Peracids, reactivity

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 ... 

Reactive halogen compounds, alkyl haUdes, and activated alkenes give quaternary pyridinium salts, such as (12). Oxidation with peracids gives pyridine Akoxides, such as pyridine AJ-oxide itself [694-59-7] (13), which are useful for further synthetic transformations (11). 

While the oxidation of ketones by peracids (Baeyer-Villiger reaction) has been used in steroids mainly for ring cleavage, it has occasionally been applied to 20-ketopregnanes for conversion to 17-acetoxy- or hydroxyandros-tanes. The synthetic utility of this method is limited since reactive double bonds and other ketones are incompatible with the reagent. 

In a first step the reactivity of the carbonyl group is increased by protonation at the carbonyl oxygen. The peracid then adds to the cationic species 3 leading to the so-called Criegee intermediate 4 ... 

The reactivity of the unsaturated system of oxepin gives rise to a variety of cycloaddition reactions. A number of 3,6-bridged oxepins have been reacted with peracids to give 2,3-ep-oxyoxepins i,129 154.213.218 At higher temperature, the 2,3,6,7-diepoxy derivatives 2 are formed.164... 

Once the active Co catalyst has been formed by peracid oxidation of Co the next step is determined by the relative rates of reaction of this species with other species present in the solution, i.e. Mn, Br" and the substrate, and its rearrangement to the much less reactive Co . As can be seen from these data (Fig. 15), the relative rates of reaction of Co with Mn Br" and p-xylene are 940, 84 and 0.03, compared to 1 for the conversion of Co to Co (ref. 9). This means that in a mixture containing Co , Mn Br" and p-xylene, > 90% of Co reacts with Mn to afford Mn and that there is no reaction of Co with the p-xylene substrate. 

As alkylaromatic hydrocarbon (toluene, p-xylene, etc.) is oxidized, aldehydes appear radicals and peracids formed from them play an important role. First, aldehydes react rapidly with the Co3+ and Mn3+ ions, which intensifies oxidation. Second, acylperoxyl radicals formed from aldehydes are very reactive and rapidly react with the initial hydrocarbon. Third, aldehydes form an adduct with primary hydroperoxide, which decomposes to form aldehyde and acid. 

The reactivities of different olefins toward seodecylsulfonic peracid (values of k and k2) are listed in Table 12.5. 

Cyclobutanone annulation onto a carbonyl group translates into y-butyrolactone annulation because of the facility of the Baeyer-Villiger reaction (Eq. 68 a)8). Indeed, the reaction proceeds sufficiently rapidly that even basic hydrogen peroxide effects the oxidation whereas, with less reactive carbonyl partners, peracids must be used. 

The reaction of allenes with peracids and other oxygen transfer reagents such as dimethyldioxirane (DM DO) or hydrogen peroxide proceeds via allene oxide intermediates (Scheme 17.17). The allene oxide moiety is a versatile functionality. It encompasses the structural features of an epoxide, an olefin and an enol ether. These reactive intermediates may then isomerize to cyclopropanones, react with nucleophiles to give functionalized ketones or participate in a second epoxidation reaction to give spirodioxides, which can react further with a nucleophile to give hydroxy ketones. 

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