In organic chemistry, an intramolecular Diels-Alder cycloaddition is a Diels–Alder reaction in which the diene and a dienophile are both part of the same molecule. The reaction leads to the formation of one new double bond and two new sigma bonds, but this time the ultimate product is a fused or bridged cyclic ring.
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Because the two reacting groups are already attached, two basic modes of addition are possible in this reaction. Depending on whether the tether that links to the dienophile is attached to the end or the middle of the diene, fused or bridged polycyclic ring systems can be formed.[1]
The tether than attaches the two reacting groups also affects the geometry of the reaction. As a result of its conformational and other structural restrictions, the exo vs endo results[2] are usually not based on the simple (intermolecular) Diels–Alder reaction effects.
Intramolecular Diels-Alder cycloaddition is extremely useful for the formation of naturally occurring polycyclic rings. The reaction provides ready access to polycyclic compounds with a great deal of stereoselectivity. The following are several useful drugs whose complete synthesis have been accomplished using the intramolecular Diels-Alder reaction.
Solanapyrone A is an inhibitor of mammalian DNA polymerase β and λ, repair type DNA polymerase. The compound was isolated from the phytopathogenic fungi Alternaria solani, the cause of “early blight” in tomato and potato plants. The drug is being look as an anti-cancer medication.[3]
Isolated from the hallucinogenic sage, Salvia Divinorum. Salvinorin A is a potent and selective κ-opioid receptor. The compound has potential uses in psychotherapuetic treatments and Alzheimer’s treatment.[4]
Himbacine is a potent muscarinic receptor antagonist, Isolated from the bark of Galbulimima baccata, a type of magnolia tree. The drug is a promising lead in Alzheimer’s disease research.[5]