54 % 7-bromo-2,4-dehydroadamantane.

[The subcortical neuronal correlates of human assessment actions]

In patients with parkinsonism to whom in accordance with medical-diagnostic indices electrodes were implanted into the nuclei of thalamus and striopallidal system, impulse activity of neurones was recorded in tests with presentation of visual and acoustic stimuli. It has been shown that neurones of these structures, reacting by a change of discharges frequency in carrying out the assessing actions by man constitute a special class of neurones, spatially separated from those, connected with the organization of motor acts. The typical feature of neuronal reactions is a high degree of their value dependence on the level of attention. Neurones of the above structures reacts also during preparation of the assessing actions and fixation of their results in the short-term memory.