Enantioselective pinacol coupling of aryl aldehydes catalyzed by chiral Salan-Mo(IV) complexes
Hongwei Yang1, Hongsong Wang, Chengjian Zhu
1State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China.
Abstract:
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.
Related Concept Videos
Vicinal Diols via Reductive Coupling of Aldehydes or Ketones: Pinacol Coupling Overview
Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction
Preparation of Diols and Pinacol Rearrangement
The reaction begins with transferring a proton from the acid catalyst to one of the hydroxyl groups, producing an oxonium ion.
Aryldiazonium Salts to Azo Dyes: Diazo Coupling
Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
Acid-Catalyzed α-Halogenation of Aldehydes and Ketones
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...


