Oxiranes hydrogen peroxide

Nucleophilic opening of oxiranes to give ultimately 1,2-diols is usually effected without isolation of the oxirane oxiranation (epoxidation) of alkenes with unbuffered peroxy-ethanoic acid or hydrogen peroxide in methanoic acid (Section 5.05.4.2.2(/)) tends to give monoesters of 1,2-diols (e.g. 53), which can be hydrolyzed to the diols (Scheme 46). 

The high degree of stereoselectivity associated with most syntheses and reactions of oxiranes accounts for the enormous utility of these systems in steroid syntheses. Individual selectivity at various positions in the steroid nucleus necessitates the discussion of a collection of uniquely specific reactions used in the synthesis of steroidal epoxides. The most convenient and generally applicable methods involve the peracid, the alkaline hydrogen peroxide and the halohydrin reactions. Several additional but more limited techniques are also available. 

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. 

Introduction of fluorine by oxirane-ring opening is described first. The 1,2-oxirane 408, prepared from nitroalkene 407 and hydrogen peroxide, was treated with KHF2 (ethylene glycol, 20 min, 112°) to 2-... 

Epoxidation of ot.fl-unsaturated ketones by hydrogen peroxide or /-butyl peroxide is promoted by the addition of tetra-n-butylammonium fluoride [10], whereas the corresponding reaction with 1,4-disubstituted but-2-en-l,4-diones is catalysed by quaternary ammonium iodides [11], Oxiranes are also produced by the catalysed reaction of /-butyl peroxide with a,f)-unsaturated sulphonates under basic conditions [12]. 

Direct phase-transfer catalysed epoxidation of electron-deficient alkenes, such as chalcones, cycloalk-2-enones and benzoquinones with hydrogen peroxide or r-butyl peroxide under basic conditions (Section 10.7) has been extended by the use of quininium and quinidinium catalysts to produce optically active oxiranes [1 — 16] the alkaloid bases are less efficient than their salts as catalysts [e.g. 8]. In addition to N-benzylquininium chloride, the binaphthyl ephedrinium salt (16 in Scheme 12.5) and the bis-cinchonidinium system (Scheme 12.12) have been used [12, 17]. Generally, the more rigid quininium systems are more effective than the ephedrinium salts. 

Methylenecyclohexane oxide has been prepared by the oxidation of methylenecyclohexane with benzonitrile-hydrogen peroxide or with peracetic acid by treatment of 1-chlorocyclo-hexylmethanol with aqueous potassium hydroxide and by the reaction of dimethylsulfonium methylide with cyclohexanone. This reaction illustrates a general method for the conversion of ketones and aldehydes into oxiranes using the methylene-transfer reagent dimethyloxosulfonium methylide. The yields of oxiranes are usually high, and the crude products, in most cases, are of sufficient purity to be used in subsequent reactions (e.g., rearrangement to aldehydes) without further purification. 

Alkaline hydrogen peroxide epoxidation / 10 Conversion of an oxirane into its stereoisomer / 14 Epoxide formation via halohydrins / 15 Spectra / 18... 

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... 

New synthetic processes for the preparation of established products were also industrially developed in Japan the manufacture of methyl methacrylate from C4 olefins, by Sumitomo and Nippon Shokubai in France, the simultaneous production of hydroquinone and pyro-catechin through hydrogen peroxide oxidation of phenol by Rhone-Poulenc in the United States the production of propylene oxide through direct oxidation of propylene operating jointly with styrene production, developed by Ralph Landau and used in the Oxirane subsidiary with Arco, which the latter fully took over in 1980 in Germany and Switzerland, the synthesis of vitamin A from terpenes, used by BASF and Hoffmann-La Roche. 

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