Reduction samarium diiodide reducing agent

The Julia olefination involves the addition of a sulfonyl-stabilized carbanion to a carbonyl compound, followed by elimination to form an alkene.277 In the initial versions of the reaction, the elimination was done under reductive conditions. More recently, a modified version that avoids this step was developed. The former version is sometimes referred to as the Julia-Lythgoe olefination, whereas the latter is called the Julia-Kocienski olefination. In the reductive variant, the adduct is usually acylated and then treated with a reducing agent, such as sodium amalgam or samarium diiodide.278... 

Another useful reagent for reduction of a-acetoxyketones and similar compounds is samarium diiodide.233 Sml2 is a strong one-electron reducing agent, and it is believed that the reductive elimination occurs after a net two-electron reduction of the carbonyl group. 

A more versatile reducing agent is samarium diiodide, which promotes chemoselective cyclizations of functionalized keto aldehydes in a stereodefined manner to form 2,3-dihydrocyclopentane carboxylate derivatives in good yields and with diastereoselectivities of up to 200 1 (equation 38)7 The reaction proceeds via selective one-electron reduction of the aldehyde component and subsequent nucleophilic attack on the ketone moiety. Stereochemical control is established by chelation of the developing diol (19) with Sm " " which thereby selectively furnishes cis diols (equation 39). The stereoselective M/-cyclization of 1,5-diketones to cis cyclopentane-1,2-diols using TiCU/Zn has been used to prepare stereodefined sterically hindered acyclic 1,2-diols when a removable heteroatom, such as sulfur or selenium, is included in the linking chain (equation 40). 

Other reducing agents, such as sodium/ammonia or diphenylstannane are unsatisfactory55. Since stereoselective reductions of this type have been a problem in the synthesis of milbemycins and avermectins57. the utility of the radical anion reduction via samarium diiodide/proton donor remains to be appreciated generally. For routine applications on a multigram scale, the price of samarium iodide is currently too high (1 mol of samarium costs ca. 25 times more than 1 mol of lithium). 

Samarium diiodide is a versatile reducing agent. It is easy to prepare, can be used in aqueous media and reduces a wide range of functional groups [88]. Reductions with Sml2 are generally carried out in the presence of proton sources (water or low-molar-mass alcohols) and electron donors (hexa-methylphosphoramide (HMPA), 1,3-dimethyl-3,4,5,6-tetrahydro-2(l//)-... 

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