Thermal Intramolecular [2+2] Cycloaddition of Allenenes and Allenynes: Diastereoselective Access to Bicyclic Nitrogen Heterocycles

Squaring the circle: A route to bicyclo[4.2.0]octane derivatives has been developed by the [2+2] cycloaddition of allenenes or allenynes. The thermal intramolecular [2+2] cycloaddition of simple allenes 1 with an additional multiple bond leads to direct and regioselective formation of the distal adducts 2 in good to excellent yields.