Florence Helion

A new preparation of samarium dibromide and its use in stoichiometric and catalytic pinacol coupling reactions

Abstract A new convenient preparation of samarium dibromide in THF is reported. Pinacol coupling reactions using SmBr 2 in catalytic amounts together with mischmetall as a coreductant have been performed with a variety of carbonyl compounds.

Barbier/Grignard-Type Allylation or Benzylation Mediated by the Mischmetall/SmI2(cat.) System

Barbier- and Grignard-type allylation and benzylation have been achieved by the use of samarium diiodide in catalytic amounts together with mischmetall (an alloy of the light lanthanides) as a coreductant. Plausible catalytic schemes are proposed. In addition, organocerium and -lanthanum reagents have been obtained from samarium diiodide catalysed reactions between organic halides and cerium or lanthanum metal, giving a new route to organolanthanoid compounds. It also appears that trivalent benzyl and allyl organometallic compounds of cerium and lanthanum are much more stable than the corresponding samarium ones. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

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

Abstract Barbier-type reactions using SmI 2 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 SmI 2 ) 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/SmI 2 (catalytic) system is more reactive than samarium diiodide in stoichiometric amounts. Tentative interpretations of the catalytic role of NiI 2 are proposed.