Enolate anions, dianions reaction with alkyl halides

Under the conditions of the Birch reduction, IV-Boc amides such as 60 can be reductively alkylated in high yields, presumably via a dianion intermediate which is protonated by ammonia at C-5 leaving an enolate anion at C-2 <96JOC7664>. Quenching the reaction with alkyl halides or ammonium chloride then affords the 3-pyrrolines 61. 

The direct a-alkylation of monoketones normally employs reaction of an alkyl halide or sulfonate with the enolate anion produced using a strong base. This method can be satisfactorily used with symmetrical ketones, which are to be dialkylated with a dihalide, and with intramolecular cyclization reactions, where the formation of five- and six-membered rings is often favored over the formation of three-, four-, seven-, and eight-membered rings (M. Mous-seron, 1937 W.S. Johnson, 1963). Regioselective alkylation of dianions according to Hauser s rule (see p. 9f.) is usually also a satisfactory procedure (F.W. Sum, 1979). 

Looking back on the history of ketone dianion chemistry, one soon notices that dianion species, derived from / -keto esters, have been in continuous steady use in organic synthesis3,4, as shown in Scheme 2. Thus, ethyl acetoacetate can be converted to the corresponding ketone o a -chainon via consecutive proton abstraction reactions. The resulting dienolate anion reacts with a variety of alkyl halides to give products, resulting from exclusive attack at the terminal enolate anions. 

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