Palladium-catalyzed cyclization of 1,omega-dienols: multiple ways to intramolecularly trap a carbocation.

The tandem catalytic cyclization-rearrangement of 1,omega-dien-3-ols by palladium(II) produces different types of products, depending on the structure of starting material. The pinacol rearrangement, benzannulation, and oxy-Cope rearrangement are major pathways of transforming the putative sigma-alkylpalladium carbocation. Turnover of the cyclization is achieved by beta-hydride elimination and reoxidation of palladium with benzoquinone. The overall course of the reaction is very sensitive to small changes in the substrate structure.