Synthesis of E-(alpha),(beta)-Unsaturated Ketones with Complete Stereoselectivity via Sequential Aldol-Type/Elimination Reactions Promoted by Samarium ­Diiodide or Chromium Dichloride

E-(alpha),(beta)-Unsaturated ketones can be obtained with complete E-selectivity by a sequential reaction of dichloroketones with a variety of aldehydes. This transformation was promoted by SmI2, SmI2 in the presence of FeCl3 or CrCl2. The best results were obtained when CrCl2 was used as the metallating agent. A mechanism based on a successive aldol-type reaction and a (beta)-elimination is ­proposed to explain these results.