Copper® acetylides

Terminal alkynes react with propargylic carbonates at room temperature to afford the alka-l, 2-dien-4-yne 14 (allenylalkyne) in good yield with catalysis by Pd(0) and Cul[5], The reaction can be explained by the transmetallation of the (7-allenylpailadium methoxide 4 with copper acetylides to form the allenyKalk-ynyl)palladium 13, which undergoes reductive elimination to form the allenyl alkyne 14. In addition to propargylic carbonates, propargylic chlorides and acetates (in the presence of ZnCb) also react with terminal alkynes to afford allenylalkynes[6], Allenylalkynes are prepared by the reaction of the alkynyl-oxiranes 15 with zinc acetylides[7]. 

Palladium also catalyses coupling of haloindolcs with acetylenes. The reaction is carried out in the presence of Cu(I) and presumably involves a copper acetylide as an intermediate[14]. 

STEPHENS CASTRO Acetylene cycloptiane synthesis Polyacetylene cyclophane synthesis from an iodophenyl copper acetylide... 

Charcoal screenings, wet Charcoal, wet Chlorine azide Chlorine dioxide Chloroacetaldehyde Chloroacetone (unstabilized) Chloroacetonitrile Chloroformates, n.o.s. Chloroprene, uninhibited Chlorosulphonic acid Coal briquettes, hot Coke, hot Copper acetylide... 

An ethylene compressor was shut down for maintenance and correctly isolated by slip-plates. When repairs were complete, the slip-plates were removed before the machine was tried out. During the tryout, some ethylene leaked through the closed isolation valves into the machine. The ethylene/air mixture was ignited, either by a hot spot in the machine or by copper acetylide on the copper valve gaskets. The compressor was severely damaged. 

A high-pressure air compressor drew its air from an area where oxy-acetylene welding was taking place. Small amounts of copper acetylide formed on a bronze valve and exploded. 

In 1963 Sladkov (63TZV2213) and Castro (63JOC3313) discovered the reaction between copper acetylides and aromatic halogen derivatives. This method was of... 

The cyclocondensation of iodoaminopyrazole with copper acetylides and the cyclization of aminopyrazolylacetylene with different mutual arrangement in the ring of interacting groups have been studied (83IZV688). 

Cyclization of o-nitroacetylenylbenzenes and cyclocondensation of o-iodonitrobenzene with copper acetylides are widely used to produce isatogens [69JCS(C)2453 69MI2 79JHC221]. The nitro group can be either in the acetylide or in the halide components. 

The cyclization of o-halogenobenzoic acids with copper acetylides mainly leads to the formation of five-membered lactones (66JOC4071 69JA6464) (Scheme 115). Only in the case of the reaction of o-iodobenzoic with CuC=C—n-C3H7 does the formation of a mixture of y- and 5-lactones occur (Scheme 116). 

Since substituents at the triple bond also determine its polarization, the copper acetylides containing both electron-releasing and electron-withdrawing groups were introduced into the reaction of cyclocondensation (78IZV1175 81IZV902). 

Thus, the cross-coupling of different iodo-A -methylpyrazolecarboxylic acids with copper acetylides leads to closure of the six-membered ring. 

Available information on the mechanism of cyclocondensation is rather contradictory. According to one hypothesis, both the condensation of aryl halides with copper acetylides and the cyclization occur in the same copper complex (63JOC2163 63JOC3313). An alternative two-stage reaction route has also been considered condensation followed by cyclization (66JOC4071 69JA6464). However, there is no clear evidence for this assumption in the literature and information on the reaction of acetylenyl-substituted acids in conditions of acetylide synthesis is absent. 

Thus, the vic-acetylenylpyrazolecarboxylic acids are isomerized into pyranoa-zoles in boiling pyridine (20-30 min) with catalytic amounts of copper acetylide. The acetylide condensation of the corresponding iodopyrazolecarboxylic acids is followed by cyclization into the same 5-lactones but with a lower rate (2-8 h). 

Whereas the condensation of o-iodonitrobenzene with copper acetylides is accompanied by cyclization into isatogens, neither 4-iodo-3-nitro- nor 5-iodo-4-nitro-l,3-dimethylpyrazole gives cyclized products in conditions of acetylide synthesis. Moreover, nitropyrazolylphenylacetylene, as compared with o-nitrotolane, does not undergo thermal, catalytic, or photochemical isomerization to give the fused five-membered rings. 

The original Sonogashira reaction uses copper(l) iodide as a co-catalyst, which converts the alkyne in situ into a copper acetylide. In a subsequent transmeta-lation reaction, the copper is replaced by the palladium complex. The reaction mechanism, with respect to the catalytic cycle, largely corresponds to the Heck reaction.Besides the usual aryl and vinyl halides, i.e. bromides and iodides, trifluoromethanesulfonates (triflates) may be employed. The Sonogashira reaction is well-suited for the synthesis of unsymmetrical bis-2xy ethynes, e.g. 23, which can be prepared as outlined in the following scheme, in a one-pot reaction by applying the so-called sila-Sonogashira reaction ... 

Kupfer-asche, /. copper scale, -azetat, n. copper acetate, -azetylen, n. copper acetylide. -bad, n. copper bath, -barre, /. copper bar copper ingot, -belze, /. copper mordant, -blatt, n. copper foil, -blau, n. blue verditer, azurite. -blech, n. sheet copper, copper foil, -blel, n. copper-lead alloy, -bleiglanz, m. Min.) cuproplumbite. -bleivitriol, m. linarite. -blende, /. tennantite. -blute, / copper bloom (capillary cuprite), -braim, n. tils ore (earthy ferruginous cuprite),... 

Butadiene could also be obtained by the reaction of acetylene and formaldehyde in the vapor phase over a copper acetylide catalyst. The produced 1,4-butynediol is hydrogenated to 1,4-butanediol. Dehydration of 1,4-butanediol yields butadiene. 

Butyne-l,4-diol and propargylalcohol are produced by reaction between formaldehyde in aqueous solution and gaseous acetylene in the presence of a copper acetylide catalyst supported on nickel. The process is carried out by trickle-flow operation (BIO, S4). 

Unactivated aryl halides react with copper acetylides to give good yields of arylacetylenes Stephens-Castro coupling)P ... 

Reaction between aryl iodides and copper acetylids... 

More recently, a study with di- and mono-carbene Pd(II) complexes has demonstrated that the Sonogashira coupling of activated and non-activated aryl iodides can be carried out in an aqueous, aerobic medium and in the absence of amines. These results suggest that the moisture-sensitive copper-acetylide may not be present in this particular transformation, and that a Pd-acetyhde could be formed by deprotonation of the coordinated alkyne instead of transmetallation [130]. 

Thus, all copper salts give an explosive reaction with calcium carbide. This is due to the formation of explosive copper acetylide, which is formed from cupric or cuprous cation and the acetylene formed. 

There are a number of procedures for coupling of terminal alkynes with halides and sulfonates, a reaction that is known as the Sonogashira reaction.161 A combination of Pd(PPh3)4 and Cu(I) effects coupling of terminal alkynes with vinyl or aryl halides.162 The reaction can be carried out directly with the alkyne, using amines for deprotonation. The alkyne is presumably converted to the copper acetylide, and the halide reacts with Pd(0) by oxidative addition. Transfer of the acetylide group to Pd results in reductive elimination and formation of the observed product. 

The first dip given to a fusehead is known as the flashing composition and is of particular importance. Originally copper acetylide was used for this purpose, but it has been superseded by more stable materials. Three common compositions are based on lead picrate, lead mononitroresorcinate and a mixture of charcoal and potassium chlorate respectively. These materials are suspended in a solution of nitrocellulose in amyl acetate and amyl alcohol, known as Zapon. One or more dips, with intermediate drying, give a layer of suitable thickness. 

Silver acetylide is a more powerful detonator than the copper derivative, but both will initiate explosive acetylene-containing gas mixtures [1]. It decomposes violently when heated to 120-140°C [2], Formation of a deposit of this explosive material was observed when silver-containing solutions were aspirated into an acetylene-fuelled atomic absorption spectrometer. Precautions to prevent formation are discussed [3], The effect of ageing for 16 months on the explosive properties of silver and copper acetylides has been studied. Both retain their hazardous properties for many months, and the former is the more effective in initiating acetylene explosions [4],... 

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