Diethyl fumarate, conjugate addition

Diethyl malonate adds to diethyl fumarate in a conjugate addition reaction promoted by sodium ethoxide in dry ethanol to give a tetraester, Diethyl fumarate is an excellent Michael acceptor because two ester groups withdraw electrons from the alkene, The mechanism involves deprotonation of the malonate, conjugate addition, and reprotonation of the product enolate by ethanol solvent, In this reaction two ester groups stabilize the enolate and two more promote conjugate addition. 

The conjugate addition of a carbanionic species across the activated double bond, such as in the esters of maleic and fumaric acid, are typical examples of Michael addition. Carbanions are usually generated using a base catalyst and, hence, reaction of MA itself has not been attempted. A representative example of the addition of diethyl malonate 74 to diethyl maleate, which produces the tetracarboxylic ester 75, is shown below. 

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