Influence of palladium(II) complexes on the cycloaddition of α-bromoalkyl ketenes to cyclopentadiene

Palladium(II) complexes, of the type PdL2X2 and PdX2, influence both the yields and endo/exo ratio in formation of several 7-bromo-7-alkylbicyclo[3.2.0]hept-2-en-6-ones. Standard dehydrochlorination of α-bromoacyl chlorides with triethylamine in the presence of cyclopentadiene and palladium catalyst promotes the formation of the exo cycloadducts, which is accompanied by an improvement in the yields for both endo and exo cycloadducts. The mechanism of the palladium-mediated cycloaddition is discussed.