Selenium-based resin

Another example of the resin-capture-release technique which should see widespread applications in the future is the selenium-mediated functionalization of organic compounds. Polymer-supported selenium-derived reagents [34] are very versatile because a rich chemistry around the carbon-selenium bond has been established in solution and the difficulties arising from the odor and the toxicity of low-molecular weight selenium compounds can be avoided. Thus, reagent 26 (X = Cl) was first prepared by Michels, Kato and Heitz [35] and was employed in reactions with carbonyl compounds. This treatment yielded polymer-bound a-seleno intermediates, which were set free back into solution as enones from hydrogen peroxide induced elimination. Recently, new selenium-based functionalized polymers 26 (X = Br)-28 were developed, which have been utilized in syntheses according to Scheme 11 (refer also to Scheme 3) [36],... 

Selenium-based linkers 590 can also be synthesized from polystyrene via lithiation and subsequent addition of dimethyldiselenide to the polymer support. Reaction of bromine gives selenenyl bromide that can be reduced to the lithium selenium resin in the presence of liBH4 that is alkylated subsequently [318]. Other approaches include the addition of former synthesized selenium-containing building blocks to the resin, for example, the hnker systems generated by Elofsson et al. [319] and Nakamura et al. [320,321]. 

Resin-bound selenium has been used as a linker for alkenes in two ways (a) as an oxidant-sensitive linker (selenoxides readily undergo [5-elimination at room temperature Entries 6-8, Table 3.43 [767-773]), or (b) as a linker cleavable by tin radicals (Figure 3.37 Entries 9 and 10, Table 3.43). The main advantages of selenides as linkers are their stability under a broad variety of (non-oxidizing) reaction conditions, including high temperatures and treatment with acids or bases, and the mild conditions required for their cleavage. 

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