Samarium reagents

Among various samarium reagents, Sml2 has been most widely used for many transformations in organic synthesis. Since many reviews on Sml2 chemistry have been already published,18,18a 18e this chapter covers the organosamarium-induced reactions other than those of Sml2. 

Hosami and co-workers (12,173,174) prepared alternative forms of nonstabilized ylides (Scheme 4.87). They generated tailor-made carbonyl ylides from substituted 1,3-dichloroethers through a 1,3-elimination pathway mediated with a samarium reagent. These simple carbonyl ylide intermediates are valuable for preparing tetrahydro- and dihydrofurans. To a mixture of bis(chloromethyl) ethers and... 

Diastereomeric ratios of pinacol dimers obtained by coupling of benzaldehyde and acetophenone with samarium reagents are summarized in Tables 3 and 4, respectively. In general, the stereochemical control of pinacol coupling reactions with a stoichiometric or catalytic samarium(ll) reagent is poor, giving nearly a 1 1 dljmeso mixture. 

Table 3 Pinacol coupling of benzaldehyde with samarium reagents...

Intramolecular geometries, database studies, 1, 597 Intramolecular hydroalkoxylation, and etherification, 10, 672 Intramolecular pinacol coupling to cyclic 1,2-diols, 11, 51 with samarium reagents, 11, 60 Intramolecular silylformylation, alkynes and alkenes, 11, 489 Intramolecular solvomercuration alkenes, 2, 436 alkynes, 2, 439... 

Ring opening of epoxides using selenolates that are generated by other methods, such as reduction with samarium reagents [19], electrochemical reduction [22], reduction with phosphine [25] or reduction with NaBH4 under microwave irradiation [34], have also been reported. 

A general approach to P-functional alkanols involves formation of a-substituted samarium reagents and their reaction with carbonyl compounds. Thus, P,P-diiodoalkanols, °. -iodohydrins, " P-phenylselenoalkanols, and P-phenylthio-alkanols are prepared from the corresponding substituted halides. The products with a syn disposition are predominant. 

Cyclopropanation of vinylorganometallic compounds. Molandcr cyclopropana-tion of allylic alcohols substituted by silyl or stannyl groups can show high diastereo-sclcctivity particularly when carried out with a large excess of the samarium reagent. 

KAGAN-MOLANDER Samarium reagent Lanthanide reagents, specifically samanum. for generation of free radicals useful in cyctaahons. 

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