Allylic rearrangement

An organic reaction in which substitution at an allylic system shifts the carbon–carbon double bond, so the incoming group bonds at a different position from the departing group.

Allylic substitution: A substitution reaction at a carbon adjacent to a carbon–carbon double bond. Allylic rearrangement is the pathway in which substitution changes which end of the allylic system reacts.
Allyl group: The three-carbon unit CH₂=CH–CH₂–, or a substituted derivative of it. The rearrangement acts across this three-carbon framework.
Palladium-catalyzed allylic substitution: A catalytic reaction in which palladium mediates nucleophilic substitution at an allylic substrate. Palladium often enables regioselective formation of rearranged allylic products.
Vinylic substitution: Substitution at a carbon directly bonded to a carbon–carbon double bond. Unlike allylic substitution, it targets an alkene carbon rather than the adjacent allylic position.
SN2′ reaction: A concerted nucleophilic substitution at an allylic system that forms a new double bond as the leaving group departs. This concerted route produces rearranged substitution without a discrete intermediate.
Allylic position: A position adjacent to a carbon–carbon double bond. The departing group or incoming nucleophile occupies an allylic position in the rearranging system.
Tsuji–Trost reaction: A palladium-catalyzed allylic substitution used to form carbon–carbon and carbon–heteroatom bonds. Its allylic intermediates commonly permit bond formation at a position shifted from the leaving group.
Allylic transposition: A change in the positions of a substituent and a double bond within an allylic framework. This term emphasizes the net positional shift that allylic rearrangement produces.
SN1′ reaction: An allylic substitution pathway in which ionization forms a delocalized carbocation before nucleophilic capture at a shifted position. The delocalized cation allows attack at either end of the allylic framework.
Resonance: A representation of a molecule using multiple contributing Lewis structures to describe delocalized electrons. Resonance depicts how allylic charge or radical character extends to the alternate reaction site.

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Allyl chlorideRelated: The allylic structure can permit products to form at either end of the three-carbon unit.