Samarium carbenoids

A computational study of cyclopropanation reactions of the divalent samarium carbenoid ISmCH2I with ethylene has been presented. The ISmCH2I species was found to have a samarium carbene complex character with... 

In addition to zinc-based carbenoids, other potential active agents of the general structure MCH2X have been proposed. For example in 1985, Yamamoto and co-workers described the preparation and use of aluminium based carbenoids (R2AICH2I). Subsequently, in 1987 Molander and coworkers reported the use of a samarium/mercury amalgam and CH2I2 to generate samarium carbenoids. While these species are less well characterized than their zinc counterparts and their use has not been so... 

Chiral fluorinated allylic alcohols obtained by enzymatic resolution (Table 5, Runs 13 and 14) were employed in diastereoselective cyclopropanation using the carbenoid from samarium and di-iodomethane [32]. This reaction proceeded smoothly at -78 °C to 0 °C, but not as smoothly as the case of non-fluorinated allylic alcohols at -78 °C. 

Two DFT studies (one in Chinese and one in English) of the cyclopropanation of ethene with samarium(II) carbenoids have been reported.53,54 The reaction path is likely to involve a methylene transfer rather than a carbometallation with or without coordination of up to two THF molecules to the rare earth. 

When a-halo ketones are treated with diiodomethane and samarium at 0 °C, cyclopropanols can be obtained in reasonable yields. Curiously, under the same conditions 1,2-dibenzoylethane also leads to cyclopropanol products (equations 34 and 35). Several pathways for conversion of a-halo ketones to the observed cyclopropanols can be envisioned. It has been proposed that the mechanism of this reaction involves reduction of the a-halo ketone by Sm (or Smh) to a samarium enolate. Cyclopropanation of this enolate with a samarium-based carbenoid subsequently provides the observed product. 

Zhao, C., Wang, D., Phillips David, L. Theoretical study of samarium (II) carbenoid (ISmCH2l) promoted cyclopropanation reactions with ethylene and the effect of THF solvent on the reaction pathways. J. Am. Chem. Soc. 2003, 125, 15200-15209. 

Other interesting selectivities are observed in the stereoselective cyclopropanation of acyclic chiral nonracemic allylic alcohols. For example, cyclopropanation of substrate 72 gave the syn isomer 73 as the major product in the case of the zinc carbenoid and the anti isomer 74 in the case of the samarium reagent. ... 

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