24syklöadditioner

24-syklöadditioner, also known as [4+2] cycloadditions or Diels-Alder reactions, are a type of pericyclic reaction in organic chemistry. This reaction involves a conjugated diene and a dienophile, which are unsaturated compounds, combining to form a six-membered ring. The reaction proceeds through a concerted mechanism, meaning all bond breaking and bond forming occurs in a single step with a cyclic transition state. This concerted nature leads to stereospecificity, where the stereochemistry of the starting materials is preserved in the product.

The reaction is named after Otto Diels and Kurt Alder, who were awarded the Nobel Prize in Chemistry in 1950 for their work on this reaction. The Diels-Alder reaction is highly versatile and widely used in organic synthesis for constructing cyclic systems. It is particularly useful for forming cyclohexene derivatives. The reactivity of the diene and dienophile can be influenced by electron-donating and electron-withdrawing groups, respectively. Electron-rich dienes and electron-poor dienophiles typically react most readily. The reaction can also be catalyzed by Lewis acids, which coordinate to the dienophile and increase its electrophilicity, thereby accelerating the reaction rate. Applications of the Diels-Alder reaction are found in the synthesis of natural products, pharmaceuticals, and polymers.