Computational study of epoxy-amine reactions

Density functional theory calculations were carried out for the title reactions. Ethylene oxide and methylamine were adopted as reactants. Amine clusters (dimer, trimer, tetramer, and pentamer) were considered, because the combination of one oxide and one amine molecule gave a large activation energy. An amine tetramer was found to react favorably with the oxide via various zwitterionic intermediates. A back-side S(N)2 nucleophilic attack of one amine and the subsequent proton relay up to the front side provide a stabilized reaction field. The amine-alcohol mixed reactant may react readily with the oxide, because the alcoholic O-H group is in contact with the oxide oxygen with the strong hydrogen-bond stabilization.     

Living cationic polymerization of amide‐functional vinyl ethers: Specific properties of SnCl4‐based initiating system

Living cationic copolymerization of amide‐functional vinyl ethers with isobutyl vinyl ether (IBVE) was achieved using SnCl₄ in the presence of ethyl acetate at 0 °C: the number–average molecular weight of the obtained polymers increased in direct proportion to the monomer conversion with relatively low polydispersity, and the amide‐functional monomer units were introduced almost quantitatively. To optimize the reaction conditions, cationic polymerization of IBVE in the presence of amide compounds, as a model reaction, was also examined using various Lewis acids in dichloromethane. The combination of SnCl₄ and ethyl acetate induced living cationic polymerization of IBVE at 0 °C when an amide compound, whose nitrogen is adjacent to a phenyl group, was used. The versatile performance of SnCl₄ especially for achieving living cationic polymerization of various polar functional monomers was demonstrated in this study as well as in our previous studies. Thus, the specific properties of the SnCl₄ initiating system are discussed by comparing with the Et_xAlCl_3?x systems from viewpoints of hard and soft acids and bases principle and computational chemistry. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6129–6141, 2008     

Reactivity of halophenol and formation of phenoxo–copper(II) complex in basic copper-catalyzed halogen displacement polymerization

The halogen displacement polymerization of 2,4,6-trihalophenol with heterogeneous basic copper(II) complex is described. The corresponding poly(dihalophenylene oxides) have been obtained from 2,4,6-trichloro-, 2,4,6-tribromo-, and 2,4,6-triiodophenol with the present catalytic system. In the halophenols used, the order of reactivity was as follows; 2,4,6-trichloro- < 2,4,6-tribromo- < 2,4,6-triiodophenol. With 2,4,6-trichlorophenol as a monomer, the 2,4,6-trichlorophenoxo–copper(II) complex, which had the composition Cu(OCH₃)(C₆H₂Cl₃O) and was considered to be a reaction intermediate, was isolated. The ESR spectrum of this complex at room temperature showed a sharp peak considered to be free organic radical, in addition to the broad one based on copper(II) ion. Poly(dichlorophenylene oxide) was obtained by thermal decomposition of the phenoxo–copper(II) complex. It was concluded that the formation and decomposition of the phenoxo–copper(II) complex were intermediate steps of halogen displacement polymerization of 2,4,6-trihalogenophenol with heterogeneous basic copper(II) catalyst.     

Transition Structures for the Aromatic Claisen Rearrangements by the Molecular Orbital Method

Ab initio calculations were performed for eight Claisen rearrangements, eqs 1-8. Transition-state (TS) structures of [3,3] sigmatropic rearrangements of reactions 1-4 are similar, but their activation energies (E(a)'s) are different, E(a)(1) < E(a)(2) and E(a)(3) < E(a)(4). From the intermediate of reaction 3, a hydrogen is moved intermolecularly to form the product, o-allyl phenol. The lower reactivities of reactions 2 and 4 relative to reactions 1 and 3 are ascribed to large endothermicities in the sigmatropic rearrangements, respectively. Chair-type transition states are more favorable than boat-type transition states in reactions 1-4. The allyl group is released from the in-plane C-X (X = O or N) sigma bond and is captured by the pi-type lone-pair electrons. The sulfur- and phosphorus-containing rearrangements, reactions 5-8, are computed to have smaller activation energies but are to be less exothermic than those of oxgyen- and nitrogen-containing rearrangements.     

New synthesis of a chiral steroid cd-ring synthon by means of enantioselective double Michael addition

A new synthetic method of (+)-(1R)-acetyl-(7aR)-methyl-4-hydroinden-5-one (2) by highly enantioselective double Michael addition involving alkenylcopper-phosphine complex, 3-trimethylsilylbutenone and 2-methyl-2-cyclo-pentenone is presented.     

Simple total synthesis of 18-hydroxyestrone

A simple total synthesis of 18-hydroxyestrone ($\text{7}$) was carried out by the cycloaddition of o-quinodimethane intermediate. 2-Methoxycarbonyl-3-vinyl-cyclopentanone ($\text{1}$) was used as the D ring component.     

Bragg diffraction of microcavity polaritons by a surface acoustic wave

Bragg scattering of polaritons by a coherent acoustic wave is mediated and strongly enhanced by the exciton states resonant with the acoustic and optic fields in the intraband and interband transitions, respectively. In this case, in contrast with conventional acousto-optics, the resonantly enhanced Bragg spectra reveal the multiple orders of diffracted light. For polaritons in GaAs microcavities driven by a surface acoustic wave of nu(SAW)=1 GHz and I(ac)< or approximately 100 W/cm(2) the main acoustically induced band gap can be as large as Delta(MC)(ac) approximately equal to 0.6 meV and the Bragg replicas up to n=3 can be observed.