Basic hydrogen peroxide conditions

Oxidation of aryl aldehydes or aryl ketones to phenols using basic hydrogen peroxide conditions. Cf. Baeyer-Villiger oxidation. 

The addition of allylic boron reagents to carbonyl compounds first leads to homoallylic alcohol derivatives 36 or 37 that contain a covalent B-O bond (Eqs. 46 and 47). These adducts must be cleaved at the end of the reaction to isolate the free alcohol product from the reaction mixture. To cleave the covalent B-0 bond in these intermediates, a hydrolytic or oxidative work-up is required. For additions of allylic boranes, an oxidative work-up of the borinic ester intermediate 36 (R = alkyl) with basic hydrogen peroxide is preferred. For additions of allylic boronate derivatives, a simpler hydrolysis (acidic or basic) or triethanolamine exchange is generally performed as a means to cleave the borate intermediate 37 (Y = O-alkyl). The facility with which the borate ester is hydrolyzed depends primarily on the size of the substituents, but this operation is usually straightforward. For sensitive carbonyl substrates, the choice of allylic derivative, borane or boronate, may thus be dictated by the particular work-up conditions required. 

Reaction of 3,5-disubstituted-1,2,4-trioxolanes (89) with oxidants (usually under basic conditions) leads to carboxylic acids (Equation (14)). This reaction is often carried out as the work up procedure for alkene ozonolysis, avoiding the need to isolate the intermediate ozonide. Typical oxidants are basic hydrogen peroxide or peracids and this type of oxidative decomposition is useful for both synthetic and degradative studies. 

The formation of trisubstituted A-4 thiazoline-2-ones from the corresponding thiones analogs can be performed by oxidation with hydrogen peroxide under basic conditions. This reaction is strongly dependent on the pH of the medium. Higher yields are obtained in strongly alkaline solution (883). 

Oxidation. Oxidation of hydroxybenzaldehydes can result in the formation of a variety of compounds, depending on the reagents and conditions used. Replacement of the aldehyde function by a hydroxyl group results when 2- or 4-hydroxybenzaldehydes are treated with hydrogen peroxide in acidic (42) or basic (43) media pyrocatechol or hydroquinone are obtained, respectively. 

In the preparation of hydroperoxides from hydrogen peroxide, dialkyl peroxides usually form as by-products from the alkylation of the hydroperoxide in the reaction mixture. The reactivity of the substrate (olefin or RX) with hydrogen peroxide is the principal restriction in the process. If elevated temperatures or strongly acidic or strongly basic conditions are required, extensive decomposition of the hydrogen peroxide and the hydroperoxide can occur. 

Many functional groups are stable to alkaline hydrogen peroxide. Acetate esters are usually hydrolyzed under the reaction conditions although methods have been developed to prevent hydrolysis.For the preparation of the 4,5-oxiranes of desoxycorticosterone, hydrocortisone, and cortisone, the alkali-sensitive ketol side chains must be protected with a base-resistant group, e.g., the tetrahydropyranyl ether or the ethylene ketal derivative. Sodium carbonate has been used successfully as a base with unprotected ketol side chains, but it should be noted that some ketols are sensitive to sodium carbonate in the absence of hydrogen peroxide. The spiroketal side chain of the sapogenins is stable to the basic reaction conditions. 

The second major discovery regarding the use of MTO as an epoxidation catalyst came in 1996, when Sharpless and coworkers reported on the use of substoichio-metric amounts of pyridine as a co-catalyst in the system [103]. A change of solvent from tert-butanol to dichloromethane and the introduction of 12 mol% of pyridine even allowed the synthesis of very sensitive epoxides with aqueous hydrogen peroxide as the terminal oxidant. A significant rate acceleration was also observed for the epoxidation reaction performed in the presence of pyridine. This discovery was the first example of an efficient MTO-based system for epoxidation under neutral to basic conditions. Under these conditions the detrimental acid-induced decomposition of the epoxide is effectively avoided. With this novel system, a variety of... 

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