In 2020, Schmidt and Argüello introduced an efficient photochemical strategy for the synthesis of 2-substituted benzothiazoles 50 via visible-light-mediated aromatic C-H thiolation of thiobenzanilides 51. This methodology employs riboflavin 2′,3′,4′,5′-tetraacetate (RFTA, 21) as a photocatalyst and potassium persulfate as a sacrificial oxidant under a nitrogen atmosphere (Scheme 16) . The key advantages of this approach include the utilization of a naturally derived organic dye (riboflavin) as a photocatalyst, the absence of transition-metal complexes or bases, and the use of blue light to drive the reaction, leading to benzothiazoles 50 in good to excellent yields (Scheme 16). This method demonstrates broad substrate tolerance, accommodating both electron-donating and electron-withdrawing substituents. Notably, it represents the first successful photochemical synthesis of nitro-substituted 2-phenylbenzothiazole. Additionally, several 2-alkylbenzothiazoles were produced in moderate to very high yields, and a double-cyclization product 52 was obtained with a yield of 41%. The proposed mechanism begins with the ET from thiobenzanilide (51, R 1 =H, R 2 =Ph) to the excited state of RFTA 21, forming the radical cation of thiobenzanilide A and the radical anion RFTA •-. In the subsequent step, deprotonation of A is facilitated by RFTA •-. Cyclization followed by rearomatization, driven by potassium persulfate, yields the desired benzothiazole 50 (R 1 =H, R 2 =Ph). The riboflavin catalyst is notable for its dual role, functioning as both a photocatalyst and a base (pKa of [RFTA-H] • = 8.3). This property eliminates the need for an external base and enables the activation of substrates containing strong electron-withdrawing groups, such as nitro substituents. Peroxydisulfate is critical for closing the catalytic cycle, regenerating RFTA in its ground state . In 2024, the same authors expanded on this work by developing a metal-and base-free aerobic photoredox protocol employing RFTA 21 for the synthesis of 2-substituted benzothiazoles 50 under similar conditions . In this updated methodology, oxygen replaced potassium persulfate as the oxidant, offering enhanced efficiency. For instance, the yield of product 52 increased from 41% to 58%, while reaction time, catalyst loading, and solvent environmental impact were significantly reduced. This innovation represents a notable advance, achieving two cyclization reactions in a single reaction step with greater sustainability and efficiency. Scheme 16. Riboflavin 2′,3′,4′,5′-tetraacetate (RFTA) 21 catalyzed synthesis of benzothiazoles 50, 52.