Study of ground state interactions of enantiopure chiral quaternary ammonium salts and amides, nitroalkanes, nitroalkenes, esters, heterocycles, ketones and fluoroamides.

Chiral Phase-Transfer Catalysis provides high level of enantiocontrol, however no experimental data showed the interaction of catalysts and substrates. We have carried out 1H-NMR titration of Cinchona and Maruoka ammonium bromides vs nitro, carbonyl, heterocycles, and N-F containing compounds. We found that neutral organic species and quaternary ammonium salts interacted via an ensemble of catalyst +N-C-H and (sp2)C-H, specific for each substrate studied. The correspondent BArF salts interacted with carbonyls via a diverse set of +N-C-H and (sp2)C-H compared to bromides. This data suggests that BArF ammonium salts may display a different enantioselectivity profile. Although not providing quantitative data for the affinity constants, the data reported proofs that chiral ammonium salts coordinate with substrates, prior to transition state, via specific C-H positions in their structures, providing a new rational to rationalize the origin of enantioselectivity in their catalyses.