Epoxide syntheses

Thus, the key reason for the paucity of methods available by analogy with epox-idation methods is the comparative inertness of N-O and N-N bonds relative to the peroxide bond. This means that the synthetic methods that have been developed for preparation of aziridines are distinct from those that have evolved for epoxide synthesis. 

Schneider, C. (2006) Synthesis of 1,2-difunctionalized fine chemicals through catalytic, enantioselective ring-opening reactions of epoxides., Synthesis, 3919-3944. 

Scheme 5.41 The reaction of alkynyltungsten with epoxides synthesis of bicyclic lactones.

Epinephrine, chemiluminescence, 647 6-Epiplakortolide E, synthesis, 256, 257 Epithelial cells, ozone effects, 612 Epothilone B, dioxirane epoxidation synthesis, 1145... 

Epoxides have been prepared on occasion by the action of certain inorganic oxidizing agents on suitable olefins. A notable example is ohromie oxide n anhydrous modia. Knowledge concerning the exart mode of action of such reagents is still incomplete, and for the purpose of epoxide synthesis they are of limited utility. For this reason only a brief discussion will be presented here. 

Below are described five approaches to epoxide synthesis by way -.if haLohydrins. These halohydrina may be isol ble purifi ble intermediates or they may be transient, unstable species that undergo spontaneous ring closure under the conditions used to generate them. Jho former are typical of (1) addition of hypobalous acids to olefins 111 chemical reduction of a-h Iocarbonyl compounds, and (3) addition if organometallic reagents to o-halocarbonyl compounds the latter,... 

The last reducing agent that will be mentioned in the present section Is aluminum uopropoxide, for which only limited application is recorded in the literature of epoxide synthesis,127-18e-18 >1062 It is doubtful, however, whether this reagent offers any advantage over those considered above. 

Illustrative of the use of methylsulfonate caters for epoxide synthesis are several preparations drawn from the steroid litera-tnj-oMH-ww. i ot, ls 3 j nd depicted in Eqs. (23fi)-(24l). Although other... 

A technique that has proved to possess considerable usefulness in epoxide synthesis is addition of diazoalkanes. particularly of the parent eubatanoe djazomethane, to suitable carbonyl groups. 

The ability of diazomethane to replace hydrogen atoms in "iodic compounds like carboxylic adds, phenolB, and enolB has long been known. Although thw aspect need not be dealt with extensively h tv. it should be stressed that with a polyfunctional substrate diazomethauc can function at several reaction sites. Some discrimination therefore necessary in selecting this reagent for epoxide synthesis. 

Treatment of a -un aturated aldehyde -with diazomethanr generally yieldB pyrazolines, and therefore needs not be considered further os a method of epoxide synthesis. 

An important exception to the applicability of diazomethane for epoxide synthesis will be apparent when it is recalled that this ivugoni is exceedingly potent in replacing acidic hydrogens in enoJs.-1 1 ... 

Pyrolytic decomposition of cyclic carbonate eaten of 1,2-diols hjus been utilized on occasion for epoxide synthesis. Ethylene Oxide jiml glycidol, for example, have been prepared26 mc from ethylene carbonate and glyceryl carbonate respectively (Eq. 314). 

The work of Pattison,1107 and more recently of Searlrs nrvl w worker. 1 4 indicate considerable generality for the above reaction in preparing cyclic ether of various ring sizes. Ita scope in epoxide synthesis baa been limited eo far to the two illustrations cited. 

Excellent reviews by Swem167 M7f have already been cited in connexion with epoxide synthesis by peroxy acid oxidation of oIMuim (see Motiiat 1111,4.). These papers are equally useful in connexion with the present topic, and should be consulted for many details that cannot be discussed here. 

Still another decomposition giving rise to ethylene oxide involves die pyrolysis f 0-hydrvjxyethyl -V,N-dialkylaminopolymethylehe carbamates. A specific illustration (Eq. 318) is -hydroxyethyl y-morpho-Kuopropyl carbamate, which on heating at 130-140° yields ethylene xide. carbon dioxide, and a urea derivative.4 Although interesting, this decomposition is of little preparative value in epoxide synthesis. 

W, V and Co has been widely investigated [28]. This section will highlight some novel and unique approaches to epoxide synthesis using environmentally benign oxidants and heterogeneous metal catalysts such as solid-supported Ti, polyoxometalates and hydrotaldte. 

Lakner FJ, Hager LP (1997) Chloroperoxidase-Mediated Asymmetric Epoxidation. Synthesis of (R)-Dimethyl 2-Methylaziridine-l,2-dicarboxylate - A Potential a-Methylamino Acid Synthon. Tetrahedron Asym 8 3547... 

R. Khan, M. R. Jenner, H. Lindseth, K. S. Mufti, and G. Patel, Ring-opening reactions of sucrose epoxides Synthesis of 4 -derivatives of sucrose, Carbohydr. Res., 162 (1987) 199-207. 

Hodgson, D. M. Norsikian, S. L. M. First direct deprotonation-electrophile trapping of simple epoxides synthesis of a,/f-epoxysilanes from terminal epoxides. Org. Lett. 2001, 3, 461—463. 

The epoxide 6 is naturally electrophilic, but where does the epoxide come from By far the most important method of epoxide synthesis is the treatment of alkenes 19 with peroxy acids RCO3H 21. Alkenes are naturally nucleophilic 2 they react with bromine to give dibromides 20 and with electrophilic peroxyacids 21 to give epoxides. Again, these reactions convert nucleophilic alkenes into electrophilic derivatives. A very popular reagent for epoxidation is mCPBA (meta-chloro-perbenzoic acid) 21 R = 3-chlorophenyl but many other compounds are used. 

J. M. Berty, in Ethylene Epoxide Synthesis, ed. B. E. Leach, Applied Industrial Catalysis, Vol. 1, Academic Press (1983). 

Epoxide Synthesis via Sulfide Alkylation/Deprotonation Procedure [51] (p. 360)... 

A. Pfenniger, Asymmetric epoxidation of allylic alcohols The Sharpless epoxidation, Synthesis 1986, 89. 

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