Cycloaddition reactions are a class of chemical reactions in which two or more reactants combine to form a cyclic compound. These reactions are commonly used in organic synthesis to construct complex ring structures in a single step. Cycloadditions can be classified into different types, such as [2+2], [3+2], and [4+2] cycloadditions, based on the number of atoms involved in the ring formation. These reactions are important in a variety of fields, including medicinal chemistry, materials science, and natural product synthesis.