Copper I acetylides

The reaction between copper(I) acetylides and o-halogenophenols or -anilines provides a general and convenient route to 2-substituted benzofurans or indoles (Scheme 71g) (66JOC4071). 

TABLE XXV. Pyranopyrazoles Prepared by Cyclocondensation of vic-Iodo-pyrazolecarboxylic Acid with Copper(I) Acetylides [86TH1 78IZV1175 81IZV902 81IZV1342]. 

A mechanism for this reaction has been proposed [75], The first key intermediate in the reaction is the copper(I) acetylide 42. The additional ligand may be solvent or H2O. The acetylene moiety in 42 is activated for a 1,3-dipolar cycloaddition with the nitrone to give intermediate 43, with introduction of chirality in the product. A possible route to ris/traws-41 might be via intermediate 44. Finally, the cis isomer is isomerized into the thermally more stable trans-41. It should be mentioned that the mechanism outlined in Scheme 6.32 was originally proposed for a racemic version of the reaction to which water was added. 

Copper(II) acetylide (black or brown) is much more sensitive to impact, friction or heat than copper(I) acetylide (red-brown) which is used in electric fuses or... 

Contact with silver nitrate solution transforms copper(I) acetylide into a sensitive and explosive mixture of silver acetylide and silver. 

ETHYL 4-METHYL-E-4,8-NON-ADIENOATE, 53, 116 Styrene, reaction with carbe-thoxycarbene, 50, 94 Suberoyl chloride, 54, 88 SUBSTITUTION OF ARYL HALIDES WITH COPPER(I) ACETYLIDES ... 

SUBSTITUTION OF ARYL HALIDES WITH COPPER(I) ACETYLIDES 2-PHENYLFURO[3,2- ]PYRIDINE... 

Copper(I) acetylides can bo prepanid from atmrioniacal co )per(l) iodide and ac cdyUaies.Tlwi generation of... 

Copper(I) acetylide is used in a diagnostic test for CH unit to prepare pure copper powder in purification of acetylene and as a catalyst in the synthesis of acrylonitrile and 2-propyn-l-ol. 

Copper(I) acetylide is prepared by passing acetylene gas over an aqueous solution of ammoniacal copper salt ... 

Copper(I) acetylide oxidizes in air forming copper(II) acetyhde, CuC2 2CU2C2 + O2 —> 2CuC2 + CuO... 

Copper(I) acetylide forms a highly explosive mixture containing silver acetyhde when mixed with silver nitrate ... 

Castro and Stephens16 developed a method for the preparation of unsymmetrical disubstituted acetylenes, which involves the reaction of copper(I) acetylides with aromatic iodo compounds. Bond and Hooper7 extended this route to the preparation of 2-arylisatogens (22). 2-Nitro-phenylpropiolic acid (19a) is readily decarboxylated to the acetylene (19b), which on treatment with copper(I) chloride gives 19c. The reaction of 19c with substituted aromatic iodo compounds (20) gives the corresponding acetylenes (21), which subsequently cyclize to the isatogens (22). The alternative route (23 + 24 - 21) has been little used.17... 

The displacement of halogen with a copper(I) acetylide and subsequent or synchronous copper catalyzed addition of a neighboring nucleophilic substituent to the triple bond (equation 2) constitutes a versatile synthesis of heterocycles. This reaction has been utilized both for the synthesis of furo[3,2-c]pyridines (equation 3) and furo[3,2-6]pyridines (equation 4) (68JHC227, 72MI31700>. 

Another interesting derivative of benzo[c]thiophene which may be useful for preparative purposes has been described by Castro and coworkers. Strictly analogous to a synthetic sequence outlined in Section 3.17.2.1.1, 3-iodothiophene-4-carboxylic acid reacts with a copper(I) acetylide in DMF at 125 °C to give a l//-thieno[3,4-c]pyran-2-one (equation 53) (68JHC227). 

The preparation of the related high molecular weight poly-1.4-phenylene sulfide has been accomplished by heating />-bromothio-phenolate salts in pyridine at 250° C (57). The commercially available polyethersulfones are reported to be prepared by condensation of 4.4 -dichlorodiphenyl sulfone with salts of biphenols in solvents such as dimethylsulfoxide at 150° C. The work of Bacon and Hill would suggest that both of these reactions might be carried out at considerably lower temperatures with copper (I) salts as catalysts. In addition, it has been demonstrated that copper (I) acetylides react quantitatively with aromatic iodides to yield tolanes (15, 77) therefore this reaction should also be the basis for a similar polymer forming reaction. 

Copper(I) acetylides can be fire pared from ammoniacal copper(l) iodide and acetylenes. 2 4" The generation of fresh... 

Copper(II) acetylide (black or brown) is much more sensitive to impact, friction or heat than copper(I) acetylide (red-brown) which is used in electric fuses or detonators [1]. An explosion during maintenance work on a copper condenser in a methanol plant was attributed to copper acetylide deposits in the heat exchanger [2]. During internal inspection of an air-purged 15 year old 330 m3 liquefied gas cylinder, it was noticed that there was a 2—3 cm layer of mst-like deposit at the bottom. As the inspection... 

It was shown that, on aging in air, copper(I) acetylide oxidises to this, which was also prepared independently from butadiyne. It also seems to result from reaction of copper solutions of mixed I and II valencies with acetylene. Further oxidation appears to give higher homologues. The explosive properties remain. Essentially, this is the Cu II mediated oxidative coupling, by which higher acetylenes are normally prepared synthetically, operating spontaneously. 

Benzofurans. 2-Substituted benzofurans can be obtained in 65-83% yield by reaction of o-iodophenols and 1-alkynes in the presence of Cu20 suspended in pyridine. This synthesis has been conducted in the past by reaction of copper(I) acety-lides with o-halophenols, but yields are somewhat lower. In addition, copper(I) acetylides can be explosive. 

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