Oxiranes epoxidation

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 chapter is divided into three sections, devoted to the discussion of the synthesis of (1) oxiranes (epoxides), (2) aziridines (ethylene imines) and (3) thiiranes (episulfides). 

B Reactions of Grignard Reagents WITH OXIRANES (EPOXIDES)... 

Simple heterocyclic compounds Three-membered heterocycles containing one heteroatom Oxiranes (epoxides), thiiranes (episulfides), aziridines Three-membered heterocycles containing more than one heteroatom Oxaziridines, dioxiranes, diazirines Four-membered heterocycles containing one heteroatom Oxetanes, thietanes, azetidines... 

The stability of cyclic ethers toward hydrolytic agents is largely a function of the size of the ring and, hence of the internal strain. Thus, whereas the oxiranes (epoxides) are particularly sensitive to these reagents,95,96 the oxetanes are relatively more stable.97 Oxolanes of the tetrahydrofuranol type seem, in particular, little affected by... 

Kaltenbronn et alJ88 and Kim et al.[89 93l synthesized oxirane (epoxide) isosteres by epox-idation of cis- and iram-alkene isosteres (Scheme 37). Kim et alJ89 93l applied these methods to the design of HIV-1 protease inhibitors. The resulting oxirane isostere can react with the Asp side chains of HIV-1 protease to form ester bonds. Thus, the compounds are acting as irreversible inhibitors. 

Oxiranes (epoxides) are important intermediates in syntheses and for industrial processes, which produce useful compounds of high practical importance,17,18 e.g. inert fluids, elastomers, and ionomer membranes. The epoxidation reaction of highly fluorinated C = C bonds are occasionally, especially in acidic media, accompanied by rearrangement of the primary epoxides (see Section 5.3.3.2.) and, in the case of stronger oxidants, by C = C bond cleavage (vide infra, see also Vol. ElOb/Part 1, p691 ff). 

Alkenes can be oxidized with peroxycarboxylic acids, RC03H, to give oxacy-clopropanes (oxiranes, epoxides), which are three-membered cyclic ethers ... 

An epoxide is a three-membered cyclic ether, also called an oxirane. Epoxides are valuable synthetic intermediates used for converting alkenes to a variety of other functional groups. An alkene is converted to an epoxide by a peroxyacid, a carboxylic acid that has an extra oxygen atom in a —O—O— (peroxy) linkage. 

Oxetanes The least common cyclic ethers are the four-membered oxetanes. Because these four-membered rings are strained, they are more reactive than larger cyclic ethers and open-chain ethers. They are not as reactive as the highly strained oxiranes (epoxides), however. 

Oxaphosphiranes are interesting as they are analogs of the well-known oxiranes (epoxides). The direct epoxidation of free phosphaalkenes most likely would be complicated or thwarted by oxygen attack at phosphorus. An elegant route to oxaphosphirane complexes 10a,b makes use of the quantitative oxydation of Tj -phosphaalkene complexes 9a,b with m-chloro-perbenzoic acid in THF see Eq. (4).8... 

Anti hydroxylation of an alkene is readily achieved with peroxycarboxylic adds. Add-catalyzed ring opening of the irutial produd, an oxirane (epoxide), forms the monoester of a 1,2-diol, hydrolysis of which affords the parent diol. Alternative reagents whi ate often used for anti hydroxylation of alkenes are hydrogen peroxide with oxides of tungsten > 4.2i gj. selenium, 444i and iodine-silver benzoate (Pr6vost reaction).. ... 

The observed stereochemistry of addition suggests that oxiranes (epoxides) may be intermediates. Oxiranes may, indeed, be isolated from the reaction of certain alkenes with hydrogen peroxide in the presence of sodium tungstate. °... 

Sulphonium ylids also react as nucleophiles towards carbonyl groups but the intermediate sulphonium betaines decompose to give oxiranes (epoxides) fioo] through an internal... 

The formation of alcohols by the hydrogenolytic opening of oxiranes (epoxides) takes place over palladium at room temperature and atmospheric pressure. The addition of some perchloric or hydrochloric acid not only increases the rate of the reaction, but can also influence the direction of ring opening of unsymmetric epoxides. 

Trans hydroxylation of an alkene involves sequential conversion to an oxirane (epoxide), and its conjugate acid, followed by nucleophilic opening of the oxirane by water... 

In this volume of Advances, Cerny and Stanek, Jr. (Prague) contribute a comprehensive article on the 1,6-anhydro derivatives of aldohexoses. This class of anhydro sugars, earlier termed the hexosans, constitutes by far the largest class of sugar anhydrides to have been studied. The scope of the topic is now so extensive that the Editors, in view of their earlier practice of limiting chapter size in individual volumes of Advances in the interest of diversification of subject material, were inclined to divide this chapter into two parts, to appear in successive volumes. However, as the latter practice has elicited some unfavorable reaction from readers on previous occasions, it was decided to present the article here in its entirety. The chapter complements previous ones on other classes of anhydro derivatives, in particular, recent ones on anhydrides of the oxirane (epoxide) and 2,5-anhydro (oxolane) types. 

Reaction with oxiranes (epoxides).2 Dimethylcopperlithium and diphenyl-copperlithium1 are more useful than other organometallic reagents for the nucleophilic ring opening of epoxides. Thus dimethylcopperlithium reacts with propylene oxide (equation 1) and 1,2-epoxybutane (equation 2) to give the expected secondary alcohols as the predominant products. 

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