Fig. 3. (A) Imine exchange 1 between 1 and 4, with ¹H NMR spectra of 1d (a), 2d (b), and exchange (c) shown. (B) Imine exchange 2 between 1ocb and 4 in the presence of DBU, with ¹H NMR spectra of 1docb (a), 2docb (b), and exchange (c) shown. (C) Summary of equilibrium constants for imine exchanges 1 and 2. (D) Illustration of the stabilizing effect of ortho-carboxyl (a) and carboxylate (b) on cyclic and open aldehyde/imine, respectively. Solvent: CD₃CN.