Secondary oxygenation

The history of asymmetric dihydroxylation51 dates back 1912 when Hoffmann showed, for the first time, that osmium tetroxide could be used catalytically in the presence of a secondary oxygen donor such as sodium or potassium chlorate for the cA-dihydroxylation of olefins.52 About 30 years later, Criegee et al.53 discovered a dramatic rate enhancement in the osmylation of alkene induced by tertiary amines, and this finding paved the way for asymmetric dihydroxylation of olefins. 

In summary, the reaction of osmium tetroxide with alkenes is a reliable and selective transformation. Chiral diamines and cinchona alkakoid are most frequently used as chiral auxiliaries. Complexes derived from osmium tetroxide with diamines do not undergo catalytic turnover, whereas dihydroquinidine and dihydroquinine derivatives have been found to be very effective catalysts for the oxidation of a variety of alkenes. OsC>4 can be used catalytically in the presence of a secondary oxygen donor (e.g., H202, TBHP, A -methylmorpholine-/V-oxide, sodium periodate, 02, sodium hypochlorite, potassium ferricyanide). Furthermore, a remarkable rate enhancement occurs with the addition of a nucleophilic ligand such as pyridine or a tertiary amine. Table 4-11 lists the preferred chiral ligands for the dihydroxylation of a variety of olefins.61 Table 4-12 lists the recommended ligands for each class of olefins. 

To solve this problem, bisoxygenation or dihydroxylation of the model tetracycle 61 was carried out followed by removal of the more activated secondary oxygen functionality in 62 or 63 using reductive methods that we had developed for these specific systems [Scheme 13].59,60 The effort in developing this methodology [61 —> 64] turned out to be significant not only in this synthetic endeavor, but also for future total syntheses employing the formal [3 + 3] cycloaddition reaction. 

It has been observed that reactions of dibutylstannylene acetals of terminal 1,3-diols, or polyols having primary hydroxyl groups free, with t-butyldimethylsilyl chloride yield primary silyl ethers, even for such compounds as methyl a-D-mannopyranoside, where the expectation (see Table VI) for most reactions is for substitution to occur on a secondary oxygen atom.85 88 These observations probably arise from a very large kinetic preference for reaction with primary oxygen atoms, that is, ki2 and k]2 > k2 and K22, in Fig. 12, rather than a rearrangement from initially formed secondary silyl ethers. 

Dibutylstannylene acetals and tributylstannyl ethers of terminal 1,3-diols also react preferentially with most electrophiles on the terminal oxygen atom. The terminal 1,3-diol can be acyclic, or the secondary oxygen atom can be on a ring adjacent to an hydroxymethyl group, such as 0-4 and O-6 of aldohexopyranoses or 0-3 and 0-5 of aldopentofuranoses. Figures 50 to 53 show some examples. 

As previously noted, dibutylstannylene acetals of all compounds that have a free primary hydroxyl group, including such compounds as methyl a-D-mannopyranoside or uridine, which have ds-l,2-diols unprotected, react with f-butylchlorodimethylsilane to give substitution on the primary oxygen atom in high yield.85 88 There is no evidence of any products of substitution on secondary oxygen atoms in these reactions. 

Uranium-secondary oxygen stretching, uranyl bending. 

Paraquat, although restricted from use in Western countries, is a highly toxic herbicide that is still readily available in developing tropical countries. Upon intake, paraquat is rapidly metabolized in the liver and the lungs with the production of secondary oxygen radicals. It is these radicals that cause injury to tissues and especially do so to the lungs. Poisoned animals die acutely of respiratory failure. 

Mayers CL, Jenke DR. Stabilization of oxygen-sensitive formulations via a secondary oxygen scavenger. Pharm Res 1993 10 445-448. 

Steam reforming followed by a secondary oxygen blown reactor (Autothermal)... 

The conventional steam reforming of natural gas is supplemented by the addition of a secondary oxygen-blown reactor where oxygen and by-pass natural gas cure added to enhance the yield of syngas. A "stoichiometric" syngas is produced, and the methanol loop purge gas is usually used as fuel in the primary steam reformer, which is approximately a quarter of the size of that in Route 1. 

Oxygen must be totally excluded from the sample and mobile phase, in order to observe MS-RTP. This is performed by bubbling purified nitrogen gas (passed through a secondary oxygen trap) through all solutions. The presence of a heavy atom (usually thallium or silver ions) as counterion is also required for generation of any appreciable... 

Triphenyllead 2-fluoro-4-nitrosophenolate is associated in chain-like supra-molecular arrays, 142, with secondary oxygen-lead bonds from the p-nitroso substituent [354],... 

For the intermediate range representing the capacity of world-scale methanol plants, a combination of tubular reforming and a secondary oxygen blown reformer is normally the optimum solution. In this concept, the tubular reformer is operating at less severe conditions, i.e. lower outlet temperature (see Section 2.6.2). 

The flow of methane, argon, primary oxygen (saturated with water), and secondary oxygen (saturated vith water) were 2.5, 2.5, 1.4, and 6.3 lh , respectively. According to the stoichiometry of the particular reaction investigated here, this leads to complete condensation of the water formed by the combustion. Two series of experiments were performed. The measured data are... 

Thus, it is proposed that the activity of soybean lipoxygenase-1 may be regulated during secondary oxygenation and / or auto-inactivation, differing according to pH of medium, coocentration of Fe etc. 

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