Alkenes oxidation with alkaline hydrogen peroxide

Hydroboration of alkene 22 was realized49 by treatment with a large excess of diborane in anhydrous tetrahydrofuran, followed by oxidation with alkaline hydrogen peroxide. This procedure resulted in the formation of 3-deoxy-3-C-(hydroxymethyl)-l,2 5,6-di-0-iso-... 

Borane, which is used as a complex with tetrahydrofuran [992] or dimethyl sulfide [611, 992] or generated in situ from lithium borohydride with boron trifluoride etherate [646] or sodium borohydride with aluminum chloride [184], reacts with 3 mol of an alkene to form a tertiary borane. The oxidation with alkaline hydrogen peroxide [183, 992, 1201] or with trimethylamine oxide [991, 992] yields an alcohol (equations 598 and 599). 

A method for converting an alkene to an alcohol. The alkene is treated with borane (BH3) to give a trialkylborane, which is then oxidized with alkaline hydrogen peroxide to give the alcohol. 

Alkenes can be hydrated to form alcohols by (1) hydroboration followed by oxidation with alkaline hydrogen peroxide and (2) acid-catalyzed hydration. Compare the product formed from each alkene by sequence (1) with those formed from (2). 

Oxidation of alkenylboranes with alkaline hydrogen peroxide is an important pathway to aldehydes and ketones (equation 13). Care must be taken to inhibit hydrolysis of the alkenylborane to the corresponding alkene and hence buffered conditions are frequently us. The reaction toloates the same wide range of functionality as the oxidation of alkylboranes. 

In contrast to the stereospecific epoxidation of acyclic alkenes with peroxy acids, oxidation of acyclic a,(3-unsaturated ketones with alkaline hydrogen peroxide is stereoselective in that only one stereoisomer is formed from cis- and trans-enones ... 

However, there is another way in which the overall conversion from propene to propan-l-ol may be accomplished. This proceeds by the indirect route of hydroboration, using diborane, followed by the oxidation of the resultant trialkylboron with alkaline hydrogen peroxide. For the present purposes, we are only concerned with the reaction between diborane and the alkene. Diborane is generated in situ, but reacts as if it were the monomer BH3, which is a Lewis acid. Write down the... 

Oxidation of organoboranes to alcohols is usually effected with alkaline hydrogen peroxide. The reaction is of wide applicability and many functional groups are unaffected by the reaction conditions, so that a variety of substituted alkenes can be converted into alcohols by this procedure. Several examples have been given above. A valuable feature of the reaction is that it results in the overall addition of water to the double (or triple) bond, with a regioselectivity opposite to that from acid-catalysed hydration. This follows from the fact that, in the hydroboration step, the boron atom adds to the less-substituted carbon atom of the multiple bond. Terminal alkynes, for example, give aldehydes in contrast to the methyl ketones obtained by mercury-assisted hydration. 

Standard oxidation of alkyldibromoboranes with alkaline hydrogen peroxide affords alcohols. Conversion of terminal alkenes to carboxylic acids using alkyldibromoboranes works well, although hydrolysis prior to oxidation is needed." Chiral alkyldibromoboranes have been used as catalysts for the asymmetric Diels-Alder reaction. 

The course of this reaction depends (1) on the stereospecific reductive addition of diborane (B2H6, introduced as the borane. tetrahydrofuran complex (BH3 -THF)) to an alkene to form an intermediate trialkylborane and (2) on oxidation of the borane with alkaline hydrogen peroxide to yield the corresponding alcohol. 

Brown, H. C., Snyder, C., Rao, B. C. S., Zweifel, G. 1986. Organoboranes for synthesis. 2. Oxidation of organoboranes with alkaline hydrogen peroxide as a convenient route for the cis hydration of alkenes via... 

Alkaline hydrogen peroxide oxidation52 has been extended to higher perfluorinated alk-1-enes, perfluorinated cycloalkenes and certain alkenes with internal C = C bonds.52 57 A convenient reagent for the preparation of perfluoroalkene epoxides is sodium hypochlorite in a mixture with aqueous acetonitrile or another aprotic solvent. Several cis- and traw.s-perfluoroalkenes are oxidized to 32 with retention of configuration (Table 4).58-63... 

The most convenient route to fluorinated epoxides is the direct epoxidation of alkenes. Since first reports of a general method using alkaline hydrogen peroxide at low temperature/ 88" " 9I several alternative synthetic approaches have been developed. Molecular oxygen under free-radical conditions has been used to oxidize alkenes such as tetrafluoroethene or hexafluoro-propene 592 394 however, internal epoxides are formed most conveniently using hypochlorites.595 399 The products, e. g. oxirane 14 from alkene 13, are usually obtained in high yield with retention of configuration.59 ... 

Alkenes are converted to epoxides by oxidation with peroxy acids, and thereby they are protected with regard to certain chemical transformations. Alkaline hydrogen peroxide selectively attacks enone double bonds in the presence of other alkenes. The epoxides can be transformed back to alkenes by reduction-dehydration sequences or using triphenylphosphine, chromous salts, zinc, or sodium iodide and acetic acid. A more advantageous and fairly general method consists, however, of the treatment of epoxides with dimethyl diazomalonate in the presence of catalytic amounts of binuclear rhodium(II) car-boxylate salts. This deoxygenation proceeds under neutral conditions and without isomerization or cy-clopropanation of the liberated alkene (Scheme 97). Furthermore, epoxides can be converted to alkenes with the aid of various metal carbonyl complexes. Thus, they may be nucleophilically opened with... 

The conversion of 3-chloropentafluoropropene to 2-(chlorodifluoromethyI)-2,3,3-trifluoro-oxirane (33) can be carried out64 by heating the mixture of the alkene and oxygen in 1,1,2-trichlorotrifluoroethane (CFC-113) in an autoclave.64 The oxidation with hydrogen peroxide in alkaline solution is negatively influenced by the high nucleophilic reactivity of allylic chlorine.65 66 The reaction is performed at very low temperatures that favor the attack of the hydroperoxy anion in competition with the hydroxy anion. Acceptable yields of 31 -38 % are obtained in the presence of a phase-transfer catalyst.66... 

Several oxidizing reagents react with alkenes under mild conditions to give, as the overall result, addition of hydrogen peroxide as HO—OH. Of particular importance are alkaline permanganate (MnO40) and osmium tetroxide (0s04), both of which react in an initial step by a suprafacial cycloaddition mechanism like that postulated for ozone. 

For the oxidation of alkenes, osmium tetroxide is used either stoichiometrically, when the alkene is precious or only small scale operation is required, or catalytically with a range of secondary oxidants which include metal chlorates, hydrogen peroxide, f-butyl hydroperoxide and N-methylmorpholine A -oxide. The osmium tetroxide//V-methylmorpholine A -oxide combination is probably the most general and effective procedure which is currently available for the syn hydroxylation of alkenes, although tetrasubstituted alkenes may be resistant to oxidation. For hindered alkenes, use of the related oxidant trimethylamine A -oxide in the presence of pyridine appears advantageous. When r-butyl hydroperoxide is used as a cooxidant, problems of overoxidation are avoided which occasionally occur with the catalytic procedures using metal chlorates or hydrogen peroxide. Further, in the presence of tetraethylam-monium hydroxide hydroxylation of tetrasubstituted alkenes is possible, but the alkaline conditions clearly limit the application. 

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