Alkyl hydroperoxide esters

As electrophilic substitutes for peracids, the use of borate ester induced decomposition of alkyl hydroperoxides and molybdenum VI peroxy-complexes have been reported in the recent literature. Although these reagents have led to the epoxidation of olefins in greater than 90% yield there are no reports yet of their application to steroid olefins. 

Alkyl hydroperoxides react with nitrous acid to give the corresponding nitrate ester. ... 

Oxidation of primary, secondary and benzylic alcohols with TBHP or CHP, mainly catalyzed by Mo and Zr derivatives, were performed by different authors. As an example, Ishii, Ogawa and coworkers reported the conversion of secondary alcohols such as 2-octanol to ketones mediated by catalyst 39 and TBHP. The oxidation of cyclic alcohols depended on steric factors. Zirconium alkoxides may act as catalysts in the conversion of different alcohol typologies with alkyl hydroperoxides . Secondary alcohols, if not severely hindered, are quantitatively converted to the corresponding ketones. The selectivity for equatorial alcohols is a general feature of the system, as confirmed by the oxidation of the sole cis isomer 103 of a mixture 103-bl04 (equation 68). Esters and acids could be the by-products in the oxidation of primary alcohols. 

A density functional study of the transition structures of Ti-catalyzed epoxidation of allylic alcohol was performed, which mimicked the dimeric mechanism proposed by Sharpless et al.5 Importance of the bulkiness of alkyl hydroperoxide to the stereoselectivity, the conformational features of tartrate esters in the epoxidation transition structure, and the loading of allylic alcohol in the dimeric transition structure model were pointed out. 

The essence of titanium-catalyzed asynunetric epoxidation is illustrated in Figure 1. As shown there, the four essential components of the reaction are tiie allylic alcohol substrate, a titanium(IV) alkoxide, a chiral tartrate ester and an alkyl hydroperoxide. The asynunetric complex formed from these reagents de-... 

Variable temperature NMR studies of the parent titanium-tartrate system (3,4, 5) revealed that isopropoxide exchange, fluxional interconversion (in which the coordinated ester and uncoordinated ester carbonyls, as well as tartrate alkoxides, exchange with respect to the titanium) and epoxidation rate are closely coupled. Thus, the faster the isopropoxide exchange, the more a vacant site becomes available for coordination of allyl alkoxide and the faster the latter anion associates with the titanium. Likewise, faster fluxional interconversion indicates more rapid dissociation of the ester carbonyls in 3 and thence more rapid coordination of the alkyl hydroperoxide to give 4. 

Sharpless asymmetric epoxidation Ti-alkoxide-catalyzed epoxidation of prochiral and chiral allylic alcohols in the presence of a chiral tartrate ester and an alkyl hydroperoxide. 408... 

Alkyl metaborate esters in combination with organic hydroperoxides are reported to be active for epoxidation [182]. The borate esters are cyclic and have general formula (ROBO)3, where R is an alkyl group like cyclohexyl (CeHn). They are six-membered ring compoimds formed from O-B units with a pendant RO, and are 1 1 dehydro adducts of alcohol and boric acid. 

P. F. Wolf, R. K. Barnes, Borate ester-induced decomposition of alkyl hydroperoxides. The epoxidation of olefins by electrophilic oxygen, J. Org. Chem. 34 (1969) 3441. 

The direct oxidation of paraffin by atmospheric oxygen is a non-selective reaction which yields a complex mixture of alcohols, ketones, acids and esters. It was used in Germany during the Second World War to manufacture fatty acids. The orientation of this reaction towards the production of alcohols results from research by the Japanese Nobori and Kawai f1943) and the Russian Bashkirov 1956). Alcohol selectivity in relation to the other oxidation products derives from the use of boric acid which withdraws the secondary alkyl hydroperoxides from any subsequent oxidation by converting them to stable boric esters. ... 

Example 5.5. Oxidation of paraffins to secondary alcohols (see also Section 10.6.2). Alcohols can be produced by oxidation of paraffins with air or oxygen at moderate temperatures (typically 120 to 180° C) in the presence of borate esters or boroxines [16-19]. These intercept the alkyl hydroperoxide, the first oxidation product, preventing it from generating radicals that would cause further degradation including scission of carbon-carbon bonds and produce aldehydes, ketones, and acids. The peroxy borates so formed then are hydrolyzed to yield the alcohol. The carbon atoms at the chain ends are largely immune to oxidation, so the product consists predominantly of isomeric secondary alcohols. 

It is found that esters which are known to undergo unimolecular alkyl-oxygen heterolysis will alkylate hydrogen peroxide and alkyl hydroperoxides (3, 4) for example, sodium 1,2,3,4-tetrahydro-l-naphthyl phthalate in 90% hydrogen peroxide rapidly yields 1,2,3,4-tetrahydro-l-naphthyl hydroperoxide ... 

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