Selenides oxidations

Homogeneous precipitation using urea (which hydrolyzes to give an alkaline solution) has been used extensively, and in a few cases films of basic salts (sulphates of A1 and Sn(lV) and formate of Fe) have been obtained. These are not considered semiconductors in the conventional sense, but do provide examples for extension of the CD method beyond the conventional sulphide-selenide-oxide compounds. 

Formation of CK-configurated cyclobutanones has also been observed with 2-methylcyclopen-tanone and 2-methylcyclohexanone/8 However, stereoreversed eyclobutanone formation can be achieved by opening the intermediate oxaspiropentane with sodium phenyl selenide, oxidation of the resulting / -hydroxy selenide with 3-chloroperoxybenzoic acid and subsequent rearrangement in the presence of pyridine/18 Thus, from one oxaspiropentane 8, either stereoisomeric eyclobutanone cis- or lrans-9 was produced. The stereoreversed eyclobutanone formation proceeds from a stereohomogenous / -hydroxy selenoxide and is thought to be conformationally controlled. 

No other derivatives of the tertiary cation, such as the aUylic alcohol in the last part, can r formed this way because the rearrangement is too fast. The reaction with PhSe-SePh and NaBH a trick to get this allylic alcohol. The true reagent is PhSe , formed by reduction of the Se-Se bcr. It is very nucleophilic and will attack even the tertiary epoxide to give a selenide. Oxidation to rh selenoxide leads to a fast concerted cis elimination. The intermediate selenide is unstable as wel m very smelly and must be oxidized immediately before it decomposes. 

To use a selenate instead of a sulfoxide rearrangement for the preparation of allylic alcohols can be advantageous if silicon is present in the starting material. Vedejs found that the allylsilane (213) could be selenylated to give (214 equation 79) this reaction includes a rapid 1,3-shift of the initially formed selenide. Oxidation and 2,3-rearrangement to the alcohol (215) followed uneventfully. 

The samples were prepared by dissolving measured volumes of H2Se(g) in degassed solutions of NaOH, which were held in 0.1 mm quartz cells. The cells were then filled with a slight overpressure of N2(g) and a colourless sample was taken to indicate that no selenide oxidation had occurred. 

Each isoxazoline subunit is built up starting from a resin-bound olefin submitted to a 1,3-dipolar cycloaddition of a nitrile oxide, followed by a selenide oxidation/elimination reaction to regenerate the olefin functionality [69]. Using different nitroseleno ethers and nitroalkanes, a library of triisoxazolines has been prepared and characterized by mass spectrometry. This flexible method to create heterocyclic oligomers via C-C bond ring closure is then versatile to combinatorial syntheses. 

All publications on mesoporous soHds with nanoparticles discussing optical properties can be generally divided into two large groups. The first group consists of works on different kinds of semiconductor particles (metal sulfides, selenides, oxides, etc.) where such particles are obtained in mesoporous solids and their UV-visible absorption and photoluminescence spectra are recorded. As a rule, these papers state the change of optical properties of nanoparticles compared to bulk, similar to semiconductor nanoparticles prepared in any... 

Cfi H5 SeCl in CH2 CI2. This reagent reacts with lithium enolates of ketones to give enones directly (equation III). However, yields are variable and often lower than those obtained by the two-step procedure. Moreover, the reagent is very hygroscopic. Reich recommends use of this compound only where normal selenide oxidation is not successful. 

The volume Rare Earth Elements C 9 deals with the rare earth selenides, oxide selenides, selenites, and selenates, as well as the associated alkali double compounds, diselenate nitrates, and the selenide halides. So far as meaningful and as in all earlier volumes of Rare Earth Elements Series C ( Seltenerdelemente Reihe C), comparative data are presented in sections preceding treatment of the individual compounds and systems. 

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