Lewis base and l-proline co-catalyzed Baylis–Hillman reaction of arylaldehydes with methyl vinyl ketone

In the Baylis–Hillman reaction of arylaldehydes with methyl vinyl ketone, we found that, in the presence of a catalytic amount of l-proline, weak Lewis bases such as imidazole and triethylamine as well as the stronger Lewis base DABCO, can promote the Baylis–Hillman reaction to give the normal Baylis–Hillman adduct in good yields. Substituent effects were also examined and a plausible reaction mechanism is proposed.