Noncovalent interactions like halogen, chalcogen, and pnictogen bonding are known for a very long time. During the last decade, these interactions have found different applications in catalysis. These forces are often called σ‐hole interactions which can be explained by the anisotropic distribution of the electron density around these atoms. In this MiniReview, we will present recent applications of halogen, chalcogen, and pnictogen bonding in catalysis and discuss experimental and computational investigations to gain more insights into the underlying mechanisms.

The Nazarov cyclization is an important pericyclic reaction that allows the synthesis of substituted cyclopentenones. We now demonstrate that this reaction can be performed under very mild, metal-free reaction conditions using molecular iodine as the catalyst. A variety of different divinyl ketones including aromatic systems undergo the iodine-catalyzed reaction with moderate to very good yields in both polar and apolar solvents. Our mechanistic studies indicate that the Nazarov system is activated through a halogen bond between the carbonyl group and the catalyst, and other modes of action like Brønsted acid or iodonium ion catalysis are unlikely. Furthermore, addition of iodine to the double bond or a putative iodine-catalyzed cis–trans isomerization of the employed olefins seem not to be an important side reaction here.

The Diels‐Alder cycloaddition is the most popular pericyclic reaction with numerous applications in synthesis and catalysis. We now demonstrate that we can perform this reaction under mild and metal‐free conditions relying on molecular iodine as the catalyst. Cycloadditions with cyclohexadiene, cyclopentadiene, or isoprene with various dienophiles can be performed typically within minutes in moderate to good yields and high endo selectivity. The mechanistic studies including kinetic and DFT investigations clearly indicate a halogen‐bond activation and rule out other modes of activation. Furthermore, iodine performs equally well as typical metallic Lewis acids like AlCl3, SnCl4, or TiCl4.

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l-proline crystallized, in its zwitterionic form, without the inclusion of any solvent or water mol­ecules through the slow diffusion of diethyl ether into a saturated solution of l-proline in ethanol. In the crystal, the mol­ecules are linked via N—H⋯O hydrogen bonds, resulting in a two-dimensional network.