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Base-promoted epoxide isomerization
Base-promoted epoxide isomerization is the conversion of alkyl epoxides to ring-opened products through the action of strong base. Isomerizations of this type are most often used to synthesize allylic alcohols, although other products are possible.〔Crandall, J. K.; Apparu, M. ''Org. React.'' 1983, ''29'', 345. 〕
== Introduction ==
In the presence of lithium or aluminum amide bases, epoxides may open to give the corresponding allylic alcohols. Removal of a proton adjacent to the epoxide, elimination, and neutralization of the resulting alkoxide lead to synthetically useful allylic alcohol products. In reactions of chiral, non-racemic epoxides, the configuration of the allylic alcohol product matches that of the epoxide substrate at the carbon whose C–O bond does not break (the starred carbon below). Besides β-elimination some other reactions〔〔 are possible, as metalation of the epoxide ring can take place competitively. Vinylogous eliminations are possible when the epoxide substrate is substituted with vinyl or dienyl groups.〔 Unconstrained systems tend to form ''trans'' double bonds, as significant non-bonding interactions are avoided in the transition state for the formation of ''trans'' products (see equation (2) below). The strongly basic conditions required for most isomerizations of this type represent the reaction's primary disadvantage.
''(1)''File:EpIsoGen.png
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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