‘Proton sponge’ amides: unusual chemistry and conversion into superbasic 6,7-bis(dimethylamino)perimidines

Starting from 1-acylamino-4,5-bis(dimethylamino)naphthalenes, the first representatives of previously unknown 6,7-bis(dimethylamino)perimidines have been synthesized. In accordance with the electron-donor nature of the heterocyclic rings in these compounds they behave as proton sponges, displaying higher basicity (pKa 8.4–9.3, DMSO) than those of the parent proton sponge (pKa 7.5, DMSO; 18.6, MeCN) and perimidine (pKa 13.6, MeCN). In accord with DFT calculations and proton transfer experiments, 1H-6,7-bis(dimethylamino)perimidines have been shown to exist as neutral rather than zwitterionic tautomers. A number of interesting observations concerning structure, synthesis, and reactivity of 1-acylamino-4,5-bis(dimethylamino)-8-nitronaphthalenes have been made.

Proton sponge peri-nitroamides, differing by their unusual hydrolytic stability, offer a simple way to construct previously unknown perimidine proton sponges with the basicities well above that of the parent proton sponge and perimidines. For compounds with the free NH group in the heterocyclic ring, a possibility to form zwitterionic structures is also considered.Figure optionsDownload as PowerPoint slide