Allyl peroxides, cyclic

Cyclic allyl peroxides are converted stereoselectively into the dihydroxypropyl peroxides using a modified Sharpless procedure with osmium tetroxide and /-butyl peroxide in the presence of benzyltrimethylammonium acetate [23]. Yields are generally good with exclusive an/f-addition with respect to the peroxy group, although both the steroselectivity and yield (<40%) are poor for the oxidation of 2,3-dihydrofuran-3-yl peroxide and 2,3-dihydro-4//-pyran-4-yl peroxide. 

The present volume comprises 17 chapters, written by 27 authors from 11 countries, and deals with theoretical aspects and structural chemistry of peroxy compounds, with their thermochemistry, O NMR spectra and analysis, extensively with synthesis of cyclic peroxides and with the uses of peroxides in synthesis, and with peroxides in biological systems. Heterocyclic peroxides, containing silicon, germanium, sulfur and phosphorus, as well as transition metal peroxides are treated in several chapters. Special chapters deal with allylic peroxides, advances in the chemistry of dioxiranes and dioxetanes, and chemiluminescence of peroxide and with polar effects of their decomposition. A chapter on anti-malarial and anti-tumor peroxides, a hot topic in recent research of peroxides, closes the book. 

The reductive elimination of a variety of )3-substituted sulfones for the preparation of di-and tri-substituted olefins (e.g. 75 to 76) and the use of allyl sulfones as synthetic equivalents of the allyl dianion CH=CH—CHj , has prompted considerable interest in the [1,3]rearrangements of allylic sulfones ". Kocienski has thus reported that while epoxidation of allylic sulfone 74 with MCPBA in CH2CI2 at room temperature afforded the expected product 75, epoxidation in the presence of two equivalents of NaHCOj afforded the isomeric j ,y-epoxysulfone 77. Similar results were obtained with other a-mono- or di-substituted sulfones. On the other hand, the reaction of y-substituted allylic sulfones results in the isomerization of the double bond, only. The following addition-elimination free radical chain mechanism has been suggested (equations 45, 46). In a closely related and simultaneously published investigation, Whitham and coworkers reported the 1,3-rearrangement of a number of acyclic and cyclic allylic p-tolyl sulfones on treatment with either benzoyl peroxide in CCI4 under reflux or with... 

Aerobic Co(II) catalysed hydroperoxysiiyiation of allylic alcohols provides silyl peroxides that can be condensed with ketones to produce 1,2,4-trioxanes or 1,2,4-trioxepanes by a simple one-pot procedure (Scheme 35A). A recent improvement in the use of Co(acac)2 is the use of Co(thd)2 (thd = bis (2,2,6,6-tetramethyl-3,5-heptanedionato)). This more reactive catalyst allows cyclic allylic alcohols to be oxygenated and the resulting peroxysilyl alcohol can be transformed to spiro trioxanes, some of which have potent in vitro antimalarial activity (Scheme 35B). For example, compound 87 expresses activity around 20 nM (artemisinin = 10 nM). 

Cyclic hydrocarbons, diastereoselective allylic hydroperoxide formation, 861-3, 864 Cyclic olefins, final ozonides, 718 Cyclic peroxides... 

The preparation of acyclic allylic hydroperoxides has been described before (3, 7, 9), but it is not clear how the reactivities differ from the better known saturated hydroperoxides and cyclic allylic hydroperoxides. Dykstra and Mosher prepared allyl hydroperoxide by the reaction of allyl methanesulfonate with hydrogen peroxide and alcpholic potassium hydroxide and purified the hydroperoxide by gas chromatography. It detonated on heating and decomposed on exposure to light but was relatively stable in the cold and dark. The isomeric allylic hydroperoxides formed from the autoxidation of the branched olefin, 4-methyl-2-pentene, have also been isolated and were not abnormally reactive (3). In the present study, cis- and trans-2-butene were photooxidized in the presence of methylene blue as a sensitizer (14), and the product, l-butene-3-hydro-peroxide, was isolated by preparative chromatography. 1-Butene proved unreactive and 2-butene-l-hydroperoxide could be formed only by isomerization of the secondary hydroperoxide. 

The allyloxy radicals generated from hydroperoxide, dialkyl peroxide and cyclic peroxide intermediates, in accordance with Reactions 6, 9, and 10, respectively, are converted to allyl alcohol moieties, as shown in Reaction 7. The latter are particularly susceptible to reaction with hydrogen chloride. 

In all four cases, the two regioisomeric allylic hydroperoxides are formed with identical diastereomeric ratios, clearly indicating a common symmetrical intermediate, presumably of the cyclic peroxide type. The relative configurations [(R, R )/(R, S )] of the photooxygenation products were not determined. 

Hydrogenolysis of dialkylperoxides or epidioxides (cyclic peroxides) also takes place over these same catalysts under mild conditions. If tertiary alcohols are the products, running the reaction in acid media can lead to dehydration. Deactivated catalysts are also needed if the product contains an allyl alcohol that could be cleaved by the more active catalysts (Eqn. 20.72). 6.I87... 

The racemic synthesis of decipienin A was accomplished in the laboratory of G.M. Massanet. In the late stages of the total synthesis, the tricyclic enone lactone was converted to the corresponding a, 3-epoxyketone by treatment with hydrogen peroxide in the presence of NaOH. The epoxyketone was subjected to the conditions of the Wharton transposition to afford the cyclic allylic alcohol in excellent yield. Several subsequent steps completed the total synthesis. 

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