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.

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