Halides acetylene derivatives

All the above-mentioned initiators are very sensitive towards substances with active hydrogen. Care must therefore be taken to exclude acids, water, thiols, amines, and acetylene derivatives. Oxygen, carbon dioxide, carbon monoxide, carbonyl compounds, and alkyl halides which can react with the initiator, also interfere with the reaction. Careful purification and drying of the starting materials and apparatus is, therefore, absolutely essential, especially when dealing with living polymers (see Example 3-19). 

Relevant mechanistic studies of electrophilic additions to acetylene derivatives and the first demonstration of a unimolecular solvolysis of vinyl halides (Grob and Cseh, 1964) stimulated a still growing interest in the field of vinyl cations. 

Addition reactions of sulphenyl halides (in particular chlorides) to acetylene derivatives have been extensively explored and recently reviewed (Modena and Scorrano, 1968). Although free radical processes may be involved under specific conditions, the addition of both arene-and alkanesulphenyl halides normally occurs by an ionic mechanism, the sulphenyl halide sulphur being the electrophilic centre. 

Treatment of l,10-distannacyclodeca-2,8,ll,17-tetrayne 100 with electrophiles leads to cleavage of the Sn-C bonds. The reaction of 100 with three different boron halides giving rise to the formation of acetylene derivatives 286 is summarized in Scheme 48 <1997MGM573>. 

Linnett o gives a discussion of the use of valence force fieid with the addition ol selected cross terms. One method of reducing the number of constants to Tdc determined from the frequencies is to carry over from molecule to molecule certain force constants for squared terms and even for cross terms. Linnett mentions in this connection the work of Crawford and Brinkley who studied acetylene, ethane, methylacetylene, dimethylacetylene, hydrogen cyanide, methyl cyanide and the methyl halides in this way, and were able, for all the molecules, to account for 84 frequencies with 31 constants. Linnetttreated some of these compounds using a different force field. He was able to account satisfactorily for 25 frequencies using 11 force constants. From our point of view the trouble with these results is that Linnett obtained a value for the C - C force constant in these acetylene derivatives which was different from that obtained by Crawford and Brinkley. For C - C in methyl cyanide for example, Linnett obtained... 

An elegant method for linking terminal alkynes with aromatic compounds and olefins is the Sonogashira reaction [15]. The palladium-catalyzed reaction enables the simultaneous introduction of two or even more alkyne units and thereby makes it possible to synthesize acetylene derivatives, for example hexaalkynyl-benzenes [16], (eq. (7)), which can be obtained only with difficulty by other methods. It has been shown by Herrmann, Beller, and co-workers that the copper reagent is not necessary as a co-catalyst for the coupling of terminal alkynes with sp -carbon halides. By using phosphapalladacyclic catalysts 1 the... 

In strict correlation with the early method for the preparation of symmetrical diaryl tellurides by treatment of tellurium(IV) halides with 4 mol equiv of aryl Grignard reagent (see Section 3.1.2.4), dialkynyl tellurides are prepared starting from bromomagnesium and lithium acetylenic derivatives. ... 

As an improved alternative to the direct cyclocarbonylation of allylic halides and acetylene derivatives, a two-step procedure has been reported49. Thus, the addition of allylic halides to acetylenic derivatives is catalyzed by palladium(II) complexes, such as bis(acetonitrile)bromo-palladium(ll), followed by cyclocarbonylalion of the resulting cfs-adducts of the alkyne with tetracarbonylnickel in acetonitrile containing precise amounts of methanol and triethylamine. This is a better procedure for the preparation of cyclopentenones than direct cyclocarbonyla-tion mediated by tetracarbonylnickel, especially for monosubstituted or weakly polarized, disubstituted acetylenes. 

However, the reaction with carbonyl compounds of the a-Grignard or a-zinc halide derivatives (prepared by exchange) affords mixtures of the allenic and acetylenic derivatives [9] ... 

Although the yields tend to be modest, coupling of alkynyl, alkenyl, and allylic halides to terminal alkynes in the presence of a cuprous halide and an amine (e.g. Et N, pyridine) by the Cadiot-Chodkiewicz reaction provides a direct route to acetylenic derivatives that are of interest in the construction of vitamin A (1) and carotenoids. For example, heating the acetylenes 104, 95 or 105 with the bromides 106 and 107 in the presence of cuprous chloride and an amine in methanol provides a convenient route to the corresponding acetylenic retinoids 108, 109 and 110 [53,54]. Similarly, heating 3-bromobut-2-en-2-ol with the acetylene 105 gives 11,12-didehydrovitamin A (108) [53] (Scheme 26). 

Sodium hydride dimethyl sulfoxide Terminal acetylene derivatives from halides... 

The Cadiot-Chodkiewcz and Glaser reactions are the synthetic reaction with acetylene type compounds. As the acetylene compounds easily form stable organo-copper compounds, these acetylenecopper compounds react directly with halides to afford the acetylene derivatives. This synthetic reaction is called the Castro reaction [43]. For example, as shown in eq. (22.22), aryl compounds having functional groups such as OMe, NO2 and COOH are able to condense with copper acetylides... 

Lithium acetylide-ethylenediamine Terminal acetylene derivs. from halides Hal C = CH... 

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