Potent Antimalarial 1,2,4‐Trioxanes through Perhydrolysis of Epoxides

Perhydrolysis of a sterically congested multifunctional epoxide was achieved in ethereal H₂O₂ with the aid of a recently developed Mo catalyst. The resulting hydroperoxide cyclized to give a 1,2,4‐trioxane, which could be readily elaborated into qinghaosu and a range of novel analogues. Some of the compounds with two such trioxane moieties showed in vitro antimalarial activity comparable to or even better than that of artesunate or chloroquine.     

Acid‐Catalyzed Oxidative Radical Addition of Ketones to Olefins

Based on a mechanistic study, we have discovered a Brønsted acid catalyzed formation of ketone radicals. This is believed to proceed via thermally labile alkenyl peroxides formed in situ from ketones and hydroperoxides. The discovery could be utilized to develop a multicomponent radical addition of unactivated ketones and tert‐butyl hydroperoxide to olefins. The resulting γ‐peroxyketones are synthetically useful intermediates that can be further transformed into 1,4‐diketones, homoaldol products, and alkyl ketones. A one‐pot reaction yielding a pharmaceutically active pyrrole is also described.     

An Exceptional Peroxide Birefringent Material Resulting from d–π Interactions

Birefringent materials, which can modulate the polarization of light, are almost exclusively limited to oxides. Peroxides have long been overlooked as birefringent materials, because they are usually not stable in air. Now, the first peroxide birefringent material Rb₂VO(O₂)₂F is reported, the single crystals of which keep transparency after being exposed in the air for two weeks. Interestingly, Rb₂VO(O₂)₂F does not feature an optimal anisotropic structure, but its birefringence (Δn=0.189 at 546 nm) exceeds those of the majority of oxides. According to the first‐principles calculations, this exceptional birefringence should be attributed to the strong electronic interactions between localized π orbital of O₂^2? anions and V⁵⁺ 3d orbitals, which may be also favorable to the stability in the air for Rb₂VO(O₂)₂F. These findings distinguish peroxides as a brand‐new class of birefringent materials that may possess birefringence superior to the traditional oxides.     

Self‐Assembly of Uranyl–Peroxide Nanocapsules in Basic Peroxidic Environments

A wide range of uranyl–peroxide nanocapsules have been synthesized using very simple reactants in basic media; however, little is known about the process to form these species. We have performed a density functional theory study of the speciation of the uranyl ions under different experimental conditions and explored the formation of dimeric species via a ligand exchange mechanism. We shed some light onto the importance of the excess of peroxide and alkali counterions as a thermodynamic driving force towards the formation of larger uranyl–peroxide species.     

Free radicals in irradiated unstabilized polypropylene, as seen by diffuse reflection absorption-spectrophotometry

The introduction of UV-Vis absorption spectrophotometry to the study of radiation chemistry of polymers has opened the possibility to investigate even very opaque samples. The virgin powder polypropylene, as obtained from the industrial production line, shows after irradiation unstable products of radiolysis. Until now they were investigated mainly by EPR method. Optical absorption spectra (by diffuse reflection spectrophotometry) contribute to better identification and study of changes in time, temperature and diffusion of reactive gases. Studying the formation of stable compounds, which do not produce EPR signal, we are able to examine these species on the basis of their electronic spectra. The most important results concern the peroxides in irradiated polypropylene.     

Activation of Hydrogen Peroxide by Ionic Liquids: Mechanistic Studies and Application in the Epoxidation of Olefins

Imidazolium‐based ionic liquids that contain perrhenate anions are very efficient reaction media for the epoxidation of olefins with H₂O₂ as an oxidant, thus affording cyclooctene in almost quantitative yields. The mechanism of this reaction does not follow the usual pathway through peroxo complexes, as is the case with long‐known molecular transition‐metal catalysts. By using in situ Raman, FTIR, and NMR spectroscopy and DFT calculations, we have shown that the formation of hydrogen bonds between the oxidant and perrhenate activates the oxidant, thereby leading to the transfer of an oxygen atom onto the olefin demonstrating the special features of an ionic liquid as a reaction environment. The influence of the imidazolium cation and the oxidant (aqueous H₂O₂, urea hydrogen peroxide, and tert‐butyl hydrogen peroxide) on the efficiency of the epoxidation of cis‐cyclooctene were examined. Other olefinic substrates were also used in this study and they exhibited good yields of the corresponding epoxides. This report shows the potential of using simple complexes or salts for the activation of hydrogen peroxide, owing to the interactions between the solvent medium and the active complex.     

Reducing Ga?H and Ga?C Bonds in Close Proximity to Oxidizing Peroxo Groups: Conflicting Properties in Single Molecules

Treatment of [Li(H₂Ga{CH(SiMe₃)₂}₂)] ? 2 OEt₂ ( 1? 2 OEt₂) with two equivalents of tert‐butyl hydrogen peroxide, H‐O‐O‐CMe₃, afforded the organogallium peroxide [({(Me₃Si)₂HC}₂Ga(OH)(OOCMe₃)Li)₂] ( 3 ), which possesses oxidizing peroxo groups in close proximity to reducing Ga? C bonds. The lithium atoms of the dimeric formula units are coordinated by both oxygen atoms of the peroxides and by two hydroxo groups. The cleavage of the Ga? C bond was not observed, even when an excess of H‐O‐O‐CMe₃ was applied. Instead, the adduct [{(Me₃Si)₂HC}₂Ga(OH)(OOCMe₃)₂Li₂(HOOCMe₃)] ( 4 ) was isolated, which has an intact H‐O‐O‐CMe₃ molecule terminally attached to lithium. A similar structural motif was found for the compound [(LiOOCMe₃)₂(HOOCMe₃)₂] ( 5 ). The trihydrido gallanate [Li(H₃Ga? {CH(SiMe₃)₂})] ? OEt₂ ( 2 ) yielded the unique peroxide [({(Me₃Si)₂HC}? Ga(H)(OOCMe₃)₂Li)₂] ( 6 ) under similar conditions that possesses Ga? C and even more reactive Ga? H bonds beside peroxo groups. It decomposed at room temperature by the insertion of oxygen atoms into the Ga? H bonds and the formation of [({(Me₃Si)₂HC}? Ga(OH)(OCMe₃)(OOCMe₃)Li)₂] ( 7 ), which was isolated in a low yield. Further decomposition gave the complete degradation of all peroxo groups with the formation of a relatively complicated Li₄Ga₄O₈ cage ( 8 ).