Alkynylmagnesium halides

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. 

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],... 

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]. 

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) . 

The Pd-catalyzed cross-coupling reactions of vinyl iodides 63 with alkynylmagnesium halides 64 have been found to produce enynes 65 with retention of configuration (>97%) [Eq. (24)] [36]. Using this procedure, the thienylacetylene 66, which is an intermediate for the synthesis of a natural antifungal and nematicidal agent can be prepared [Eq. (25)] [37]. 

Treatment of crude akynylalkanols (92), which are obtainable from (91) and 1-alkynylmagnesium halides, with hot aqueous acid provides a convenient synthesis of 3,5-di- and 2,3,5-trisubstituted (five-, six-, and seven-membered ring-fused) thiophenes (93) (Scheme 25) <89S2io>. Starting materials (91) are easily synthesized from a-halo ketones in high yields. The reaction may involve electrophilic attack of vinyl cation, produced by protonation of the triple bond, on the sulfur. 

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