Oxygen, exclusion

The cyclic carbamate (oxazoIidin-2-one) 313 is formed by the reaction of phenyl isocyanate (312) with vinyloxirane[I92]. Nitrogen serves as a nucleophile and attacks the carbon vicinal to the oxygen exclusively. The thermodynamically less stable Z-isomer 315 was obtained as a major product (10 I) by the reaction of 2-methoxy-l-naphthyI isocyanate (314) with a vinyloxir-... 

Details for the use of cncsilylation for 1,2-transposition of ketones (8, 289-290) have been published.2 The paper includes the conversion of vinylsilanes to rearranged allylic alcohols. The trimcthylsilyl group directs the cnc reaction with singlet oxygen exclusively to the a-position. A typical reaction is shown in equation... 

A number of papers report investigations of the pyrolytic cleavage of aromatic hydrocarbons. The oxidation and pyrolysis of anisole at 1000 K have revealed first-order decay in oxygen exclusively via homolysis of the O—CH3 bond to afford phenol, cresols, methylcyclopentadiene, and CO as the major products.256 A study of PAH radical anion salts revealed that CH4 and H2 are evolved from carbene formation and anionic polymerization of the radical species, respectively.257 Pyrolysis of allylpropar-gyltosylamine was studied at temperatures of 460-500 °C and pressures of 10-16 Torr. The product mixture was dominated by hydrocarbon fragments but also contained SO2 from a proposed thermolysis of an intermediate aldimine by radical processes.258... 

Body fluids, such as serum, contain several different carotenoids in low amounts. The crucial point in the isolation and analysis of these samples is the enrichment factor. Serum samples can be directly analysed with hyphenated extraction-sample enrichment-separation systems, such as on-line SPE-HPLC employing tailored stationary phases [29]. By using special restricted access materials (RAMs) for sample enrichment, the carotenoids are retarded on the pre-column while the protein binding is broken and the macromolecules are eluted. The preparation of artifacts is hindered, as the whole analysis steps take place under conditions of light- and oxygen-exclusion. The scheme of on-line SPE-HPLC is presented in Figure 5.2.2. 

This process is stereospecific and has the advantage of giving a quantitative conversion. Although AMP, the usual acceptor substrate for adenylate kinase, is achiral at phosphorus and so not subject to stereospecific phosphorylation, the phosphorus in AMPS is a prochiral center. Adenylate kinase catalyzes the phosphorylation of the pro-R oxygen exclusively to produce the (Sp) configuration. 

With the substrate (Z)-2-benzamido-(3,4-dimethoxy)-dnnamic acid 5d, as used in the technical process, we could realize turnover numbers of 10000-12000 in our laboratory under very careful oxygen exclusion. However, when substrate suspensions were used, this good result could be obtained only with the colorless methanol solvate 5dxMeOH. It is not clear why the methanol-free, yellow colored samples of the substrate with the otherwise same chemical purity led to a much poorer result and with a TON of only 2000. This yellow solvent-free modification can be obtained... 

No mention was made of other counterions being studied or substituent effects. If heterolytic cleavage had occurred, then benzyl ethyl ether would have been observed. Although no mention was made of the experimental procedure with regard to oxygen exclusion, oxidized phosphorus products were observed. 

Oxygenation of p-cresols. In the presence of excess potassium t-butoxide, the methyl group of 2,6-disubstituted p-cresols is oxygenated exclusively to an... 

Some results showed that pistachio AFL contamination in storage can be controlled by oxygen exclusion (Iqbal et al., 2006). 

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