Variation of the reaction conditions for the C-C coupling reaction of aromatic carbonyl compounds to their 1,2-diol structures in the presence of samaraium(I1)-iodide led to different diastereoselectivities. The molar ratio of the starting materials, substituents, and solvent variation had a significant influence on 1,2-diol formation. An interpretation of the observed results is suggested. Sterical demands ofthe active complex and an intramolecular samarium-oxygen interaction could lead to the diastereomer ratio obtained.