Diels–Alder reaction

In <a href="/facts/Organic_chemistry/djxhxaNg">organic chemistry</a>, the Diels–Alder reaction is a chemical reaction between a <a href="/facts/Conjugated_system/Ddx9qzox">conjugated</a> <a href="/facts/Diene/F5NxrLPW">diene</a> and a substituted <a href="/facts/Alkene/RtYcS6kU">alkene</a>, commonly termed the dienophile, to form a substituted <a href="/facts/Cyclohexene/EWIV90Fx">cyclohexene</a> derivative. It is the prototypical example of a <a href="/facts/Pericyclic_reaction/UQ3nKSSD">pericyclic reaction</a> with a <a href="/facts/Concerted_reaction/sPAIkRGa">concerted mechanism</a>. More specifically, it is classified as a thermally allowed [4+2] <a href="/facts/Cycloaddition/Gme6TDFP">cycloaddition</a> with <a href="/facts/Woodward%E2%80%93Hoffmann_rules/4tW2tBIF">Woodward–Hoffmann symbol</a> [π4s + π2s]. It was first described by <a href="/facts/Otto_Diels/Lov8SkYD">Otto Diels</a> and <a href="/facts/Kurt_Alder/tpQR0LQS">Kurt Alder</a> in 1928. For the discovery of this reaction, they were awarded the <a href="/facts/Nobel_Prize_in_Chemistry/8Nb8Ajjy">Nobel Prize in Chemistry</a> in 1950. Through the simultaneous construction of two new carbon–carbon bonds, the Diels–Alder reaction provides a reliable way to form six-membered rings with good control over the regio- and stereochemical outcomes. Consequently, it has served as a powerful and widely applied tool for the introduction of chemical complexity in the synthesis of natural products and new materials. The underlying concept has also been applied to π-systems involving <a href="/facts/Heteroatom/QzxXyfCT">heteroatoms</a>, such as <a href="/facts/Carbonyl_group/KJ71bo3X">carbonyls</a> and <a href="/facts/Imine/yK72z07j">imines</a>, which furnish the corresponding <a href="/facts/Heterocyclic_compound/8oYSjJxY">heterocycles</a>; this variant is known as the hetero-Diels–Alder reaction. The reaction has also been generalized to other ring sizes, although none of these generalizations have matched the formation of six-membered rings in terms of scope or versatility. Because of the negative values of ΔH° and ΔS° for a typical Diels–Alder reaction, the microscopic reverse of a Diels–Alder reaction becomes favorable at high temperatures, although this is of synthetic importance for only a limited range of Diels–Alder adducts, generally with some special structural features; this reverse reaction is known as the <a href="/facts/Retro-Diels%E2%80%93Alder_reaction/Pjj4WQLW">retro-Diels–Alder reaction</a>.

Diels–Alder reaction open-in-new

Diels–Alder reaction