Evaluation of a flow-photochemistry platform for the synthesis of compact modules

A custom-made meso-scale continuous flow-photochemistry platform was evaluated with the aim to enable the synthesis of synthetically relevant amounts (>5 g, with the option of 10-100 g) of novel compact modules, whose synthesis is based upon a photochemical transformation. The flow-photochemistry concept relies on the irradiation of thin-layers (20-90 μm) of reactant dissolved in a suitable solvent that is pumped through the single-pass photoreactor. The commercially available Ehrfeld Photoreactor XL system was equipped with standard UV lamps (emission maximum at 254 nm) which are cheap, durable and low in power consumption (8 W). The flow photochemistry system was evaluated using a known intramolecular [2+2] cycloaddition reaction investigating influence of flow rate (irradiation time), layer-thickness and reactant concentration. After a short initial optimisation phase, the system delivered in a first run 6 g of tricycle 4 which was further successfully up-scaled to 48 g, demonstrating the robustness and reliability of this flow photoreactor-platform.