Reactivity of urethanes at high temperature: Transurethanization and side reactions

The reactivity of urethanes based on 1,6‐hexamethylene diisocyanate (HDI) and 4,4′‐methylene diphenyl diisocyanate (MDI) was investigated at temperatures between 190 °C and 235 °C. Diurethane model compounds end‐capped with either 1‐dodecanol (D‐core‐D) or 1‐hexadecanol (H‐core‐H) were mixed and annealed at high temperature. The core was either MDI or HDI. The transurethanization reaction was followed based on the formation of the compounds (H‐core‐D). The amount of H‐core‐D and of side products, which had formed after variable annealing times, were identified with ¹H NMR, FTIR, SEC, and MALDI‐TOF. Transurethanization was considerably faster for MDI‐based urethanes than for HDI‐based urethanes. Only traces of side products were formed during annealing of MDI‐based urethanes, whereas a significant amount of allophanates was formed from HDI‐based urethanes under the same conditions. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 621–629     

Dissociation of Ethoxy Methyl Carbenium Hexachioroantimonate in Methylene Chloride Solution. II. The Nature and Extent of the Dissociation

Ethoxy methyl carbenium hexachioroantimonate has been synthesized as a model compound for the propagating species in the cationic polymerization of the vinyl ethers. Its degree of dissociation in methylene chloride has been studied as a function of concentration by using the method described in Part I. A simple one two dissociation was found. The degree of dissociation, however, was less than that found with a typical initiator such as triphenyl methyl hexachioroantimonate.     

Kicked-rotor quantum resonances in position space: application to situations of experimental interest

We discuss a model for quantum computing with initially mixed states. Although such a computer is known to be less powerful than a quantum computer operating with pure (entangled) states, it may efficiently solve some problems for which no efficient classical algorithms are known. We suggest a new implementation of quantum computation with initially mixed states in which an algorithm realization is achieved by means of optimal basis independent transformations of qubits.     

Asymmetric hydrogenation of trisubstituted N-acetyl enamides derived from 2-tetralones using ruthenium-SYNPHOS catalysts: a practical synthetic approach to the preparation of β3-adrenergic agonist SR58611A

The asymmetric hydrogenation of various trisubstituted enamides derived from 2-tetralones under mild reaction conditions using Ru-SYNPHOS catalysts is reported. This practical and clean method gives access to several chiral 2-aminotetralins derivatives in high isolated yields and enantiomeric excesses up to 95% depending on the substitution pattern of the aromatic ring and the nature of the amide moiety. In addition, the usefulness of the current method is demonstrated via a practical synthetic approach to the enantiomerically pure SR58611A compound, a potent and selective β₃-adrenergic receptor agonist.     

Total synthesis of TMS-ent-bisabolangelone

The absolute configuration of bisabolangelone has been established by an eleven step total synthesis of the corresponding TMS protected antipode starting from (R)-(+)-pulegone. Comparison of the TMS-derivatives by GC on a chiral column, allowed us to assign the absolute configuration of the synthetic compound and thus of the corresponding natural product. The latter has been confirmed by the Mosher's ester analysis of the known secondary carbinol derivative.     

Influence de la temperature de polymerisation sur le taux de branchement de divers polybenzofurannes obtenus par amorçage cationique

Several polybenzofuranes, obtained by cationic initiation at various temperatures, have been fractionated by preparative G.P.C. The fractions have been studied by various physical methods, mainly osmometry, light scattering, viscometry and G.P.C. These determinations have been made in benzene and the Mark-Houwink relations have been obtained. From the differences observed between these various relations, the gyration radii and the determination of branching indexes, we have found very numerous branches in the samples obtained at the highest temperatures. These branches very probably result from a Friedel-Crafts attack on benzene rings by the carbocations of growing chains. Quantum chemistry determinations are in agreement with this view.     

Etudes des sélénophènes mono et bisubstitués par Résonance Magnétique de 1H et de 13C

Proton and carbon magnetic resonance spectra of mono-and disubstituted selenophenes are investigated. The proton chemical shifts are discussed in terms of magnetic anisotropy and electric field effects of the substituents, with a view to studying the conformational equilibrium of the carbonyl group. π Electronic charges, computed by the PPP method, are correlated with the proton and carbon chemical shifts. The coupling constants between ¹³C and ¹H (1, 2 or 3 bonds) and ¹³C? ⁷⁷Se are shown to be good structural parameters and a set of substituent additivity constants is calculated.     

Self-similarities in the frequency-amplitude space of a loss-modulated CO2 laser

We show the standard two-level continuous-time model of loss-modulated CO2 lasers to display the same regular network of self-similar stability islands known so far to be typically present only in discrete-time models based on mappings. Our results suggest that the two-parameter space of class B laser models and that of a certain class of discrete mappings could be isomorphic.