Hydroperoxides allyl rearrangement

Dye-sensitized photo-oxygenation of the norbornenes (189 X = Me) and (190 X = H), which have been synthesized cleanly from the acid (191), occurs in a one-step cyclic process via a dipolar transition state with no evidence for a perepoxide intermediate (189 X = Me) gives the alcohol (190 X = OH) from the corresponding allylically rearranged hydroperoxide along with some exo-alcohol and the ketone... 

In some instances the primary product of alkene photooxidatitxi is not the allylically rearranged hydroperoxide, but the dioxetane addition product, e.g. (56), which may or may not formed by concerted [2 + 2] cycloaddition. Some of these dioxetanes, e.g. (57), ate relatively stable, although most suffer cleavage to produce carbonyl compounds or other materials. For example, photooxidation of indene gives homophthaldehyde (58) which was not produced under identical reaction conditions from hydroperoxide (59). Isomeric hydroperoxides (60) and (61) were also isolated when the oxidation was carried out in methanolic solution (Scheme 14). 

Rose oxide is usually prepared from citronellol which can be converted into a mixture of two allyl hydroperoxides (e.g., by photosensitized oxidation with oxygen). Reduction of the hydroperoxides with sodium sulfite yields the corresponding diols [183]. Treatment with dilute sulfuric acid results in allylic rearrangement and spontaneous cyclization of one of the isomers a mixture of diastereoisomeric rose oxides is thus formed. The unreacted diol isomer is separated by distillation. (—)-Citronellol as the starting material yields approximately a 1 1 mixture of (—)-cis- and (—)-tra s-rose oxide. 

Hydroperoxide formation is characteristic of alkenes possessing tertiary allylic hydrogen. Allylic rearrangement resulting in the formation of isomeric products is common. Secondary products (alcohols, carbonyl compounds, carboxylic acids) may arise from the decomposition of alkenyl hydroperoxide at higher temperature. 

Sharpless has achieved the allylic oxidation of alkenes using arylselenenic acids, generated in situ from the diselenide and r-butyl hydroperoxide, a reaction claimed to occur with exclusive allylic rearrangement. ... 

R and R — allylic groups of the starting and rearranged hydroperoxides respectively)... 

The allylperoxystannanes, like the allyl hydroperoxides, undergo the Schenck and Smith allylic rearrangements as illustrated in equation 14-87 for cholesterol derivatives.146 147 The rearrangements of the hydroperoxides are well established to be radical chain reactions 148,149 the rearrangements of the tin derivatives are inhibited by phenols, and it is assumed that they also proceed by a radical chain mechanism as illustrated for the Schenck rearrangement in Scheme 14-7.150 151 It will be noted that the mechanism... 

Allylic alcohols, 1, 17, 28-29, 30-31, 85-86, 182, 261, 318, 335, 338, 425, 444, 588, 602-603, 604, 664 AUyUc amines, 604-605 Allyhc chlorides, 598, 645 Aiiylic dibromides, 418 AUylic ethers, 269 Allylic halides, 327, 329 Allyhc hydroperoxides, 287 Allylic phosphine oxides, 340 Allylic rearrangement, 11-12 Allylic trifluoroacetoxylation, 360-361 Allylidenetriphenylphosphorane, 14-15 a-Allylpalladium chloride complexes, 45-47... 

Iron(II) salts, usually in conjunction with catalytic amounts of copper(II) compounds, have also been used to mediate radical additions to dienes91,92. Radicals are initially generated in these cases by reductive cleavage of peroxyesters of hydroperoxides to yield, after rearrangement, alkyl radicals. Addition to dienes is then followed by oxidation of the allyl radical and trapping by solvent. Hydroperoxide 67, for example, is reduced by ferrous sulfate to acyclic radical 68, which adds to butadiene to form adduct radical 69. Oxidation of 69 by copper(H) and reaction of the resulting allyl cation 70 with methanol yield product 71 in 61% yield (equation 29). 

A closer examination by ex situ analysis using NMR or gas chromatography illustrates that intrazeolite reaction mixtures can get complex. For example photooxygenation of 1-pentene leads to three major carbonyl products plus a mixture of saturated aldehydes (valeraldehyde, propionaldehyde, butyraldehyde, acetaldehyde)38 (Fig. 33). Ethyl vinyl ketone and 2-pentenal arise from addition of the hydroperoxy radical to the two different ends of the allylic radical (Fig. 33). The ketone, /i-3-penten-2-one, is formed by intrazeolite isomerization of 1-pentene followed by CT mediated photooxygenation of the 2-pentene isomer. Dioxetane cleavage, epoxide rearrangement, or presumably even Floch cleavage130,131 of the allylic hydroperoxides can lead to the mixture of saturated aldehydes. 

FIGURE 6 Speculative mechanism of Crl hydrocarbon biosynthesis from fatty acid hydroperoxides in algae. Homolytic cleavage of the hydroperoxide is assumed to give an allyl radical, which cyclizes to the thermolabile (1S,2R)-cyclopropane. The sequence is terminated by transfer of a hydrogen radical from C(16) to the -X-0 function. The cyclopropane rearranges to (6S)-ectocarpene as shown in Figure 4. 

AUyl transfer reactions, 73, 1 Allylic alcohols, synthesis from epoxides, 29, 3 by Wittig rearrangement, 46, 2 Allylic and benzylic carbanions, heteroatom-substituted, 27, 1 Allylic hydroperoxides, in... 

Such a rearrangement was detected only in the presence of sulfuric acid, and furthermore at 100°C. it was supplanted by a homolytic breakdown. The products found in the purely thermal decomposition—methyl vinyl ketone and methyl vinyl carbinol—are in fact consistent with the behavior of alkyl hydroperoxides and are analogous to the products produced from the cyclic allylic hydroperoxide from cyclohexene (2). 

Dr. Brill One would expect frans-2-butene-l-hydroperoxide to be the more stable isomer and the one formed in largest quantity by rearrangement of l-butene-3-hydroperoxide. In a previous study, only trans-2-methyl-3-pentene-2-hydroperoxide was obtained by equilibration with its allylic isomer. 

From these results it seems that the epoxy alcohol, IX, does not arise via an intramolecular vanadium-catalyzed rearrangement of cyclohexenyl hydroperoxide, V. An alternative pathway is an intermolecular epoxida-tion reaction between the allylic hydroperoxide, V, and the allylic alcohol which is formed during the oxidation (Reaction 17). We found that IX was produced from reaction of V with VII in the presence of [C5H5V-... 

Bauer G (2000) Reactive oxygen and nitrogen species efficient, selective and interactive signals during intercellular induction of apoptosis. Anticancer Res 20 4115-4140 Beckwith AU, Davies AG, Davison IGE, Maccoll A, Mruzek MH (1989) The mechanisms of the rearrangements of allylic hydroperoxides 5a-hydroperoxy-3p-hydrocholest-6-ene and 7a-hydro-peroxy-3(1-hydroxycholest-5-ene. J Chem Soc Perkin Trans 2 815-824 Behar D, Czapski G, Rabani J, Dorfman LM, Schwarz HA (1970) The acid dissociation constant and decay kinetics of the perhydroxyl radical. J Phys Chem 74 3209-3213 Benjan EV, Font-Sanchis E, Scaiano JC (2001) Lactone-derived carbon-centered radicals formation and reactivity with oxygen. Org Lett 3 4059-4062 Bennett JE, Summers R (1974) Product studies of the mutual termination reactions of sec- alkylper-oxy radicals Evidence for non-cyclic termination. Can J Chem 52 1377-1379 Bennett JE, Brown DM, Mile B (1970) Studies by electron spin resonance of the reactions of alkyl-peroxy radicals, part 2. Equilibrium between alkylperoxy radicals and tetroxide molecules. Trans Faraday Soc 66 397-405... 

Dioxetanes have been also proposed [44] as intermediates. However, the pathway through dioxetanes has been found to give only carbonyl cleavage products rather than rearrange to allylic hydroperoxides [45],... 

Hydrogen atoms in allylic position are favorite sites for hydroperoxidation of chains. So, this mechanism proceeds in the formation of lateral hydroperoxides, and not like for other polymers, in intramolecular peroxides. Rearrangement of chemical structures coming from ozonides are rapidly observed (Scheme 33). 

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