Wataru Ando

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.

(Salicylaldiminato)Ni(II)-catalysts for hydrosilylation of olefins

A series of (salicylaldiminato)methylnickel complexes efficiently catalyse hydrosilylation of various olefins. The complexes are highly active for secondary hydrosilanes and exhibit excellent selectivity for monohydrosilylation. A possible mechanism, which includes a silylnickel complex as a key active species, is proposed.

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.

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.

Oxidative total chlorine free photochemical bleaching of cellulosic fabrics

Water-insoluble natural colored compounds adsorbed or chemically bound on cellulosic fabrics were bleached effectively by a selective photolysis of the colored compounds using various excimer lasers (KrF, XeCl, XeF), a low-pressure mercury lamp, and a black-light fluorescent lamp in the presence of sodium peroxocarbonate or mixtures of sodium carbonate and hydrogen peroxide aqueous solutions at room temperature. The efficiency of the photochemical bleaching was found to be comparable to that of the commercial thermal bleaching processes when a XeF excimer laser or a black-light fluorescent lamp were used as light sources.

Reductive total chlorine free photochemical bleaching of cellulosic fabrics, an energy conserving process

Water-insoluble natural colored compounds adsorbed or chemically bound on cellulosic fabrics were bleached effectively at room temperature by a selective photolysis of the colored compounds using various excimer lasers (ArF, KrF, XeCl, XeF), a low-pressure mercury lamp, and a black-light fluorescent lamp in the presence of aqueous solutions of various reducing reagents. Sodium borohydride gave the best efficiency on the bleaching when KrF, XeCl, XeF excimer lasers or a low-pressure mercury lamp were used as light sources and the efficiency of the bleaching was found to be comparable to that of the conventional thermal bleaching processes.

Pd/C-catalyzed cross-coupling reaction of benzyloxysilanes with halosilanes for selective synthesis of unsymmetrical siloxanes

A new protocol for the nonhydrolytic synthesis of unsymmetrical siloxanes has been developed. The cross-coupling reaction of benzyloxysilanes with halosilanes catalyzed by Pd/C afforded various unsymmetrical siloxanes with co-production of benzyl halides.

Synthesis of 2-Alkylidene-3,1-Benzoxathiin-4-Ones by the Pummerer Type Reaction

GRAPHICAL ABSTRACT Abstract We investigated synthesis of 2-alkylidene-3,1-benzoxathiin-4-ones (2-alkylidene BOTs) from 2-alkyl BOTs with the Pummerer type reaction. The reaction of 2-alkyl BOT 1-oxides, which were obtained by oxidation of 2-alkyl BOTs with mCPBA, with trifluoroacetic anhydride was carried out in the presence of pyridine at 100 °C for 3 h. Consequently, 2-alkylidene BOTs were obtained in 30–88% yields.

Synthesis and Reaction of N-Sulfenylpyrroles

GRAPHICAL ABSTRACT Abstract N-Sulfenylpyrroles were synthesized by the condensation of N-unsubstituted sulfenamides with 1,4-dicarbonyl compounds, such as hexane-2,5-dione or 2,5-dimethoxytetrahydrofuran. Primary amines as nucleophiles did not attack to the sulfur atom of the N-S bonds in the N-sulfenylpyrroles, which was different from other N-sulfenyl heterocycles.