Epoxide Reactivity and Stereoselective Synthesis

The proposed biosyntheses of ether-containing natural products employ enzymes to introduce epoxide groups with complete stereocontrol and, in some cases, to dictate the regioselectivity of the nucleophilic addition reactions. Chemical mimicry of these pathways reqnires extensive understanding of the fundamental structural relationships for epoxide reactivity toward tetherednucleophiles. Additionally, 

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In addition to (3-elimination, epoxides are also known to undergo rearrangement to a carbonyl group, and this reactivity can be synthetically useful as well. For example, Kita and co-workers <97JOC4991> have used a novel acid-promoted rearrangement of cyclic a,(3-epoxy acylates e.g., 110) for the stereoselective synthesis of spirocyclanes (e.g.. Ill), a technique which is... 

In their synthesis of the proposed glabrescol (90) (Scheme 3.30) [65], Kodama and coworkers reported that compound 88 was regio- and stereoselectively epoxidized at the central alkene with ketone 42 to give compound 89 after ring closure. The alkene inductively deactivated with the allylic acetate is less reactive. 

In contrast, a three-member cyclic ether (e.g., epoxide) is highly strained and reactive. Such rings are commonly used in synthesis, beeause, like bromonium ion rings, they lead to stereoselective products. 

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