In synthetic organic chemistry, so-called cycloadditions are a particularly important class of reactions. With this type of reaction, ring-shaped molecules can be constructed simply and efficiently by joining ("adding") two compounds that each contain double bonds. A team led by Prof. Dr. Frank Glorius from the University of Münster has now succeeded in performing an unconventional cycloaddition in which a carbon-carbon double bond reacts with a carbon-carbon single bond. In double bonds, atoms are connected by two pairs of electrons; in single bonds, only one pair of electrons is involved. The key to success was the use of particularly "strained" single bonds. To enable mild reaction conditions, the chemists used a photosensitizer, a catalyst that drives the reaction using light energy. The study has now been published in the journal Nature.