Ketones reaction with peracids

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 ... 

Garyophyllene. (-)-CaryophyUene can be isolated from Indian turpentine and has been used to prepare a number of woody aroma products. The epoxides are produced by reaction with peracids. Acetylation of caryophyUene also gives a usehil methyl ketone (180) (Fig. 8). Acid-catalyzed rearrangement of caryophyUene in the presence of acetic acid gives a mixture of esters, which are related to caryolan-l-ol and clovan-2-ol (181). 

Ketones react with peracids (RCO3H) to give esters in the Baeyer-Villiger oxidation. The peracid is usually m-chloroperbenzoic acid (mCPBA) peracetic acid and trifluoroperacetic acid are also commonly used. Peracids have an O—OH group attached to the carbonyl C. They are no more acidic than alcohols, because deprotonation of the terminal O does not give a stabilized anion, but they are usually contaminated with some of the corresponding acid. The Baeyer-Villiger reaction is thus usually conducted under mildly acidic conditions. Protonation of the ketone O occms first to make the carbonyl C even more electrophilic than it... 

The choice of the oxidant is primordial, as it acts both as the nucleophile and the leaving group. A reactivity order of oxidants has been established [174]. Peracids and especially m-CPBA [296] are the most efficient oxidants for the Baeyer-Villiger reaction, followed by alkyl peroxides. The reaction with peracids proceeds faster under acid catalysis [297], but buffered solutions can also be used. Some ketones are un-reactive under standard conditions, and need to be transformed into their hemiketals [298]. Safer peracids such as MMPP (magnesium monoperphthalate) [299, 300] and sodium perborate [301] have also been applied giving similar results as m-CPBA. Recently, processes with solid-supported peracids [302] and transformations in the solid state [303] have been developed. 

Commercially, pure ozonides generally are not isolated or handled because of the explosive nature of lower molecular weight species. Ozonides can be hydrolyzed or reduced (eg, by Zn/CH COOH) to aldehydes and/or ketones. Hydrolysis of the cycHc bisperoxide (8) gives similar products. Catalytic (Pt/excess H2) or hydride (eg, LiAlH reduction of (7) provides alcohols. Oxidation (O2, H2O2, peracids) leads to ketones and/or carboxyUc acids. Ozonides also can be catalyticaHy converted to amines by NH and H2. Reaction with an alcohol and anhydrous HCl gives carboxyUc esters. 

A later variation of the general method, which extends the scope to 20-ketones, involves reaction of the ketone with benzylamine to give the imine, followed by conversion to the A-acetyl derivative with acetic anhydride. Although the resulting compound also has a A -double bond, it does not react sufficiently fast with peracid, and a A -double bond can not be preserved. 

The reaction of peracids with ketones proceeds relatively slowly but allows for the conversion of ketones to esters in good yield. In particular, the conversion of cyclic ketones to lactones is synthetically useful because only a single product is to be expected. The reaction has been carried out with both percarboxylic acids and Caro s acid (formed by the combination of potassium persulfate with sulfuric acid). Examples of both procedures are given. 

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. 

The CD fragment 1s synthesized starting with resolved bicyclic acid 129. Sequential catalytic hydrogenation and reduction with sodium borohydride leads to the reduced hydroxy acid 1. The carboxylic acid function is then converted to the methyl ketone by treatment with methyl-lithium and the alcohol is converted to the mesylate. Elimination of the latter group with base leads to the conjugated olefin 133. Catalytic reduction followed by equilibration of the ketone in base leads to the saturated methyl ketone 134. Treatment of that intermediate with peracid leads to scission of the ketone by Bayer Villiger reaction to afford acetate 135. The t-butyl protecting... 

Free-radical autoxidation of aldehydes with 02 is facile and affords the corresponding peradds, which are used as oxidants for carbonyl compounds. The peracid can transfer an oxygen atom to a substrate such as an olefin or ketone, resulting in the formation of one equivalent of epoxide or ester and add as a co-produd in the absence of metal catalysts [59]. Kaneda and coworkers have developed several HT materials that are active for heterogeneous Baeyer-Villiger reactions with 02/aldehyde [60]. Combination with Lewis addic metals improved the reaction by allowing coordination of the peracid and the intermediate. 

Cyclobutanones are the only ketones that undergo Baeyer-Villiger rearrangements not only with peracids but even with alkaline H202 or alkaline ferf-BuOOH (Figure 11.35). In this case, the driving forces of two crucial reaction steps are higher than... 

These reactions become more realistic if derivatives of a,/3-epoxy ketones are used. These can be easily prepared by oxidation of the corresponding a,/3-unsa-turated ketones with peracids or hydrogen peroxide (Scheme VIII/13). The driving force in studying this kind of reactions is the importance of the economic synthesis of the natural 15-membered ketones, muscone and cyclopentadeca-none, from cyclododecanone, an easy available and inexpensive starting material (Scheme VIII/14) [35] [36]. 

Since Hassner s initial report in 1975,7 oxidation of an enol silyl ether with peracid has been a reliable method for the preparation of a-siloxy and ot-hydroxy ketones. However, the submitters have found that, if the enol silyl ether possesses certain structural features, the reaction, with more than two equivalents of the oxidant, affords oc.a -dihydroxylated ketones (i.e., introduction of two oxygen atoms in a single-step) instead of the expected monohydroxylated compounds.8... 

The use of dioxiranes (typically DMDO or methyl(trifluoromethyl)dioxirane) as the oxygen-transfer source in epoxidations provides a commonly used and powerful alternative to peracids. The dioxiranes are prepared from the corresponding ketones via reaction with an oxygen-transfer source, usually Oxone (KHSOs) or hydrogen peroxide, the ketone in principle being a catalytic species. 

Reaction (D) will for example provide one possible route to alcoholic groups, while an alternative reaction, 6-scission of a secondary alkoxy radical, will give aldehyde, reaction (H), which rapidly oxidizes further to peracid. 6 scission of a tertiary alkoxy radical result in ketones. Aldehydes and ketones may react further with peracid to give acid and ester groups. 

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