Hydroxylic solvents, epoxidation with

Cobalt tetracarbonyl anion in such hydroxylic solvents as water or methanol also reacts with epoxides at temperatures of 60—100 and at an elevated pressure of carbon monoxide (2000 Ib./in. ) to give esters of j8-hydroxy acids. Thus, ethylene oxide has been found to react with sodium cobalt tetracarbonyl and carbon monoxide in methanol solution at 65 and 2000 Ib./in. to give methyl 3-hydroxy-propionate in a yield of 55% the remainder of the product was acetaldehyde and an involatile oil. It was also shown that this reaction proceeds almost as well at a much lower pressure (three or four atmospheres of carbon monoxide). ... 

Furanose derivatives undergo facile epoxidations with DMD <90JOC42ll>. A remarkable solvent effect was observed in these epoxidations. In acetone solvent the hydroxyl group in (124) did not exert a directive effect on the stereochemical course of the epoxidation, as it does with MCPBA or... 

In ketone-directed peroxy acid epoxidations of cyclic alkenes the actual epoxidizing agent has been shown by 180-labeling not to involve a dioxirane <94TL6155>. Instead, an a-hydroxy-benzoylperoxide or a carbonyl oxide is believed to be responsible for observed stereoselectivities in the intramolecular epoxidations. The extent of syn-selectivity is greater for ketones than with esters the syn/anti ratios increase when ether is used as solvent rather than CH2C12, the reverse situation for hydroxyl-directed epoxidations. Fused-ring oxiranes can also be prepared from acyclic precursors. Four different approaches are discussed below. 

This alkoxycarbonylation reaction is also catalytic, if the alkylcobalt tetracarbonyl is formed from an epoxide and cobalt carbonyl anion in a hydroxylic solvent (9). A stoichiometric amount of base is not required in this reaction. The initial product, a derivative of the anion of 2-hydroxy-ethylcobalt tetracarbonyl, may undergo three reactions (a) react with more epoxide to give polymer, (b) undergo an internal hydride shift to form aldehyde or ketone, or (c) undergo protonation, carbon monoxide insertion, and alcoholoysis (or hydrolysis) to form ester (or acid). Varying amounts of... 

Effects of hydroxylic solvents on epoxidation of styrene with H2O2 have been studied. Consistent results were obtained when the impact of a single molecule of water, ethanol, and t-BuOH on the reaction was simulated using the discrete model. Reactivity was greatest for /-BuOH followed by ethanol protic solvent molecules promote the heterolytic cleavage of H2O2 and form active oxygen species that reduce the reaction barrier. ... 

The presence of hydroxyl groups in the benzylidene sugars does not interfere with the reaction and by-products are usually minor. Suitable solvents other than carbon tetrachloride, include benzene and tetra-chloroethane. Epoxide, amide, and other commonly encountered functionalities in sugar derivatives are unaffected under the reaction conditions. The corresponding 6-bromo-4-benzoates are valuable intermediates... 

A 1,2-diol arising from a trans-hydroxylation process is formed from an alkene by way of an intermediate epoxide which is subjected to a ring-opening reaction and hydrolysis. The epoxides may be isolated when the alkene is reacted with perbenzoic add or m-chloroperbenzoic acid (Section 4.2.56, p. 457) in a solvent such as chloroform or dichloromethane the preparation of epoxides by this method and by other important procedures are discussed and illustrated... 

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