Epoxide, epoxides

Henbest Epoxidation- epoxidation directed by a polar group... 

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... 

Alkene conversion to epoxide (%) Epoxide selectivity (%) Epoxide conversion (%) Cyclic carbonate selectivity (%)... 

Epoxides. Epoxides or oxiranes are quite reactive metabolically. These three-membered rings will readily open in the presence of most nucleophiles. They will react with most biopolymers, including proteins and nucleic acids. Compounds with epoxides have very short half-lives and tend to be toxic. 

Other possible reactions, such as homopolymerization (epoxide+epoxide) and epox-ide+hydroxyl group (in the latter stages of cure), can be neglected when the ratio of epoxide to amine is stoichiometric and in the absence of catalyst or accelerator [194], For TGDDM/DDS resins, the homopolymerization reaction may be neglected at cure temperature below 180°C [84], At temperatures between 177°C and 300°C, dehydration and/or network oxidation occur, which results in formation of ether cross-linkings with loss of water. Decomposition of the epoxy-OH cure reaction can also take place, which results in propenal... 

Reduction of epoxides. Epoxides can be reduced by slow addition of methanol to a refluxing mixture of the epoxide and NaBH4 in (-butyl alcohol. The more substituted alcohol is formed preferentially. Presumably the actual reducing agent is NaBH4. n(OCH3)n. Amide, nitro, and nitrile groups are not reduced by the procedure. 

Stereoselective epoxidation. Epoxidation of the diene 2 with m-chloroperben-zoic acid, monoperphthalic acid, or r-butyl hydroperoxide-vanadylacetylacetonate gives a mixture of two epoxides in 89% yield.1... 

Epoxidation + epoxide opening Epoxidation + epoxide opening 30 92 at C= 80... 

Enantioselective epoxidation Epoxide hydrolase Solution phase [424]... 

The epoxidation-epoxide opening sequence with this reagent provides a convenient access to the products of an //-Markovnikov addition of water to olefins. Interestingly, the Cp2TiCl/H20 couple combination shows anti stereoselectivity in the reduction step [73, 74], which is complementary to the hydroboration-oxidation method (Scheme 32). 

Now for some examples with epoxides. Epoxides are very important because they can be formed stereo specifically from alkenes cis- alkenes give cis (or syn) -epoxides and tram- alkenes give tram (or anti) -epoxides. 

Reduction of epoxides. Epoxides are reduced in CH2CI2 by these two reagents. Unsymmetrical epoxides are reduced with some regioselectivity favoring the less substituted alcohol. 

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