Reductions with samarium(II) iodide

[2][3][4] In 1979, Henri Kagan observed the reduction of a variety of organic functional groups by samarium(II) iodide under mild conditions.

[5] Since that time, samarium(II) iodide has been employed in a variety of contexts in organic synthesis for both functional group manipulation and carbon-carbon bond formation.

The use of hexamethylphosphoramide (HMPA) as a co-solvent in samarium(II) iodide reductions allows the reaction to be carried out under much milder conditions than in its absence.

[6] It has recently been investigated and determined that tripyrrolidinophosphoric acid triamide (TPPA) can be used in lieu of HMPA as an activator for SmI2 reductions, producing faster reactions and similar yields while avoiding the use of a known carcinogen.

In the presence of samarium(II) iodide, the halogen atom of alkyl, alkenyl, and aryl halides is replaced by hydrogen.

Initial electron transfer and loss of halide generate an organic radical, which may combine with a second molecule of samarium(II) iodide to form an organosamarium species.

[13] (6)Nitro compounds may be reduced to either the hydroxylamine or amine oxidation level with samarium(II) iodide, depending on the conditions employed.

[15] (9)Samarium(II) iodide may be used to reduce ketones and aldehydes to alcohols; however, diastereoselectivity is low and a variety of more stereoselective methods exist.

[18] (12)Samarium(II) iodide is effective for the reduction of a wide array of functional groups; however, other reducing agents are more useful in certain contexts.

[6] Reductive fragmentations with samarium(II) iodide have the disadvantage that they are not stereospecific; however, stereoselectivity is higher in some cases when SmI2 is used in place of other reducing agents.

[19] Reduction of α,β-unsaturated carboxylic acids and derivatives to the corresponding saturated carbonyl compounds by SmI2 is a useful transformation mediated by few other reducing agents.

Samarium salts are usually insoluble in these conditions, but do form a suspension in the aqueous phase from which the desired organic product can be extracted.