An unexpected highly diastereoselective double Baylis-Hillman reaction of per- (or poly)fluorophenyl aromatic aldimines with methyl vinyl ketone

Aza-Baylis-Hillman reaction of per- (or poly)fluorophenyl aromatic aldimines 1 with methyl vinyl ketone (MVK) was studied. It was found that both the used Lewis base and solvent can significantly affect the reaction. Using triphenylphosphine as a Lewis base, the reaction of 1 with MVK proceeded smoothly to give the normal Baylis-Hillman adduct 2 along with the double Baylis-Hillman adduct 3 as by-product in THF. When 1,4-diazabicyclo[2.2.2]octane was used as a Lewis base in DMF, the aza-Baylis-Hillman reaction of 1 with MVK gave the double aza-Baylis-Hillman adduct 3 exclusively in moderate to good yields with excellent diastereoselectivities. The double Baylis-Hillman adduct 3 was conveniently converted to fluorine-containing 4-alkylidene-2-cyclohexen-1-ones under mild reaction conditions in good yields.