Oxidation reactions copper-catalysed

Oxidation.— Two copper-catalysed reactions have been described for the degradation of the 22-aldehyde (298) to give a pregnan-20-one (299). Oxygenation of a solution of the aldehyde with the copper(n) acetate-2,2 -bipyridyl complex and diazabicyclo-octane in dimethylformamide gave the 20-ketone in 90% yield. A free-radical mechanism is proposed (Scheme 14). 

Chlorine reacts with most elements, both metals and non-metals except carbon, oxygen and nitrogen, forming chlorides. Sometimes the reaction is catalysed by a trace of water (such as in the case of copper and zinc). If the element attacked exhibits several oxidation states, chlorine, like fluorine, forms compounds of high oxidation state, for example iron forms iron(III) chloride and tin forms tin(IV) chloride. Phosphorus, however, forms first the trichloride, PCI3, and (if excess chlorine is present) the pentachloride PCI5. 

Peguy, A. el al., J. Appl. Poly, Science, 1990, 40(3/4), 429 Solutions of cellulose in wet methylmorpholine oxide can undergo exothermic reaction to the point of explosion if confined at elevated temperatures from about 120°C or if otherwise heated to 180°C. The reaction is catalysed by some metals, notably copper. 

The efficiency of a new chiral non-racemic and C2-symmetric 2,2-bipyridyl ligand (6) in copper(I)-catalysed asymmetric allylic oxidation reactions of the cyclic alkenes with f-butyl peroxybenzoate has been evaluated. On performing the reaction of cyclopentene, cyclohexene, and cycloheptene in acetonitrile the corresponding product, (lS)-cycloalk-2-enyl benzoate, was isolated in up to 69% yield and in 91% ee 29... 

Corey chose a Wittig-style (HWE) reaction to control the aldol process and copper-catalysed addition of vinyl Grignard for the conjugate addition. Oxidation with NaI04 and catalytic OSO4 gave the keto-aldehyde 35 which cyclised cleanly under equilibrating conditions. 

Iron and copper catalyse the formation of oxyradicals. Three reactions are relevant in this context (1) Autoxidation of metal complexes may yield the superoxide radical which by itself is not very reactive, but is a precursor of more reactive radical species. (2) The one-electron reduction of hydrogen peroxide -the Fenton reaction - results in hydroxyl radicals via a higher oxidation state of iron [2]. (3) A similar reaction with organic peroxides leads to alkoxyl radicals, although a recent report alleges that hydroxyl radicals are also formed [3]. There is a fourth radical, the formation of which does not require mediation by a metal complex. This is the alkyldioxyl radical, ROO , which is formed at a... 

Caeruloplasmin (Cp) is the major copper-containing protein of human serum and is an acute phase reactant, being synthesised in increased amounts by the liver in inflammation [27]. Several groups have suggested that the pool of non-Cp-bound copper, capable of catalysing oxidative reactions, was elevated in rheumatoid extracellular fluids [28,29], However, these reports are likely to be artifactual, since Cp readily loses its copper during storage-induced oxidation/proteolysis [30,31]. 

Toluene has been oxidized by the silver ion catalysed reaction with peroxy-disulfate. The reaction produces a mixture of bibenzyl, benzaldehyde and benzoic acids.299 Russian workers have described the conversion of 4-methoxy-toluene to the benzaldehyde by oxidation with peroxydisulfate in the presence of silver or copper ions and oxalic acid.300 The presence of copper salts in iron or copper catalysed peroxydisulfate oxidation is believed to suppress side-reactions.301 Phillips have patented a palladium(II)/tin(IV)/persulfate system for the oxidation of toluene derivatives.302 The reactions are carried out in carboxylic acid solvents (Figure 3.78). 

A copper catalysed click (azide-alkyne cycloaddition) reaction has been used to prepare a fluorous-tagged TEMPO catalyst (Figure 7.20). TEMPO is a stable organic free radical that can be used in a range of processes. In this case, its use in metal-free catalytic oxidation of primary alcohols to aldehydes using bleach as the terminal oxidant was demonstrated. The modified TEMPO can be sequestered at the end of the reaction on silica gel 60 and then released using ethyl acetate for reuse in further reactions in this way the TEMPO was used four times with no loss in activity. 

PS has also been used in the copper catalysed aerobic oxidation of primary alcohols (Scheme 9.3). The selective oxidation of primary alcohols into aldehydes can be complicated by overoxidation to carboxylic acids or even decomposition products. These side reactions were not observed in PS, and a high turnover frequency (>31 h ) was achieved. The product could be easily isolated by extraction into -pentane and the PS catalyst-containing phase could be recycled three times. 

In contrast to silver-catalysed cumene oxidation, the evidence concerning the mechanism of copper-catalysed reactions favours radical initiation via surface hydroperoxide decomposition. Gorokhovatsky has shown that the rate of ethyl benzene oxidation responds to changes in the amount of copper(ii) oxide catalyst used, in a manner which is characteristic of this mechanism. Allara and Roberts have studied the oxidation of hexadecane over copper catalysts treated in various ways to produce different surface oxide species, Depending on the catalyst surface area and surface oxide species present, a certain critical hydroperoxide concentration was necessary in order to produce a catalytic reaction. At lower hydroperoxide levels, the reaction was inhibited by the oxidized copper surface. XPS surface analysis of the copper catalysts showed a... 

The number of S- and N-arylations with arylbismuth reagents is relatively limited. The reaction of thiols with pentavalent organobismuth reagents leads mostly to oxidation products and, in some instances, to 5-phenylation. In the case of the nitrogen derivatives, the most efficient arylation by arylbismuth reagents are reactions which are copper-catalysed, and these will be reviewed in a later part of this chapter (see section 6.7). 

The direct oxidation of unfunctionahsed alkanes in an asymmetric fashion is a formidable challenge. However, oxidation of C—H bonds adjacent to suitable functional groups gives a handle on which to operate. In particular, the aUyKc oxidation of cyclic alkenes utilising asymmetric variants of the Kharasch—Sosnovsky reaction has received considerable attention. The reaction is catalysed by copper salts and requires a perester to give the allylic ester as product. 

Aryltrimethyl- or tri- -butylstaimanes as common Stille reagents are also successfully homo-coupled under palladium catalysed reactions in the presence of ethyl 2,3-dibromophenylpropionate (443) [26], or more conveniently by oxidation with copper(I) salts, e.g. CuCl [27], or copper(II) salts, e.g. Cu(N03)2 3H20 [28,29], which proceed smoothly at room temperature in tetrahydrofuran or DMF to afford symmetrical biaryls in excellent 3uelds. The Cu(N03)2-mediated homo-coupling works well also with diaryldimethyl(or -butyl)stannanes [30]. Moreover, the reaction can be accomplished with a catalytic amount of copper(II) chloride or manganese(II) bromide (10 mol%) in the presence of iodine as stoichiometric oxidant [31]. For example, compound 443, acting as an oxidant, converts the phenyltri-n-butylstannane (184) to biphenyl (8) in 86% yield [26], Scheme 11. 

Finally, copper is not entirely inert during wort boiling and appears to catalyse oxidation reactions involving polyphenols, giving rise to greater colour in boiled worts than is the case with stainless steel. While this may not be desirable, the oxidation of some compounds with sulphydryl groupings in copper vessels is said to reduce undesirable sulphurous aromas from the final beer. 

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