Aryl[2.2]paracyclophane-Based Chiral Regioisomeric Analogs of Salicyl Aldehyde: Novel Sources for Construction of Phenoxy-Imine Ligands

The efficient, high-yield approaches to two novel regioisomeric salicyl aldehyde analogs, 4-formyl-13-(2-hydroxyphenyl)-[2.2]paracyclophane and 4-formyl-12-(2-hydroxyphenyl)-[2.2]paracyclophane (iso-FHPhPC and pseudo-FHPhPC, respectively), constructed on the basis of an aryl[2.2]paracyclophane backbone are described. The key stage of the backbone formation is the Suzuki cross-coupling of paracyclophanyl halides with arylboronic acids. Efficient procedures for the resolution of the racemic hydroxy aldehydes into enantiomers via Schiff bases with enantiomers of a-phenylethyl amine were elaborated, and the absolute configurations of enantiomers were established on the basis of X-ray analysis of diastereomeric imines. Starting from these chiral hydroxy aldehydes the first representatives of bi-, tri-, and tetradentate phenoxy-imine ligands belonging to an aryl[2.2]paracyclophane family were obtained. The induction power of the ligands was tested in the Et2Zn asymmetric addition to aldehydes.