Pinacol Couplings of a Series of Aldehydes and Ketones with SmI2/Sm/Me3SiCl in DME.

Abstract The pinacol coupling is one of the most significant methods to synthesize vic -diols. The combination of samarium diiodide (SmI 2 ) and samarium metal successfully induces the selective pinacol couplings of not only aromatic aldehydes and ketones but also aliphatic ones in the presence of trimethylchlorosilane (Me 3 SiCl) in 1,2-dimethoxyethane (DME). DME is the most suitable solvent for the reduction system using SmI 2 and Me 3 SiCl. Me 3 SiCl, a widely available additive, prevents the decomposition of the formed vic -diols, i.e., meso -isomers, and controls their stereochemistry. In particular, the pinacol couplings of sterically hindered aliphatic aldehydes and ketones proceed with excellent diastereoselectivities to afford dl -isomers in good yields.