Sec-Butyllithium

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sec-Butyllithium (CH₃CHLiCH₂CH₃), or 1-methylpropyllithium, is an organometallic compound used as a source of sec-butyl carbanion in organic synthesis.

It can be prepared by the reaction of sec-butyl halides with lithium metal; sec-butyl iodide is the most reactive halide in this preparation. The carbon-lithium bond is mainly ionic in character, making the carbon very nucleophilic and basic, as in other organolithium reagents. Due to the electron-releasing nature of the methyl and ethyl substituents, sec-butyllithium is even more basic than primary organolithium reagents.

It is also more sterically hindered, though it is still useful for syntheses. Synthetic reactions involving sec-butyllithium are similar to those involving other organolithium reagents; for example, they can react with carbonyl compounds or esters to form alcohols, or with copper(I) iodide to form 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.