Synthesis of an Optically Active Al(salalen) Complex and Its Application to Catalytic Hydrophosphonylation of Aldehydes and Aldimines

Optically active aluminum(salalen) complex 2 was newly synthesized in a modular synthetic manner, and it was found to serve as an efficient catalyst for hydrophosphonylation of aldehydes and aldimines, giving the corresponding alpha-hydroxy and alpha-amino phosphonates with high enantioselectivity, respectively. The scope of the hydrophosphonylation was wide, and both aliphatic and aromatic aldehydes and aldimines were successfully used as substrates for the reaction. The potent catalysis of the complex is attributed to its unique structure: it adopts a distorted trigonal bipyramidal configuration which allows the salalen ligand to take a cis-beta-like structure wherein the chiral amino group is located close to the metal center.