Binaphthyl substituted 1,8-bis(dimethylamino)naphthalenes, the first chiral, atropisomeric, proton sponges

Atropisomeric naphthalene proton sponges (R,S)-3 (meso), (R,R + S,S)-3 (racemic) and (S,S)-3 (enantiopure) were prepared by bis-N,N-dialkylation of 1,8-diaminonaphthalene, using both racemic (R + S)- and enantiopure (S)-2,2′-bis(bromomethyl)-1,1′-binaphthyl, respectively, as alkylating agents. The amino function of the corresponding mono-binaphthyl substituted tertiary/primary diamines (R + S)-4 (racemic) and (S)-4 (enantiopure), obtained as side products, was N,N-dimethylated to give the corresponding bis(tertiary) diamines (R + S)-2 and (S)-2, respectively. Thermal isomerisation of the meso adduct (R,S)-3 to the corresponding racemic adduct (R,R + S,S)-3 occurred in the solid state. Reversible evolution of the 1H NMR spectra of (R,S)-3, (R,R + S,S)-3 and (R + S)-2 in toluene-d8 solution as a function of temperature was observed, showing conformational changes but no isomerisation of the binaphthyl skeleton. 1H NMR of the protonated diamines showed the resonance of a single proton at very low field (18.7–20.2 ppm) in all cases.