Observations on the alkylation of beta-acetalic carbanions: monoalkylation versus dialkylation and elimination

The reaction with methyl iodide and a base (t-BuOK) of 1,3-dioxolanes and 1,3-dithiolanes substituted at the beta-position with an electron-withdrawing substituent (EWG = CO2Me, SO2Ph, SO2Ph-p-NO2, SO2Ph-p-NO2) leads to mono- or dialkylated or ring-opened products in good yields.