The Alder ene reaction refers to a chemical reaction in which an alkene (ene) bearing an allylic hydrogen reacts with an enophile to form a new σ-bond, with a migration of the alkene double bond and a 1,5-hydrogen shift. The product is a substituted alkene in which the double bond has shifted to the allylic position.

This reaction was discovered in 1943 by Kurt Alder and is named in his honor.

• Reagents: Lewis acids

• Reactants: Alkenes bearing allylic hydrogen, enophiles

• Products: Substituted alkenes

• Reaction Type: Pericyclic reaction

Experimental Tips:

• Enophiles are π-bonded molecules with electron-withdrawing substituents. Their reactivity increases when they contain heteroatoms such as C=O, C=N, N=N, N=O, or S=O. Enophiles with alkynes exhibit the highest reactivity, while those with C=C have the lowest;

• The ene component must contain at least one allylic, propargylic, or α-position active hydrogen atom. This includes alkenes, alkynes, allenes, aromatics, cyclopropyl groups, and carbon–heteroatom bonds;

• Intramolecular ene reactions generally proceed more easily than intermolecular ones. Intramolecular ene reactions can be classified into four types: I, II, III, and IV.

Reaction Mechanism

Original Literature:
Kurt Alder, Franz Pascher, Andreas Schmitz. Berichte der deutschen chemischen Gesellschaft (A and B Series), 1943, 76(1–2), 27–53.

Notable References:

• A chirally catalysed ene reaction in a novel formal total synthesis of the antitumor agent laulimalide, Tetrahedron Letters, 2002, 43(47), 8471.

• C₂-Symmetric Copper(II) Complexes as Chiral Lewis Acids. Catalytic Enantioselective Carbonyl−Ene Reactions with Glyoxylate and Pyruvate Esters, J. Am. Chem. Soc., 2002, 122(33), 7936.