Additional investigations were made with the attempt to gain insights into the mechanism of this reaction. For a crossover experiment, a solution of equimolar amounts of 15e and 15v was irradiated with blue LED light under standard conditions (Scheme 6). No evidence for crossover products 17ev and 17ve was found and only 17e and 17v could be isolated in yields of 64% and 39%, respectively, suggesting that the cyclisation occurs in an intramolecular manner. The initiation of the cyclization reaction from 15a to 17a (Scheme 4) with radical starters AIBN and DBPO under thermal conditions was not successful and no product could be isolated, indicating that the conversion can only be achieved photochemically. Radical quenching experiments with TEMPO and BHT showed diminished yields depending on the amount of scavenger used (Table , SI) with 3 equiv. of TEMPO being sufficient for the complete suppression of the reaction. These findings suggest that the reaction might proceed through a radical pathway, even though the respective quenching products could not be isolated and no direct chemical evidence could be obtained. As the mechanism of the reaction could not be proven in this study, further investigations will be part of future work.