Intramolecular hydroperoxides

In addition to these extensive studies on electrophile-mediated intramolecular peroxydation of electron-rich C=C bonds, some examples of intramolecular hydroperoxide addition to electron-poor C=C bonds have been described. For example, several racemic analogues 371 of the naturally occurring plakinic acid were readily obtained by peroxymercuration followed by hydridodemercuration of the dienic acids 370 (Scheme 95 f °. Intramolecular Michael addition of hydroperoxide function to the double... 

If the grafting is carried out in air, the active sites on the polymeric backbone is attacked by atmospheric oxygen leading to the formation of macroperoxy radical, which might abstract the hydrogen atom from the backbone polymer by an inter- or intramolecular process to give hydroperoxide groups as shown. 

Irradiation of the polymer in air prior to grafting introduces hydroperoxide groups in the backbone polymer by the intermolecular, intramolecular, or hydrogen abstraction process. 

The mechanism for such a process was explained in terms of a structure as depicted in Figure 6.5. The allylic alcohol and the alkyl hydroperoxide are incorporated into the vanadium coordination sphere and the oxygen transfer from the peroxide to the olefin takes place in an intramolecular fashion (as described above for titanium tartrate catalyst) [30, 32]. 

An intramolecular variation of this method, employing 3-bromocycloalkyl hydroperoxides 24, has proved a versatile procedure for the synthesis of bicyclic peroxides with an [n.2,1] skeletal arrangement, 25 (Eq. 20). 

Metal alkoxides undergo alkoxide exchange with alcoholic compounds such as alcohols, hydro-xamic acids, and alkyl hydroperoxides. Alkyl hydroperoxides themselves do not epoxidize olefins. However, hydroperoxides coordinated to a metal ion are activated by coordination of the distal oxygen (O2) and undergo epoxidation (Scheme 1). When the olefin is an allylic alcohol, both hydroperoxide and olefin are coordinated to the metal ion and the epoxidation occurs swiftly in an intramolecular manner.22 Thus, the epoxidation of an allylic alcohol proceeds selectively in the presence of an isolated olefin.23,24 In this metal-mediated epoxidation of allylic alcohols, some alkoxide(s) (—OR) do not participate in the epoxidation. Therefore, if such bystander alkoxide(s) are replaced with optically active ones, the epoxidation is expected to be enantioselective. Indeed, Yamada et al.25 and Sharp less et al.26 independently reported the epoxidation of allylic alcohols using Mo02(acac)2 modified with V-methyl-ephedrine and VO (acac)2 modified with an optically active hydroxamic acid as the catalyst, respectively, albeit with modest enantioselectivity. 

A molecule of linear alkyl ether possesses a very convenient geometry for intramolecular hydrogen atom abstraction by the peroxyl radical. Therefore, chain propagation is performed by two ways in oxidized ethers intermolecular and intramolecular. As a result, two peroxides as primary intermediates are formed from ether due to oxidation, namely, hydroperoxide and dihydroperoxide [62],... 

Another probable reaction of homolytic decomposition of ester hydroperoxide is the intramolecular interaction of the hydroperoxide group with the carbonyl group of ester with the formation of labile hydroxyperoxide succeeded the splitting of the weak O—O bond (see decomposition of hydroperoxides in oxidized ketones in Chapter 8). 

The peculiarities of the oxidation of PP, whose molecules have alternating tertiary C—H bonds in the (3-position, are of special interest. Such branched alkanes are oxidized with the formation of polyatomic hydroperoxides produced by the intramolecular isomerization of the peroxyl radical [88],... 

During PP oxidation, hydroxyl groups are formed by the intramolecular isomerization of alkyl radicals. Since PP oxidizes through an intense intramolecular chain transfer, many of the alkyl radicals containing hydroperoxy groups in the 0-position to an available bond can undergo this reaction. An isomerization reaction has also been demonstrated for the liquid-phase oxidation of 2,4-dimethylpentane [89], Oxidation products contain, in addition to hydroperoxides, oxide or diol. 

The nucleophiles that are used for synthetic purposes include water, alcohols, carboxylate ions, hydroperoxides, amines, and nitriles. After the addition step is complete, the mercury is usually reductively removed by sodium borohydride. The net result is the addition of hydrogen and the nucleophile to the alkene. The regioselectivity is excellent and is in the same sense as is observed for proton-initiated additions.16 Scheme 4.1 includes examples of these reactions. Electrophilic attack by mercuric ion can affect cyclization by intramolecular capture of a nucleophilic functional group, as illustrated by entries 9-11. Inclusion of triethylboron in the reduction has been found to improve yields (entry 9).17... 

The second largest number of hydrogen bonds in crystal structures of alkyl hydroperoxides refers to interactions of the type OO—H OR R, where R is an alkyl group and R denotes H, alkyl or R O. The OO OR R distances vary between 2.67-2.91 A and the associated O—H O angles range from 152 to 177°. In some compounds, formation of intramolecular hydrogen bonds of the type OO—H 0=X would in principle have been feasible. The number of examples documented in the literature so far is clearly in favor of the intermolecular type of H bonding. 

FIGURE 14. Intramolecular hydrogen bonds the carbonyl, sulfoxide and phosphine oxide group as acceptor for the hydroperoxide proton ... 

B. Cyclization of Hydroperoxides through Intramolecular Nucleophilic Substitution and Addition... 

Cyclic peroxides can be prepared from hydroperoxides and their synthetic equivalents throngh processes involving intramolecular nucleophilic substitution at a carbon... 

Acid-catalyzed intramolecular attack of nucleophilic hydroperoxide function on an oxirane ring results in formation of 3-(l-hydroxyalkyl)endoperoxides. For example, epoxidation of unsaturated hydroperoxide 320 affords oxirane-hydroperoxide 321 (66%), which through acid-catalyzed regioselective cyclization gives 1,2-dioxolane 322 (70%) (Scheme 79) . This type of reaction is applicable also to a more complex epoxide-hydroperoxide such as 323, which cyclizes to polyfunctionalized 5-membered cyclic... 

It is noteworthy that BCIH-mediated peroxyiodination of unsaturated hydroperoxide 269 follows an intramolecular addition of hydroperoxide onto an electron-poor C=C bond to give the bridged bicyclic iodoperoxide 384 (Scheme 100) . This reaction is as effective as the conversion of 385 to 386, which involves iodonium-mediated intramolecular attack of a hydroperoxide group on an electron-rich donble bond. ... 

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