Hydroperoxy epoxides

In addition to the monohydroperoxides, unsaturated aldehydes and ketones undergo autoxidation and provide additional sources of volatile compounds. Nonvolatile secondary products that undergo further decomposition into volatile products include dimers and oligomers, hydroperoxy epoxides, hydroperoxy epidioxides and dihydroperoxides. These secondary products contain one or more hydroperoxide groups and decompose the same way as monohydroperoxides to produce similar volatile materials. As with the monohydroperoxides, the multitude of volatile compounds formed from secondary products are important contributors to the flavor quality of lipid-containing foods. 

Boron trifluoride has been used as an efficient catalyst for the selective synthesis of tricyclic monoperoxides 101 from triketones and H2O2 (13S246). The first total synthesis of andavadoic acid 103 used a novel base-catalyzed 5-exo-tet cychzation from a P-hydroperoxy epoxide 102 (13T334). 

The zwitterion (6) can react with protic solvents to produce a variety of products. Reaction with water yields a transient hydroperoxy alcohol (10) that can dehydrate to a carboxyUc acid or spHt out H2O2 to form a carbonyl compound (aldehyde or ketone, R2CO). In alcohoHc media, the product is an isolable hydroperoxy ether (11) that can be hydrolyzed or reduced (with (CH O) or (CH2)2S) to a carbonyl compound. Reductive amination of (11) over Raney nickel produces amides and amines (64). Reaction of the zwitterion with a carboxyUc acid to form a hydroperoxy ester (12) is commercially important because it can be oxidized to other acids, RCOOH and R COOH. Reaction of zwitterion with HCN produces a-hydroxy nitriles that can be hydrolyzed to a-hydroxy carboxyUc acids. Carboxylates are obtained with H2O2/OH (65). The zwitterion can be reduced during the course of the reaction by tetracyanoethylene to produce its epoxide (66). 

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. 

Epoxidation of 632c with m-CPBA to 634, followed by silylation with bis(trimethylsilyl) acetamide (BSA) to 635, and TMSOTf-indnced cyclization gives 6-hydroxymethyl-3-phenyl-l,2,4-trioxane 636 (Scheme 181) °. Epoxides 638, which are characterized by geminal dimethyl substitnents, are obtained by m-CPBA oxidation of the (0-3,3-dimethyl-allyl)hydroperoxy acetals 637. While the strnctnral change in 638, as compared to epoxide 634, direct the acid-catalyzed cyclizations to the endo mode yielding the 7-membered... 

SCHEME 70. Titanium-catalyzed epoxidation of ene-diols 145 by, 6-hydroperoxy alcohols 148... 

The hydroperoxy functionality can be introduced into an alkene by a singlet oxygen ene reaction and subsequently reduced quantitatively to an allylic alcohol, by addition of reducing agents such as PPhs, Me2S or NaBHj ". In addition, the allylic hydroperoxides can be transformed stereospecilically in the presence of Ti(OPr-i)4 to an epoxy allylic alcohol, where epoxide and hydroxyl functionalities are cis to each other (e.g. substrate 160, Scheme 58) - . ... 

Pulse radiolysis experiments have shown that "OH radical adds preferentially at C5 of the uracil moiety, giving rise to the reducing 5-hydroxy-5,6-uracil-6-yl radical. Interestingly, the two cis diastereomers of 6-hydroperoxy-5-hydroxy-5,6-dihydrouridine, two of the expected final products of the latter radicals in aerated aqueous solutions, have been prepared by trifluoroacetic acid treatment of uridine (3, R = H, = ribose) in the presence of H202 (equation 14). The mechanism of the reaction that involves transient formation of an epoxide-type intermediate followed by nucleophilic attack by a perhy-droxyl group at C6 presents similarities with the substitution of thymine bromohydrin by... 

C-H bond oxygen insertion, 1163 configuration retention, 1163 epoxidation, 1144-50 hydroperoxy anion transfer, 382 Steric effects hydrogen dioxide, 96-7 peroxide dihedral angle, 101, 177 Steric strain... 

Other methods for a-hydroxy ketone synthesis are addition of O2 to an enolate followed by reduction of the a-hydroperoxy ketone using triethyl phosphite 9 the molybdenum peroxide-pyridine-HMPA oxidation of enolates 10 photooxygenation of enol ethers followed by triphenylphosphine reduction 11 the epoxidation of trimethyl silyl enol ethers by peracid 1 - the oxidation of trimethylsilyl enol ethers by osmium tetroxide in N-methylmorpholine N-... 

In plants a-dioxygenases (Chapter 18) convert free fatty acids into 2(R)-hydroperoxy derivatives (Eq. 7-3, step d).32a These may be decarboxylated to fatty aldehydes (step e, see also Eq. 15-36) but may also give rise to a variety of other products. Compounds arising from linoleic and linolenic acids are numerous and include epoxides, epoxy alcohols, dihydroxy acids, short-chain aldehydes, divinyl ethers, and jasmonic acid (Eq. 21-18).32a... 

The transformation of carboxylic acids and their functional derivatives to the corresponding peroxycarboxylic acids or diacyl peroxides are generally known reactions.200-201 Among the hydroperoxy derivatives, trifluoroperacetic acid is a frequently used epoxidizing reagent in organic chemistry and is usually prepared in situ.200-201... 

B is( p-ni trobenzoylperoxy)-di cyclobexylp epoxide, C26H26N20)2. This compd, probably expl, is not described in the literature, but it seems, that it may be prepd by treating bis(l-hydroperoxy-cyclohexyl)-peroxide in pyridine with p-nitro-benzoyl chloride... 

It has been suggested that poly-L-leucine (PLL)-catalysed epoxidation of substituted chalcones proceeds via a reversible addition of chalcone to a PLL-bound hydroperoxide, forming a fleeting hydroperoxy enolate species. The origin of enantioselectivity in this system has been rationalized.194... 

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