Synthesis of CF3-containing dihydropyrido[1,2-a]indolones via a visible-light-promoted radical cascade [4 + 2]/[4 + 2] cycloaddition.

Both dihydropyrido[1,2-a]indolones and CF3-containing compounds are widely found in natural products and pharmaceutical agents. Therefore, the development of new synthetic methods for the construction of CF3-containing dihydropyrido[1,2-a]indolones remains highly significant, as these compounds represent promising candidates for drug discovery. In this study, a photo-driven Ir(ppy)3-catalyzed radical cascade [4 + 2]/[4 + 2] cycloaddition of simple N-acryloyl indoles and Umemoto reagent I is reported, which provides a straightforward and efficient route to a range of CF3-containing dihydropyrido[1,2-a]indolones under mild conditions. The protocol exhibits broad functional group tolerance, including various synthetically useful substituents. The reaction proceeds through four sequential radical additions, leading to the dimerization of N-acryloyl indoles along with the formation of four C-C bonds and two fused six-membered rings. The successful scale-up experiment and product derivatization studies further demonstrate its synthetic utility. A plausible reaction mechanism has also been proposed based on mechanistic studies and the isolation of several undesired [4 + 2] cycloaddition byproducts.