Low-Temperature Intramolecular [4+2] Cycloaddition of Allenes with Arenes for the Synthesis of Diene Ligands.

The intramolecular [4+2] cycloaddition between arenes and allenes first reported by Himbert gives rapid access to rigid polycyclic scaffolds. Herein, we report a one-pot oxyalkynylation/cycloaddition reaction proceeding under mild conditions (23-90 °C) and providing complex polycyclic architectures with high efficiency, and atom and step economy. The bicyclo[2.2.2]octadiene products were obtained with a wide variety of useful functional groups and were successfully applied as chiral ligands for metal catalysis. Computational studies gave a first rationalization of the low activation energy for the cycloaddition based on counter-intuitive favorable dispersive interactions in the transition state.