10 - Enolate Ions as Intermediates

Abstract

In the presence of strong bases, carbonyl compounds form enolate ions that may be employed as nucleophilic reagents to attack alkyl halides or other suitably electron-deficient substrates giving carbon–carbon bonds. In this chapter, several methods for the carbethoxylation of cyclic ketones via their enolates have been described. The methods differ primarily in the nature of the acylating agent employed. Thus, diethyl oxalate, diethyl carbonate, and ethyl diethoxyphosphinyl react with cycloalkanone enolates under suitable conditions to give acylated products. On treatment with a strong base such as sodium hydride or sodium amide, dimethyl sulfoxide yields a proton to form the methylsulfinyl carbanion, which is a strong basic agent. Reaction of dimsyl ion with triphenylalkylphosphonium halides provides a convenient route to ylides, and with triphenylmethane the reagent affords a high concentration of triphenylmethyl carbanion. The chapter also describes that when a solution of magnesium methoxide is saturated with carbon dioxide, an active carboxylating agent, magnesium methyl carbonate, is produced.