4.2.1.3 Samarium(II) Iodide (SmI2)
SmI2 is air sensitive and should be handled under inert atmosphere. It may be stored over THF for longer period.
Barbier-Type Reactions
SmI2 is quite useful in promoting Barbier-type reactions between aldehydes or ketones and a variety of organic halides (Scheme 10). The reaction time and temperature can be reduced by adding catalytic amount of FeCl3 or HMPA. For example, annulations of six member ring occur
Scheme 9
Scheme 10
with excellent diastereoselectivity via an intramolecular Barbier-type reaction in the presence of catalytic FeCl3 at mild conditions (Scheme 10). Moreover, this method provides effective route for the construction of fused bicyclic systems.
Nucleophilic Acyl Substitutions
The above described reaction conditions can be used to facilitate the selective intramolecular acyl substitution of halo esters (Scheme 11). Unlike the organolithium reagents, SmI-promoted nucleophilic substitutions don't proceed with double addition to the carbonyl.
Scheme 11
Ketone-Alkene Coupling Reactions
Ketyl radicals generated from reduction of ketones or aldehydes with SmI2 can be coupled both inter- and intramolecularly to a variety of alkenic species. Excellent diastereoselectivities are accomplished in intramolecular coupling reactions. For example, ketone–alkene cyclization can be pursued in a stereocontrolled manner (Scheme 12).
Scheme 12