Carboxylic acids dianions, reaction with epoxides

The dianions derived from furan- and thiophene-carboxylic acids by deprotonation with LDA have been reacted with various electrophiles (Scheme 64). The oxygen dianions reacted efficiently with aldehydes and ketones but not so efficiently with alkyl halides or epoxides. The sulfur dianions reacted with allyl bromide, a reaction which failed in the case of the dianions derived from furancarboxylic acids, and are therefore judged to be the softer nucleophiles (81JCS(Pl)1125,80TL505l). 

Epoxides - The first indication of the synthetic utility of metalated carboxylic acids resulted from efforts to prepare steroidal aldosterone inhibitors from spiroepoxides.39 Model studies indicated that the reaction fails as a result of severe steric hindrance in either the epoxide or carboxylic acid and that monosubstitution occurs for the same reason.39 The reaction has been used in a key step of an elegant synthesis of vernolepin, 5. 40 Forcing conditions are required, and, in contrast to acid dianions, anions of unactivated esters fail to react with epoxides.39 41... 

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