The effect of Lewis acids on the pinacol homocoupling reaction of aldehydes promoted by samarium diiodide

The effect of various Lewis acids on the samarium diiodide promoted pinacol homocoupling of aldehydes was investigated. The reaction of benzaldehyde proceeded with fair to good 1,2-anti-stereoselectivity, while in the case of other aromatic and aliphatic aldehydes syn-stereoselectivity was generally observed. Chiral alpha-alkylaldehydes allowed for an almost complete stereocontrol favoring syn-1,2-diols.