Our optimization starts with an equimolar amount of MVCl2, 3 equivalents of isoprene in 1 mL TFE (dried over molecular sieves overnight), irradiated with 520 nm green light for 24 h, under these conditions, the expected [4+2] cycloadduct was formed in 60% NMR yield (Table ). After successful product formation, we gradually reduced the amount of MVCl2 to 5 mol% (entry 2,3), the NMR yield remained constant (entry 3, 60% NMR yield). After decreasing the amount of solvent (entry 4) and reaction time (entry 5), the desired product was isolated in a good yield (entry 6, 72%). We tested various solvents that also exhibit potential ability to stabilize formed radical cation intermediates such as MeNO2 and MeOH (entry 7-8), but the desired product was not observed.45 Control reactions (entry 9-11) showed that methyl viologen and light are crucial to form the desired product and oxygen was found to play a vital role in the reaction cycle, likely to regenerate the methyl viologen acceptor. The radical cation cyclization reaction Initiated by the methyl viologen mediated EDA complex formation demonstrates a relatively broad generality for this type of radical chain reaction. (Scheme 3). Anethole and compounds with similar structures efficiently formed the [4+2] cycloadduct as anticipated (6a-6e). Previous studies have exhibited the crucial role of the alkoxy group on the benzene ring in visible light induced radical cation-based cyclization reactions.46-52 The methyl viologen mediated EDA complexes demonstrate an improved tolerance to other para substituents compared to most strategies and substrates substituted with para-phenyl and para-methyl groups could be converted to the desired products in good yields (6f-6g). Electrondeficient olefins typically favor thermal or acid-mediated [4+2] cycloadditions and their exploration in photochemical reactions has been limited.53 In this context, electron-deficient olefins generally do not function well as electron donors in EDA complex formations. However, in this study, we found that these electron withdrawing group (EWG)-conjugated olefins exhibited yields of up to 90% (6h-6j), with aldehyde groups being well-tolerated. N-Vinylcarbazole could also be successfully employed in the [4+2] cyclization as an electron-rich olefin (6k), broadening the scope of potential electron donors to be paired with methyl viologen as the acceptor.