Hydroperoxide anions

The reaction is characteristic of the usual Michael addition of hydroperoxide anion, yielding enantiomeric excesses up to 45%. 

Through a short sequence of functional group manipulations, compound 6 could be elaborated from allylic alcohol 7, the projected product of a Wharton fragmentation4 of epoxy ketone 8 (vide infra). In turn, compound 8 could be derived from enone 9. In the synthetic direction, a Michael addition5 of hydroperoxide anion to enone 9 would be expected to take place from the less hindered side of the molecule. Epoxy ketone 8 would fhen form upon collapse of the intermediate enolate with concomitant expulsion of hydroxide ion (see arrows, Scheme 2). 

The pH dependence of the rate suggests that nucleophilic attack by the sulphur atom of the sulphoxide on the undissociated hydroperoxide is unimportant while nucleophilic attack by the hydroperoxide anion on the sulphoxide is the preferred reaction under these conditions. Changing the alkyl substituent of the sulphoxide had little effect on the rate and thus the reaction probably proceeds in a similar manner as for oxidation by peracids... 

How does oxygen insert in between the B—bonds Let s take a closer look at the reagents— a hydroxide ion can deprotonate hydrogen peroxide to form a hydroperoxide anion ... 

This hydroperoxide anion can attack the trialkylborane (remember that the boron atom still has an empty p orbital, and therefore, it is still scavenging for electron density) ... 

Arguments for a nonchain reaction between the enolate and oxygen to give the hydroperoxide anion directly have been advanced as well.249... 

Step 5. H+ adds to the system generating a heme-bound hydroperoxide anion complex formally equivalent to heme Fe02H2+. 

A survey of crystal structures of 29 compounds (Table 8), in which the alkyl hydroperoxide anions serves as ligand to metal ions, transition metal ions or group 13-17 elements, provides a mean 0—0 bond length of 1.46 0.03 A, an O—O—C angle of 109 2.1° and a M—O—O angle of 112 6.9°. More specialized aspects that deserve to be addressed separately refer to the nature of the M—O bond, the magnitude of the dihedral angle M—O—O—C and the tetrahedral distortion of the peroxide bound C atom. 

Alkyl halides, hydroperoxide synthesis, 327-8 Alkyl hydroperoxides anion ligands, 114-19 covalent radii, 114, 118-19 dihedral angles, 119 geometric parameters, 115-8 tetrahedral distortion, 119 artemisinin formation, 133-4 chlorotriorganosilane reactions, 779-83 crystal structure, 105-14 anomeric effect, 110-11 geometric parameters, 106-9 hydrogen bonding, 103-5, 111-14 tetrahedral distortion, 110 determination, 674... 

Covalent radii, alkyl hydroperoxide anion hgands, 114, 118-19... 

There is much evidence, including inhibition by superoxide dismutase and stimulation by added potassium superoxide,384 that the superoxide anion radical is the species that attacks the substrate (Eq. 18-39). In this reaction one electron is returned to the Fe(III) form of the enzyme to regenerate the original Fe(II) form. Subsequent reaction of the hydroperoxide anion would give the observed products. 

Methyl acrylate and acrylonitrile (Eq. 80), on the other hand, nt reportod by Yang and Finnegan1 to give no epoxides, but instead the peroxides corresponding to Michael addition of left-butyl hydroperoxide anion to the conjugated systems. 

Mechanism. The earliest mechanistic interpretation of alka- ini hydrogen peroxide epoxidation waa given by Bunton and Min- who found, for the case of ethylideneaoetone and mesityl oxide, iii>t-nrder kinetics with respect to both the unsaturated ketone and the hydroperoxide anion. Accordingly, the reaction was presumed to occur l.v the path shown in Eq. (Si), step (6) being rate-determining- The... 

Consideration of reasonable mechanisms for producing formic acid from an aldose led to the hypothesis that the sugar forms an addition product with the hydroperoxide anion, comparable with an aldehyde sulfite or the addition product of aldoses with chlorous acid (52). The intermediate product (12) could decompose by a free-radical or an ionic mechanism. In the absence of a free-radical catalyst, the ionic mechanism of Scheme VIII seems probable. By either mechanism the products are formic acid and the next lower sugar. The lower sugar then repeats the process, with the result that the aldose is degraded stepwise to formic acid. Addition of the hydroperoxide anion to the carbonyl carbon is in accord with its strong nucleophilic character (53) and with certain reaction mechanisms suggested in the literature (54) for related substances. 

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