Epoxidation, of alkenes

Application of Hydrogen Peroxide for the Synthesis of Fine Chemicals 

Polymerization of short chain diepoxides is an important industrial route to cross-linked polymers.13 

The oxygen atom transfer from a peroxy acid to an alkene is facilitated by electron-donating substituents on the carbon-carbon double bond and electron-withdrawing groups on the peroxy acid.16 Further, conclusions which can be made from the experimental data collected over the years, include  

The order of reactivity of the peroxy acid increases with the pKa value, i.e. peroxytrifluoroacetic monopermaleic / -nitroperbenzoic m-chloro-perbenzoic performic perbenzoic peracetic. 

On the basis of theoretical studies by Bach and co-workers,17 it was found that the nucleophilic 71-bond of the alkene attacks the 0-0 cr-bond in an Sn2 fashion with displacement of a neutral carboxylic acid. There are, however, some mechanistic anomalies. For example, a protonated peracid should be a much more effective oxygen transfer agent over its neutral counterpart, but experiments have shown only modest rate enhancements for acid catalysed epoxidation. Early attempts to effect acid catalysis in alkene epoxidation where relatively weak acids such as benzoic acid were employed proved unsuccessful.18 The picture is further complicated by contradictory data concerning the influence of addition of acids on epoxidation rates.19 Trichloroacetic acid catalyses the rate of epoxidation of stilbene with perbenzoic acid, but retards the rate of a double bond containing an ester constituent such as ethyl crotonate.20 Recent work has shown that a seven-fold increase in the rate of epoxidation of Z-cyclooctene with m-chloroperbenzoic acid is observed upon addition of the catalyst trifluoroacetic acid.21 Kinetic and theoretical studies suggest that the rate increase is due to complexation of the peroxy acid with the undissociated acid catalyst (HA) rather than protonation of the peroxy acid. Ab initio calculations have shown that the free energy of ethylene with peroxy-formic acid is lowered by about 3 kcal mol-1 upon complexation with the catalyst.21 

Epoxidation is often preliminary to solvolytic or nucleophilic ring-opening in synthetic sequences. In acidic aqueous media, epoxides are opened to give diols by an anti addition process. In cyclic systems, ring-opening occurs to give the diaxial diol. 

Acid-Catalyzed and Electrophilic Ring-Opening Reactions 

Epoxides can be reduced to alcohols. Lithium aluminum hydride effects reduction by nucleophilic attack, and hydride is therefore added at the less substituted carbon atom. Lithium triethylborohydride is more reactive than LiAlH4 and is superior for epoxides that are resistant to reduction. A good deal of work has been done on the reduction of epoxides with species generated from reaction of aluminum 

Base-catalyzed ring-opening of epoxides constitutes a route to allylic alcohols  

Strongly basic reagents, such as the lithium salt of dialkylamines, are required to promote the reaction, which presumably involves concerted proton-abstraction and ring-opening. The stereochemistry of the ring-opening has been investigated by 

Give the structure of the product formed when each of the following alkenes reacts with bromine in water  

Sample Solution (a) The hydroxyl group becomes bonded to the more substituted carbon of the double bond, and bromine bonds to the less substituted one. 

Substitutive lUPAC nomenclature treats epoxides as epoxy derivatives of alkane parents the epoxy-piefix is hsted in alphabetical order like other substituents. Some industrial chemicals have common names formed by adding the word oxide to the name of the alkene. 

Countless numbers of naturally occurring substances are epoxides. Disparlure, the sex attractant of the female gypsy moth is but one example. 

Give the substitutive lUPAC name, including stereochemistry, for disparlure. 

The first step in the aerobic degradation of alkenes is epoxidation. Epoxidation is then followed by several alternatives. In one of them, the epoxides may nndergo carboxylation the enzyme 

Class II Three-component enzyme, e.g., benzene and toluene 

Futher division may be made according to the FMN or FAD flavin requirement, and the nature of the [2Fe-2S] protein 

FIGURE 3.2 Classification of bacterial dioxygenases. (From Neilson, A.H. and Allard, A.-S. Microbial metabolism of PAHs and heteroarenes. The Handbook of Environmental Chemistry, Vol. 3J, pp. 1-80, Springer, 1998. With permission.) 

FIGURE 3.4 Mechanism for carboxylation of acetone involving FAD, NADP, and coenzyme M. 

Give the major organic product formed when hydrogen bromide reacts with each of the alkenes in Problem 6.4 in the absence of peroxides and in their presence. 

Sample Solution (a) The addition of hydrogen bromide in the absence of peroxides exhibits a regioselectivity just like that of hydrogen chloride addition Markovnikov s rule is followed. 

Under free-radical conditions in the presence of peroxides, addition takes place with a regioselectivity opposite to that of Markovnikov s rule. 

You have seen that cyclic halonium ion intermediates are formed when sources of electrophilic halogen attack a double bond. Likewise, three-membered oxygen-containing rings are formed by the reaction of alkenes with sources of electrophilic oxygen. 

Three-membered rings that contain oxygen are called epoxides At one time, epoxides were named as oxides of alkenes. Ethylene oxide and propylene oxide, for example, are the common names of two industrially important epoxides. 

A second method for naming epoxides in the lUPAC system is described in Section 16.1. 

Substitutive lUPAC nomenclature names epoxides as epoxy derivatives of alkanes. According to this system, ethylene oxide becomes epoxyethane, and propylene oxide becomes 1,2-epoxypropane. The prehx epoxy- always immediately precedes the alkane ending it is not listed in alphabetical order like other substituents. 

Functional group transformations of epoxides rank among the fundamental reactions of organic chemistry, and epoxides are commonplace natural products. The female 

Most pubhcations regarding this field are based on immobilized chiral salen U-gands [62] which are coordinated with manganese [45 a, 78-82] or chromium [83] 

Schem Polybinaphtyl resin as catalyst in asymmetric epoxidations of 

Similar results were reported by Kim et al. [45 a] and Che et al., [83] who both employed salen complexes attached to zeolite MCM-41. Similarly, Seebach and coworkers generated dendritic elongated salen derivatives that could be embedded in polystyrene by co-polymerization [80]. 

The unsymmetrical analog of a Katsuki-type salen ligand was attached to Merri-field s resin (1% cross-Hnked) yielding a catalyst (22) (Fig. 4.3) which showed good efficiency and selectivity in the asymmetric epoxidation of 1,2-dihydronaphtalene with good performance after several recycling steps [81]. Related complexes (23) immobilized on silica were recently disclosed by Seebach and coworkers (Fig. 4.3) [82]. 

Chem Rev 89 431 (1989) (transition metal catalyzed) 92 873 (1992) (metal-mediated) Comprehensive Organic Synthesis, Eds. B. M. Trost and I. Fleming, Pergamon, Oxford (1991), Vol 7, Parts 3.1 and 3.2, pp 357 36 Russ Chem Rev 60 123 (1991) (enantioselective) 

Houben-Weyl, Methods of Organic Chemistry, 4th ed, Vol E21e, G. Thieme, Stuttgart-New York (1995), p 4599 (enantioselective) 

cat tungstic acid, Et3N (allylic alcohols) 

cat Na2W04-2H20, H3P04, H2S04, phase transfer catalyst 

cat chloromanganese(tetra-2,6-dichloro-phenylporphyrin), imidazole 

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Epoxidation of alkenes with peroxy acids is a syn addition to the double bond Substituents that are cis to each other in the alkene remain cis in the epoxide substituents that are trans in the alkene remain trans m the epoxide... 

Epoxidation of alkenes is a stereospecific syn addition Which stereoisomer of 2 butene reacts with peroxyacetic acid to give meso 2 3 epoxybu tane Which one gives a racemic mixture of (2/ 3/ ) and (25 35) 2 3 epoxybutane ... 

Epoxidation of alkenes (Sec tion 6 18) IS another example of a cycloaddition... 

Epoxidation of alkenes by reaction with peroxy acids... 

Epoxidation of alkenes was discussed m Section 6 18 and is represented by the general equation... 

Peroxy acids have been seen before as reagents for the epoxidation of alkenes (Section 6 18)... 

Olefin isomerization can be catalyzed by a number of catalysts such as molybdenum hexacarbonyl [13939-06-5] Mo(CO)g. This compound has also been found to catalyze the photopolymerization of vinyl monomers, the cyclization of olefins, the epoxidation of alkenes and peroxo species, the conversion of isocyanates to carbodiimides, etc. Rhodium carbonylhydrotris(triphenylphosphine) [17185-29-4] RhH(CO)(P(CgH )2)3, is a multifunctional catalyst which accelerates the isomerization and hydroformylation of alkenes. 

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 most important oxirane syntheses are by addition of an oxygen atom to a carbon-carbon double bond, i.e. by the epoxidation of alkenes, and these are considered in Section 5.05.4.2.2. The closing, by nucleophilic attack of oxygen on carbon, of an OCCX moiety is dealt with in Section 5.05.4.2.1 (this approach often uses alkenes as starting materials). Finally, oxirane synthesis from heterocycles is considered in Section 5.05.4.3 one of these methods, thermal rearrangement of 1,4-peroxides (Section 5.05.4.3.2), has assumed some importance in recent years. The synthesis of oxiranes is reviewed in (B-73MI50500) and (64HC(19-1U). 

The molybdenum-catalyzed oxidation of alkynes by /-butyl hydroperoxide has been investigated 73JCS(P1)2851) (the epoxidation of alkenes by this system has become an important reaction Section 5.05.4.2.2(i)) but the formation of oxirenes was excluded. 

Oxaziridines are generally formed by the action of a peracid on a combination of a carbonyl compound and an amine, either as a Schiff base (243) or a simple mixture. Yields are between 65 and 90%. Although oxygenation of Schiff bases is formally analogous to epoxidation of alkenes, the true mechanism is still under discussion. More favored than an epoxidation-type mechanism is formation of a condensation product (244), from which an acyloxy group is displaced with formation of an O—N bond. 

Directing influence of functional groups and geometry of reactant molecules on the peroxide epoxidation of alkenes 99UK206. 

Oxiranes, synthesis, bioactivity, and mechanism of peroxide epoxidation of alkenes 99MI3. 

Development of chiral, nonracemic dioxiranes for the catalytic enantioselective epoxidation of alkenes 99SL847. 

The Prilezhaev reaction is a rarely used name for the epoxidation of an alkene 1 by reaction with a peracid 2 to yield an oxirane 3. The epoxidation of alkenes has been further developed into an enantioselective method, that is named after Sharpless. 

E The writing has again been revised at the sentence level, streamlining the presentation, improving explanations, and updating a thousand small details. Several little-used reactions have been deleted (the alkali fusion of arene-sulfonic acids to give phenols, for instance), and a few new ones have been added (the Sharpless enantioselective epoxidation of alkene.s, for instance). 

Asymmetric epoxidations of alkenes have been intensively studied since Sharpless initial report on asymmetric epoxidation of allylic alcohols in 1980. This reaction, discussed in Section 9.1.3, has become one of the most widely employed reactions in asymmetric synthesis, due to its reliability and high enantioselectivity [2],... 

Catalysis. Cytochrome P-450 model compounds catalyze the epoxidation of alkenes by hypochlorite ions.16 A typical catalyst is OMn(TMP)L+. 

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