Catalytic Barbier-type reactions of lactones and esters mediated by the Mischmetall/SmI2(cat.) system or the Mischmetall/[SmI2/NiI2(cat′.)](cat.) system

Barbier-type reactions using SmI2 in catalytic amounts together with Mischmetall as a coreductant, involving lactones or esters and a variety of organic halides (allylic, benzylic and alkyl), have been performed. With alkyl halides and five- or six-membered ring lactones, catalytic quantities of nickel diiodide (with respect to SmI2) must be added to achieve reactions. Thus, a ‘two-stage catalysis’ is carried out. Unexpectedly, it was found that with esters or an unstrained lactone the Mischmetall/SmI2 (catalytic) system is more reactive than samarium diiodide in stoichiometric amounts. Tentative interpretations of the catalytic role of NiI2 are proposed.