Oxidative photoinduced electron transfer (PET) reactions irradiation times could be reduced by using the cosensitized PET method. Modifying the substrate at the silyl group led have been performed with various silyl enol ethers and silyloxy-2H-chromones bearing an olefinic or silylacetylenic to enhanced yields. In addition, we found that solvent and pressure dependences are important tools, allowing control side chain. The reactions result in regioselective ring closure with the formation of bi-to tetracyclic ring systems with a of the regiochemistry. Both the synthesis of 6-endo products by radical cationic reaction pathways, as well as 5-exo ring well-defined ring juncture, e.g. perhydrophenanthrenones 13 or benzo-annellated xanthenones 24. Our investigations closure by radical intermediates was achieved. Mechanistic details, including findings from deuterium labelling have focussed on the optimization of this cyclization method with regard to irradiation time and product yield. The experiments, are discussed.