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.Ovaska, T. V. "s-Butyllithium" in Encyclopedia of Reagents for Organic Synthesis, 2001 John Wiley & Sons: New York. doi|10.1002/047084289X.rb397]

Sec-BuLi can be prepared by the reaction of "sec"-butyl halides with lithium metal: [cite journal | author = Hay, D. R.; Song, Z.; Smith, S. G.; Beak, P. | title = Complex-induced proximity effects and dipole-stabilized carbanions: kinetic evidence for the role of complexes in the α-lithiations of carboxamides | journal = J. Am. Chem. Soc. | year = 1988 | volume = 110 | pages = 8145–8153 | doi = 10.1021/ja00232a029] :CH₃CHClCH₂CH₃ + 2 Li → CH₃CHLiCH₂CH₃ + LiClThe 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. 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.

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