Protonation-controlled Axial Chirality in Maleopimaric Imides

Maleopimaric N-naphthylimides (1-3) underwent slow aR-aS conversion and were induced in a gradual change of different [aR]/[aS] ratio during dissolution in various polar solvents at ambient temperatures. N-Quinoline-imides 2 with 28-100% ee of aR isomer were found to be protonation-controllable under hydrophobic condition. Mechanistic studies showed that this dramatic acid induced change was due to stabilization of the planar transition state by formation of an intramolecular hydrogen bond between the protonated quinoline nitrogen (N+-H) and an imide carbonyl (O=C).