Samarium Diiodide-A Versatile Reagent in Organic Synthesis

Abstract

Since samarium diiodide (SmI₂) was introduced into organic synthesis as a synthetic means by Kagan et al., quite unique and useful properties of the reagent has been emerging. In this article will be disclosed our recent efforts in this area. (1) Transition metal-catalyzed C-H, C-C, and C-Sn bond formation via polarity inversion of allylic and propargylic acetates. (2) Transition metal-catalyzed reduction of triple bonds. (3) Facile reduction of organic halides, epoxides, α, β-epoxy esters, α -oxygenated esters, organoheteroatom oxides, and conjugated acid derivatives with the highly efficient reduction system, SmI₂-THE-HMPA. (4) A variety of C-C bond-forming reactions : The use of β-, γ-, and δ-bromoesters as home-, bishomo-, and trishomoenolate equivalents, respectively, in Barbier-type reaction ; iodomethylation of carbonyl compounds at room temperature ; construction of benzofuran and indole frameworks via aryl radical cyclization ; a novel masked-formylation of carbonyl compounds with 1, 3-dioxolane ; preparation of medium- and large-ring lactones by intramolecular Reformatsky-type reaction ; reductive self-dimerization of a-bromo esters and conjugated acid derivatives. (5) Intermolecular addition of ketyls to olefins and acetylenes. A high degree of acyclic stereoselection was realized in an intermolecular radical reaction for the first time by utilizing the distinct property of SmI₂.