R-BuOOH

Allylic alcohols can be converted to epoxy-alcohols with tert-butylhydroperoxide on molecular sieves, or with peroxy acids. Epoxidation of allylic alcohols can also be done with high enantioselectivity. In the Sharpless asymmetric epoxidation,allylic alcohols are converted to optically active epoxides in better than 90% ee, by treatment with r-BuOOH, titanium tetraisopropoxide and optically active diethyl tartrate. The Ti(OCHMe2)4 and diethyl tartrate can be present in catalytic amounts (15-lOmol %) if molecular sieves are present. Polymer-supported catalysts have also been reported. Since both (-t-) and ( —) diethyl tartrate are readily available, and the reaction is stereospecific, either enantiomer of the product can be prepared. The method has been successful for a wide range of primary allylic alcohols, where the double bond is mono-, di-, tri-, and tetrasubstituted. This procedure, in which an optically active catalyst is used to induce asymmetry, has proved to be one of the most important methods of asymmetric synthesis, and has been used to prepare a large number of optically active natural products and other compounds. The mechanism of the Sharpless epoxidation is believed to involve attack on the substrate by a compound formed from the titanium alkoxide and the diethyl tartrate to produce a complex that also contains the substrate and the r-BuOOH. ... 

Since its discovery in 1980,7 the Sharpless expoxidation of allylic alcohols has become a benchmark classic method in asymmetric synthesis. A wide variety of primary allylic alcohols have been epoxidized with over 90% optical yield and 70-90% chemical yield using TBHP (r-BuOOH) as the oxygen donor and titanium isopropoxide-diethyl tartrate (DET, the most frequently used dialkyl tartrate) as the catalyst. One factor that simplifies the standard epoxidation reaction is that the active chiral catalyst is generated in situ, which means that the pre-preparation of the active catalyst is not required. 

Scheme 16 Allylic oxidation of A5-steroids catalyzed by Bi(III) salts, using r-BuOOH...

At = NaOH, aq. H202/toluene A2 = NaOH, r-BuOOH/toluene B = LiOH, aq. H2O2/CHCI3, -10 °C C = NaOH, TBHP or fluorenyl hydroperoxides, in toluene containing little amounts of water, between —10 °C and r.t D = LiOH, aq. H202/n-Bu20, 4 °C. 

HRP-catalyzed oxidation of luminol in a FLA system was used to follow the development of H2O2 during forced oxidation of beer211. A microreactor consisting of immobilized HRP placed in the CL cell, in front of a photomultiplier in a FLA system, is claimed to greatly enhance the CL signal. The CL response for cumyl hydroperoxide (27) and r-BuOOH is much lower than for H2O2. The method was proposed for clinical... 

Cells may show a low level of autofluorescence at 413 nm when irradiated at 324 nm. This fluorescence dramatically increases when cA-parinaric acid (159) is incorporated into the cell membrane, either by intercalation or esterification. Exposure to oxidation stress of cells enriched with the 159 fluorescent probe causes diminution of the fluorescence intensity and is directly correlated with formation of lipid hydroperoxides. Addition of antioxidants, such as Vitamin E (21), abates fluorescence diminution. A blanc run of cells enriched with 159 but not subjected to oxidation stress is necessary to follow the degradation of 159 when exposed to UV irradiation423. This method was applied to track lipid oxidation during apoptosis and other phenomena, triggered by toxic compounds such as H202, r-BuOOH and cumyl hydroperoxide (27)110- ln-424. 

Although the reaction depicted in equation 34 may be applied also to the simplest hydroperoxides, it fails for bulkier ones, such as r-BuOOH, due to the steric requirements of the HRP catalyst. A three step method was proposed for the analysis of mixtures of... 

A highly selective method for determination of lipid hydroperoxides is based on the oxidation of ferrocenecarboxylic acid (201) to the corresponding ferrocenium compound (202), as shown in equation 69, followed by amperometric reduction of this complex with a GCE set at —100 mV vs. SCSE, in phosphate buffer at pH 5.5. The method is insensitive to dissolved oxygen and no interference is observed, either from reductors such as ascorbic acid (22) or uric acid (29) nor from other hydroperoxides such as H2O2 and r-BuOOH at the 1 p,M concentration level. At this concentration, a slight interference is observed for cumyl hydroperoxide (27) and 2-butanone peroxide (46 + 47). The LOD... 

These complexes are effective catalysts in epoxidation reactions with H2O2 and alkyl hydroperoxides. Several detailed mechanistic studies have been carried out in particular, it has been shown that, when the alkyl chain contains a double bond, no autoepoxidation is observed both in the solid state and in solution. Nevertheless, if r-BuOOH is added, the epoxidation of the olefinic moiety immediately takes place. Therefore, it has been suggested that these complexes are not the active species in the oxygen transfer step to the substrate, but they behave as catalysts for the primary peroxidic oxidant. On the basis of kinetic, spectroscopic and theoretical studies, the authors provided a mechanism, whose key steps are sketched in Scheme 12. In this context a major role appears to be played by the fluxionality of the particular ligands used157. 

Palladium f-butyl peroxide trifluoroacetate (PPT), CF3C02PdOOC(CH3)3 (1). Mol. wt. 296.52, stable orange crystals. This material can be prepared from Pd(OCOCF3)2 and r-BuOOH or from Pd(OAc)2, t-BuOOH, and CF3COOH (85% yield). 

Oxidation of —CH=CH2 to —COCH3. Mimoun et al. have prepared a number of reagents in which the CF3 group of I is replaced by other groups. However 1 is the most effective for conversion of terminal alkenes to methyl ketones. Yields are high and the reaction is usually complete within an hour. The reaction can be catalytic with respect to 1 if r-BuOOH is present (equation I). 

Allylic and cis-homoallylic alcohols are epoxidized readily, but frans-homoallylic and bishomoallylic alcohols react slowly, if at all. The stereoselectivity in the epoxidation of acyclic allylic alcohols is the same as and is comparable to that observed with r-BuOOH/VO(acac)2. The stereoselectivity in epoxidation of acyclic homoallylic alcohols is also the same but lower than that obtained with t-BuOOH/ VO(acac)2. Epoxidation of cyclic allylic alcohols proceeds more slowly and in lower yield than that of acyclic allylic alcohols. 

Diethyl tartrate is the best tartaric acid derivative for enantioselective oxidation of thioethers. This finding was established for the asymmetric oxidation of methyl p-tolyl sulfide with cumene hydroperoxide, that is, 96% ee (DET) 87% ee (diisopropyl tartrate) 62% ee (dimethyl tartrate) [24] and 1.5% ee (bis A, V-dimethy I tart rami de, r-BuOOH as the oxidant) [17]. 

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