Deprotonation proton sponge cations

It was already mentioned (Section III.A.2) that 4,5-dihydroxy-l,8-bis(dimethylamino) naphthalene actually exists in the form of the internal salt 11139. Somewhat similar is the situation with 2,7-dihydroxynaphthalene 140, also behaving in solution as a betaine165. The latter, on treatment with acids, gives the cation 140-H+, while the action of alkali results in protonated dianion 141 (Scheme 15). All attempts to deprotonate 141 (even with the KOH-DMSO system at 100 °C or with LiH-DMSO) failed. This implies that the basicity of still unisolated dianion 142 lies in the limit of pKa = 25-26 (H2O scale). Thus, dianion 142 can be presently considered as the strongest base among all proton sponge and aniline derivatives. 

Figure 14.17 labeled systems exhibiting strong intramolecular NHN hydrogen bonds. 28 deprotonated mono-anion of 6-nitro-2,3-dipyrrol-2-ylquinoxaline [59]. 29 protonated mono-cation of 1,6-dimethyl-1,6-diazacyclodecane [59] and 30 of 1,8-bis(dimethylamino)-naphthalene (OMAN, proton sponge) [60]. For comparison, the neutral molecules W,W -diphenyl-6-aminopentafulvene-1-aldimine (1, see... 

---