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 α-hydroxy and α-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-β-like structure wherein the chiral amino group is located close to the metal
center.