THF: An Efficient Electron Donor in Continuous Flow Radical Cyclization Photocatalyzed by Graphitic Carbon Nitride

Mesoporous graphitic carbon nitride (mpg‐C3N4) was found to be an efficient heterogeneous photocatalyst for the metal‐free radical cyclization of 2‐bromo‐1,3‐dicarbonyl compounds. Reactions leading to functionalized cyclopentanes proceed under mild conditions and can be conducted in a continuous flow photoreactor. Compared to the batch reaction, the use of a continuous flow reactor resulted in a significant reduction in reaction time (complete conversion of 0.04 mmol of substrate in a batch was achieved after 4 h, whereas in a flow reactor the same amount of substrate was fully converted into a product within 40 min). Mechanistic studies of the reaction showed that THF plays not only the role of solvent, but is also a crucial hydrogen and electron donor. Donation′s saving grace: The metal‐free catalyst mesoporous graphitic carbon nitride (mpg‐C3N4) and light induced the radical cyclization of bromomalonates in a heterogeneous continuous flow reactor. The reaction, in which THF plays the role of hydrogen and electron donor, is a practical method for rapid synthesis of functionalized cyclopentanes in high yields under mild conditions.