The [1,2]-Wittig rearrangement converts an ether bearing a carbanion or organolithium center adjacent to oxygen into an alcohol through migration of one carbon substituent from oxygen to the carbanionic carbon. The α-alkoxy organolithium precursor is commonly generated by deprotonation, tin–lithium exchange, or another metalation method. Carbon–oxygen bond homolysis then gives a radical pair whose recombination forms the new carbon–carbon bond; work-up protonates the resulting alkoxide ^[1]. The migrating group and the lithium-bearing terminus move across one atom, which accounts for the [1,2] designation. Configurational behavior often includes retention at the migrating carbon and inversion at the organolithium terminus under suitable substrate control ^[2]. The reaction is distinct from phosphorus-ylide olefination and from the concerted [2,3]-Wittig rearrangement of allylic ethers. Its defining substrate is an ether-derived α-oxy carbanion, and its defining product is a rearranged alcohol with a newly formed C–C bond.