Continuous-flow liquid phase oxidation chemistry in microreactors receives a lot of attention as the reactor provides enhanced heat and mass transfer characteristics, safe use of hazardous oxidants, high interfacial areas, and scale-up potential. In this review, an up-to-date overview of both technological and chemical aspects of liquid phase oxidation chemistry in continuous-flow microreactors is given. A description of mass and heat transfer phenomena is provided and fundamental principles are deduced which can be used to make a judicious choice for a suitable reactor. In addition, the safety aspects of continuous-flow technology are discussed. Next, oxidation chemistry in flow is discussed, including the use of oxygen, hydrogen peroxide, ozone and other oxidants in flow. Finally, the scale-up potential for continuous-flow reactors is described.

Dual nickel/photocatalytic C–N couplings are performed with an organic heterogeneous photocatalyst, in an oscillatory plug flow reactor. Reaction was complete in 20 min residence time, enabling 2.7 g h−1 throughput and 10-fold catalyst recycling.

Trifluoromethylated and perfluoroalkylated heterocycles are important building blocks for the synthesis of numerous pharmaceutical products, agrochemicals and are widely applied in material sciences. To date, trifluoromethylated and perfluoroalkylated hetero-aromatic systems can be prepared utilizing visible light photoredox catalysis methodologies in batch. While several limitations are associated with these batch protocols, the application of microflow technology could greatly enhance and intensify these reactions. A simple and straightforward photocatalytic trifluoromethylation and perfluoroalkylation method has been developed in continuous microflow, using commercially available photocatalysts and microflow components. A selection of five-membered hetero-aromatics were successfully trifluoromethylated (12 examples) and perfluoroalkylated (5 examples) within several minutes (8-20 min).

A mild and versatile protocol for the C–H acylation of indoles via dual photoredox/transition-metal catalysis was established in batch and flow. The C–H bond functionalization occurred selectively at the C-2 position of N-pyrimidylindoles. This room-temperature protocol tolerated a wide range of functional groups and allowed for the synthesis of a diverse set of acylated indoles. Various aromatic as well as aliphatic aldehydes (both primary and secondary) reacted successfully. Interestingly, significant acceleration (20 to 2 h) and higher yields were obtained under micro flow conditions.

A mild and selective C–H arylation strategy for indoles, benzofurans and benzothiophenes is described.