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Sec-Butyllithium

Template:DISPLAYTITLE:sec-Butyllithium sec-Butyllithium is the chemical compound with the formula CH₃CHLiCH₂CH₃, abbreviated sec-BuLi or s-BuLi This organolithium reagent is used as a source of sec-butyl carbanion in organic synthesis.^[1]

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Sec-BuLi can be prepared by the reaction of sec-butyl halides with lithium metal:^[2]

CH₃CHClCH₂CH₃ + 2 Li → CH₃CHLiCH₂CH₃ + LiCl

The carbon-lithium bond is highly polar, rendering the carbon very nucleophilic and basic, as in other organolithium reagents. Sec-butyllithium is more basic than primary organolithium reagents such as n-butyl lithium. It is also more sterically hindered, though it is still useful for syntheses.

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 its solutions of n-BuLi are stable.^[1] Many transformatins involving sec-butyllithium are similar to those involving other organolithium reagents. For example, sec-BuLi react with carbonyl compounds and esters to form alcohols. With copper(I) iodide sec-BuLi forms lithium di-sec-butylcuprates. The first two reactions can also be accomplished by using sec-butylmagnesium bromide, a Grignard reagent; in fact, the latter is the typical reagent for this purpose.

References

^ ^a ^b Ovaska, T. V. "s-Butyllithium" in Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons: New York. doi:10.1002/047084289X.rb397
^ Hay, D. R.; Song, Z.; Smith, S. G.; Beak, P. (1988). "Complex-induced proximity effects and dipole-stabilized carbanions: kinetic evidence for the role of complexes in the α-lithiations of carboxamides". J. Am. Chem. Soc. 110: 8145 - 8153. doi:10.1021/ja00232a029.