Diels–Alder reaction

A pericyclic cycloaddition in which a conjugated diene and a dienophile form a six-membered ring, usually creating two carbon–carbon bonds in one step.

HOMO–LUMO interaction: An interaction between the highest occupied molecular orbital of one species and the lowest unoccupied molecular orbital of another. The diene’s HOMO and dienophile’s LUMO help explain the reaction’s favored bonding pattern.
Conjugated diene: A molecule containing two carbon–carbon double bonds separated by one single bond. It supplies the four-atom π system that becomes four atoms of the new ring.
Intramolecular Diels–Alder reaction: A Diels–Alder reaction in which the diene and dienophile are tethered within the same molecule. A single cycloaddition can rapidly assemble fused or bridged ring systems.
Otto Diels: A German chemist who shared the 1950 Nobel Prize in Chemistry for discovering the reaction named with Kurt Alder. Diels co-discovered the cycloaddition that bears his name.
1,3-Dipolar cycloaddition: A cycloaddition between a three-atom 1,3-dipole and a two-atom dipolarophile, usually forming a five-membered ring. It also forms rings through concerted bonding but uses a three-atom dipole rather than a diene.
Woodward–Hoffmann rules: Rules predicting whether pericyclic reactions are allowed from orbital-symmetry conservation. They explain why the thermal six-electron cycloaddition proceeds with suprafacial bonding.
Dienophile: An alkene or alkyne that reacts with a diene in a cycloaddition. It supplies the two remaining atoms of the six-membered ring.
Asymmetric Diels–Alder reaction: A Diels–Alder reaction designed to favor one enantiomer of a chiral cycloadduct. Chiral catalysts or auxiliaries can control the stereochemistry of newly formed centers.
Kurt Alder: A German chemist who shared the 1950 Nobel Prize in Chemistry for discovering the Diels–Alder reaction. Alder’s work established the reaction as a powerful method for making cyclic compounds.
[2+2] cycloaddition: A cycloaddition between two two-atom π systems that forms a four-membered ring. Its thermal orbital-symmetry restrictions differ from the allowed thermal Diels–Alder pathway.

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