Fig. 4. Mechanism investigations.
a, TEMPO-radical inhibition experiment. The reaction was completely inhibited in the presence of TEMPO as a radical scavenger, which is consistent with the radical nature of the 1,2-amino migration process. b, Radical-trapping experiment. The experiments indicate the involvement of phosphonyl radical intermediates. c, Capture of the γ-FG-β-radical of the α-amino-acid derivative and the γ-FG-α-radical of the β-amino-acid derivative. The experiments indicate that the reaction probably proceeds through a cyclization–ring-opening sequence involving the intermediate azacyclopropyl carbinyl radical. d, DFT free-energy profile of 1,2-amino migration. ΔGsol, Gibbs free energy of solvation. e, Spin density isosurface of the radical intermediates. Details are provided in Supplementary Section 13.