Enantioselective Pinacol Coupling of Aryl Aldehydes Catalyzed by Chiral Salan−Mo(IV) Complexes

Reported herein is the asymmetric pinacol coupling of aromatic aldehydes with chiral Salan−Mo(VI)
dioxo complex as an effective precatalyst. Chiral diols were obtained with high diastereoselectivity and
enantioselectivity up to 92/8 and 95%, respectively. The possible mechanism of the pinacol coupling
reaction with the catalytic system was investigated. The X-ray crystal structure of the precatalyst Mo(L3)O2 was determined and the oxidation state of the intermediate C was confirmed as +4 with X-ray
photoelectron spectroscopy study. The proposed mechanism speculated the stereochemical outcome of
the reaction, and a working model for the radical coupling of E was proposed, which explained the
absolute configuration of the favored (S,S)-enantiomer of the dl isomer.