Reduction of ketones and alkyl iodides by SmI(2) and Sm(II)-HMPA complexes. Rate and mechanistic studies.
21 May 2002-Journal of the American Chemical Society (American Chemical Society)-Vol. 124, Iss: 24, pp 6895-6899
TL;DR: The results obtained indicate that coordination or chelation is possible in the transition state geometry for SmI(2)/ketone systems even in the presence of the sterically demanding ligand HMPA.
Abstract: The effect of HMPA on the electron transfer (ET) rate of samarium diiodide reduction reactions in THF was analyzed for a series of ketones (2-butanone, methyl acetoacetate, and N,N-dimethylacetoacetamide) and alkyl iodides (1-iodobutane and 2-iodobutane) with stopped flow spectrophotometric studies. Activation parameters for the ET processes were determined by temperature-dependence studies over a range of 30-50 degrees C. The ET rate constants and the activation parameters obtained for the above systems in the presence of different equivalents of HMPA were compared to understand the mechanism of action of HMPA on various substrates. The results obtained from these studies indicate that coordination or chelation is possible in the transition state geometry for SmI(2)/ketone systems even in the presence of the sterically demanding ligand HMPA. After the addition of 4 equiv of HMPA the ET rate and activation parameters for ketone reduction by Sm is unaffected by further HMPA addition while a linear dependence of ET rate on the equivalents of HMPA was found in the SmI(2)/alkyl iodide system. The results of these studies are consistent with an inner-sphere-type ET for the reduction of ketones by SmI(2) (and SmI(2)[bond]HMPA complexes) and an outer-sphere-type ET for the reduction of alkyl iodides by SmI(2) or SmI(2)[bond]HMPA complexes.
Citations
More filters
TL;DR: The mechanisms and the applications in organic synthesis, materials, supramolecular, and polymer synthesis of most organic reactions mediated by single electron transfer are discussed, even though both biology and radical chemistry rely extensively on one-electron transfer processes.
Abstract: The article discusses the mechanisms and the applications in organic synthesis, materials, supramolecular, and polymer synthesis of most organic reactions mediated by single electron transfer. Each reaction or class of reactions will be discussed by starting with the original discovery publication, followed by a summary of all or most review articles published in the field, and a discussion of the mechanism(s) and of the most important methodologic and synthetic developments since the most recent review was published. The mechanisms of most organic reactions are considered to proceed by two-electron transfer pathways, even though both biology and radical chemistry rely extensively on one-electron transfer processes. Radicals generated by homolytic cleavage at high temperature were traditionally employed in the industrial production of polymers and to a lesser extent in the synthesis of organic molecules.
320 citations
303 citations
TL;DR: An overview of the current knowledge of the reagent SmI2 as a reducing agent, in particular with additives that increase its reactivity is given in this article, where the use of various proton sources is covered, as well as the effect of co-solvents.
Abstract: Samarium(II) iodide is a one-electron transfer reagent that has become highly appreciated as a mild and selective reducing agent in recent years. It has been found experimentally that various additives and co-solvents largely control the reactivity of SmI2. This microreview provides an overview of the current knowledge of the reagent SmI2 as a reducing agent, in particular with additives that increase its reactivity. The use of various proton sources is covered, as well as the effect of co-solvents. Furthermore, the very powerful reagent mixture SmI2/H2O/amine is also described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
166 citations
TL;DR: Herein, it is illustrated how new samarium(II) complexes and nonclassical lanthanide( II) reagents are changing the landscape of modern reductive chemistry.
Abstract: Reactions proceeding through open-shell, single-electron pathways offer attractive alternative outcomes to those proceeding through closed-shell, two-electron mechanisms. In this context, samarium diiodide (SmI(2)) has emerged as one of the most important and convenient-to-use electron-transfer reagents available in the laboratory. Recently, significant progress has been made in the reductive chemistry of other divalent lanthanides which for many years had been considered too reactive to be of value to synthetic chemists. Herein, we illustrate how new samarium(II) complexes and nonclassical lanthanide(II) reagents are changing the landscape of modern reductive chemistry.
133 citations
TL;DR: This tutorial review discusses recent advances in the field of ketyl-(het)arene cyclisations promoted by samarium diiodide and related processes, and summarizes diversity orientated approaches towards nitrogen heterocycles and emphasize other approaches with SmI(2) as well as electrochemical cyclisation methods providing similar N-heterocycles.
Abstract: In this tutorial review we discuss recent advances in the field of ketyl-(het)arene cyclisations promoted by samarium diiodide and related processes Couplings of samarium ketyls with carbon–carbon multiple bonds are perhaps the most useful reactions to create carbocycles and heterocycles of various ring sizes They have also successfully been exploited for the synthesis of biologically active compounds or natural products In this article we intend to summarise our diversity orientated approaches towards nitrogen heterocycles and emphasize other approaches with SmI2 as well as electrochemical cyclisation methods providing similar N-heterocycles We also briefly discuss our recently published formal total synthesis of strychnine employing a new samarium diiodide induced cascade reaction as key step All these examples demonstrate the high synthetic potential of samarium ketyl-(het)arene cyclisations for the preparation of various types of important heterocyclic compounds
116 citations
References
More filters
1,128 citations
895 citations
415 citations
216 citations
193 citations