Z/E Stereoselective synthesis of β-bromo Baylis-Hillman ketones using MgBr2 as promoter via a one-pot three-component reaction

The first time steroselective synthesis of (Z)-β-bromo Baylis-Hillman ketones has been achieved using a one-pot three-component reaction. The new system uses MgBr₂ as both the Lewis acidic promoter and the bromine source for the Michael-type addition with α,β-acetylenic ketones to form an active β-bromo allenolate intermediate, which in turn attacks various aldehydes to afford β-bromo Baylis-Hillman adducts in good yields and Z-selectivity.