Chemists have discovered a way to use visible light to synthesize a class of compounds particularly well suited for use in pharmaceuticals. The class of compounds, called azetidines, had been previously identified as a good candidate to build therapeutic drugs, but the compounds are difficult to produce in chemical reactions. Now, a team has developed a method to produce a specific class of azetidines called monocyclic azetidines using visible light and a photocatalyst.