The asymmetricalkylation of 2-methoxycarbonyl-1-indanone (2) and ethyl 2-methylacetoacetate (5) with an alkylsulfonium salt containing a sugar group were investigated. (S)-Ethyl 2-allyl-2-methylacetoacetate (6b) was obtained with up to 25% optical purity on alkylation of the enolate ion of 5 using the allyl(p-tolyl)sulfonio D-glucoside derivative (1h).
of cyclic β-keto ester with racemic sulfonium salts containing optically active alkyl groups such as (S)-2-octyl and (S)-2-butyl was found to afford C-alkylated products with inversion of configuration at asymmetric alkyl carbon atom. Stereochemical reaction course via formation of S–O sulfurane intermediate and successive stereoselective intramolecular alkyl migration to enolate is described.
A new asymmetric alkylation of cyclic β-keto esters with optically active sulfonium salts, which are easily prepared by optical resolution methods, has been investigated. Relative reactivities for alkyl substituents are found to be quite different from those for SN2 alkylation. Stereochemical reaction course via S–O sulfurane intermediate for this new reaction is proposed.