Organosamarium reagents 1,4-addition

The initial products of such additions under aprotic conditions are organosamarium reagents and further (tandem) transformations are possible, including addition to ketones, anhydrides, or carbon dioxide. 

Scheme 2.68. Copper-catalyzed 1,4-addition of organosamarium reagents.

The C-linked (1 6)-disaccharides 176, 178 and 180 are all obtained in good yields (83 to 89%). The addition of the organosamarium reagents to the carbonyl group of aldehyde 175 also occurred with a high facial selectivity (diastereomeric ratio of about 95 5), exclusively controlled by the asymmetry of the C-glycosyl donor. 

It was found that Me3SiCl accelerates the conjugate addition of in situ prepared organosamarium reagents to a,f3-unsaturated carbonyl compounds and nitriles in the presence of HMPA and catalytic amounts of Cu(l) salts (Scheme 296). HMPA is also necessary for the in situ preparation of the organosamarium species from alkyl halide and Sml2.1081... 

Addition to C =0. Organosamarium reagents, formed by treatment of r-butyl a-haloalkyl ketones with Sml2 in THF at —78°, are active toward carbonyl compounds. ... 

The cross-coupling of alkylsamarium reagents with alkyl halides may be catalyzed by copper salts such as CuX (X=Br, Cl or I) or Li2CuCl4 [158]. The most effective catalyst for the desired cross-coupling was CuBr or Li2CuCl4. The reaction was performed at room temperature in THF with 8 equiv of HMPA. Some examples are listed in Scheme 59. In order to optimize cross-coupling products R -R2, the reaction was performed in two steps, with initial formation of the organosamarium from RxX and then addition of the catalyst and of R2X. 

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