Intermediates peroxyacids

With a peroxyacid, the reagent used in their preparation, oxaziridines further react to yield aliphatic nitroso compounds. An electrophilic attack to ring nitrogen is plausible, leading to an intermediate oxaziridine N-oxide (81), which immediately decomposes to a nitroso compound and an aldehyde (57JA6522). 

Peroxyacids transfer an oxygen atom to the alkene with syn stereochemistry—both C-0 bonds form on the same face of the double bond-through a one-step mechanism without intermediates. The oxygen atom farthest from the carbonyl group is the one transferred. 

The Baeyer-Villiger process for conversion of open-chain ketones to esters, or cyclic ketones to lactones by a peracid involves an intermediate a-hydroxyperester (235) step, as shown in equation 83. Determination of 235 in the reaction mixture involves selective reduction of the peroxyacid with diphenyl sulfide and reduction of 235 with excess iodide, followed by titration of the liberated iodine. The presence of various transition metal ions may affect the determination by accelerating the final step of the synthetic process, thus... 

Diphenyl-1 -pyrenylphosphine hydroperoxide determination, 679-80 peroxide value, 659, 680 Diphenyl sulfide, peroxyacid reduction, 700-1 Dipolar intermediate, ene reaction, 853 Dipole moments, dioxiranes, 1132 DIPT (diisopropyl tartrate), 395 Dipyridamole, low-density hpoprotein antioxidant, 611 Di radicals... 

Oxepane (159) was obtained in high yield as an unexpected product of rearrangement from the peroxyacid oxidation of the substituted furan shown in equation (45) (81JOC2589). The isomerization of a bis-epoxide intermediate to the ring expansion product (159) occurs in the final step of the latter reaction. ... 

The two major characteristic oxidation processes of alkynes are their transformation to 1,2-dicarbonyl compounds and their cleavage reaction to carboxylic acids.710 The structure of the starting compounds has a decisive effect on the selectivity of oxidation. Since 1,2-dicarbonyl compounds proved to be intermediates in further oxidations, carefully controlled reaction conditions are often necessary to achieve selective synthesis. Certain oxidizing agents such as peroxyacids and ozone are nonselective oxidants. 

L-m <2ft / o-Hex os- 5- u l ose (220) can be prepared from /f-D-galactopyrano-sides via peroxyacid oxidation of intermediate 4-deoxy-a-L-t/ireo-hex-4-enopyranosides (Scheme 22).437... 

When an alkene is treated with a peroxyacid (RC03H) it forms a epoxide (Following fig.). m-Chloroperoxybenzoic acid is one of the most commonly used peroxyacids for this reaction. The reaction is unusual because there is no carbocation intermediate, and it involves a one-step process without intermediates. 

An epoxide is a three-membered cyclic ether, also called an oxirane. Epoxides are valuable synthetic intermediates used for converting alkenes to a variety of other functional groups. An alkene is converted to an epoxide by a peroxyacid, a carboxylic acid that has an extra oxygen atom in a —O—O— (peroxy) linkage. 

A peroxyacid epoxidizes an alkene by a concerted electrophilic reaction where several bonds are broken and several are formed at the same time. Starting with the alkene and the peroxyacid, a one-step reaction gives the epoxide and the acid directly, without any intermediates. 

Direct anti hydroxylation of an alkene (without isolation of the epoxide intermediate) is possible by using an acidic aqueous solution of a peroxyacid. As soon as the epoxide is formed, it hydrolyzes to the glycol. Peroxyacetic acid (CH3CO3H) and peroxyformic acid (HCO3H) are often used for the anti hydroxylation of alkenes. 

In the transition state (marked %) the peroxyacid prefers to be well away from R, even if R is only a methyl group. The selectivity is 76 24 with methyl. The opposite stereoselectivity can be achieved by bromination in water. The bromonium ion intermediate is formed stereoselectively on the less hindered side and the water is forced to attack stereospecifically in an Sj j2 reaction from the more hindered side. 

Another route to the preparation of a-hydroxy derivatives consists of the transformation of enolates into silyl enolates and their subsequent oxidation. Oxidation of triaLkylsUyl enolates with peroxyacids, most frequently cpba, has been applied for preparation of a-hydroxy- and a-acetoxy aldehydes or ketones. Reactions require mild conditions and generally give good yields of the expected compound . Mechanistic investigations suggest the intermediate formation of epoxides which evolve to the final products via 1,4-sUyl group migration. 

The epoxidation reaction of arene oxide-oxepins has been encountered in the formation of the arene dioxides of naphthalene and anthracene rings A similar approach to the synthesis of epoxides of benzene oxide-oxepin using a peroxyacid oxidant, however, was unsuccessful (Z,Z)-muconaldehyde was isolated presumably via an oxepin-epoxide intermediate. The disubstituted benzene... 

Regioselectivity usually arises when an unsymmetrical electrophile attacks an unsymmetrical alkene. Familiar examples would be the action of bromine water or peroxyacids on a terminal alkene 8. The intermediate bromonium ion would be attacked by water at the more substituted end 9 and the epoxide by a nucleophile at the less substituted end 7. 

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