Alkynyl halides, reactions

Reactions of 1-Alkenyl Metals with 1-Alkynyl Halides Reactions of Terminal Alkynes with -Carbon Halides General aspects Synthesis of terminal alkynes Stereospecific synthesis Phase-tranter catalysis... 

Some recent studies have underlined the effect that certain physical properties of the reaction medium have in governing the nature and yields of the products obtained when indole Grignard reagents react with alkyl or alkynyl halides. Such factors include the basicity and dielectric constant of the medium and its ability to solvate any of the reacting species. ... 

Palladium-catalyzed carbon-carbon bond forming reactions like the Suzuki reac-tion as well as the Heck reaction and the Stille reaction, have in recent years gained increased importance in synthetic organic chemistry. In case of the Suzuki reaction, an organoboron compound—usually a boronic acid—is reacted with an aryl (or alkenyl, or alkynyl) halide in the presence of a palladium catalyst. 

This reaction works with aryl, allylic and 1-alkynyl halides, but not vinylic halides. A vinylic group can be introduced into the 4 position of an isoquinoline by using PdBr2 as the electrophile and an alkene (Scheme 9).10 This process... 

The remaining alkenyl copper moiety in 50 can react intramolecularly with the carbon—carbon triple bond to give metallofulvene derivatives 53. However, the coupling of the intermediate with the second molecule of alkynyl halide would seem to be faster than the cyclization reaction. Therefore, the dienediyne is obtained as the major product. 

An entirely different situation is found in alkynyl halides. Here only examples in which the rearrangement is supported by carbonyl groups [106, 164] or electron-withdrawing pentafluorophenyl groups [165] are known. As one example, the selective reaction of the alkynyl bromide next to the carbonyl group, in the presence of a second alkynyl bromide with a propargylic C-O sigma bond, is shown (88 —> 89) [164] (Scheme 1.38). 

Bis-acetylene synthesis from alkynyl halides and alkynyl copper reagents. Cf. Castro-Stephens reaction. 

While the mechanisms of these reactions have not been investigated in detail, it is likely that an intermediate copper(I) alkynyl is formed, which undergoes an alkynyl-halide exchange with the metal halide, resulting in the formation of the transition metal cr-alkynyl complex and a Cu(I) halide, which completes the catalytic cycle (Scheme l), ... 

Indenyl)rhodium(I) complexes, preparation, 7, 184—185 Indium complexes acid halide reactions, 9, 683 in alkene and alkyne allyindations, 9, 693 alkyl, aryl, alkynyls, 3, 288 in alkynylations, 9, 720... 

Fig. 31 Reductive radical cyclization reactions of alkynyl halides catalyzed by Ni(I) complexes...

F. Cross-coupling Reactions with Alkynyl Halides. 1288... 

Much of the new chemistry on the coupling of alkynyl halides has dealt mostly with applications of known methods. The Cadiot-Chodkiewicz-type coupling reactions (i.e. terminal acetylene coupling with alkynyl halides) have formed the cornerstone of synthesis of acetylenic retinoids (i.e. 9)58. 

Indium trichloride promotes catalytically the addition of alkynylstannanes to aldehydes (Table 25).42 Metallic indium also mediates the same Barbier-type coupling between alkynyl halides and aldehydes or ketones to give secondary or tertiary propargyl alcohols (Table 26). Secondary alcohols can be oxidized in situ according an Oppenauer process.395 Thus, alkynyl ketones have been prepared from aldehydes via an indium-mediated alkynylation reaction followed by an indium-mediated Oppenauer oxidation. They are also obtained via an indium-mediated alkynylation of the relevant acyl chlorides (Table 27).396... 

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