Effect of a substituent on an aromatic group in diastereomeric resolution

The diastereomeric resolution of p-substituted 1-arylethylamines by enantio pure (S)-3',4'-methylenedioxymandelic acid ((S)-2) was carried out in order to know how an electron-donating or -withdrawing group on the aromatic gro up of the racemic amines would affect the efficiency of resolution. As a re sult, it was found that 1-arylethylamines having an electron-withdrawing su bstituent could be efficiently resolved by (S)-2, while the amines having a n electron-donating group could not. The crystal structures of the less- an d more-soluble salts, and the molecular orbital calculations of the ammoniu m cations indicated that the p-substituted electron-withdrawing group enhan ced the positive charge on the meta-hydrogen of the aromatic group of the a mmonium cations, which is favorable for the formation of a CH ...pi interac tion in crystal. (C) 2000 Elsevier Science Ltd. All rights reserved.