Cycloaddition is a chemical reaction where two or more unsaturated molecules combine to form a cyclic structure. This process typically involves the formation of new bonds, resulting in a ring-shaped compound. Cycloaddition reactions are important in organic chemistry and are often used to create complex molecules in pharmaceuticals and materials science. One common type of cycloaddition is the Diels-Alder reaction, which involves a diene and a dienophile. This reaction is valuable for synthesizing six-membered rings and is widely utilized in the development of various organic compounds, including natural products and synthetic materials.