Synthesis and properties of polyfluoro(silyl)acetylene nanoparticles by reaction of fluoro(silyl)acetylenes with triethylamine

Fluoro(silyl)acetylenes, which were prepared by reaction of 1,1-difluoroethylene with silyl chlorides, reacted with triethylamine to give dark-brown colored polyfluoro(silyl)acetylene powders in excellent to moderate isolated yields. In contrast, the corresponding nonfluorinated acetylene was unable to react with triethylamine at all to afford poly(silyl)acetylene under similar conditions. Polyfluoro(silyl)acetylenes thus obtained were nanometer size-controlled cubic fine particles with a good dispersibility and stability in a variety of solvents. These polyfluoro(silyl)acetylene nanoparticles exhibited clear absorption and emission spectra related to the conjugated units in polymer main chain. Furthermore, these polyfluoro(silyl)acetylene nanoparticles were applied to the surface modification of poly(methyl methacrylate) [PMMA] film to exhibit a higher oleophobicity imparted by fluorine on their surface, compared to that on the reverse side.

Modification effect of spherical zirconia with SiCl4 as a support of methylaluminoxane for heterogeneous single-site catalyst

Unmodified and SiCl₄-modified spherical zirconia-supported methylaluminoxane were used as cocatalyst for propylene polymerization as well as ethylene/1-hexene copolymerization in combined with Me₂Si(η³-C₁₃H₈)(η¹-N^tBu)TiMe₂ (1) at 0 °C. The modification with SiCl₄ improved the catalytic activity. The improvement was clearer in ethylene/1-hexene copolymerization than in propylene polymerization. The number average molecular weight (M_n) of polypropylenes increased linearly against the polymerization time regardless the cocatalyst used to give polymers with narrow molecular weight distribution (M_w/M_n < 1.32), indicating the living nature of the catalytic systems. Thus, propagation rate constant (k_p) and the number of active centers (C^*) were evaluated from M_n and the number of polymer-chains. When the zirconia was modified with SiCl₄, the k_p value decreased and the C^* increased. The latter effect was more significant to enhance the catalytic activity.     

A convergent total synthesis of antiplasmodial C2 symmetric (+)-ekeberin D4

The first concise total synthesis of C₂ symmetric (+)-ekeberin D₄ (1) that exhibits antiplasmodial activity has been achieved in total nine steps and 27% yield from the known diol 4. The efficient synthetic method features the regio- and diastereoselective epoxidation of 4 and convergent coupling between half fragments 2 and 3 by taking into account the C₂ symmetric property.     

Photocrosslinking of copolymers of vinyloxyethyl methacrylate–styrene initiated by sulfonium salts. I. Transient species formed on photolysis of sulfonium salt

Benzyl cation was detected by transient absorption spectroscopy with a spectroscopic multichannel analyzer on pulse excitation (fourth harmonic of Nd:YAG laser, 266 nm; 10 ns fwhm) of benzyl(4-hydroxyphenyl) methylsulfonium hexafluoroantimonate(BSS) in 1,2-dichloroethane (EDC). The benzyl cation was long-lived (lifetime, 59 ms) at room temperature and quenched by a vinyl ether compound. The formation of the benzyl cation as active species on photolysis of BSS is in contrast to the formation of Brønsted acids in other sulfonium salts so far reported. © 1992 John Wiley & Sons, Inc.     

An oxazaphospholidine approach for the stereocontrolled synthesis of oligonucleoside phosphorothioates

The stereocontrolled synthesis of oligodeoxyribonucleoside phosphorothioates (PS-ODNs) using nucleoside 3'-O-oxazaphospholidine derivatives as monomer units is described. 2-Chloro-1,3,2-oxazaphospholidine derivatives were prepared from six kinds of enantiopure 1,2-amino alcohols and used for the phosphitylation reactions of 5'-O-protected nucleosides. A detailed study of these reactions revealed that the diastereoselectivity of the reaction depended on the structure of the enantiopure 1,2-amino alcohol, the reaction temperature, and the amine used as a scavenger of HCl. In addition, ab initio molecular orbital calculations for the 2-chlorooxazaphospholidine derivatives were carried out to elucidate the mechanism of these diastereoselective phosphitylation reactions. The LUMO of the 2-chloro-5-phenyloxazaphospholidine derivatives on the phosphorus atom was found to be almost orthogonal to the P-Cl bond. This LUMO may be involved in the phosphitylation reactions with predominant retention of the P-configuration. A series of dialkyl(cyanomethyl)ammonium salts were developed and used as activators for the condensation reactions of the diastereopure nucleoside 3'-O-oxazaphospholidines with 3'-O-protected nucleosides. In the presence of the new activators, the reactions proceeded rapidly to give the corresponding dinucleoside phosphite triesters. The diastereoselectivity of the condensation reaction did not depend on the counteranion but on the structure of the dialkyl(cyanomethyl)amine. In the presence of the activator, which consists of a relatively small dialkyl(cyanomethyl)amine, the condensation proceeded with excellent diastereoselectivity. After sulfurization and deprotection, diastereopure (R(p))- and (S(p))-dinucleoside phosphorothioates were obtained in excellent yields. The present methodology was also applied to the solid-phase synthesis of stereoregulated PS-ODNs. all-(R(p))-[T(PS)](3)T, all-(S(p))-[T(PS)](3)T, all-(R(p))-d[G(PS)A(PS)C(PS)]T, and all-(R(p))-[T(PS)](9)T were synthesized on a highly cross-linked polystyrene resin.     

Intramolecular cyclization with nitrenium ions generated by treatment of N-acylaminophthalimides with hypervalent iodine compounds: formation of lactams and spiro-fused lactams

N-Phthalimido-N-acylnitrenium ions are generated from N-acylaminophthalimides, a new class of precursors, by treatment with hypervalent iodine compounds (PIFA and HTIB). In HFIP, the nitrenium ions undergo intramolecular electrophilic substitution reactions to afford N-aminonitrogen heterocycles in high yields. In TFEA, spirodienones bearing the 1-azaspiro[4.5]decane skeleton are obtained by treatment of N-phthalimido-3-(4-halogenophenyl)propanamides with HTIB as a result of ipso attack of the intermediate nitrenium ion. Similarly, using PIFA in TFEA, ipso cyclization of unactivated benzenoid compounds occurs to afford spirodiene derivatives. This involves loss of aromaticity despite the absence of other activating substituents on the phenyl group.