First Example of Intramolecular [2pi+2pi] Alkene-Arene Photocyclization in the Chromone Series and its Synthetic Utility.

Diels-Alder adducts of chromones are shown to undergo an intramolecular [2(pi)+2(pi)] alkene-arene photocyclization, leading to a versatile polycyclic diene, which is capable of dimerization or can be introduced into a high yielding photoprotolytic oxametathetic sequence. This allows for an expeditious growth of molecular complexity over a few experimentally simple steps with stereochemistry being defined and locked at the very first Diels-Alder step. The overall reaction can potentially be utilized in Diversity-Oriented Synthesis as it allows for three or more diversity inputs furnishing novel unique polycyclic scaffolds, which can readily be decorated with a variety of functionalities and aromatic/heterocyclic pendants.