Alkynylmagnesium

With higher homologs e.g., propynyl, butynyl), 3j5-hydroxyandrost-5-en-17-one does not react well with the alkyne and potassium r-butoxide, or with the lithium alkyne in tetrahydrofuran. However, satisfactory results are obtained by use of the alkynylmagnesium bromide in tetrahydrofuran, ... 

Allenyl and 1- and 2-alkynyl sulfoxides have also been prepared by reaction of organomagnesium halides with sulfinate ester 19. 1-Alkynyl p-tolyl sulfoxides were prepared in good yield from 1-alkynylmagnesium halides plus ester 19 in toluene (equation ll)63. The corresponding organolithium compound was unsatisfactory as a... 

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. 

Disubstituted 1,2,3-triazoles are formed in 1,3-dipolar cycloaddition of alkynylmagnesium reagents to azides. This reverse regioselectivity is also achieved in ruthenium-catalyzed cycloadditions. Examples of such reactions can be found in Section 5.01.9. 

Interaction of pyrroline-iV-oxides (373) with alkynylmagnesium bromide gives alkyne substituted nitroxyl radicals (374), (376), and (377) (Scheme 2.164) (620). 

Alkenyl p-tolyl sulfoxides.1 Various 1-alkynylmagnesium bromides react stereospecifically (with inversion) with 1 in ether/toluene to give chiral 1-alkynyl sulfoxides 2. Reduction of 2 with LiAlH4 (THF, - 90°) affords optically pure (E)-1-alkenyl p-tolyl sulfoxides (3). The corresponding (Z)-isomers are obtained by hydrogenation of 2 with the Wilkinson catalyst. 

The formadon of alkynenitriles from alkynylmagnesium halides and cyanogen chloride was described far die fust tune by Grignard [114], A number of these nitriles have been prepared in our laboratory from alkynyllithium and cyanogen chloride using I O as a solvent [115], Cyanogen bromide is unsuitable because the alkynylide attacks on bromine [2],... 

The reactions of propargyl bromide or propargyl tosylate with alkynylmagnesium bromide gives small amounts of 1,3-substitution products, allenynes, RC=C-CH=C=C. These can be removed however, by heating the product mixture. During this treatment, the allenynes... 

In addition to their use as precursors for alkynylboron, tin or zinc compounds, alkynylmagnesium reagents show a moderate reactivity toward the coupling with haloarenes and haloalkenes. They are often commercially available, or easy to prepare. Their main drawback is their low chemoselectivity and high nucleophilicity, which implies incompatibilities with functional groups such as nitro and carbonyl. 

An example of a non-palladium-based system was reported by Madec et al. They made use of Ni(PPh3)2Gl2 for the coupling of vinylcarbamates and alkynylmagnesium reagents in benzene at higher temperatures (70 °G), and obtained good yields of product. ... 

Terminal alkynes by virtue of the presence of an acidic hydrogen atom can be converted into the corresponding alkynylsodium or alkynylmagnesium halide (see Section 5.4.2, p. 531) which may then be alkylated to give a homologous alkyne. 

Allylation of 1-alky nes.1 Cu(I)-promoted allylation of 1-alkynes was first reported in patents (1957-1959) and has since been markedly improved by use of a 1-alkynylmagnesium halide or by use of phase-transfer conditions (Bt NCl/NaCOj), both of which allow use of substituted allylic halides. Under the latter conditions, substituted 1,4-enynes can be obtained in 76-95% yield. 

Nucleophilic addition without change of the oxidation state, similar to couplings of alkynylmagnesium halides [lib]. 

Alkynylmagnesium bromides (general procedure for metallation of 1-alkynes by ethylmagnesium bromide) [6]... 

The method has been of particular value in the preparation of difunctional compounds. For example, the action of elemental halogen on sodium acetylides or alkynylmagnesium halides gives 1-halo-1-alkynes (70-90%). t Also, halo esters, phenols, or acids result when the appropriate aromatic mercurial is treated. Sometimes p-toyl-sulfonyl chloride is substituted for chlorine gas. p-Iododimethylaniline is easily made in 42-54% yield by the reaction of p-dimethylaminophenyl-lithium and iodine. ... 

Alkynylmagnesium halides are less basic than the alkali metal acetylides and therefore can be applied to sensitive alkylating agents. In contrast to the alkali metal acetylides they do not react with saturated primary halides. On the other hand, they do react with allylic, propargylic and benzylic halides, but only in the presence of cuprous chloride catalysts. They also react with a-haloethers (e.g. equation 136)" . 

A large number of skipped systems, 1,4-enynes and 1,4-diynes, have been prepared by the reaction of alkynylmagnesium halides with allyl and propargyl halides, as illustrated in equations (139)-(144). Several of these products have served in the preparation of annulenes. These reactions are carried out in THF solution close to reflux temperature and in the presence of CuCl as catalyst. 

Of other classes of acetylenic compounds which have been prepared recently by alkylation, 1-alkynylphosphonates should be mentioned. They are prepared in moderate yields from alkynylmagnesium halides and dialkyl or diaryl phosphoro-chloridates in ether at room temperature (equation 145) . 

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