Samarium tetrahydrofuran

Samarium and ytterbium metals dissolve in tetrahydrofuran (THF) solutions of diiodoethane to yield solutions of their diiodides, (JL) as... 

This radical cyclization strategy was utilized for the synthesis of the smaller fragment silyl ether 54 as well (Scheme 8). Evans aldol reaction of the boron eno-late derived from ent-32 with aldehyde 33, samarium(III)-mediated imide methyl ester conversion, and protecting group exchange led to tosylate 51. Elaboration of 51 to ketone 53 was achieved under the conditions used for construction of the second tetrahydrofuran moiety of 49 from 46. A highly diastereoselective reduc-... 

This point is borne out by the structure of tris indenyl samarium (5d). An earlier report of the nmr spectrum was interpreted as evidence of covalent bonding in the tetrahydrofuran adduct of samarium triindenide 66). Indenyl anion. 

Figure 4.11. Examples of redox-initiated radical reactions. Samarium diiodide reduction of the bromide gives a radical that cyclizes faster than the second reduction reaction. Manganese triacetate oxidation of the P-keto ester gives an enol radical that is not further oxidized by the manganese reagent. The IBX oxidizes anilides to the corresponding radicals. Hexamethylphosphoramide = HMPA and Tetrahydrofuran = THE.

Si3NO,DPiRu1CsaHMI, Ruthenate(l -), deca-carbonyl-lK C,2K C,3KJC-(x-hydrido-l 2K2//-bis(triethylsilyl)-lK5i,2KS/-trion-gu(o-tri-p-nitrido-bis(triphenyl-phosphorus)-(l +), 26 269 SmOC H2, Samarium(III), tris(rf-cyclo-pentadienyl)(tetrahydrofuran)-, 26 21... 

Into a solution of residue 59 (101 mg, 0.1 mmol) in 20 mL of dry toluene, kept at 60°C, was syringed, during 18 h and under argon, a freshly prepared solution of samarium diiodide in benzene-HMPA (9 1, v/v 6.3 mL, 0.51 mmol) which has been diluted with 3.8 mL of dry benzene. The solvents were distilled off under reduced pressure, and the residue was taken up in 10 mL of diethyl ether. The ether solution was washed with 10% aqueous solution of sodium bisulfite, then water, dried (MgS04), and concentrated. The crude product was dissolved in 1.5 mL of tetrahydrofuran and treated during 30 min at room temperature with 1.5 mL of a 40% aqueous solution of HF. The solution was neutralized with solid sodium carbonate, and concentrated. Flash chromatography on silica gel (cyclohexane-ethyl acetate, 3 1 to 1 2) afforded the product 80 (40.6 mg, 50%), a single isomer, as an amorphous solid. It was characterized by its diacetate [a]D +36° (c 4.0, CHClj). 

REDUCTION, REAGENTS Aluminum amalgam. Borane-Dimethyl sulfide. Borane-Tetrahydrofurane. t-Butylaminoborane. /-Butyl-9-borabicyclo[3.3.1]nonane. Cobalt boride— f-Butylamineborane. Diisobutylaluminum hydride. Diisopropylamine-Borane. Diphenylamine-Borane. Diphenyltin dihydride. NB-Enantrane. NB-Enantride. Erbium chloride. Hydrazine, lodotrimethylsilane. Lithium-Ammonia. Lithium aluminum hydride. Lithium borohydride. Lithium bronze. Lithium n-butylborohydride. Lithium 9,9-di-n-butyl-9-borabicyclo[3.3.11nonate. Lithium diisobutyl-f-butylaluminum hydride. Lithium tris[(3-ethyl-3pentylK>xy)aluminum hydride. Nickel-Graphite. Potassium tri-sec-butylborohydride. Samarium(II) iodide. Sodium-Ammonia. Sodium bis(2-mcthoxyethoxy)aluminum hydride. 

Mesoporous silica supported complexes of samarium(II), also having an amine and tetrahydrofuran ligand, were found to incandesce on exposure to air. The initial deposition was from samarium(II) bis(dimethylsilyl)amide, and bis(dimethylsilyl)-amine is itself not a compound likely to be air stable. 

Samarium(II) iodide in the synthesis of tetrahydrofuran and dihy-drobenzofuran derivatives 92SL943. 

There exists also a synthesis of cyclopentadecanone (VII/81) and ( )-mus-cone, based on a three-carbon annulation of cyclic ketones followed by the regioselective radical cleavage of the zero bridge of the so formed bicyclic system [44], The synthesis of cyclopentadecanone is summarized in Scheme VII/16. The cyclization of VII/78 to the bicyclic alcohol VII/79 proceeds best (94 % yield) with samarium diiodide in the presence of hexamethylphosphoric acid triamide and tetrahydrofuran [45], The oxidative cleavage of VII/79 to the ring expanded product VII/80, was performed by treatment with mercury(II)-oxide and iodine in benzene, followed by irradiation with a 100 Watt high pressure mercury arc. Tributyltinhydride made the de-iodination possible. 

N-Acylated indoles 1520 furnished tricyclic compounds 1521 in the presence of samarium diiodide (2.5 equiv) in tetrahydrofuran along with an excess of hexamethylphosphoramide (10 equiv) and phenol (2 equiv) as proton source (Equation 311) <20030L4305>. Whereas methyl ketone 1520 (R = Me) smoothly cyclized to compound 1521 (in 73% yield), the corresponding aldehyde 1520 (R = H) provided compound 1521 only in low yield (28%). 

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. 

Anhydrous samarium(III) chloride [Rare Earth Products, Johnson Matthey] (2.40 g, 9.40 mmol) is placed in a 200-mL Schlenk tube containing a magnetic stirring bar. Tetrahydrofuran (THF) (100 mL) is introduced via a cannula at 20 °C. The mixture is stirred at 20 °C for 2 h. Solid (2,6-di-tert-butylphenoxo)-lithium-diethyl etherate (8.13g, 28.4 mmol) is added to this slurry at 20 °C. A reflux condenser is then fitted to the Schlenk tube, and the reaction mixture is heated under reflux for 8 h. After h, the solid dissolves to yield a clear yellow-green solution. The solvent is removed at 25 °C and 10 torr, leaving a yellow-green solid, which is scraped from the sides of the Schlenk tube with a spatula and transferred to a sublimation tube. Sublimation at 255-260°C and 10 torr affords yellow crystals of tris(2,6-di-tert-butyl-phenoxo)samarium. Yield 4.46 g (62%). ... 

Samarium(U), bis(7) -pentamethylcyclopen-tadienyl)bis(tetrahydrofuran)-, 27 155 Samarium(III), tris(7) -cyclopenta-dienyl)(tetrahydrofuran)-, 26 21 Samarium trichloride—2tetrahydrofuran-, 27 140... 

P2RhC2jH47, Rhodium(I), carbonylphen-oxobis(triisopropylphosphine)-, 27 292 02SC,H, Benzenesulfonic acid, 4-methyl-, rhodium complex, 27 292 02SmCa,H4t, Samarium(II), bis(T) -penta-methylcyclopentadienyl)bis-(tetrahydrofuran)-, 27 155 OjYbCMHM, Ytterbium(H), bis(Ti -cyclo-pentadienyl)( 1,2-dimethoxyethane)-, 26 22... 

SmOCraH22, Samarium(III), tris(Ti -cyclo-pentadienyl)(tetrahydrofuran)-, 26 21... 

Samarium diiodide is very conveniently prepared by oxidation of samarium metal with organic di-halides or with iodine (equations 10-12). Deep blue solutions of SmI (0.1 M in THF) are generated in virtually quantitative yields by these processes. This salt can be stored as a solution in THF for long periods when it is kept over a small amount of samarium metal. Tetrahydrofuran solutions of SmI are commercially available as well. If desired, the solvent may be removed to provide Sml2-(THF)n as a powder. For synthetic purposes, Smh is typically generated and utilized in situ. 

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