Diels–Alder Reaction

Section Overview

• What is the Diels Alder Reaction?
• Precautions
• Applications for Diels Alder Reaction
• Recent Research and Trends
• References

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

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.

Applications for Diels Alder Reaction

The Diels–Alder reaction is useful for the synthesis of:

• Novel Diels−Alder reactions of arynes with functionalized acyclic dienes have been reported for the synthesis of useful cis-substituted dihydronaphthalene building blocks.²

• 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

• 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

• 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