Samarium II iodide

InChl = l/2HI.SmAi2 lH /q +2/p-2/f2I.Sm/h2 lhyq2 -l m InChIKey = UAWABSHMGXMCRK-ZFDXCKRNCZ 

Preparative Methods typically prepared in situ for synthetic purposes. Sml2 is conveniently prepared by oxidation of Samarium(O) metal with organic dihalides.  

Handling, Storage, and Precautions is air sensitive and should be handled under an inert atmosphere. S111I2 may be stored over THE for long periods when it is kept over a small amount of samarium metal. 

Gary A. Molander Christina R. Harris University of Colorado, Boulder, CO, USA 

Alkyl halides are readily reduced to the corresponding hydrocarbon by Sml2 in the presence of a proton source. The ease with which halides are reduced by Sml2 follows the order I Br Cl. The reduction is highly solvent dependent. In THE solvent, only primary alkyl iodides and bromides are effectively reduced however, addition of HMPA effects the reduction of aryl, alkenyl, primary, secondary, and tertiary halides (eq 1). Tosylates are also reduced to hydrocarbons by Sml2. Presumably, under these reaction conditions the tosylate is converted to the corresponding iodide which is subsequently reduced.  

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The reductive coupling of aldehydes or ketones with 01, -unsaturated carboxylic esters by > 2 mol samarium(II) iodide (J.A. Soderquist, 1991) provides a convenient route to y-lactones (K. Otsubo, 1986). Intramolecular coupling of this type may produce trans-2-hy-droxycycloalkaneacetic esters with high stereoselectivity, if the educt is an ( )-isomer (E.J. Enholm, 1989 A, B). 

The occurrence of the indole subunit is well established within the class of natural products and pharmaceutically active compounds. Recently, the Reissig group developed an impressive procedure for the assembly of highly functionalized in-dolizidine derivatives, highlighting again the versatility of domino reactions [8]. The approach is based on a samarium(II) iodide-mediated radical cydization terminated by a subsequent alkylation which can be carried out in an intermolecular - as well as in an intramolecular - fashion. Reaction of ketone 3-11 with samarium(ll) iodide induced a 6-exo-trig cydization, furnishing a samarium enolate intermediate... 

Examples of samarium-promoted radical procedures, which were combined with anionic processes, were detailed in Section 3.3. Here, we describe two-fold radical reactions initiated by Sml2. A combination of two samarium(II) iodide-promoted... 

Similar results were observed with 3-173 as substrate. Using zinc amalgam, the hydridane 3-174 was obtained in 43% yield, whereas samarium(II) iodide furnished 3-174 in 77% yield (Scheme 3.46). 

The use of samarium(II) iodide in synthesis permits the assembly of complex molecules as already shown in many examples. They profit from the electron-transfer ability of samarium(II) iodide thus, if ketones are employed as substrates the furnished ketyl-radical can react in a multitude of different ways. 

An example, where two C-C-bonds are formed and one C-C-bond is broken is the synthesis of the tricycle 3-285, which has some similarity with the eudesmane framework 3-286, developed by Kilburn and coworkers (Scheme 3.72) [113]. Thus, exposure of the easily accessible methylenecyclopropyl-cyclohexanone 3-281 to samarium(II) iodide led to the generation of ketyl radical 3-282, which builds up a six-membered ring system with simultaneous opening of the cyclopropane moiety. Subsequent capture of the formed radical 3-283 by the adjacent alkyne group afforded the tricycle 3-285 via 3-284 as a single diastereoisomer in up to 60% yield. It should be noted that in this case the usual necessary addition of HMPA could be omitted. 

A useful and simple method for the one-pot preparation of highly functionalized, enanhomerically pure cyclopentanes from readily accessible carbohydrate precursors has been designed by Chiara and coworkers [73]. The procedure depends on a samarium(II) iodide-promoted reductive dealkoxyhalogenahon of 6-desoxy-6-iodo-hexopyranosides such as 7-160 to produce a 6,e-unsaturated aldehyde which, after reductive cyclization, is trapped by an added electrophile to furnish the final product. In the presence of acetic anhydride, the four products 7-161 to 7-164 were obtained from 7-160. 

Samarium(II) iodide also allows the reductive coupling of sulfur-substituted aromatic lactams such as 7-166 with carbonyl compounds to afford a-hydroxyalkylated lactams 7-167 with a high anti-selectivity [74]. The substituted lactams can easily be prepared from imides 7-165. The reaction is initiated by a reductive desulfuration with samarium(ll) iodide to give a radical, which can be intercepted by the added aldehyde to give the desired products 7-167. Ketones can be used as the carbonyl moiety instead of aldehydes, with good - albeit slightly lower - yields. 

In another reduction, the propargylic phosphate 64 is reduced with samarium(II) iodide in the presence of tetrakis(triphenylphosphine)palladium and tert-butanol as a proton source the allene 65 is produced almost exclusively, <1% of the isomeric alkyne 66 being present in the product mixture [19]. 

An interesting novel coupling reaction of allenes with carbonyl compounds mediated by a lanthanide metal species was reported recently [80], The samarium(II) iodide-mediated reaction of various ketones or aldehydes 153 with methoxyallene (56) afforded exclusively y-addition products 4-hydroxy-l-enol ethers 154 in moderate to good yields with low cis/trans selectivity (Scheme 14.39). 

Thermolysis of 219a and 219b produced the benzofulvenes 221 as expected. However, the formation of 222 from 219c can best be accounted for by regarding the biradical 220a as the carbene 220b to allow an intramolecular C-H insertion reaction. The presence of a carbonyl group in 219 also permits the use of samarium(II) iodide, samarium(III) chloride, boron trifluoride and trifluoroacetic acid to promote the Schmittel cyclization reaction. 

Aldimines are converted into diamines in up to 94% yields by heating with samarium(II) iodide in THF, followed by treatment with silica gel in methanol, e.g. equation 3 3 83. 

In the presence of samarium(II) iodide, A-(2-iodobenzyl)dialkylamines 347 react with electrophiles at an a-carbon atom to yield deiodinated products by way of intermediate samarium compounds 348. Thus TV-(2-iodobenzyl)diethylamine and pentan-3-one afford the hydroxy amine 349 and 7V-(2-iodobenzyl)pyrrolidine and propyl isocyanate give the amide 350390. 

Reduction of nitroalkanes RNO2 with samarium(II) iodide, obtained from samarium and 1,2-diiodoethane, yields either alkylhydroxylamines RNHOH or alkylamines RNH2, depending on the amount of the reagent434. The base-catalysed reaction of nitroalkanes with phenyl(vinyl) sulphoxide (399) yields the conjugate adducts 400, which fragment to allylic nitro compounds 401 on thermolysis435. 

Samarium(II) iodide, 46, 3 Sandmeyer reaction, 2, 7 Schiemann reaction, 5, 4 Schmidt reaction, 3, 8, 9 Selenium dioxide oxidation, 5, 8 24, 4 Seleno-Pummerer reaction, 40, 3 Selenoxide elimination, 44, 1 Shapiro reaction, 23, 3 39, 1 Silanes ... 

Samarium(II) iodide smoothly reduces primary, secondaryand tertiary aliphatic as well as aromatic nitro compounds to hydroxylamines (equation 52). This reaction was found to be highly versatile although with limited scalability, since at least four equivalents of Sml2 are necessary. Most functional groups, except aldehydes and sulfones, are compatible with Sml2 reduction (equation 53). 

Electrochemical properties of samarium(ii) iodide are very sensitive to the nature of solvents. Reduction potential increases by replacing THE with a more polar solvent, such as DME or CH3CN. Addition of HMPA to a THE solution of samarium(ii) iodide leads to a substantial increase in the electron-donating nature of samarium(ii). The principal samarium(ii) species in a mixed solvent of THE and HMPA is an ionic cluster of [Sm(HMPA)4(THE)2] 2I in HMPA-THF (4 1) or [Sm(HMPA)6] 2I in HMPA-THE (>10 1). The reactivity order of the samarium(ii) complexes is [Sm(HMPA)6] 2I > [Sm(HMPA)4(THF)2] 2P > Sml2 in the reaction with 1-iodobutane. 

Addition of HMPA to Sml2 in THE changes the reaction course of the benzaldehyde dimerization. Although samarium(ii) iodide promotes pinacol coupling of benzaldehyde, use of 2.8equiv. of HMPA leads to the formation of, in addition to the pinacol (10% yield), a dimer (60% yield) that results from the connection of a carbonyl carbon and a phenyl para-c3.rbon (Equation (31)). ... 

A monoprotected pinacol can be obtained in 81% yield by intramolecular coupling of 2,2 -biaryldicarbaldehyde mono-dibenzyloxy acetal, using samarium(ii) iodide in THF in the presence of BF3-OEt2 (Equation (47)). As in the case of homocoupling of 2,2 -biaryldicarbaldehyde, the /ra r-isomer is produced selectively. Addition of the Lewis acid is important to obtain high yields, otherwise the yield drops to 37%. ... 

EPOXIDES Diphosphorus tetraiodide. Lithium. 3-Methyl-2-selenoxo-l,3-benzothiazole. Phosphorus triiodide. Lithium. Potassium iodide-Zinc-Phos-phorus(V) oxide. Samarium(II) iodide. Sodium O.O-diethyl phosphorotelluro-ate. Triphenylphosphine hydroiodide-Triplienylphosphine diiodide. 

F. Ketyl-olefin cyclization mediated by samarium(II) iodide 563... 

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