Highly meso-Diastereoselective Pinacol Coupling of Aromatic Aldehydes Mediated by Al Powder/Copper Sulfate in Water

Abstract

Pinacol-type coupling reaction products presenting a high meso-diastereoselectivity (the ratio dl/meso was 4/96 up to 1/99) were obtained in fair to good yields (24–69%) using several aromatic aldehydes as starting materials and aluminium powder/copper sulfate as catalysts, in water, under reflux conditions.

Keywords:

• Aqueous media
• meso-diastereoselectivity
• reductive coupling

Notes

^a The reaction conditions were 50 mmol as substrate and 40 ml as solution in entries 1–7.

^b In entries 1, 3, and 4, the temperature of the reaction solution increased up to 90 °C.

^c The products were determined by melting point (meso: 139–140 °C), GC, and ¹H NMR spectra. The chemical shifts of methine proton in dl- and meso-isomer were δ 4.73 and 4.83 ppm, respectively.

^a Substrate is 5 mmol; the obtained products were identified by GC-MS.

^b The dl/meso ratio was determined by ¹H NMR spectra.