Esters, conjugated, reaction with nitrile enolates

In summary, reactions of nitronates with acid anhydrides or acyl chlorides give the O-acylated products, and reactions with acyl imidazoles, phenyl esters, acyl nitriles, and enol-lactones gives the C-acylated products, (see Eq. 5.13).25 The C/O selectivity of nitronate acylation by RCOX is qualitatively correlated with strength (pKJ of the acid HX conjugated to the leaving group X .25... 

The previous sections have dealt primarily with reactions in which the new carbon-carbon bond is formed in an Sn2 reaction between the nucleophilic carbon species and the alkylating reagent. There is another general and important method for alkylation of carbon that should be discussed at this point. This reaction involves the addition of a nucleophilic carbon species to an electrophilic multiple bond. The reaction is applicable to a wide variety of enolates and enamines. The electrophilic reaction partners are typically a,j8-unsaturated ketones, esters, or nitriles, but other electron-withdrawing substituents also activate the carbon-carbon double bond to nucleophilic attack. The reaction is called either the Michael reaction or conjugate addition The process can also occur with other nucleophiles, such as alkoxide ions or amines, but these reactions are outside the scope of the present discussion. 

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