Efficient synthesis of the 6,6-spiroacetal of spirofungin A

The 6,6-spiroacetal segment of spirofungin A, an antifungal antibiotic isolated from Streptomyces violaceusniger Tü 4113, was efficiently prepared via the coupling reaction of the Weinreb amide and the alkyne which are readily available from the common intermediate. The synthesis includes the unsymmetrization through a stereoinversion at the C11 position and the transacetalization as the key steps.     

Effect of diphenylbutadiyne on the free radical polymerization of vinyl monomers in solution

The free radical polymerization of vinyl monomers such as styrene, methylmethacrylate, methyacrylate, acrylonitrile, vinylacetate, etc. in the presence of diphenylbutadiyne, was investigated. Both rates of polymerization and molecular weights of polymer decreased by the addition of diphenylbutadiyne. The degree of retardation depended on the stability of propagating radicals. The butadiyne does not react with the propagating radicals having high Q values, but it seems to trap the radicals temporarily thus retarding the polymerization     

Effect of water treatment and Ce doping of Pt/Al2O3 catalysts on Pt sintering and propane oxidation

The effect of Ce doping and pretreatment of Pt/Al₂O₃ on its catalysis of propane oxidation was investigated after aging the catalysts. The Ce amount and pretreatment conditions were varied, and the propane oxidation activity was measured. The properties of the catalysts were investigated by means of XRD, STEM-EDX, FT-IR, and H₂-TPR. The size of the Pt nanoparticles (PtNPs) decreased for water-treated catalysts doped with a small amount of Ce, suggesting that water treatment of Ce-doped catalysts inhibits Pt sintering. The minimum PtNP size was obtained with ca. 3.6 wt% of Ce. The Ce species with less than 3.6 wt% existed in a dispersed state, whereas above this value, CeO₂ particulates co-existed. The propane oxidation temperature of the water-treated catalysts was lowered to an extent that depended on the Ce content. This tendency is consistent with the PtNP size in the catalysts. It is considered that highly dispersed Ce species take a primary role in promoting propane oxidation on PtNPs. The reduction temperature of Ce species on water-treated catalysts was lower than that of untreated catalysts, probably owing to a stronger interaction between Pt and Ce, demonstrated by FT-IR measurements. The increased reducibility of Ce species may be the reason for the improved oxidation activity of the catalysts.

Graphic abstract

     

Model reactions of functionalization of polycarbonate. Reactions of phenyl chloroformate with nucleophiles and cationic polymerization behavior of bicyclo orthoesters containing carbonate group

Some model experiments for functionalization of a polycarbonate were carried out. At first, reactivity of phenyl chloroformate with a few nucleophiles was examined. Reaction with alkyl amines gave corresponding carbamates, but in the case of aniline, formation of a byproduct diarylurea was observed. Reactions with alcohols and phenols afforded carbonates in moderate yields, in which p-nitrophenol and isopropyl alcohol were less reactive. On the basis of these results, 1-ethyl-4-phenoxycarboxymethyl-2,6,7-trioxabicyclo[2.2.2]octane (2) and 1-ethyl-4-ethoxycarboxymethyl-2,6,7-trioxabicyclo[2.2.2]octane (3) were prepared by the reaction of phenyl and ethyl chloroformates with 1-ethyl-4-hydroxymethyl-2,6,7-trioxabicyclo[2.2.2]octane in the presence of tert-amine. 2 polymerized cationically with BF₃OEt₂ at more than 80°C to give a polyether containing both ester and carbonate groups in the side chain, with contamination of a gelled polymer.     

The doublet instabilities of the Hartree-Fock solutions for the cation and anion radicals of fulvalene systems

The doublet instabilities of the restricted Hartree-Fock (RHF) solutions for the ion radicals of fulvalene systems, some of which have been known to show the lattice instabilities, are examined in the framework of the semiempirical SCF MO approximation. The RHF solutions for the anion radical of heptafulvalene and the cation radical of pentafulvalene are found to be doublet unstable at the conventional D_2h nuclear arrangement. We calculate the broken-symmetry charge-density-wave (CDW) solutions lower in energy than the usual symmetry-adapted RHF solutions and examine their properties. It is shown that the energy lowerings due to the CDW solutions are very small in both the ion radicals, but their density matrix elements are remarkably different from those for the symmetry-adapted RHF solutions. It is also shown that the proton hyperfine splittings for the anion radical of heptafulvalene calculated assuming the CDW solution are in good agreement with the experimental values. Finally, we refer to the relationship between the doublet instability of the RHF solution and the lattice instability.     

A stereoselective total synthesis of (±)-oxylubimin

(±)-Oxylubimin (1), the highest oxidized spirovetivane-type phytoalexin, was totally synthesized with high stereoselectivity using a novel method for α′-hydroxylation of α,β-unsaturated ketones.     

Reaction of singlet oxygen with α,β-unsaturated aldimines

The reaction of singlet oxygen with N-1-(2-alkenylidene)-t- butylamines ( and ) gives the unsaturated hemiperacetal derivatives ( and 4) of the hydroperoxy aldimines ( and ). Several α, β-unsaturated aldimines which are held in the s-trans conformation failed to react with singlet oxygen.