Notable solvent effects on the regioselectivity in the Paternò–Büchi reaction of 1,3-dimethylthymine with 4-methoxybenzophenone

Notable solvent effects on the regioselectivity and the photochemical efficiency were observed in the Paternò–Büchi (PB) reaction of 1,3-dimethylthymine (DMT) with 4-methoxybenzophenone (MBP). As a comparison, photochemical reactions of 4,4′-difluorobenzophenone (DFBP) and benzophenone (BP) with DMT were performed under the same condition. With increasing the proportion of water in the solution, besides the PB reaction, an electron-transfer reaction was observed in the DFBP–DMT system. The PB reaction of BP–DMT system revealed similar effects on the regioselectivity and the efficiency with that of MBP–DMT system, but the latter is more remarkable. The notable solvent effects may be responsible for a strongly solvent-dependent properties of the excited triplet MBP.