In summary, the first catalytic and enantioselective [1,2]-rearrangement of allylic ammonium ylides has been developed. The factors necessary for affecting [1,2]-rearrangement have been examined, with higher reaction temperature resulting in increased [1,2]: [2,3] rearrangement product ratio. Treatment of a range of terminally-substituted allylic ammonium salts with isothiourea catalyst tetramisole led to the [1,2]-rearrangement of allylic ammonium ylides, giving amino acid derivatives in up to 87% yield and 97:3 er. C-Isotopic labeling in crossover and radical-trapping experiments have revealed an intriguing interplay between intermolecularity and enantioselectivity. Computational analysis indicates that C-Nbond homolysis from an acyl ammonium ylide intermediate, followed by regioselective radical recombination at the primary site of the intermediate allylic radical leads to the [1,2]-product. The [2,3]product can be formed through either concerted [2,3]-sigmatropic rearrangement or radical recombination at the tertiary site of the allylic radical. The insights provided from this study, particularly regarding the relationship between intermolecularity and product enantioselectivity, will have important consequences for future investigations of solvent-caged enantioselective radical recombination reactions.