Halides samarium iodide

Samarium iodide catalyzes the reduction of halides in damp THF120-122 and yields may be significantly improved if HMPA is added to the reaction mixture121,123. a-Halocarbonyl compounds are readily hydrodehalogenated by the use of this and similar methods124-126. Bis-cyclopentadiene complexes of samarium catalyze the reduction of benzylic and ally-lie halides via an organosamarium complex intermediate127-129. This reaction may be controlled so that monodeuteration occurs if the reaction is carried out under dry aprotic conditions followed by addition of D20 (equation 12). 

Samarium iodide reacts with alkyl halides or ketones to generate radicals by electron transfer (see Volume 1, Chapter 2.1). An example is shown in Scheme 20. It is known that other transition metal compounds (Mn, Ni, Cu, Fe etc.) also act as radical initiators [19j. 

A radical-mediated two-step synthesis of spiroketals has recently been reported the strategy (an example is shown in Scheme 8) involves an intramolecular radical cyclization of a ketal precursor (14), which could be easily prepared from 2-methylene-3,4-epoxyoxolanes (13). As alternative to tin-hydride mediated cyclization of alkynyl halides, samarium(II) iodide has been used to generate the alkyl radical which adds intramolecularly to the triple bond. ... 

Samarium iodide (Sml2) has been introduced as an efficient reducing agent for alkyl bromides and iodides in the presence of a proton source (alcohol) Alkyl chlorides are not reduced by this reagent. It has been further observed that the Sml2 reductions proceed exceedingly well in the presence of HMPA. Thus, primary, secondary and tertiary halides are reduced to alkanes under mild conditions and in very high yields (equation 44). ... 

Scheme 3. Samarium iodide mediated coupling reaction between halides, isocyanides and carbonyl substrates to form Q -hydroxyketones.

The thermal decomposition of trihalides is a good way to prepare divalent ytterbium and samarium halides (especially iodides). For example, Baernighausen (1961) has prepared excellent samples of Sm or Yb dihalide by the thermal decomposition of trihalide hydrates. Only a few preparations involve this type of reaction in the field of divalent organometallic compounds. 

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

Divalent samarium is known to reduce alkyl halides. However, reductions of iodides and bromides in tetrahydrofuran (THF) require a long reaction time and chlorides are not reduced even at refluxing temperature. 

A number of low-valent metal ions have been shown to reduce a-halocarbonyl compounds. The most commonly used species for this purpose have been chromium(II) and low-valent titanium " salts, although vanadium(II), samarium(II), iron(II) and tin(II) salts have also been used. 7 222 chloro, bromo and iodo ketones can all be reduced by chromium(II) and titanium(III) salts. Selective reductions are possible axial halides are reduced in preference to equatorial, and a,a-dihalo ketones can be selectively reduced to the corresponding monohalides (equation 10). 7 The use of samarium(II) iodide has recently been advocated for such a-cleavages.72 a-Halo esters and ketones are reduced instantaneously at -78 °C in excellent yields. a-Acetoxy esters are stable to this reagent. 

Curran, D. P., Fevig, T. L., Jasperse, C. P., Totleben, M. J. New mechanistic insights into reductions of halides and radicals with samarium(ll) iodide. Synlett 1992, 943-961. 

Samarium selenides. Reductive cleavage of ArSeSeAr by samarium is catalyzed by a great number of metal halides bismuth(III) chloride, cadmium chloride, chromium(IIl) chloride, cobalt(II) chloride, potassium iodide, and titanium(lV) chloride. The resulting samarium arylselenides readily react with various organic halides. 

Samarium(II) iodide provides a means to reduce substrates in which the halide is resistant to reduction by hydride reducing agents (eq 2). 

Samarium(n) iodide further mediates the cyclization reactions of alkynyl halides (eq 31). When treated with Sml2, the alkynyl halides are converted to the cyclized product in good yield. Addition of DMPU as cosolvent provides slightly higher yields in some instances. 

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