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The dienophile undergoes Diels–Alder reaction with a diene introducing such a functionality onto the product molecule. A series of reactions then follow to transform the functionality into a desirable group. The end product cannot be made in a single DA step because equivalent dienophile is either unreactive or inaccessible.
Maleic anhydride is a classic substrate for Diels-Alder reactions. [9] It was used for work in 1928, on the reaction between maleic anhydride and 1,3-butadiene, for which Otto Paul Hermann Diels and Kurt Alder were awarded the Nobel Prize in 1950. It is through this reaction that maleic anhydride is converted to many pesticides and pharmaceuticals.
However, when the dienophile substituents are endo, there is considerable orbital overlap with the diene. In the case of DA INV the overlap of the orbitals of the electron withdrawing substituents with the orbitals of the diene create a favorable bonding interaction , stabilizing the transition state relative to the exo transition state. [ 7 ]
Maleic anhydride is the precursor to various resins by copolymerization with styrene. Maleic anhydride is a dienophile in the Diels-Alder reaction. [7] Dianhydrides, molecules containing two acid anhydride functions, are used to synthesize polyimides and sometimes polyesters [14] and polyamides. [15]
Among the types of reactions that can be catalyzed by Lewis acids, those with carbonyl-containing substrates have received the greatest amount of attention.The first major discovery in this area was in 1960, when Yates and Eaton reported the significant acceleration of the Diels-Alder reaction by AlCl 3 when maleic anhydride is the dienophile.
In terms of the stereoselectivity of the reaction between maleic anhydride and cyclopentadiene, the endo-product is favored, a result best explained through FMO theory. The maleic anhydride is an electron-withdrawing species that makes the dieneophile electron deficient, forcing the regular Diels–Alder reaction.
In industry, maleic acid is derived by hydrolysis of maleic anhydride, the latter being produced by oxidation of benzene or butane. [4] Maleic acid is an industrial raw material for the production of glyoxylic acid by ozonolysis. [8] Maleic acid may be used to form acid addition salts with drugs to make them more stable, such as indacaterol ...
The reaction product is a very unstable ortho-quinodimethane but this molecule can be trapped in an endo addition with a strong dienophile such as maleic anhydride to the Diels-Alder adduct.