Perbenzoate anion oxidant

The reaction of iV-(2,4-dinitrophenyl)amino acids with base in aqueous dioxane has been shown to give benzimidazole iV-oxides (7). The rate-determining step is likely to be formation of an iV-alkylidene-2-nitrosoaniline intermediate (6), which is followed by rapid cyclization and decarboxylation.19 The loss of carbon dioxide from perbenzoate anions has been investigated by mass spectrometry and electronic structure calculations. The results, including isotopic labelling experiments, support a mechanism involving initial intramolecular nucleophilic attack at either the ortho- or ipso-ring positions. They also indicate that epoxides may be intermediates en route to the phenoxide products.20 There has also been a theoretical study of the formation of trichlorinated dibenzo-/ -dioxins by reaction of 2,4,5-trichlorophenolate ions with 2,4-dichlorophenol.21... 

The newly formed Si—F bond in 6 enables the oxidative cleavage in the next step in a manner similar to what is observed in the Tamao oxidation. Thus, displacement of the fluoride with perbenzoate anion 7 results in 8. Peroxide 8 can rearrange by a mechanism similar to the Baeyer-Villiger oxidation to yield 9. This process can be repeated twice more resulting in 10. Finally, hydrolysis of 10 produces the desired alcohol. 

Oxidation of C—bonds by copper ion catalyzed reaction with an organic peroxy ester (the Kha-rasch-Sosnovsky reaction) was at one time very popular for allylic oxidation and has been thoroughly reviewed. The reaction is usually carried out by dropwise addition of peroxy ester (conunonly r-butyl peracetate or r-butyl perbenzoate) to a stirred mixture of substrate and copper salt (0.1 mol % commonly copper(I) chloride or bromide) in an inert solvent at mildly elevated temperature (60-120 C). The mechanism involves three steps (i) generation of an alkoxy radical (ii) hyttogen atom abstractitm and (iii) radical oxidation and reaction with carboxylate anion (Scheme 11). 

N-Methylmorpholine oxide peroxide tert-Butyl perbenzoate Acyl peroxides Acetyl-, Benzoyl peroxide Diethyl peroxy-dicarbo-nate. Diisopropyl -Ion exchangers. Anion-, Cation-... 

---