Nucleophiles peroxides

Use of mild conditions was crucial and the development of diimide reduction of singlet oxygenates, silver-salt-assisted displacement of halide by peroxide nucleophiles, peroxymercuration and demercuration, peroxide transfer from organotin to alkyl triflates, and oxygen trapping of azoalkane-derived diradicals have all played a part in providing the rich harvest of new bicyclic peroxides described herein. 

Brown and Darwent (1979) recently demonstrated that the hydrophobic effect is also important in the micellar activation of peroxide nucleophiles. Engberts and coworkers reported that proton abstraction by sulfinate anions is facilitated (103-104-fold) in the CTAB micelle (Jagt and Engberts, 1977 van Langkruis and Engberts, 1979). 

As discussed above, the nitro groups of tetranitromethane and trinitromethyl compounds are susceptible to nucleophilic attack. Both potassium iodide and alkaline hydrogen peroxide affect the reductive denitration of trinitromethyl groups to em-nitronitronates 1,1,1-trinitroethane (33) is quantitatively reduced to potassium 1,1-dinitroethane (24) on treatment with alkaline hydrogen peroxide. Nucleophiles such as potassium fluoride in DMF can displace nitrite anion from tetranitromethane. Various nucleophiles, including azide, chloride, fluoride and ethoxide have been used to displace one of the nitro groups from fluorotrinitromethane. 

The two principal routes to the organotin peroxides involve substitution by a peroxide nucleophile at a tin centre (equations 14-69 and 14-70), or (pericyclic) reaction of an allyltin compound with singlet oxygen (equation 14-71). Distannyl peroxides have also been prepared by the (homolytic) reaction of distannanes with triplet oxygen (equation 14-72). 

The olefin attacks the activated peroxide nucleophilically in this reaction vide supra) and substrate reactivity increases as the olefinic electron density increases [32]. For example, epoxidation of p-methoxycinnamyl alcohol is ten times faster than that of p-nitrocinnnamyl alcohol. 

Despite the numerous and detailed studies concerned with the luminol reaction mechanism, the exact nature of the pathways and intermediates involved are somewhat speculative. However, the most likely starting point appears to be the oxidation of the cyclic diacyl hydrazine moiety to give an azaquinone (Scheme 6). In the presence of basic hydrogen peroxide, nucleophilic attack by the hydroperoxide ion would seem most likely this idea is supported by the luminescence intensity dependence upon hydrogen peroxide concentration. Although there are several possible outcomes from the reaction of the azaquinone with hydroperoxide ion, we shall (for reasons of simplicity) concentrate on that shown in Scheme 6. 

CycJohexyl free radicals, generated by photolysis of t-butyl peroxide in excess cyclohexane, also possess nucleophilic character (410). Their attack on thiazole in neutral medium leads to an increase of the 2-isomer and a decrease of 5-isomer relative to the phenylation reaction, in agreement with the positive charge of the 2-position and the negative charge of the 5-position (6). 

The electrophilic character of boron is again evident when we consider the oxida tion of organoboranes In the oxidation phase of the hydroboration-oxidation sequence as presented m Figure 6 11 the conjugate base of hydrogen peroxide attacks boron Hydroperoxide ion is formed m an acid-base reaction m step 1 and attacks boron m step 2 The empty 2p orbital of boron makes it electrophilic and permits nucleophilic reagents such as HOO to add to it... 

Step 2 Anion of hydrogen peroxide acts as a nucleophile attacking boron and forming an oxygen-boron bond... 

The other group of transition metals comprises those metals that retain d electrons in their normal valence states, eg, Co " and Pp". These metals form peroxides from dioxygen or from hydrogen peroxide. Their colors result from d—d transitions. These peroxo species act as nucleophiles. 

The susceptibihty of dialkyl peroxides to acids and bases depends on peroxide stmcture and the type and strength of the acid or base. In dilute aqueous sulfuric acid (<50%) di-Z fZ-butyl peroxide is resistant to reaction whereas in concentrated sulfuric acid this peroxide gradually forms polyisobutylene. In 50 wt % methanolic sulfuric acid, Z fZ-butyl methyl ether is produced in high yield (66). In acidic environments, unsymmetrical acychc alkyl aralkyl peroxides undergo carbon—oxygen fission, forming acychc alkyl hydroperoxides and aralkyl carbonium ions. The latter react with nucleophiles,... 

DiaLkyl peroxides also undergo nucleophilic displacements by organometaUic compounds ... 

Substitution reactions on dialkyl peroxides without concurrent peroxide cleavage have been reported, eg, the nitration of dicumyl peroxide (44), and the chlorination of di-/ fZ-butyl peroxide (77). Bromination by nucleophilic displacement on a-chloro- or a-hydroxyalkyl peroxides with hydrogen bromide produces a-bromoalkyl peroxides (78). 

CgH COO from BPO. The first type involves direct radical displacement on the oxygen—oxygen bond and is the preferred mode for nucleophilic radicals, eg, -CH(R)OR7 The second type involves radical addition to, or abstraction from, the hydrocarbyl group adjacent to the peroxide this is the preferred mode for electrophilic radicals, eg, Cl C (eq. 32). In the last type (eq. 33), there is hydrogen donation from certain hydrogen-donating radicals, eg, ketyls (52,187,188,199). 

Amines also react with diacyl peroxides by nucleophilic displacement on the oxygen—oxygen bond forming an ion pair iatermediate (187) ... 

The NOBS system undergoes an additional reaction that forms a diacyl peroxide as a result of the nucleophilic attack of the peracid anion on the NOBS precursor as shown in equation 21. This undesirable side reaction can be minimized by the use of an excess molar quantity of hydrogen peroxide (91,96) or by the use of shorter dialkyl chain acid derivatives. However, the use of these acid derivatives also appears to result in less efficient bleaching. The dependence of the acid group on the side product formation is apparentiy the result of the proximity of the newly formed peracid to unreacted NOBS in the micellar environment (91). A variety of other peracid precursor stmctures can be found (97—118). 

The purely chemical analogy involving nucleophilic attack and subsequent oxidation can be achieved by hydrogen peroxide, which converts pteridin-6-one into pteridine-6,7-dione (52JCS1620), and xanthopterin (4) into leucopterin (6) (39LA(539)179). Isoxanthopterin (5) reacts with nitrous acid to give pteridine-2,4,6,7-tetrone (44LA(555)146). 

Nucleophilic opening of oxiranes to give ultimately 1,2-diols is usually effected without isolation of the oxirane oxiranation (epoxidation) of alkenes with unbuffered peroxy-ethanoic acid or hydrogen peroxide in methanoic acid (Section 5.05.4.2.2(/)) tends to give monoesters of 1,2-diols (e.g. 53), which can be hydrolyzed to the diols (Scheme 46). 

The most important oxirane syntheses are by addition of an oxygen atom to a carbon-carbon double bond, i.e. by the epoxidation of alkenes, and these are considered in Section 5.05.4.2.2. The closing, by nucleophilic attack of oxygen on carbon, of an OCCX moiety is dealt with in Section 5.05.4.2.1 (this approach often uses alkenes as starting materials). Finally, oxirane synthesis from heterocycles is considered in Section 5.05.4.3 one of these methods, thermal rearrangement of 1,4-peroxides (Section 5.05.4.3.2), has assumed some importance in recent years. The synthesis of oxiranes is reviewed in (B-73MI50500) and (64HC(19-1U). 

Double bonds in a,/3-unsaturated keto steroids can be selectively oxidized with alkaline hydrogen peroxide to yield epoxy ketones. In contrast to the electrophilic addition mechanism of peracids, the mechanism of alkaline epoxidation involves nucleophilic attack of hydroperoxide ion on the con-... 

Nitrated fluoro compounds are synthesized by electrophilic (NOz+), radical (NO2 ), or nucleophilic (NO2-) methods Indirect nitration routes can suppress the side reactions associated with severe reaction conditions and some nitration reagents Novel fluoronitro compounds, unobtainable by direct nitration, can also be pre pared For example, the nitration of (2-fluoro-2,2-dinitroethoxy)acetaldoxime followed by oxidation of the nitroso intermediate with hydrogen peroxide yields 2-fluoro-2,2-dinitioethyl 2,2-dinitroethyl ether [f] (equation 1)... 

Campaigne et al. have used 3-thenyl bromide obtained by benzoyl peroxide-catalyzed, side-chain bromination of 3-methylthiophene with A -bromosuccinimide, as a starting material for 3-substituted thiophenes. - 22 3-Methylthiophene is now prepared commercially from itaconic acid. The reactive halogen in 3-thenyl bromide could be directly reacted with a variety of nucleophiles, such as cyanide, or malonate, to give more complex 3-substituted compounds. 3-Thenyl bromide was converted by the Sommelet reaction to 3-thio-phenealdehyde which, with silver oxide, was oxidized to 3-thio-... 

In addition to having typical A -oxide reactions, quinazoline 3-oxide also shows the same reactivity as quinazoline toward nucleophilic reagents, but the reaction goes a step further by eliminating water as shown in reaction 2d. Oxidation with hydrogen peroxide... 

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