Expeditious cascade reactions: controlled syntheses of fenestradienes and cyclooctatrienes under palladium catalysis

Palladium cyclization cascades represent an elegant way to access complex polycyclic scaffolds in a minimum amount of steps. Herein we provide a complete account on two new methodologies including these kind of cascades, each leading to two types of attractive compounds, cyclooctatrienes and [4.6.4.6]fenestradienes. The reader will first discover a strategy requiring three steps starting from alkenyl bromides, based on a first 4-exo-dig carbopalladation/Sonogashira coupling tandem reaction, and a subsequent P-2 Ni induced semi-hydrogenation. This leads to a first generation of cyclooctatrienes and [4.6.4.6]fenestradienes. Next, the second approach will be presented, in which the second generation of these compounds is accessed in a one-pot reaction including five steps, starting from the same alkenyl bromide compounds. These methods are appealing in terms of atom economy, the use of easy to handle conditions as well as the variability of its scope.