Diels–Alder Reaction
What is the Diels Alder Reaction?
The Diels–Alder reaction is the reaction between a conjugated diene and an alkene (dienophile) to form unsaturated six-membered rings. Since the reaction involves the formation of a cyclic product via a cyclic transition state, it is also referred to as a "cycloaddition". The Diels–Alder reaction is an electrocyclic reaction, which involves [4+2]‑cycloaddition of 4 π-electrons of the conjugated diene and 2 π-electrons of the dienophile (an alkene or alkyne). The reaction involves the formation of new σ-bonds, which are energetically more stable than the π-bonds. This reaction has great synthetic importance and was discovered by two German chemists, Otto Diels and Kurt Alder in 1928. They were awarded the Nobel Prize in 1950.1
![Diels–Alder Reaction Chemical reaction diagram showing 1,3-Butadiene (Conjugated Diene) reacting with Ethylene (Dienophile) to form Cyclohexene. The diagram includes structural representations of the reactants and the product.](/deepweb/assets/sigmaaldrich/marketing/global/images/technical-documents/articles/chemistry-and-synthesis/organic-reaction-toolbox/diels-alder-reaction-01r/diels-alder-reaction-01r.jpg)
The hetero-Diels–Alder reaction is a variant of this reaction and is useful for the synthesis of six-membered heterocyclic rings. In this reaction, either the diene or the dienophile contains a heteroatom, usually nitrogen or oxygen.1
Precautions
Please consult the Safety Data Sheet for information regarding hazards and safe handling practices.
![Diels–Alder Reaction Chemical reaction scheme illustrating the synthesis of cis-substituted dihydronaphthalene building blocks from an aryne and a functionalized acyclic diene via a [4+2] cycloaddition mechanism. The product is a complex polycyclic aromatic compound with specified substituents.](/deepweb/assets/sigmaaldrich/marketing/global/images/technical-documents/articles/chemistry-and-synthesis/organic-reaction-toolbox/diels-alder-reaction-02r/diels-alder-reaction-02r.jpg)
- Natural and unnatural polycarbocycles and polyheterocycles.3
- Substituted (tetrahydro)quinolines and diverse N-polyheterocycles, including some alkaloids, which contain pyrroloquinoline or cyclopentaquinoline ring systems.4
- Pyrano[3,2-c]quinolines and indeno[2,1-c]quinolones.5
- Symmetrically substituted 1,8-diaza-9,10-anthraquinone derivatives.6
- Oxazaborolidine derived from N-tosyl (αS,βR)-β-methyltryptophan has been employed as the catalyst for the enantioselective Diels-Alder reaction of 2‑bromoacrolein and furan. This reaction leads to the synthesis of chiral 7‑oxabicyclo[2.2.1]heptene derivatives.7
![Diels–Alder Reaction Chemical reaction scheme illustrating the synthesis of chiral 7-oxabicyclo[2.2.1]heptane derivatives from 2-bromoacrolein and furan using a catalyst. The process involves multiple steps and highlights the role of catalysis in forming complex organic molecules.](/deepweb/assets/sigmaaldrich/marketing/global/images/technical-documents/articles/chemistry-and-synthesis/organic-reaction-toolbox/diels-alder-reaction-03r/diels-alder-reaction-03r.jpg)
- Functionalized 4-(R)-1,2-bis(trimethylsilyl)benzenes.8
- Functionalized oxabicyclic alkenes.9
Recent Research and Trends
- Intra- and intermolecular imino Diels–Alder reactions (Povarov reactions) of N-aryl imines and diverse electron-rich alkenes have been studied.4
- Ultrasonic irradiation promoted the Diels–Alder reaction of substituted furans with reactive dienophiles such as dimethyl acetylenedicarboxylate (DMAD) and dimethyl maleate afforded functionalized oxabicyclic alkenes in good yields.9
![Diels–Alder Reaction Chemical reaction scheme showing the transformation of 2-vinylic furans into functionalized oxabicyclic alkenes through ultrasonic irradiation in the presence of DMAD. The starting material, 2-vinylic furan, has a variable group ‘R’ attached to a five-membered furan ring with a vinyl group at the second position. The product is an oxabicycle with two ester groups (‘COOMe’) and the same variable group ‘R’.](/deepweb/assets/sigmaaldrich/marketing/global/images/technical-documents/articles/chemistry-and-synthesis/organic-reaction-toolbox/diels-alder-reaction-04r/diels-alder-reaction-04r.jpg)
- The Diels–Alder reaction of graphite and tetracyanoethylene has been used for the mechanical exfoliation of graphite into graphene adducts.10
- Cross-linked hydrogels have been prepared using Diels-Alder “click” reaction without employing a catalyst.11
- The asymmetric Diels–Alder reaction between N-acryloyloxazolidinone and cyclopentadiene has been catalyzed by heterogeneous copper(II)-bis(oxazoline)-based polymer immobilized ionic liquid phase (PIILP) systems.12
- Chiral oxazaborolidine−aluminum bromide complexes are potential catalysts for enantioselective Diels–Alder reactions.13
- Halocycloalkenones have been investigated as potent dienophiles in inter- and intramolecular Diels–Alder cycloadditions.14
- The chemical thermodynamics of Diels–Alder addition reactions of a series of acenes (anthracene, 9,10-dimenthylanthracene, tetracene and pentacene) to C60 fullerene has been analyzed.15
References
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