The opposite regiochemistry, observed for the reactions 7a → 8a and 7d → 8d, as compared with additions 7b → 9b, 7c → 9c and 7e → 9e, supports the hypothesis that in the transition state of nitrone-olefin additions the new C,C bond is more advanced than the C,0, bond. Further examples show the superimposition of substituent effects on this intramolecular control. © 1979.
Oppolzer, W., Siles, S., Snowden, R. L., Bakker, B. H., & Petrzilka, M. (1979). The regiochemistry of intramolecular n-alkenylnitrone additions: preparative and mechanistic implications. Tetrahedron Letters, 20(45), 4391–4394. https://doi.org/10.1016/S0040-4039(01)86596-5