A general preparation of alkenylmagnesium derivatives bearing an electron-withdrawing function in the α-position (Y= CN, CO2R, CONR2, SO2Ph) has been made possible by using a low temperature (− 40 to− 30° C) bromine–magnesium exchange with i-PrMgBr in THF. This reaction has also been used to prepare 5-magnesiated-1, 3-dioxin-4-one derivatives bearing an alkoxy substituent in β-position to the carbon–magnesium bond.
