A highly stereoselective synthesis of α,β-unsaturated oxazolines

Lithiated 2,4,4-trimethyl-2-oxazoline 2a and 2-chloromethyl-4,4-dimethyl-2-oxazoline 2b react smoothly with a number of nitrones 3 to produce α,β-unsaturated oxazolines 6 and 7 highly stereoselectively.     

BH3-promoted stereoselective β-lithiation of N-alkyl-2-phenylaziridines

BH(3) complexes of N-alkyl-2-phenylaziridines have been synthesized and their structure and stereochemistry proved with DFT calculations and NMR experiments. It has been demonstrated that the Lewis acid complexation is able to promote a regioselective β-lithiation in 2-phenylaziridino-borane complexes. The lithiated intermediates were configurationally stable, allowing an enantioselective preparation of cis-2,3-disubstituted aziridines.     

Stereospecific synthesis of optically active phenylpropylene oxides

The stereospecific lithiation of diastereomeric phenylpropylene oxides has been studied as well as the trapping reaction with electrophiles. The reduction of the cis-alpha-benzoylpropylene oxide to give prevalently the anti-epoxy alcohol has been investigated as well.     

The effect of CpG-ODN on antigen presenting cells of the foal

Background  

Cytosine-phosphate-guanosine oligodeoxynucleotide (CpG-ODN) has been used successfully to induce immune responses against viral and intracellular organisms in mammals. The main objective of this study was to test the effect of CpG-ODN on antigen presenting cells of young foals.     

Reaction of 1,2-bis(2,6-dicarboxypyridin-4-yl)ethyne and imidazole with Cu(II) generates a discrete complex not a coordination polymer: crystal structure of [μ-4,4′-(1,2-ethynediyl)-bis(pyridine-2,6-dicarboxylato)-N,O, O′-μ-N′, O′′, O′′′]-diaqua-bis(imidazole)-dicopper(II)

Reaction of 1,2-bis(2,6-dicarboxypyridin-4-yl)ethyne and imidazole with Cu(II) produces crystals containing a discrete complex of [μ-4,4′-(1,2-ethynediyl)-bis(pyridine-2,6-dicarboxylato)-N, O, O′-μ-N′, O′′, O′′′]-diaqua-bis(imidazole)-dicopper(II) complex (1), [(C₁₆H₄N₂O₈)(C₃H₄N₂)₂(H₂O)₂Cu₂] instead of a linear coordination polymer. The complex crystallizes in the monoclinic space group P2₁/n with a = 5.3763(8) ?, b = 18.522(3) ?, c = 11.4827(7) ?, β = 93.705(3) ° and Z = 2. The complex sits on a center of symmetry such that the two halves of the molecule are related by inversion symmetry. The molecules pack in layers in which the molecules are joined by intermolecular N–H⋯O hydrogen bonds between imidazole and carboxylate groups and O–H⋯O hydrogen bonds between carboxylate groups and water.     

Relationship between Molecular Properties and Conformation of Chiral Alkanes

Mixtures of the diastereomers of 2,2,3,5,6-pentamethylheptane were prepared in two ways, either starting with compounds of (3R)-configuration, or from compounds of (5R)-configuration. Comparison of the GC. and optical rotatory power of the fractions of these two mixtures permitted the unambiguous assignment of the absolute configuration and molar rotatory power to the various diastereomers ([M] = + 119.1° for the (3R, 5R)- and [M] = + 79.8° for the (3R, 5S)-diastereomer). The very high molar rotatory power which was expected on the basis of the conformational analysis carried out with a rotational-isomeric-3-states model is interpreted as arising from the molecular ‘conformational rigidity’, i.e. from the presence of only few conformers. Conformational properties of these compounds were computed using a new approach, which scans the whole space of each bond (2 π) in 5° steps and calculates the conformational energy based upon semiempirical potential functions. The conformational flexibility of each bond of the two diastereomers is evaluated in terms of the a priori probability density function of that bond. This allows us to analyze in detail how configurational differences affect conformational properties. The molar rotatory power of the two diastereomers as calculated with a new method recently developed in our group is in excellent agreement with experimental data. The molar rotatory power is analyzed in terms of the contribution of the single bonds.     

Stereoselective synthesis of pentacarbonyl(3-oxa-2-bicyclo[3.1.0]hexylidene)- and pentacarbonyl(cyclopropylmethoxymethylene)tungsten compounds on the route to cyclopropane-gamma-lactones and -carboxylates

The diastereoselective synthesis of pentacarbonyl-3-oxa-2-bicyclo[3.1.0]hexylidene- and pentacarbonyl(cyclopropylmethoxymethylene)tungsten compounds 4 and 9 by the reaction of lithiated oxazolinyloxiranes 2 and 8 and Fischer carbene tungsten complexes 3 is described. A mechanism for the formation of 4 and 9 is reported as well as their oxidation to cyclopropane-gamma-lactone 13 and -carboxylate 14.     

Stereospecific beta-lithiation of oxazolinyloxiranes: synthesis of alpha,beta-epoxy-gamma-butyrolactones

[reaction: see text]. Stereospecific beta-lithiation of beta-aryl-substituted oxazolinyloxiranes is described. The trapping reaction of such reactive intermediates with carbonyl compounds gave alpha,beta-epoxy-gamma-butyrolactones after deblocking of the oxazoline moiety. This methodology has been also extended to the synthesis of optically active alpha,beta-epoxy-gamma-butyrolactones.     

Conformational flexibility in open chain molecules: chiral and achiral alkanes

Conformational partition functions of chiral and achiral alkanes have been computed by using a continuum approach (instead of rotational isomeric state approximations). The accessible conformational space per bond depends upon the structure of the compound and is only in the range of 5–13% of the maximum accessible range. In order to partly overcome the intrinsic ambiguity of the term “conformational flexibility”, the distinction between number flexibility (a measure of the number of accessible energy minima) and space flexibility (a measure of the total allotted space) is proposed. Further, the conformational versatility of each bond of a molecule is evaluated in terms of the a priori probability density function of that bond, and it is shown that the use of this function permits a comparison of the relative conformational flexibilities of the individual bonds, which is particularly useful for molecules having more than two rotation angles (where the conventional energy maps cannot be used). Optical rotations are calculated for a series of chiral alkanes by combining the continuum approach for conformational analysis and a recent optical activity calculation scheme. Contributions of single bonds to the molar optical rotation are evaluated and discussed. The influence of temperature upon conformational and chiral properties is evaluated.     

Organogels from liquid and gaseous hydrocarbons

It is shown that n-butane, condensed in autoclave, can readily dissolve the anionic surfactant AOT (bis-2-ethylhexylsodium sulphosuccinate) and that this solution solubilizes water up tow ₀=molar ratio/water-AOT).The microemulsion can be transformed into a gel by solubilizing gelatin in the water microphase. These microemulsion gels are characterized by a very high viscosity (several hundred poise). However, the partial vapour pressure of the n-butane component in the gel is as high as in the liquid state. Infrared studies show that part of the water in the gel is still free.Stability diagrams of this system and¹H-NMR studies to assess the state of water are presented. Analogously to reverse micelles from liquid hydrocarbons, the chemical shift of water protons is shifted to higher fields with respect to bulk water. This effect increases with decreasing temperature andw ₀. At loww ₀ values (< 10), a part of the water in the micelles does not freeze even at –35°C.Due to the rapid evaporation of n-butane from the gel, gelatin films can be prepared simply by casting. Differential scanning calorimetry studies of the gels (from n-butane as well as from isooctane and other hydrocarbons) show that the films have a thermal stability comparable with, and sometimes higher than, gelatin films prepared by conventional methods. Preliminary permeability studies of these films with solutions of amino acid derivatives and with gas such as nitrogen and helium are presented.