Proton Sponge Analogue of the Troger's Base: A Compound with Remarkable Enantiomeric Stability

Proton sponge analogue of the Troger's base (4) has been obtained upon treatment of 1-amino-4,5-bis(dimethylamino)naphthalene with paraformaldehyde. It was found that in contrast to classical Troger's base 1, protonation of 4 occurs, at least thermodynamically, exclusively on peri-NMe2 groups producing a dication with two chelated [NHN](+) hydrogen bonds. This prevents the protonation of the bridge nitrogen atoms, which is responsible for rather easy racemization of 1. Indeed, two enantiomers of 4 were resolved by chiral chromatography and their much higher stability in acidic media as compared to 1 has been confirmed. Some other properties of base 4 including structure, basicity, dynamic NMR behavior, host-guest interactions and reactions with electrophiles are also discussed.