Alkynyl exchange reaction

Alkynyl anions are more stable = 22) than the more saturated alkyl or alkenyl anions (p/Tj = 40-45). They may be obtained directly from terminal acetylenes by treatment with strong base, e.g. sodium amide (pA, of NH 35). Frequently magnesium acetylides are made in proton-metal exchange reactions with more reactive Grignard reagents. Copper and mercury acetylides are formed directly from the corresponding metal acetates and acetylenes under neutral conditions (G.E. Coates, 1977 R.P. Houghton, 1979). 

The coupling with alkynyl iodides in the presence of CuCl and DMPU proceeds quite differently from that with alkynyl bromides. Although the first step of the coupling is the same, the subsequent Cu/I exchange reaction of the intermediate is different. As the final product, iododienyne 54 is obtained in high yields, as shown in Eq. 2.37 [35]. In the case of alkynyl bromides, Cu/Br exchange does not proceed. Therefore, the alkenyl copper moiety couples with the second alkynyl bromide molecule. 

Copper iodide acts as an efficient reagent for the nucleophilic displacement of 1-haloalkynes. It transforms 1-bromoalkynes (72) into 1-iodoalkynes (73) which, on further treatment with copper(II) bis(arenesulfinate), are converted into the corresponding alkynyl aryl sulfones (74). An electron transfer between 1-haloalkynes and copper(I) salts is believed to take place for the copper-assisted halogen-exchange reaction at the acetylenic carbon atom. 

Alkynyl iodides and bromides react smoothly with various zinc-copper organometaUics at — 60 "C leading to polyfunctional aUcynes. lodoalkynes, such as 296, react at very low temperature, but lead in some cases to copper acetylides as by-products (1/Cu exchange reaction). 1-Bromoalkynes are the preferred substrates. Corey and Helel have prepared a key intennediate 297 of the side chain of Cicaprost by reacting the chiral zinc... 

One of the characteristic features of the metal-bis-acetylide complexes in chemical reactions is that they undergo a ligand exchange reaction with metal dihalides in amines in the presence of a cuprous halide catalyst to produce a monoalkynyl-metal-monohalide complex (Eq. IS) which results from selective cleavage of the metal-carbon bond weakened by the /ram-alkynyl group in the bis-acetylide... 

Miscellaneous Reactions Exchange Reaction of Alkynyl Halides [114]... 

Exchange reactions of aryl and iodo ligands and of aryl and alkynyl ligands are not observed at all. Analogous alkynyl ligand transfer from aryl(alkynyl)palladium complexes to aryl(iodo)platinum complexes shown in Eq. 5.52 occurs above 35°C to cause complete alkynyl group transfer from Pd to Pt [183]. 

Generally, the preparation of these species is achieved by (i) reaction of a platinum alkynyl complex with a platinum substrate containing labile ligands and (ii) chloride-alkynide exchange reactions. 

Polystyrene-supported Au catalysts 17 and 18 have been prepared using the route outlined in Scheme 40. Polystyrene bound triphenyl phosphine was treated with [(Me2S)Au]Cl in dichloromethane at room temperature for 6h to obtain 16. Two different heterogeneously supported Au catalysts, 17 and 18 were obtained by simple ion exchange reaction of AgOTf and AgNTf2 wifh 16. These two catalysts were used to provide the furan derivative by the intramolecular 5-endo-dig cycloisomerization of alkynyl-diol (Scheme 41) [63]. 

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