Epoxides chemistry

This kind of chemical reactivity of epoxides is rather general Nucleophiles other than Gng nard reagents react with epoxides and epoxides more elaborate than ethylene oxide may be used All these features of epoxide chemistry will be discussed m Sections 16 11-16 13... 

J. Marco-Contelles, Cyclohexane epoxides—Chemistry and biochemistry of (+)-cyclophellitol, Eur. J. Chem. (2001) 1607-1618. 

Ethylene oxides, like other three-membered ring systems, possess many singular features that invite a basis in theory. To satisfy Hub demand, much effort has boon devoted to the task of determining with precision such fundamental properties of the molecule os bond lengths, bond angles, and bond energies- With the advent of modern instrumental methods it has been possible to develop a dependable physical basis fin- theoretical speculations on the electronic structure of ethylene oxide. The present section is concerned with this aspect of epoxide chemistry. 

Rearrangement of several substituted chlorohydrins of fixed conformation has recently been reported by Curtin and Harder,3M and attention is directed to this interesting paper, since it is related to the abnormal reaction of a-haloketonos with Grignard reagents and hence pertinent to epoxide chemistry,... 

The early literature of epoxide chemistry contains several accounts of the reaction of hydrogen cyanide with epichlorohydrin, 11-1T1 epibromohydrin,10 ethyl glycidyl ether,J- and related substance Attack by the nucleophilic aperies, CN- ion in this case, occurs uniquely at the site furthest from the polar atom,. e. at the terminal epoxidi-carbon atom (Eq. 787), An important contribution was made by... 

Perhaps no example can better illustrate the defects associated with o tajytio reduction in epoxide chemistry than a hydrogenation reported by Striebel and Tamm,1 8 involving the l ,2a-epoxy-3-kelo steroid shown below (Eq. 366). It is seen that the anticipated diol mixture constitutes a mere ten percent of tho total product The remainder has fallen prey to over reduction. 

V. Analytical Aspects of Epoxide Chemistry One of the important problems confronting chemists ever since the discovery of ethylene oxide has been a growing need for reliable and expedient analytical methods, both at the qualitative and at the quantitative level. 

It is the object of this section to consider briefly the existing analytical procedures of epoxide chemistry at each of these levels. Mora detailed discussions are given in two excellent recent reviews. J°. ... 

Molybdenum complexes are the most effective catalysts known for the selective epoxidation of olefins with alkyl hydroperoxides (210-212). Commonly known is the Arco or Halcon process for the large-scale manufacture of propylene oxide from propylene. This process uses t-BuOOH or ethyl benzene hydroperoxide (EBHP) as an oxidant and Mo(CO)6, for example, as a source of Mo. The Mo(CO)6 acts as a catalyst precursor, which is converted into a soluble active form by complexation with diols (3). Chemists have designed several supported versions of the catalysts for this epoxidation chemistry. A clear classification can be made on the basis of the nature of the support. 

In a neat combination of thirane W-dioxide and epoxide chemistry, a RambergBbcklund reaction gives allyl alcohols 38 via thiirane sulfur dioxide under the reaction conditions (Scheme 27) <1997TL3055>. 

For a review on epoxide chemistry, see J. Gorzynski Smith, Synthesis, 1984, 629. 

The zinc halides have a mixed reputation in the field of epoxide chemistry. Znh is recommended as a catalyst for epoxide opening, without rearrangement, in the addition of thiosilanes and selenosi-lanes. Conversely, rearrangements catalyzed by zinc salts have been clearly documented for several epoxides. Sutherland s comparison suggests that ZnCh should be rated on the weaker end of the strong acid scale. 

Although a large number of chiral porphyrin catalysts has been developed for study in asymmetric epoxidation chemistry [12], to date only one example has been applied to aziridination. In that instance, Lai and coworkers reported the use of the Halterman porphyrin catalyst in the aziridination of styrene derivatives with moderate enantioselectivity (Scheme 5) [13]. 

Cyclohexane epoxides—chemistry and biochemistry of (+ )-cyclophellitol 01EJ01607. 

Scheme 8.10. Reaction of divinyl carbinol under (+)-AE conditions as an example of enantiotopic group selectivity in epoxidation chemistry. Matched cases of enantiofacial selectivity are shown with bold arrows. Qualitative rate differences are on the order kj k2, ks k4 (without specifying an order for k2 vi. k3 (however, cf. Scheme 8.8b). Note that the products arising from the pairs ki/k3 and k2/k4 are enantiomers.

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