Butyllithium, reaction with alkynes

Lithiated 1-alkynes can be metallated relatively smoothly in the 3-position, using an extra equivalent of butyllithium. The efficiency of the dimetallation may be at least 90%, as can be concluded from the excellent results of the quenching reaction with Me3SiG [2] ... 

Acyliron complexes have found many applications in organic synthesis [40]. Usually they are prepared by acylation of [CpFe(CO)2] with acyl chlorides or mixed anhydrides (Scheme 1.13). This procedure affords alkyl, aryl and a,P-unsaturated acyliron complexes. Alternatively, acyliron complexes can be obtained by treatment of [Fe(C5Me5)(CO)4]+ with organolithium reagents, a,P-Unsaturated acyliron complexes can be obtained by reaction of the same reagent with 2-alkyn-l-ols. Deprotonation of acyliron complexes with butyllithium generates the corresponding enolates, which can be functionalized by reaction with various electrophiles [40]. 

The stannylcupration of alkynes has been widely studied. Reaction of alkynes with lithium bis(tributylstannyl) cuprate leads to r -2-(tri butyl stannyl) vinyl cuprates, which are synthetically equivalent to cis- 1,2-ethylene dianions. Addition of the tin-copper reagent across the triple bond occurs i>7/-stereospecifically, thus providing Z-vinylstannanes. Phenylacetylene reacts with the tin cuprate with a regiochemistry opposite to that of 1-decyne.294 The intermediate cuprates react well with the various electrophiles.295 For example, the reaction with ethylene oxide gives primary alcohols, and further treatment of their />-toluenesulfonates with butyllithium gives 1-substituted cyclobutenes (Equation (120)) 294... 

Alkynes. Primary alkyl halides react with dichloromethyllithium in the presence of HMPT (1 equiv.) to form homologated 1,1-dichloroalkanes in 60-90% yield. Several methods have been used for dehydrochlorination of the products. A new method is the reaction with 3 equiv. of n-butyllithium to form a lithium... 

Alkyl-l-alkynes. Reaction of 1-bromo-l-alkynes (1) with at least 2 eq. of n-butyllithium in hexane gives 3-butyl-1-alkynes (2) in excellent yields. The favored mechanism involves metal-halogen exchange (a) and further reaction with n-butyllithium to give the dUithioalkyne (b), which is then alkylated at the propargylic carbon atom ... 

As noted above, alkyne anions are very useful in Sn2 reactions with alkyl halides, and in acyl addition reactions to a carbonyl.46 Alkyl halides and sulfonate esters (tosylates and mesylates primarily) serve as electrophilic substrates for acetylides. A simple example is taken from Kaiser s synthesis of niphatoxin B, in which propargyl alcohol (36) is treated with butyllithium and then the OTHP derivative of 8-bromo-1-octanol to give a 47% yield of 37.48... 

Protection of Terminal Alkynes. Terminal alkynes can be protected as TMS alkynes by reaction with Butyllithium in THF followed by TMSCl (eq 17). A one-pot -elimination-silylation process (eq 18) can also yield the protected alkyne. 

This concept of flash chemistry was extended for the generation of 2-chlor-ovinyllithium from 1,2-dichloroethane and butyllithium [72]. Typically, such reactions are carried out at —78°C to avoid decomposition of intermediates via (3-elimination however, it was possible to carry out the microfluidic generation of 2-chlorovinyllithium and subsequent reactions with numerous electrophiles even at 0 °C by shortening the residence time up to 0.055 s (Scheme 5.54). By intentionally prolonging the residence time over 50 s, and thereby allowing the (3-elimination to take place, the authors were able to generate both symmetrically and unsymmetrically disubstituted alkyne. 

Reactions with Epoxides. These reactions allow preparation of /3-alkynic alcohols (eq 4) the use of -butyllithium, followed by diethylaluminum chloride, may increase the yield. 

Extension of this reaction to electrophiles other than aldehydes was unsuccessful [22, 23], However, propargylic boronates were found to react with allylic halides and various carbonyl compounds [23], The boronates were prepared by lithiation of a methyl-substituted alkyne with t-butyllithium followed by treatment with a trialkylborane. The propargylic boronate preferentially reacts with the electrophile at the y-position to yield propargylic products (Eq. 9.20). The methodology has also been applied to alanates with comparable results. 

A first structural characterization of a cyclobutadiene dianion was performed by Boche and coworkers, who generated the dilithium salt of the 1,2-diphenylbenzocyclobutadiene dianion (143) (by deprotonation with n-butyllithium in the presence of TMEDA) (Figure 17) . Nevertheless, the molecular structure of 143 resembles more the structures of dilithiated alkenes, synthesized by reaction of the corresponding alkynes with metallic lithium. In that class of compounds, carbon-carbon bonds, capped by two lithium centres, are the structural motif (see Section II. E). 

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