Lithium alkynides alkylation

In addition, conjugate addition of lithium alkynides and thermally unstable lithium carbenoids, which is very difficult to achieve in organocopper chemistry, is realized with this amphiphilic conjugate alkylation system (Sch. 98). 

Lithium alkynides in tetrahydrofuran or dioxane often give substitution products with secondary haloalkanes, while alkynide Grignard reagents do not usually react with haloalkanes except in the presence of other metals such as cobalt and copper. Substitution of iodine or bromine for chlorine in the halo-alkane often leads to an increased yield of the alkylation product and alkanesulfonates may give greater yields than haloalkanes. Scheme 1 illustrates examples of alkylation of haloalkanes and alkyl sulfates with alkynides of Group I metals. 

Butadiyne has also been alkylated through the lithium alkynide. Thus, Holmes and Jones treated bis(trimethylsilyl)buta-l,3-diyne with MeLi in the presence of lithium bromide and obtained the monolithium alkynide, which was then alkylated in HMPA (Scheme 30). If the lithium alkynide was complexed with ethylenediamine then DMSO could be used as solvent. In addition, Himbert and Feustel prepared the lithium derivative of l-A A(-dialkylbuta-l,3-diyne by treatment of 4- -dialkyl-l,l,2-trichlorobut-l-en-3-yne with butyllithium. The lithium salt was not isolated but was alkylated to the l-alkyl-4-lV-di-alkylbuta-l,3-diyne (Scheme 31). 

Preparation of alkynes. The 1,1-dichloro-l-alkenes have been converted into 1-alkynes or internal alkynes by treatment with n-butyllithium at -10° to -70°. The resulting lithium alkynides can be hydrolyzed or alkylated (equation 1). 

The insertion tendency decreases in the order r-BuLi > 5-BuLi > n-BuLi > PhLi > MeLi. These insertions can be carried out by using lithium alkanides, alkenides, alkynides, and aromatic or heterocyclic lithium compounds. The lithiation should not be carried out by using alkyl halides, because the lithium tellnrolates that are formed in the reaction may react with the alkyl halide reagent to produce organyl alkyl tellurides. ... 

One of the characteristic features of this approach is the successful fert-alkyl-al-kynyl coupling with dialkylaluminum alkynides which enables the introduction of a quaternary carbon in a position adjacent to an alkynyl group. Such transformation was previously achieved by the cross-coupling of ferf-alkyl chlorides with trialkynyl-aluminums as already described in this section [92]. The reaction of 98 with dimethyl-aluminum phenylacetylide (1.5 equiv.), readily prepared from lithium phenylacetylide and Me2AlCl, in toluene at -78 °C for 30 min resulted in formation of a cross-coupling product in 70 % yield. This result indicates the efficient and selective transfer of the alkynyl group from the aluminum center in dialkylaluminum alkynides as depicted in Sch. 65. 

Lithium alkynylcuprates react with haloallenes to give similar skipped diacetylenes (see below). The related skipped enynes can be prepared by treatment of (pentadienyl)iron(tricarbonyl) halide complexes with dilithium trialkynylcuprates, the compounds being isolated as the iron(tricarbonyl)(diene) complexes (Scheme 4). Further examples of alkylation reactions of copper alkynides are illustrated in Scheme 5. Reaction between a lithium cyanoaikynecuprate and an iodoallene leads to a skipped diacetylene. This useful reaction has been used by Corey in his synthesis of hybridalactone (Scheme 6). °... 

---