1-Alkynyllithiums

Peterson and coworkers were the first who showed that 1-alkenes can react with lithium dispersion under relatively mild conditions to give the corresponding 1 -alkynyllithium compounds and lithium hydride as the major products. Thus 1 -hexene 113 was converted into 1-hexynyllithium 116 in 65% yield within 1 h at the reflux temperature of the olefin (64 °C). It is reasonable to assume that 1,2-dilithio-hexane 114 is formed first loosing lithium hydride to give 1-hexenyllithium 115, which was detected as a side-product in 4% yield. 

The reaction of an excess of 1-alkynyllithium reagents with tellurium tetrachloride afforded good yields of the dialkynyltellurides (67) (42-69%). Moreover, diynes (68) were isolated as major by-... 

Eliminations. 1-Fluoroalkenes afford 1-alkynyllithiums, which can be used to form propargylic alcohols. ... 

The ate complexes 80 can be similarly employed in the coupling of organic substituents on aluminum. The addition of 1-alkynyllithium to the 1-alkenylalu-minum 79, followed by treatment with VO(OEt)Cl2, leads to the trans-enyne 81 via chemoselective and stereoselective bond formation between sp and sp carbons (Scheme 2.67) [136]. 

Lithium acetylide and other 1-alkynyllithiums add cleanly onto ethylene oxide and onto 2-, 2,2-, and even 2,3-substituted oxiranes. However, often long reaction times and elevated temperatures are required (e.g., 20 h in refluxing l,4-dioxane)J Polar solvents such as dimethyl sulfoxide enable the reaction to be carried out at ambient temperature. 

Iwasawa et al. also developed a new reaction involving a three-component coupling process which affords five-membered heterocycles. This [2s+2sh-1c] cycloaddition reaction supposes the consecutive addition of an alkynyllithium derivative to a Fischer carbene complex followed by the addition of a third component which can be an aldehyde, an imine, an isocyanate, or C02 [119] (Scheme 74). 

Grignard reagents and organolithium compounds abstract protons that are much less acidic than those of water and alcohols => a useful way to prepare alkynylmagnesium halides and alkynyllithium. 

Reaction of a tungsten carbene complex with alkynyllithium followed by treatment of aldehyde in the presence of Et3Al afforded trisubstituted furans in good to excellent yields <06AG(I)6874>. Dienes were the products without Ft,AI. 

Table 5 1,2,3-Oxazolidinone 3-oxides 117 by reaction of nitric oxide with alkynyllithium reagents (Equation 21) <2004CC16>...

The structures of 106 and 107 were also investigated in ether and THF solutions by using IR and NMR methods. Compound 107 was synthesized in order to avoid problems with the rapid rearrangement at > — 20 °C of 106 to an alkynyllithium derivative. The lithiomethoxyallene had to be synthesized at ca —78 °C in THF or diethyl ether and it was measured in situ without isolation of the metalated product. Its NMR data are given in Table 42. 

The reaction of alkynyllithium compounds with alkoxycarbene tungsten complexes leads to anionic propargyl tungsten complexes (Figure 2.33 see also Figure 3.9). These intermediates are stable at low temperatures and react upon Lewis acid catalysis with aldehydes or A -sulfonyl imines to yield five-membered heterocycles [280]. Oxidative methoxycarbonylation [375] of the intermediate vinyl tungsten complex, followed by elimination of methanol leads to pyrroles or furanes (Figure 2.33 Entry 6, Table 2.22). 

These species, which provide Te + electrophiles, react with alkynyllithium reagents, giving dialkynyl teUurides in moderate yields. ... 

Sequential treatment of 00-bromoalkyl triflates with an alkyllithium at 0°C followed by addition of a second alkynyllithium and Nal and heating the reaction mixture gave unsymmetrical diynes in one-pot in good yields. This methodology was used to stereoselectively transform these diynes to diene pheromones such as Z,Z)- and... 

If the addition involves an alkynyllithium such as 34, the first-formed alkoxide intermediate 35 isomerizes into the propargylic-allenic lithium reagent. Reactions with electrophiles lead to either 36a or the allenol silyl ethers 36b (equation 13). ... 

The reaction occurs quickly at low temperature, with inversion of configuration at the attacked carbon center. The oxirane is reacting usually at the less hindered site. This reaction has found widespread use in organic synthesis , particularly in the case of stabilized organolithium and alkynyllithium species (see Section IV.B.2). In the intramolecular versions, the presence of BF3 has been reported to modify the regioselectivity". Other Lewis acids such as organolanthanids or LiC104 have also been used to a lesser extent. 

The oxirane ring opening reaction with alkynyllithiums is of considerable synthetic value, as stereodefined homopropargylie alcohols can be obtained. The lithium acetylide ... 

The corresponding lithium reagent remains uncychzed at —78°C but cyclizes on warming.88 In the case of y-, 8-, and e-alkynyllithium reagents, exo-cyclization to a-cycloalkylidene isomers occurs.89 Anion-stabilizing substituents are required for the three-and four-membered rings, but not for the exo-5 cyclization. 

Addition of TMEDA to a solution of BuLi in hexane gives a solution of the 1 1 complex BuLi.TMEDA, which is a highly efficient deprotonating reagent. It is capable of deprotonating alkynyllithium at the propargylic carbon atom in a relatively short rime. In the procedure of exp. 19, a 15% excess of BuLi.TMEDA is used to compensate for losses due to... 

A solution of 0.10 mol of anhydrous zinc chloride (note 1) in 40 ml of THF is added over a few sec to a solution or suspension of 0.10 mol of alkynyllithium in 60 ml of THF and 70 ml of hexane (compare exp. 8) cooled to -30 C. Temperature control is generally not essential the temperature is usually allowed to rise to 0 10"C during the addition. Depending upon the temperature and the ratio of THF to hexane, a homogeneous solution or a two-layer system is formed. 

Methyl Alkynyl Ketones from Alkynyllithium and Dimethylacetamide... 

Phenyl isothiocyanate reacts less readily with alkynyllithium than methyl isothiocyanate. The thioamide from the reaction of CHjC=CLi with PhN=C=S is not easy to obtain in a crystalline state. 

Di(l-alkynyl)sulfides are formed in excellent yields, if (freshly distilled) sulfur dichloride is added to a solution or suspension of a lithium alkynylide in Et20 [106). In an analogous manner, di(l-alkynyl)sulfoxides are formed from thionyl chloride and an alkynyllithium [106], while sulfinyl chlorides R S(=0)G may be used to prepare the sulfoxides RC=CS(=0)R Preliminary experiments suggest that interaction between alkynyllithium and sulfonyl chlorides R S02C1 can give both sulfones ROCSOjR and chlofo-alkynes RCsCCl [2). 

Reaction of Alkynyllithium in THF with Sulfur or Selenium and Subsequent Alkylation with Bromochloromethane... 

A suspension or solution of 0.20 mol of alkynyllithium in 140 ml of Et20 and 140 ml of hexane (see pag. 24) is cooled to -40"C and 6.4 g dry, powdered sulfur is added over 1 min. The cooling bath is removed and the temperature allowed to rise to 15-20 C. In all cases brown solutions are farmed. Stirring at 15-20 C is continued for about 1 h until all sulfur has dissolved. The solution is then transferred into the dropping funnel and added over 30 min to a mixture of 0.22 mol of freshly distilled acetyl bromide or 0.25 mol of ethyl chlorofonnate, and 200 ml of Et20. During, and for 30 min after this addition, the temperature of the mixture... 

The small amount of unconvened alkynyllithium (see exp. 8, note 2) may react with CICaN to give RCsCCaN. This has to be separated from the desired product by careful distillation. 

Preparation of Di(l-alkynyl(sulfides and Di(l-alkynyI)suifoxides from Alkynyllithium and Sulfur Dichloride or Thionvl Chloride... 

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