Diels-Alder Reaction
Diels-Alder Reactions are concerted, thermal [4+2] cycloadditions. It involves the 1,4-addition of an alkene(i.e.dienophile) to a conjugated diene to form a six membered-adduct. The reaction is initiated by heat, light or Lewis acid catalyst with or without the use of solvent. The reaction is usually thermodynamically favourable due to the conversion of two π-bonds into two new stronger σ-bonds. The Diels-Alder reaction is stereospecific with respect to both the diene and the dienophile.
Electron withdrawing groups in the dienophile or electron donating groups in the diene accelerates the rate of reaction and also the product is high yield.
When both the diene and dienophile are unsymmetrical, two products are possible. However 1,2- and 1,4-products predominates.
Diels-Alder reaction mechanism proceeds through the suprafacial (i.e. same-face involvement of the 𝝅 system or isolated orbital in the process) interaction between a 4𝝅 electron system with a 2𝝅 electron system.
Since the Diels-Alder reaction is a concerted process (i.e. both the bond formations and bond cleavages takes place simultaneously), so the reaction occurs in a single step cycloaddition reaction. The two unsaturated molecules (i.e. diene and dienophile) combine to form a cyclic adduct. Overall the bond multiplicity is reduced in this reaction.
Diene reacts in the s-cis conformation, which allows the ends of the conjugated system to reach the doubly bonded carbons of the dienophile.
There are two possible modes of addition i.e. exo and endo. The endo product is more stable.
Electron withdrawing groups in the dienophile or electron donating groups in the diene accelerates the rate of reaction and also the product is high yield.
When both the diene and dienophile are unsymmetrical, two products are possible. However 1,2- and 1,4-products predominates.
Mechanism of Diels-Alder Reaction
The possible mechanism is given below-Diels-Alder reaction mechanism proceeds through the suprafacial (i.e. same-face involvement of the 𝝅 system or isolated orbital in the process) interaction between a 4𝝅 electron system with a 2𝝅 electron system.
Since the Diels-Alder reaction is a concerted process (i.e. both the bond formations and bond cleavages takes place simultaneously), so the reaction occurs in a single step cycloaddition reaction. The two unsaturated molecules (i.e. diene and dienophile) combine to form a cyclic adduct. Overall the bond multiplicity is reduced in this reaction.
Diene reacts in the s-cis conformation, which allows the ends of the conjugated system to reach the doubly bonded carbons of the dienophile.
There are two possible modes of addition i.e. exo and endo. The endo product is more stable.
