Alkynyllithium reagents

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

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

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. 

MgS12 clusters of isomaleonitrile (35 M = Cu, Ag) have also been characterized.49-51 A recent study of the addition of alkynyllithium reagents to the S—S bond of (n-dithio)bis(tricarbonyliron) revealed the formation of the ligand (36) bridging the two iron atoms of a hexacarbonyldiiron group. Several further reaction products of this compound were synthesized.52... 

Ytterbium(III) chloride can also reverse the diastereoselectivity of reactions of 1 with alkynyllithium reagents. Cerium(III) shows similar effects, but yields are also lowered. 

Molecular models of 3 clearly indicate that the C(7)-0-pivaloyl group is appropriately positioned to engage in chelation with the alkynyllithium reagent in the manner shown overleaf. Chelation of this sort would obviously help guide in the nucleophile to the more-hindered top face of... 

A more general and efficient approach to alkynyl carboxylates, also thought to involve alkynyliodonium carboxylate intermediates, entails the treatment of bis(acyloxyiodo)-arenes with alkynyllithium reagents (equation 88)81. These reactions are best conducted in the presence of 2-nitroso-2-methylpropane in order to suppress oxidative coupling of the lithium acetylides by the acyloxyiodanes. 

The complex Fe2(S2)(CO)6 reacts with alkynyllithium reagents to give dithiolenes after treatment with electrophiles (303). The synthesis proceeds... 

Alkynyllithium reagents cleave the S—S bond of [Fe2(CO)6(/t-S)2] to give 524, which can undergo intramolecular addition of sulfur to the a (525) or P (526) carbon atom of the acetylenic group when treated with electrophiles (Q ) like H+, aldehydes, and group 4 organometallic halides. With alkyl halides and acetyl chloride, only S-alkylation or S-acylation is observed (292,293). 

Kotsuki, H, Kadota, I, Ochi, M, An efficient method for the alkylation of chiral triflates with alkynyllithium reagents. A highly concise total synthesis of (-l-)-panaxacol. Tetrahedron Lett., 31, 4609-4612, 1990. 

Alkynyllithium reagents add readily to metal carbonyls, leading to thermally unstable anionic alkynic metal carbonylates (8), which give mainly the 1,3-diyne, by treatment with iodine-methanol in THF (Scheme... 

Reaction of alkynyllithium reagents with epoxides. This reaction, particularly in the case of substituted epoxides, can be sluggish when conducted in THF alone. Doolittle1 has examined the effect of various cosolvents. Use of THF-HMPT (1 1) results in high yields and reasonable reaction rates at 0°. Of other additives examined, TMEDA is equivalent to HMPT and is more effective than DABCO or ethylenediamine. Note that use of HMPT does not permit reaction of 1-dodecynyllithium with either cis- or trans-2,3-dimethyloxirane even at 50° for 2 hours. 

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-... 

Sommer2 emphasized that high ionic character of the C-Li bond in itself is not sufficient to promote inversion since alkyllithium and alkynyllithium reagents have similar stereochemical outcomes. Both high ionic character and charge delocalization are required. 

Aryliodonium salts. Unsymmetrical diaryliodonium triflates and aryl(alkynyl)-iodonium triflates are readily synthesized from the title compounds by reaction with ArLi and alkynyllithium reagents, respectively. Ethylene is one of the byproducts. 

B-l-Alkynyl-9-BBN derivatives are prepared as 1 1 THF complexes in excellent yields. B-Methoxy-9-BBN in THF on treatment with an alkynyllithium reagent at -78 °C results in the formation of an adduct. This adduct is stable and may be isolated as a complex with THF. However, the treatment of this ate complex with 1.3 equiv of BFj-OEtj at -78 °C, followed by warming to 25 "C results in the formation of trimethylborate, lithium tetrafluoroborate, and the desired B-l-alkynyl-9-BBN THF complex. This complex is easily isolated by evaporation of the THF solvent, extraction with pentane, and crystallization. The B-1-alkynyl-9-BBN THF complexes are stable crystalline solids that can be stored at room temperature for up to 1 year with no apparent decomposition (Chart 23.9 Table 23.6) [11]. 

Carbanion Reactivity. An increase in reaction rate is observed for the reaction of alkynyllithium reagents with alkyl halides and oxiranes (eq 10). The strongly coordinating HMPA probably complexes the lithium cation, thereby increasing the negative charge density on the carbon and creating a much more nucleophilic alkynyl anion. A similar effect is observed for (Trimethyl-stannylmethyl)Uthium, which does not react with oxiranes in THF but in THF-HMPA the reaction proceeds readily. ... 

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