The discovery of new drug candidates and the development of new lead structures for future active pharmaceutical ingredients are continuous processes, which combine the expertise of many scientific disciplines. The race for novel molecular building blocks with potent biological activity triggered the development of new synthesis methodologies and forced the scientific communities to interact even stronger with each other. The result of one very fruitful interaction is the application of continuous flow chemistry and micro reaction technology to photochemistry and photocatalysis. The synergy of those research fields combined is an environment for mild and controlled reaction conditions, which allows new synthesis routes with higher conversion and selectivity, straightforward scale-up and possible integration in multi-step syntheses. In this chapter, several examples for molecular transformations are highlighted, which are important for the synthesis of complex molecular structures or for the integration of pharmaceutically active functional groups. This snapshot gives an overview of a vivid research field for drug discovery and illustrates the benefits for synthetic organic photochemistry by going to flow.
