Oxidation reactions with ketyls

The radical produced by OH reaction with acetone CHsCOCHa, is not oxidized by the phenone. When a solution containing high concentrations of both acetone and isopropyl alcohol is irradiated in the presence of benzophenone, the yield of ketyl anion is approximately twice that observed in isopropyl alcohol-free solutions (8). The concentrations of acetone and isopropyl alcohol can be adjusted so that all electrons react with acetone and OH radicals react exclusively with isopropyl... 

Ascorbic acid is highly reactive to all the primary water radicals, because of its carbonyl group and double bond. Reaction with ei or H reduces ascorbic acid to a ketyl radical, while reaction with OH oxidizes it to the relatively unreactive tricarbonyl radical ion [9]. Aside from a possible reaction with cytochrome-c (or ferrimyoglobin), the radical ion is most likely to undergo a complex disproportionation reaction that regenerates the ascorbic acid and produces dehydroascorbic acid, which has essentially the same vitamin activity. These reactions need to be considered, because ascorbic acid is added to foods to fortify them, to facilitate curing meats, and to enhance antioxidants. 

The resulting organometallic species can be further reduced to a carbonyl anion with Na/Hg alloy or potassium ketyl, which can be reacted with other cationic species giving rise to a whole range of substituted derivatives. A problem that can arise, however, is that, particularly for the carbonyl anions of the larger cluster complexes, reaction with the cationic species may lead to oxidation of the cluster... 

The di(/x-disulfido)diiron complex 243 (L = Gp ) is converted into the di(/U3-sulfido)triiron complex 244 by thermal reaction with iron carbonyls. Selective mono-GO substitution of 244 by PPh3 is accelerated by photolysis or by treatment with reductant (benzophenone ketyl) or oxidant (ferrocenium cation). ... 

In the pyridine A-oxide anion-radical, the greatest spin density belongs to the carbon atom in the position 2 (Chaha 1986). In accordance with this, a reaction between the pyridine A-oxide anion-radical and the benzophenone metal ketyl yielded preferentially 2-diarylcarbinole derivatives (Kurbatova et al. 1980, Turaeva et al. 1993 Scheme 3.10). 

Treatment of diphenylmethane in basic solution with a trace of oxygen in DMSO solutions fails to produce significant amounts of a paramagnetic product detectable by ESR spectroscopy. On the other hand, treatment of benzhydrol with traces of oxygen in basic solution can produce significant amounts of the ketyl. Pyridylthiazolylcarbinols are readily converted to the ketyls by base in alcoholic solution. (24). In pure DMSO significant amounts of the ketyl are formed whereas in tert-butyl alcohol or DMSO (80% )-tert-butyl alcohol (20% ) only traces of the ketyl can be detected. These results are consistent with the formation of the ketyl under oxidative conditions by Reaction 31. Only under the most basic conditions (pure DMSO) is the dianion formed by... 

Oxidation of xanthenol or fluorenol with deficient quantities of oxygen in tert-butyl alcohol produced large quantities of the ketyl, as did reaction of equal molar amounts of the ketone and alcohol in basic solution. In fact, the reaction of the pinacol of fluorenone with excess base in tert-butyl alcohol produced an essentially quantitative yield of the ketyl (19). 

The reaction depicted also proceeds between pyridine oxide in its neutral form and the double amount of benzophenone metal-ketyl. Pyridine bases (not N-oxides) do not react with the ketyls. The N-oxides of pyridine and y-picoline give both the N-oxide of the pyridyl carbinol and the pyridyl carbinol without the N-oxide oxygen. Yields can be 70 and 80%, respectively (depending on the metal nature in the metal-ketyl). Having pronounced physiological activity, these compounds are the key materials in syntheses of atropine-like drugs. 

The reaction of the ketyl radical anion with the oxidized rhenium complex is the energy-releasing electron transfer step. This reaction cannot be carried out separately. While ketyl radical anions are stable species, the oxidized complex is not stable and must be generated as short-lived intermediat. ... 

In parallel the cocatalysis of cobalt compounds with A7-hydroxyphthalimide 398 was developed extensively for oxidative radical reactions [434]. Ishii and colleagues showed that these conditions can be used in radical additions (Fig. 92). Ketyl radicals generated by hydrogen abstraction from secondary alcohols 396 add to a.p-unsaturated esters 397 affording 2,4-dihydroxy esters, which cyclized to lactones 399 under the reactions conditions [435]. Using 0.1 mol% of Co(OAc)2, 1 mol% of Co(acac)3, and 10 mol% of 398 under 1 atm of oxygen, the cyclic products 399 were isolated in 14—90% yield. As observed for similar reactions, Co(III) alone needs an induction period (see below). 

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