ORGN 12

With helical electronic effect as a tool, in this paper we present an intensive literature analysis for representative systems in chiral molecular recognition and in asymmetric induction. The results suggest that chiral recognition occurs via a homohelical interaction mechanism, i.e., a chiral host is capable of recognizing a guest enantiomer of the same helical handedness through a homohelical transition state complexation. This homohelical recognition mechanism is found to be of remarkable effectiveness in predicting the retention behaviors of a wide variety of chiral HPLC separation systems: the more retained enantiomers are always the ones that form homohelical selectand/selector diastereomeric associations. In asymmetric catalysis, it is proposed that the enantiofacial complexation of a pro-chiral substrate to a catalytic metal/nonmetal center and the subsequent establishment of the product stereochemistry are mainly governed by the helical handedness of the chiral ligand employed via a homohelical induction pathway, and asymmetric induction is essentially a process in which the handedness of the original ligand/catalyst is conserved. Based on the helical asymmetry of chiral ligands, catalysts can be generally categorized into two classes: being either right-handed or left-handed. For both asymmetric reactions a correlation between the ligand helical handedness and the sign of absolute stereoinduction is found.