Epoxide ring opening reactions epoxides from

Angle strain is the main source of strain in epoxides but torsional strain that re suits from the eclipsing of bonds on adjacent carbons is also present Both kinds of strain are relieved when a ring opening reaction occurs... 

Rearrangement of fluorine with concomitant ring opening takes place in fluorinated epoxides Hexafluoroacetone can be prepared easily from perfluo-ropropylene oxide by isomerization with a fluorinated catalyst like alumina pre treated with hydrogen fluoride [26, 27, 28] In ring-opening reactions of epoxides, the distribution of products, ketone versus acyl fluoride, depends on the catalyst [29] (equation 7) When cesium, potassium, or silver fluoride are used as catalysts, dimenc products also are formed [29]... 

The use of various heterocyclic additives in the MTO-catalyzed epoxidation has been demonstrated to be of great importance for substrate conversion, as well as for the product selectivity. With regard to selectivity, the role of the additive is obviously to protect the product epoxides from deleterious, acid-catalyzed (Brons-ted or Lewis acid) ring-opening reactions. This can be achieved by direct coordination of the heterocyclic additive to the rhenium metal, thereby significantly decreasing its Lewis acidity. In addition, the basic nature of the additives will increase the pH of the reaction media. 

The asymmetric oxidation of organic compounds, especially the epoxidation, dihydroxylation, aminohydroxylation, aziridination, and related reactions have been extensively studied and found widespread applications in the asymmetric synthesis of many important compounds. Like many other asymmetric reactions discussed in other chapters of this book, oxidation systems have been developed and extended steadily over the years in order to attain high stereoselectivity. This chapter on oxidation is organized into several key topics. The first section covers the formation of epoxides from allylic alcohols or their derivatives and the corresponding ring-opening reactions of the thus formed 2,3-epoxy alcohols. The second part deals with dihydroxylation reactions, which can provide diols from olefins. The third section delineates the recently discovered aminohydroxylation of olefins. The fourth topic involves the oxidation of unfunc-tionalized olefins. The chapter ends with a discussion of the oxidation of eno-lates and asymmetric aziridination reactions. 

The wide scope application of this transformation arises not only from the utility of epoxide compounds but also from the subsequent regiocontrolled and stereocontrolled nucleophilic substitution (ring-opening) reactions of the derived epoxy alcohol. These, through further functionalization, allow access to an impressive array of target molecules in enantiomerically pure form. 

Figure 8. Epoxide ring opening reactions of bay-region diol epoxides and epoxides from dibenzo[a,h] acridine, and epoxides from benzo[a]acridine and benzo[c]acridine. Figure adaptedfrom reference 27. 

Figure 10. Epoxide ring opening reactions of the fluor mated derivatives of dibenzo [a,h] acridine-1,2-epoxide. Figure adapted from reference 27.

Figure 15. Epoxide ring opening reactions of epoxides and diol epoxides from benzo[a]pyrene, 4-azabenzo[a]pyrene and 10-azabenzo [a]pyrene.

When EO is formed, single bonds from two adjacent carbons are connected to an oxygen atom. A three-member ring is always in a strained condition, due to the geometry of the molecule. Because of the propensity to relieve the strain, epoxides are very reactive. Practically all the EO produced is converted to chemical intermediates as a result of a ring opening reaction. 

Wordy Over the past few years, we have encountered numerous examples of water as the perfect solvent. We observed this first in osmium-catalyzed dihydroxylation reactions and also in nucleophilic ring-opening reactions of epoxides. We also observed this in cycloaddition reactions and in most oxime ether, hydrazone, and aromatic heterocycle condensation processes.Finally, we observed it in formation reactions of an amide from a primary amine and an acid chloride using aqueous Schotten-Baumann conditions. ... 

In this connexion, Baker and Kobineon also noted, in a different case, that acid-catalyzed nucleophilic attack occurs preferentially at the epoxide carbon atom furthest from the carbonyl function of an a 3-epoxyketone (Eq. 67a). Interestingly, however, under alkaline conditions a rearrangement took place instead of the anticipated ring-opening reaction. 

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