Reduction catalyzed by samarium diiodide

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//)- 

Hasegawa and Curran have shown that water serves not only as a proton source, but can also accelerate certain reductions [89]. An example is reported in Table 6.11. The presence of water is essential for the rapid conversion of A to B, and quenching dry reactions with water only serves to promote this conversion. 

At room temperature the Sml2-H20 system rapidly reduces carboxylic acids, esters, amides, nitriles, chlorides, alkenes, nitro compounds and heteroaromatic rings [90]. Some examples are reported in Table 6.12. 

Hanessian recently reported a facile and direct preparation of 2-deoxy-aldonolactones from their unprotected oxygenated progenitors by using Sml2 in THF-H2O [91]. The a-deoxygenation of D-arabino-1,4-lactone is illustrated below  

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