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The pentacyclic compounds 1–3 are thermodynamically very strong and kinetically active “proton sponges,” which are obtainable by means of symmetric construction from 4. In addition, they exhibit a relatively high nucleophilicity. Despite a short distance (254.1 pm) between the two N atoms involved, the intramolecular hydrogen bond in 3-H⊕ is unsymmetrical.
Schwesinger et al. (Sun,) studied this question.