Issue 13, 2014

Asymmetric transfer hydrogenation of unsymmetrical benzils

Abstract

In this paper, the asymmetric transfer hydrogenation of unsymmetrical benzils with m, p-substituents was conducted with a substrate/catalyst molar ratio of 100 at 40 °C for 24 h to produce (S,S)-hydrobenzoins in good yields (76.2% to 97.1%) with high diastereomeric (syn/anti = 10.8 to 29.7/1) and enantiomeric purities (86.1%ee syn to 98.9%ee syn). Unfortunately, the unsymmetrical benzils with the o-substituents such as electron-donating (R = CH3, OCH3) and electron-withdrawing groups (R = F, Cl, CF3) resulted in poor yields (0% to 31.2%), even at 40 °C for 72 h. These products had inefficient diastereoselectivities (syn/anti = 1.5 to 5.0/1) caused by steric effects. Furthermore, the results of a dynamic–kinetic study were used to propose a plausible reaction pathway of unsymmetrical benzil using 3-methoxy-1,2-diphenyl ethanedione as an example.

Graphical abstract: Asymmetric transfer hydrogenation of unsymmetrical benzils

Supplementary files

Article information

Article type
Paper
Submitted
28 Nov 2013
Accepted
18 Dec 2013
First published
20 Dec 2013

RSC Adv., 2014,4, 6417-6423

Asymmetric transfer hydrogenation of unsymmetrical benzils

H. Zhang, D. Feng, H. Sheng, X. Ma, J. Wan and Q. Tang, RSC Adv., 2014, 4, 6417 DOI: 10.1039/C3RA47129B

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