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1.
2.
The nucleophilic addition of lithiated allylphenylsulfone to nitrones at −80 °C proceeds exclusively α to the phenylsulfonyl group affording anti adducts in high yield. At 0 °C isoxazolidines are obtained with complete all-trans selectivity. The formation of these compounds involves isomerization of the allylsulphonyl moiety to give a transient vinylsulfone that then undergoes a subsequent intramolecular Michael addition. The addition to several nitrones has been studied and theoretical calculations have been refined to accurately explain the selectivity of the allylation reaction. 相似文献
3.
Pedro Merino Julia RevueltaTomas Tejero Ugo ChiacchioAntonio Rescifina Giovanni Romeo 《Tetrahedron》2003,59(20):3581-3592
In the 1,3-dipolar cycloaddition of glyoxylic nitrones with electron-poor and electron-rich alkenes, the configurational instability of the nitrone leads to parallel models when regio- and stereoselectivities are rationalized. The energetics of the cycloaddition reactions have been investigated through molecular orbital calculations at the B3LYP/6-31-G(d) theory level. By studying different reaction channels and reagent conformations, leading to a total of sixteen transition structures for each dipolarophile, the regio- and stereochemical preferences of the reaction are discussed. 相似文献
4.
Nitrones 1 undergo addition of vinyl organomagnesium bromide to give the allyl hydroxylamines 3 which are easily reduced to the corresponding N-benzyl allyl amines 2. 相似文献
5.
Robert Lassfolk Manuel Pedrón Prof. Tomás Tejero Prof. Pedro Merino Johan Wärnå Prof. Reko Leino 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(34):e202200499
Acyl group migration affects the synthesis, isolation, manipulation and purification of all acylated organic compounds containing free hydroxyl groups, in particular carbohydrates. While several isolated studies on the migration phenomenon in different buffers have been reported, comprehensive insights into the overall migration process in different monosaccharides under similar conditions have been lacking. Here, we have studied the acyl migration in different monosaccharides using five different acyl groups by a combination of experimental, kinetic and theoretical tools. The results show that the anomeric configuration in the monosaccharide has a major influence on the migration rate, together with the relative configurations of the other hydroxyl groups and the nature of the migrating acyl group. Full mechanistic model, based on computations, demonstrates that the acyl migration proceeds through an anionic stepwise mechanism with linear dependence on the [OH−] and the pKa of the hydroxyl group toward which the acyl group is migrating. 相似文献
6.
Evidence of a liquid-liquid equilibrium in simple fluids has recently been exposed for a density-dependent pair potential in the framework of a van der Waals theory. Here this double criticality is investigated by means of computer simulation, a perturbation theory, and integral equation theory. It is found that the critical point estimated from the integral equation thermodynamics is not associated with divergent correlations. To cope with these features, a special simulation procedure, based on the definition of local densities, is devised. Monte Carlo calculations confirm the existence of two critical points, in agreement with the predictions of perturbation theory. 相似文献
7.
Javier Garín Enrique Melndez Francisco L. Merchn Pedro Merino Jesús Orduna Toms Tejero 《Journal of heterocyclic chemistry》1990,27(5):1345-1349
The title compounds 3 were synthesized in one step from bisdithiocarbamates 2 , and their structures were confirmed by two independent syntheses. Alkylation and hydrolysis of 3 gives 3,3′-arylenebis(2,4-dioxo-1,2,3,4-tetrahydroquinazolines) 8 . 相似文献
8.
The nucleophilic addition of both silyl ketene acetals and lithium enolates derived from methyl acetate to chiral non-racemic N-(benzyloxyethyl)nitrones has been studied both experimentally and theoretically. Aromatic nitrones showed lower reactivity that aliphatic nitrones and the addition of the silyl ketene acetal led to lower selectivities than the addition of the corresponding lithium enolate. Whereas low selectivity was obtained for the addition of the silyl ketene acetal, only one diastereomer could be detected in all cases for the addition of lithium enolate to aliphatic nitrones. The synthetic utility of the two chiral auxiliaries employed lies in the preparation of enantiomeric compounds. DFT theoretical calculations confirmed the stepwise mechanism for the addition of silyl ketene acetals to nitrones and are in good agreement with the observed experimental results. 相似文献
9.
Tejero EM Amatucci WE Ganguli G Cothran CD Crabtree C Thomas E 《Physical review letters》2011,106(18):185001
Laboratory observations of electromagnetic ion-cyclotron waves generated by a localized transverse dc electric field are reported. Experiments indicate that these waves result from a strong E×B flow inhomogeneity in a mildly collisional plasma with subcritical magnetic field-aligned current. The wave amplitude scales with the magnitude of the applied radial dc electric field. The electromagnetic signatures become stronger with increasing plasma β, and the radial extent of the power is larger than that of the electrostatic counterpart. Near-Earth space weather implications of the results are discussed. 相似文献
10.
C. F. Tejero 《Journal of statistical physics》1987,48(3-4):531-538
We present a new method for the study of a one-dimensional inhomogeneous Ising chain with nonconstant nearest neighbor interactions. The external field required to produce a given magnetization profile is derived exactly. Some properties of the pair direct correlation function are derived. Our findings generalize previous results of Percus. 相似文献