DielsAlderreaktiot

The DielsAlder reaction is a fundamental organic chemical reaction that forms a six-membered ring through a concerted cycloaddition between a conjugated diene and a dienophile. It is a [4+2] cycloaddition, meaning that four pi electrons from the diene and two pi electrons from the dienophile participate in the reaction to form two new sigma bonds and one new pi bond. The reaction typically proceeds under thermal conditions and is highly stereospecific and regioselective.

The diene component must be in the s-cis conformation for the reaction to occur, as this brings the termini of the diene into proximity for bond formation. Electron-withdrawing groups on the dienophile generally increase the reaction rate, while electron-donating groups on the diene also enhance reactivity. The endo product is often favored kinetically due to secondary orbital interactions between the pi system of the dienophile and the developing pi bond in the diene, although the exo product may be thermodynamically more stable.

This reaction is exceptionally versatile and has found widespread use in the synthesis of a vast array of cyclic and polycyclic organic molecules, including natural products and pharmaceuticals. Its predictable stereochemistry and regiochemistry make it a powerful tool for constructing complex molecular architectures with precise control over stereoisomerism. The DielsAlder reaction was discovered by Otto Diels and Kurt Alder in 1928, for which they were awarded the Nobel Prize in Chemistry in 1950.