The iron-catalysed photoreaction gave 38% of the desired C-H functionalised products 3a and 3b under the conditions mentioned in Table .1 (entry a). FeCl3 6H2O proved to be the most efficient metal salt for the photo-transformation (entry h). Interestingly, in the absence of additional chloride anions, there was a significant decrease in product formation, particularly evident for FeCl3•6H2O as the catalyst (entry n) and complete absence of product with Fe(ClO4)3•H2O as the metal salt (entry c). Moreover, the yield of products 3a and 3b, as observed in F-NMR, decreased in presence of additional ligands such as salicylic acid or 5-sulfosalicylic acid dihydrate (entries e-g, im). The reaction does not proceed in the absence of light, with Fe(III) present (entries e and p), or without the presence of an iron salt at 365 nm or 385 nm (entries b, d, g, and s). The presence of oxygen from air should be avoided as it leads to the formation of side products upon irradiation of the reaction (entries o and p). Despite the bathochromic shift observed in the absorption of the metal-salicylic acid complex (Supporting Information, Spectra S1 and S2) the reaction worked most efficiently at 385 nm. At 400 nm, the yield with FeCl3•6H2O as the catalyst (entries k) significantly decreased, and beyond 450 nm, no photo-transformation was observed (entries l and m). Further reaction optimisation attempts are listed in Table in the Supporting Information.