Conjugate addition vs. vinylic substitution in palladium-catalysed reaction of aryl halides with β-substituted-α,β-enones and -enals

The reaction of β-substituted-α,β-enones and -enals with aryl halides in the presence of a palladium catalyst has been investigated. The outcome of the reaction was found to be greatly dependent on the nature of the added base. Tertiary amines tend to favour the formation of conjugate addition-type products while sodium bicarbonate or sodium acetate that of vinylic substitution products. Usually, the use of sodium acetate produced results comparable or better than those obtained with sodium bicarbonate. Furthermore, in the reaction of aryl halides containing strongly electronwithdrawing groups, sodium acetate afforded a dramatic increase in the yield of vinylic substitution products.