(untitled) - Chatterjee, A; König, B (Angew. Chem. Int. Ed., 2019)
Although 6. and 6+ were more stable than 8. and 8+ by 2.2 kcal/mol and 5.7 kcal/mol, respectively, both 6. and 8. could be formed in the protonation stage of 2a.– because a difference of their HOFs (2.2 kcal/mol) was comparatively small and also because the formation of 8. might be kinetically favored than 6.. In fact, both 6. and 8. were described in the existing research. For instance, see ref. 16 and also the following paper: