The Wagner-Meerwein rearrangement is a carbocation-mediated 1,2-shift that reorganizes a carbon skeleton. Alkyl or hydride migration occurs when it leads to a more favorable cationic intermediate or relieves structural strain.
Common outcomes
Typical transformations include ring expansion, contraction, and migration adjacent to a leaving group or protonated alcohol. The rearrangement is frequently encountered in terpene chemistry and other densely substituted frameworks.
Controlling the pathway
Regiochemistry depends on carbocation stability, migrating aptitude, conformation, and reaction conditions. Mechanistic analysis helps distinguish the intended shift from elimination or competing nucleophile capture.