The Diels-Alder reaction is a powerful chemical process used to create six-membered rings. It involves a diene, which is a molecule with two double bonds, and a dienophile, a compound that can react with the diene. When these two react, they form a new, more complex molecule in a single step, making it a valuable tool in organic chemistry. This reaction is particularly important in the synthesis of natural products and pharmaceuticals. It allows chemists to build intricate structures efficiently. The Diels-Alder reaction is also known for its ability to create stereochemistry, which is crucial for the function of many biological molecules.