Peracids Baeyer Villiger reaction

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. 

A variety of esters can be prepared from the corresponding ketones usiag peracids ia a process usually referred to as the Baeyer-Villiger reaction (95) ie, cyclopentanone is converted to 5-valerolactone upon treatment of the ketone with peroxytrifluoroacetic acid ... 

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. 

Co2 +-Substitution at the addenda atoms gives catalysts for the epoxidation of olefins in the presence of aldehyde [293). PWM-Co is the most active among the mono-transition-metal-substituted polyanions the order of activity is PWn-Co > -Mn 2= -Fe 2= -Cu > -Ni. Here, PWll(M + )0(379", ) (M = Co2 +, Cu2+, Fe3 +, Ni2 +, Mn2 + ) is denoted by PWn M. The same order was observed for the oxidation of isobutyraldehyde, suggesting that the oxidation of aldehyde to give peracid is an important step in the reaction. It has been reported that substitution of V5+ for Mo6+ in PMo O3 gives a good catalyst for epoxidation and the Baeyer-Villiger reaction [294). 

An interesting asymmetric Baeyer-Villiger reaction of prochiral ketones via chiral ketals (9) allowed the synthesis of chiral 3-butyrolactones in ees of up to 89%.167 An SnCU mCPBA ratio of >1 in dichloromethane at —100 °C gave the best results and this is attributed to a high 5k 1 character due to lowered nucleophilicity of peracid by coordination to S11CI4. This is mirrored by die beder selectivity of BH3 dian EtjSiH in acetal reductions. 

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. 

Peracids may epoxidize alkenes faster than they take part in Baeyer-Villiger reactions, so unsaturated ketones are not often good substrates for Baeyer-Villiger reactions. The balance is rather delicate. The two factors that matter are how electrophilic is the ketone and how nucleophilic is the alkene You might like to consider why this reaction does work, and why the C=C double bond here is particularly unreactive. 

Baeyer-Villiger reactions also occur under alkaline conditions, although poorer results are usually obtained compared with the use of peracids (see... 

Treatment of heterocyclic enamides with peracids resulted in the oxidative fission of the double bond, followed by Baeyer-Villiger reaction of the methoxylated benzaldehyde intermediate45 (Scheme 30). 

FAD ready for a subsequent catalytic cycle. This enzyme catalyzed Baeyer-Villiger oxidation bears great resemblance to the analogous chemical reaction performed by peroxides or peracids, which act as nucleophiles. Globally these flavin-enzymes can perform the same reactions as peracids, i.e. epoxidations, Baeyer-Villiger-reactions and nucleophilic heteroatom oxidation [26-28]. 

Baeyer-Villiger reaction. This peracid is recommended for large-scale Baeyer-Villigcr oxidation of unreactivc ketones. It is almost as reactive as trifluoropcracetic acid, but is less expensive. The 90% H 0, originally used for in situ preparation of the pcracid can be replaced by the less hazardous 30% H,0,. By suitable modifications, dodccanolide (2) can be prepared in 77% yield from cyclododecanone. 

The peracid oxidizes secondary hydroxy groups to ketones, which then undergo the Baeyer-Villiger reaction. 

Peroxy propionic acid (C2H5CO3H) [340], peroxylauric acid (C11H23CO3H) [174], and other aliphatic peroxy acids [341] are used rarely, and the results do not differ appreciably from those obtained from more common peracids. The same is true of peroxypentafluorobenzoic acid, C FjCOjH, which is obtained from pentafluorobenzaldehyde and ozone and is used for epoxidations the Baeyer-Villiger reaction and the preparation of amine oxides, sulfoxides, and sulfones [342]. 

Ethers are most prone to autoxidation because O can stabilize an adjacent alkyl radical, but aldehydes are also quite prone to autoxidation. In the latter case, the immediate products, carboxylic peracids, react with the starting aldehydes to give carboxylic acids by a Baeyer-Villiger reaction (Chapter 2). 

Baeyer-Villiger reactions. The oxidation of aromatic, open-chain, and cyclic ketones to esters and lactones by peracids. 

Oxidation. Hexafluoroacetone (available from Aldrich) and hydrogen peroxide form a complex which functions as a peracid. Thus it can be used in the Baeyer-Villiger reaction and for oxidation of a primary aromatic amine to a nitro compound. Preliminary results, however, indicate that the adduct is less powerful than pertrifluoroacetic acid.1... 

Flavin hydroperoxides, acting as nucleophiles, can oxidize ketones to esters in Baeyer-Villiger reactions, analogous to peracids in organic synthesis (Equation (18)). 

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... 

Baeyer-Villiger reaction. This peracid has been used for the Baeycr-Villiger reaction with cyclopentanones and cyclohexanones. The reaction is carried out with 1.25 molar equiv. of benzeneseleninic acid and 10 molar equiv. of H2O2 in THF or CH2CI2 buffered to pH 7. Yields are comparable to those with other peracids. One example, 1 2, was reported where oxidation was achieved only with this peracid. 

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