Flow Chemistry for Cycloaddition Reactions

: Continuous flow reactors form part of a rapidly growing research area that has changed the way synthetic chemistry is performed not only in academia but also at the industrial level. This Review highlights the most recent advances in cycloaddition reactions performed in flow systems. Cycloadditions are atom‐efficient transformations for the synthesis of carbo‐ and heterocycles, involved in the construction of challenging skeletons of complex molecules. The main advantages of translating these processes into flow include using intensified conditions, safer handling of hazardous reagents and gases, easy tuning of reaction conditions, and straightforward scaling up. These benefits are especially important in cycloadditions such as the copper(I)‐catalyzed azide alkyne cycloaddition (CuAAC), Diels‐Alder reaction, ozonolysis and [2+2] photocycloadditions. Some of these transformations are key reactions in the industrial synthesis of pharmaceuticals. Everything flows: This Review highlights advances in cycloadditions using flow chemistry. These powerful transformations are safe and easily scalable under flow conditions. Thus, they are applicable at industrial level for the synthesis of pharmaceuticals and other interesting products. Recent advances related to continuous procedures include Diels‐Alder, ozonolysis, Huisgen, and photochemical [2+2] cycloaddition reactions.