Cycloaddition of nitrones and α,β-unsaturated sugar lactones

It was found that 1,3-cycloaddition of nitrones 1–3 to α,β-unsaturated sugar carbonyl compounds 4–8 proceeds regiospecifically to give mixtures of stereoisomers. Nitrones 1–3 entered compounds 4–8 in trans-relation to the existing ring substituent.     

Linear polythioesters. III. Products of interfacial polycondensation of 1,4-, 1,5-di(mercaptomethyl)-naphthalene,and their mixture with adipoyl and sebacoyl chlorides

New polythioesters of naphthalene derivatives by polycondensation of 1,4-di(mercaptomethyl)-naphthalene, 1,5-di(mercaptomethyl)naphthalene, as well as their mixture with adipoyl and sebacoyl chlorides have been obtained. Low-temperature and high-temperature solution polycondensation as well as interfacial polycondensation have been used. Interfacial polycondensation proved to be the most useful. To define the optimal conditions of interfacial polycondensation, the following factors influencing the process have been studied: ratio of aqueous to organic phase, concentration of hydrochloride acceptor, temperature of reaction and rate of addition of acid chloride, contribution of emulsifier and catalyst. Yield for all reaction products and reduced viscosity have been found. The structure of polythioesters of high-value viscosity and good yield was determined from elementary analysis, infrared spectra, x-ray, and thermogravimetric analysis. Some mechanical and electrical properties of the polythioesters obtained from the mixture of 1,4- and 1,5-di(mercaptomethyl)naphthalene have been studied after pressing in increased temperature. The molecular weight was not determined because of very low solubility.     

Polyurethanes containing sulfur. II. New thermoplastic nonsegmented polyurethanes with diphenylmethane unit in their structure

New thermoplastic nonsegmented thiopolyurethanes were synthesized from the new low‐melting aliphatic‐aromatic thiodiols bis[4‐(2‐hydroxyethyl)thiomethylphenyl]methane, bis[4‐(3‐hydroxypropyl)thiomethylphenyl]methane, and bis[4‐(6‐hydroxyhexyl)thiomethylphenyl]methane and hexamethylene diisocyanate both by melt and solution polyaddition with dibutyltin dilaurate as a catalyst. All the thiodiols were prepared with high yields by the condensation reaction of bis(4‐mercaptomethylphenyl)methane with 2‐chloroethanol, 3‐chloro‐1‐propanol, or 6‐chloro‐1‐hexanol. The hard‐segment‐type polyurethanes obtained were plastic materials with partially crystalline structures. Polymerization in solution produced products with higher molecular weights (η_red = 0.97–1.24 dL/g) than polymerization in melt (η_red = 0.44–1.05 dL/g). The structures of all the polyurethanes were determined with elemental analysis, Fourier transform infrared, and X‐ray diffraction analysis. Thermal properties of the polymers obtained in solution were examined by differential scanning calorimetry and thermogravimetric analysis. Shore A/D hardness and tensile properties for all the polyurethanes were also determined. Of the two kinds, the polyurethanes obtained in solution possessed better tensile properties and showed yield stress (tensile strength) in a range of 27.8–30.0 MPa at an elongation of 17.4–25.1%. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1767–1773, 2000     

A non-symmetric transition probability in quantum mechanics

The purpose of this paper is to show the possibility of introducing a non-symmetric transition probability in quantum mechanics, starting from the axiomatic basis of the theory known as the “quantum logic approach”. The quantum-mechanical postulates are later reformulated in the language of the transition probability and the operations (filtering procedures) transforming pure states of a physical system into themselves, ans some advantages of this formulation are shown consisting mainly in resolving the old troubles connected with quantum logics (e.g., the questions of the complete lattice structure of the logic, atomicity, the validity of the covering law).As a consequence of the axioms assumed, the representation theorem for the logic of proposition is deduced.     

Axioms for statistical physical theories and GL-spaces

The paper contains an axiomatic formulation of statistical physical theories, which may be considered as an alternative to the famous Mackey's approach. In contrast to the Mackey's axiomatics, in which the so-called propositional logic appears as a basic object, our approach takes the partially ordered vector space spanned by states of a physical system as a starting point. The propositional logic appears then as a set of positive functionals on this space.     

Linear polythioesters. VII. Products of interfacial polycondensation of 1,4-di(mercaptomethyl)-2,3,5,6-tetramethylbenzene with some aliphatic acid dichlorides

Several polythioesters by interfacial polycondensation of 1,4-di(mercaptomethyl)-2,3,5,6-tetramethylbenzene with oxalyl, succinyl, adipoyl, suberoyl, and sebacoyl chlorides were obtained. To determine the optimal conditions for interfacial polycondensation, the influence of the following factors on yield and value of reduced viscosity were studied: type of organic phase, concentration of hydrogen chloride acceptor, the quantitative ratio of aqueous to organic phase, molar ratio of reagents; temperature of reaction, rate of acid chloride addition, and contribution of catalyst. Thorough studies were carried out only for polycondensation of the dithiol with adipoyl and sebacoyl chlorides. The structure of all polythioesters obtained under the model conditions was determined by elementary analysis and infrared spectra. Initial decomposition temperature, mass loss in percentage at the same temperature, maximum rate of decomposition, and mass loss percentage at 100–400°C were defined by thermogravimetric analyses. Chemical resistance of the polythioesters was determined by treatment with some organic solvents, mineral acids (concentrated and 10%), and sodium hydroxide (10 and 50%). Some mechanical and electrical properties of the polythioesters obtained from dithiol and adipoyl and sebacoyl chlorides were determined. The molecular weight was not measured because of the low solubility of the polythioesters.     

Pure operations and the covering law

The paper is devoted to the study of properties of pure operations. The main results are: Axiomatic characterization of pure operations consisting in a precise formulation of their basic properties and the representation theorem, which shows that pure operations possessing these (axiomatically defined) properties and satisfying the so-called Compatibility Postulate are in fact the usual ones, of special kind, defined by the well-known formula. The other main result of the paper is the justification of the covering law in the logic of propositions, which is shown here to follow from the Compatibility Postulate, the latter being of direct physical significance.     

A formal synthesis of ezetimibe via cycloaddition/rearrangement cascade reaction

A formal synthesis of a powerful cholesterol inhibitor, ezetymibe 1, is described. The crucial step of the synthesis is based on Cu(I)-mediated Kinugasa cycloaddition/rearrangement cascade reaction between terminal acetylene derived from acetonide of L-glyceraldehyde and suitable C,N-diarylnitrone. The adduct with (3R,4S) configuration at the azetidinone ring, obtained with high stereoselectivity, was subsequently subjected to deprotection of the diol side chain followed by glycolic cleavage and base-induced isomerization at the C3 carbon atom to afford the (3S,4S) aldehyde, which has been already transformed into ezetimibe by the Schering-Plough group.     

Optimization of Adiabatic Selective Pulses

Adiabatic RF pulses play an important role in spin inversion due to their robust behavior in presence of inhomogeneous RF fields. These pulses are characterized by the trajectory swept by the tip of theB_effvector and the rate of motion upon it. In this paper, a method is described for optimizing adiabatic inversion pulses to achieve a frequency-selective magnetization inversion over a given bandwidth in a shorter time and to improve slice profile. An efficient adiabatic pulse is used as an initial condition. This pulse allows for flexibility in choosing its parameters; in particular, the transition sharpness may be traded off against the inverted bandwidth. The considerations for selecting the parameters of the pulse according to the requirements of the design are discussed. The optimization process then improves the slice profile by optimizing the rate of motion along the trajectory of the pulse while preserving the trajectory itself. The adiabatic behavior of the optimized pulses is fully preserved over a twofold range of variation in the RF amplitude which is sufficient for imaging applications in commercial high-field MRI machines. Design examples demonstrate the superiority of the optimized pulses over the conventional sech/tanh pulse.