Ketones, oxidative reactions with

The chemical properties of cycHc ketones also vary with ring size. Lower members (addition reactions, than corresponding acycHc ketones. The Cg—C 2 ketones are unreactive, reflecting the strain and high enol content of medium-sized ring systems. Lactones are prepared from cycHc ketones by the Bayer-ViUiger oxidation reaction with peracids. S-Caprolactone is manufactured from cyclohexane by this process ... 

The radicals that are formed from the enolate in this process are rapidly destroyed so that only the stable semidione species remains detectable for EPR study. Semidiones can also be generated oxidatively from ketones by reaction with oxygen in the presence of base. The diketone is presumably generated oxidatively and then reduced to the semidione via reduction by the enolate derived from the original ketone. 

TS-1 is a material that perfectly fits the definition of single-site catalyst discussed in the previous Section. It is an active and selective catalyst in a number of low-temperature oxidation reactions with aqueous H2O2 as the oxidant. Such reactions include phenol hydroxylation [9,17], olefin epoxida-tion [9,10,14,17,40], alkane oxidation [11,17,20], oxidation of ammonia to hydroxylamine [14,17,18], cyclohexanone ammoximation [8,17,18,41], conversion of secondary amines to dialkylhydroxylamines [8,17], and conversion of secondary alcohols to ketones [9,17], (see Fig. 1). Few oxidation reactions with ozone and oxygen as oxidants have been investigated. 

Dehydrogenation of alcohols.1 Ally lie or secondary alcohols can be oxidized to the ketones by reaction with 1 catalyzed by RuH2[P(C6H5) ,]4 in benzene. The... 

Common oxidants cannot be used, because they oxidize the 0=C bond. Since the starting compound is a methyl ketone, its reaction with NaOI removes CH, and converts. 

Oxidative deoximation/ Ketoximes revert to ketones by reaction with H,0, in an alkaline medium (75 95° yield, five examples). 

A Mo02(acac)2-Bu 02H reagent has been shown to yield mixtures of allyl alcohols and a,(3-unsatu-rated ketones on reaction with ir-allyl species (equation 88).275 Photo-oxidation of preformed allyl complexes has also been reported (equation 89).276 277... 

In spite of the fact that numerous oxidation reactions are known, that lead to a-functionalization of ketones [159,160], in most cases enol radical cations are not involved in these transformations, and rigorous evidence for their formation through selective oxidation of the enol tautomer (Fig. 2, path 2) has only been obtained in a few cases. For example, it could be inferred from kinetic studies that in many cases enols are not intermediates in aqueous oxidation reactions with V(V), Co(III), Ce(IV) and Mn(III) [161-163], whereas in acetic acid Mn(III) was postulated to attack the enol form of ketones [164,165], but not by electron transfer [166]. On the other hand, oxidants as Cr(VI), Tl(III), Hg(II) and Mn(VII) [167] as well as Pb(IV) [168] definitely react with the enol form, but since with these inner-sphere oxidants electron transfer is assumed to occur in a bonded fashion, radical cation intermediates are most likely not implicated. 

Hence, the first clearcut evidence for the involvement of enol radical cations in ketone oxidation reactions was provided by Henry [109] and Littler [110,112]. From kinetic results and product studies it was concluded that in the oxidation of cyclohexanone using the outer-sphere one-electron oxidants, tris-substituted 2,2 -bipyridyl or 1,10-phenanthroline complexes of iron(III) and ruthenium(III) or sodium hexachloroiridate(IV) (IrCI), the cyclohexenol radical cation (65" ) is formed, which rapidly deprotonates to the a-carbonyl radical 66. An upper limit for the deuterium isotope effect in the oxidation step (k /kjy < 2) suggests that electron transfer from the enol to the metal complex occurs prior to the loss of the proton [109]. In the reaction with the ruthenium(III) salt, four main products were formed 2-hydroxycyclohexanone (67), cyclohexenone, cyclopen tanecarboxylic acid and 1,2-cyclohexanedione, whereas oxidation with IrCl afforded 2-chlorocyclohexanone in almost quantitative yield. Similarly, enol radical cations can be invoked in the oxidation reactions of aliphatic ketones with the substitution inert dodecatungstocobaltate(III), CoW,20 o complex [169]. Unfortunately, these results have never been linked to the general concept of inversion of stability order of enol/ketone systems (Sect. 2) and thus have never received wide attention. 

Peroxy adds may epoxidize unsaturated ketones [299, 332], but a concomitant Baeyer-Villiger reaction is possible [254] (equations 389 and 391). Other ways of forming epoxy ketones are reactions with salts of hypochloric acid [691, 704] and with V-bromosuccinimide [746]. Mesityl oxide is converted into its epoxide, as shown in equation 437 [142, 220, 254, 746]. 

On the one hand, thioacetals of a,B-unsaturated ketones resulting from the a-alkylation reaction reported above have been transformed efficiently into the corresponding unsaturated ketones on reaction with mercury(II) chloride and oxide in methanol (Scheme 71, entry or on reaction - with... 

A useful route for the unequivocal synthesis of complex derivatives of this ring system involves cyclization of compounds of general formula 63. These are readily prepared from the appropriate 2-chloro-3-nitropyridine and an aminoketone. If the requisite amino ketone is too unstable, the corresponding amino alcohol may be used and oxidized to the ketone after reaction with the chloropyridine. 

Allyl alkyl ethers are converted to ketones on reaction with /-BuOOH in the presence of a catalytic amount of CrO, in dichloromethane at room temperature. This oxidation does not affect THP, TBS, and MOM ethers. 

New Applications of Tetracyanoethylene (TCNE) in Organic Chemistry, A. J. Fatiadi (1986). This review with 501 references deals with reactions of tetracyanoethylene used in organic synthesis. Information on molecular complexes, ozonization of alkenes and acetylenes, dehydrogenation and tricyanovinylation, reactions of TCNE oxide, reactions with ketones and diketones, synthesis of heterocycles and cationic polymerizations are included in this survey. Some industrial and analytical applications are also discussed. 

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