Palladium-catalyzed intramolecular cyclization of vinyl and aryl triflates. Associated regioselectivity of the beta-hydride elimination step.

The Pd(0)-catalyzed intramolecular olefination of vinyl and aryl triflates has been studied with a view to gaining insight into the question of kinetically preferred reductive elimination when at least two options are available. In either series, a non-activated alkene participant was found to be converted most readily into the non-conjugated cyclization product. This trend is seen despite the more forcing conditions necessary to engage the less reactive aryl triflates in ring closure. On the other hand, when the pendant chain is terminated by an alpha-methyl acrylate unit, the conjugated diene is kinetically preferred. The two reactions appear to be closely balanced energetically since product distributions are not greatly disparate. Nevertheless, their complementarity could be utilized to advantage in the synthesis of polycyclic molecules possessing multiple sterogenic centers.