Epoxides, transformation

Fries rearrangement, 18 336, 337 isomerization and transalkylation of alky-laromatics, 18 329 epoxide transformations, 18 351-352 hydration and ammonolysis of ethylene oxide, 18 351, 352 isomerization, 18 351 framework composition, 33 226-228 hydrogenation, dehydrogenation, and related reactions, 18 360-365 dehydrocyclization of s-ethylphenyl using zeolites and carbonyl sulfide, 18 364, 365... 

Applications of the AD to epoxide transformation propranolol and diltiazem Part V - Jacobsen Epoxidation Part VI - Desymmetrisation Reactions Opening anhydrides Opening epoxides... 

Quantum Chemical Modeling of Enzymatic Reactions Applications to Epoxide-Transforming Enzymes... 

In this chapter, we will provide an overview of the employed methodology. To illustrate the various aspects of the methodology and to give the reader a feeling about the state of the art of the field, three very recent applications will be discussed in detail. All three enzymes are concerned with epoxide-transforming reactions, namely limonene epoxide hydrolase (LEH), soluble epoxide hydrolase (sEH), " and haloalcohol dehalo-genase C (HheC). First, however, a brief presentation of DFT and its accuracy will be given. 

We will provide here three examples of recent applications concerned with the modeling of enzymatic epoxide transformation. Epoxides are versatile compounds and understanding their enzymatic transformation in detail is not only important from a fundamental enzymology point of view but also practically useful for biocatalytic applications. The three enzymes considered are LEH, the human sEH, and HheC. 

Epoxides.—Reviews on aspects of epoxide transformation which have appeared include catalytic hydrogenation, photochemical reactions, stereoselective cleavage, and basic epoxide behaviour in the presence of halide ions. ... 

Abstract Transformation of epoxides is a key step for numerous processes important both for synthetic organic chemistiy and biochemistry. Since experimental methods are restricted by the fixation of sonrce compoimds, intermediates and prod-nets of reactions, quantum chemical calculations serve as the only direct approach for prediction of the structure and energy of transition states thus clarifying detailed mechanisms of chemical reactions. This chapter stunmarizes resrrlts of quantum chemical investigation of epoxides transformation mechanisms in alkaline, neutral and acidic environments. Special attention has been paid to stereo- and regiochem-istry of the processes, influence of solvation effects and natrrre of catalytic action of mono- and bidentate acids. 

These results indicate that to exercise very reliable and predictive regioselective epoxide transformations one has to be well aware of the mechanistic details of the process. 

As in these last examples, the descriptions of diastereoselective epoxidations were accompanied already by details on their subsequent use in ring fission reactions, we shall now switch to the various options of controlled regioselective and diastereoselective epoxide transformations. The nucleophilic opening of epoxides shows a strong dependence on substrate structure, nature of the nucleophile, and the catalyst involved, similarly to nucleophilic substitutions. Lastly, one has to consider the solvent and other details of the reaction conditions including the transition state conformation. 

Bearing in mind that most of the epoxide transformations are catalyzed by oxophilic Lewis acids, we will also have to consider rearrangements that may occur... 

Liang, J., Moher, E.D., Moore, R.E., and Hoard, D,W, (2000) Synthesis of cryptophycin 52 using the Sharpless asymmetric dihydroxylation diol to epoxide transformation optimized for a base-sensitive substrate./. Org. Chem., 65, 3143—3147. 

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