Aerobic oxidation of thiols to disulfides catalyzed by diaryl tellurides under photosensitized conditions.

Aerobic oxidation of thiols is efficiently catalyzed by diaryl tellurides such as bis(4-methoxyphenyl) telluride under photosensitized conditions to give the corresponding disulfides in good to excellent yields. In this catalytic system, the tellurone oligomer, produced by the reaction of a telluride with singlet oxygen, is assumed to be the active species and is capable of oxidizing 4 equiv of a thiol.

Formation of diaryl telluroxides and tellurones by photosensitized oxygenation of diaryl tellurides.

Aerobic oxygenation of diaryl tellurides under photosensitized conditions is investigated. Unlike Ph(2)S and Ph(2)Se, reaction of diaryl tellurides with singlet oxygen proceeds smoothly to yield diaryl telluroxides and the corresponding tellurones. The product distribution is largely affected by the substrate and the reaction conditions. In particular, the photooxygenation of bulky diaryl tellurides principally produces tellurones. The results of a series of trapping experiments suggest that the diaryl telluroxides can capture transient intermediates such as Me(2)S(+)OO(-) and Ar(2)Te(+)OO(-), generated in the singlet oxygen oxidation of chalcogenides, to yield diaryl tellurones, and therefore it may be the most potent precursors of the tellurones.

Diorganotelluride-catalyzed oxidation of silanes to silanols under atmospheric oxygen.

Diorganotellurides efficiently catalyze the aerobic oxidation of organosilanes under photosensitized conditions to afford the corresponding silanols in excellent yield.

Aerobic photooxidation of phosphite esters using diorganotelluride catalysts.

Diorganotellurides containing bulky aromatic substituents are found to catalyze the photooxidation of phosphite esters using aerobic oxygen as a terminal oxidant. A Hammett plot with substituted triaryl phosphites yielding rho = 2.88 agrees with a nucleophilic oxygen transfer from telluroxide to phosphite.

Synthesis, characterization and oxidizing properties of a diorgano tellurone carrying bulky aromatic substituents.

Bis(2,4,6-triisopropylphenyl) tellurone (Tip(2)TeO(2)) was prepared, fully characterized by spectroscopic and X-ray crystallographic analyses, as well as theoretical calculations, and found to be an effective oxidizing agent that was capable of converting alcohols into carbonyl compounds under mild reaction conditions.

Stereoselective synthesis of triply isotope-labeled Ser, Cys, and Ala: amino acids for stereoarray isotope labeling technology.

Efficient access to highly enantioselective isotope-labeled serine, cysteine, and alanine for stereoarray isotope labeling (SAIL) is described.

Photophysical and photochemical processes of 9,10-dihydro-9-silaphenanthrene derivatives: photochemical formation and electronic structure of 9-silaphenanthrenes.

Photophysical and photochemical processes of 9-methyl- and 9-phenyl-9,10-dihydro-9-silaphenanthrene derivatives have been studied at room temperature and 77 K in comparison with the carbon analogue, 9,10-dihydrophenanthrene. These 9,10-dihydro-9-silaphenanthrene derivatives show smaller fluorescence quantum yield and remarkably larger Stokes shifts than those of the carbon analogue. In contrast, their phosphorescence quantum yields are two times larger than those of the carbon analogue, although the absolute value is not so large (approximately 0.1). Reaction products and intermediates produced by the 266 nm light photolysis have been studied, and it has been confirmed that 9-methyl- and 9-phenyl-9-silaphenanthrenes have been photochemically formed in methylcyclohexane at 77 K, in addition to the formation of radical cations of 9,10-dihydro-9-silaphenanthrene derivatives and the carbon-centered radical: 9-hydro-9-silaphenanthrenyl radical.

Photosensitized oxygenation of diaryl tellurides to telluroxides and their oxidizing properties.

Photosensitized oxidation of tellurides carrying bulky aromatic substituents afforded the corresponding telluroxides which were found to react with simple alcohols to give the corresponding carbonyl compounds in excellent yields along with the starting tellurides.

Synthesis and reactions of a novel 3,4-didehydropyroglutamate derivative.

Some reactions such as catalytic hydrogenation, Diels-Alder reaction, cyclopropanation, dihydroxylation, and Michael addition of a novel 3,4-didehydropyroglutamate derivative, in which the carboxylic group is protected as an ABO ester, are examined and found to take place in a stereospecific manner giving 3- and/or 4-substituted pyroglutamate derivatives without loss of enantiomeric purity at the alpha-position.