Aryl-aryl cross-coupling reactions without reagents or catalysts: photocyclization of ortho -iodoaryl ethers and related compounds via triplet aryl cation intermediates.

Cyclisations of benzyl ortho -iodoaryl ethers to benzo[ c ]chromenes can be effected without reagents or catalysts by irradiation with UVC under flow. Reactions proceed via triplet aryl cation generation, 5- exo and 3- exo -cyclisations, and rearomatisation. They have wide scope, are easy to effect and extend to a myriad of related ring systems.