sec-Butyllithium

''sec''-Butyllithium is an organometallic compound with the formula CH₃CHLiCH₂CH₃, abbreviated ''sec''-BuLi or ''s''-BuLi. This chiral organolithium reagent is used as a source of ''sec''-butyl carbanion in organic synthesis..

Synthesis

''sec''-BuLi can be prepared by the reaction of ''sec''-butyl halides with lithium metal:

Properties

Physical properties

''sec''-Butyllithium is a colorless viscous liquid. Using mass spectrometry, it was determined that the pure compound has a tetrameric structure. It also exists as tetramers when dissolved in organic solvents such as benzene, cyclohexane or cyclopentane. The cyclopentane solution has been detected with ⁶Li-NMR spectroscopy to have a hexameric structure at temperatures below −41 °C. In electron-donating solvents such as tetrahydrofuran, there exists an equilibrium between monomeric and dimeric forms.

Chemical properties

The carbon-lithium bond is highly polar, rendering the carbon basic, as in other organolithium reagents. ''Sec''-butyllithium is more basic than the primary organolithium reagent, ''n''-butyllithium. It is also more sterically hindered. ''sec''-BuLi is employed for deprotonations of particularly weak carbon acids where the more conventional reagent ''n''-BuLi is unsatisfactory. It is, however, so basic that its use requires greater care than for ''n''-BuLi. For example diethyl ether is attacked by ''sec''-BuLi at room temperature in minutes, whereas ether solutions of ''n''-BuLi are stable.

The compound decomposes slowly at room temperature and more rapidly at higher temperatures, giving lithium hydride and a mixture of butenes.

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Applications

Many transformations involving ''sec''-butyllithium are similar to those involving other organolithium reagents.

In combination with sparteine as a chiral auxiliary, sec-butyllithium is useful in enantioselective deprototonations. It is also effective for lithiation of arenes.

References

{{DEFAULTSORT:Butyllithium, sec-

Organolithium compounds