Mesoporous graphitic carbon nitride (mpg-C3 N4 ) 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.

The use of a flow reactor significantly reduces the reaction time.