Acetylides oxidative coupling

C6HBC C.C C.C C.C C.C6H5 mw 250.28, yel ndls, mp li5—16°(browning), stable at RT for 13 months in the dark when placed on a hot metallic place it. decompd explosively with much soot. It shows no color reaction with sulfuric acid is more sol than tolan Sc (C6H.5C C)3 in polar solvs such as MeOH, ale Sc acetone. It was prepd by oxidative coupling of cuprous acetylide, C6HB.C C.C C.Cu, with CuCl2 (Refs)... 

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. 

The oxidative coupling of two terminal alkynes via their copper acetylide complexes to form a 1,3-butadiyne function is known variously as Glaser, Eglinton, or Hay... 

A more general and efficient approach to alkynyl carboxylates, also thought to involve alkynyliodonium carboxylate intermediates, entails the treatment of bis(acyloxyiodo)-arenes with alkynyllithium reagents (equation 88)81. These reactions are best conducted in the presence of 2-nitroso-2-methylpropane in order to suppress oxidative coupling of the lithium acetylides by the acyloxyiodanes. 

In the polycoupling reactions, the formation of the diyne units proceeded via a Glaser-Hay oxidative coupling route [35-38]. Despite its wide applications in the preparation of small molecules and linear polymers containing diyne moieties, its mechanism remains unclear [38-40]. It has been proposed that a dimeric copper acetylide complex is involved, whose collapse leads to the formation of the diyne product (Scheme 9). 

Alkynyl complexes, also known as metal acetylides, possess both rigid linear skeleton and tt-conjugation. In the structural aspect, alkynyls make excellent linear bridging units. By means of the reactions of transmetallation (see Transmetalation), poly-Pt-acetylides are readily synthesized (Scheme 24). Copper(I)-mediated oxidative coupling... 

Several studies of the kinetics and effects of structure on reactivity lend support to a mechanism of oxidative coupling of the type first proposed by Bohlmann and coworkers The rate is second order with respect to Cu(ii) and alkyne, and varies inversely with [H+] . This is interpreted in terms of rapid steps involving displacement of a solvent molecule or other ligand from the coordination sphere of Cu(n) by an alkyne molecule, followed by acid dissociation of the coordinated alkyne to give an acetylide complex. In the rate-determining step, copper(ii) is reduced and simultaneously the alkynyl groups are coupled. These steps are summarized in equations (6), (7) and (8), where L represents a ligand—solvent, for... 

Although copper acetylides seem to be able to perform a nucleophilic substitution reaction at the sp-carbon atom of a bromo- or iodoacetylene (Cadiot-Chodkievicz reaction), this reaction has only rarely been used for the preparation of cyclic 1,3-diacetylenes. Copper-mediated oxidative coupling reactions (Glaser, Hay and Eglinton coupling) are more popular in this area and have attracted much attention in the construction of carbon-rich cyclic and polycyclic systems (see Chapter 13). One of the earliest carbon-rich systems of this type was the CzoHg system 19 [11,16] [Eq. (5)]. 

Polymeric Gu- and Hg-acetylides 165 (M = Gu or Hg L = no substituent, where L = neutral two-electron donor ligand) were briefly reported in the 1960s via the use of oxidative coupling of diyne precursors (Scheme 16, Equation (58)). These... 

Related techniques have been developed to prepare (Z-,Z)- (Z-, )- and ( -, )- dienes. Hydroboration of diacetylenes followed by protonolysis is a convenient route to (Z-,Z)-dienes, as in the conversion of 89 to 90. The requisite symmetrical diacetylenes are prepared by oxidative coupling with oxygen and cuprous chloride, as in the conversion of 1-cyclohexylethyne (78) to 89. Unsymmetrical conjugated dienes can be prepared by formation of a diacetylene ate complex, prepared from disiamylmethoxyborane by sequential reaction with different acetylides. A similar borane route to unsymmetrical diacetylenes uses dicyclohexyl methyl-thioborane. ... 

C-Labelled dotriacontane has been used to study the retention of tobacco smoke in the respiratory system of smoke-exposed laboratory animals. High-resolution autoradiography studies within the respiratory tract needed tritium-labelled dotriacontane (34) with a specific activity of 0.5 Cimmol" This compound has been prepared by synthesizing the diacetylene 35 and by its reduction to dotriacontane-15,15,16,16,17,17,18,18- H, 34 (equation 48). Sodium acetylide with myristyl bromide yielded hexadec-l-yne 36. Oxidative coupling of 36 using cupric acetate gave the diyne 35 which, upon reduction with tritium gas in the presence of Adams catalyst, yielded 34, with the specific activity of 0.50 Ci mmol as required. 

Oxidative coupling of acetylenic compounds proceeds more eflBciently in the solid state than in water. In this procedure, powedered cuprous aryl acetylide and CUCIJ.2H2O was kept for 3 hr to give the coupled product in 40-75% yield (Scheme 35), compared to 10-30% in water. 

Oxidation of Carbanions. Oxidative coupling of terminal alkynes to diynes (eq 1) with Cu(OAc)2 and pyridine can be carried out in MeOH or in benzene/ether. The reaction requires the presence of copper(I) salt the rate-determining step corresponds to the formation of the Cu acetylide. ... 

The excellent coordination properties of alkynes with ruthenium catalysts led to their use as partners for the coupling with a large variety of unsaturated molecules. The first examples of dimerization of terminal alkynes involved acetylide or vinylidene intermediates. By contrast, with (CsR5)Ru catalysts, a completely different stoichiometric head-to-head coupling of alkynes has been discovered affording ruthenacyclopentatrienes, which are cyclic biscarbenes produced by the oxidative coupling of two alkynes [1-3] (Scheme 1). 

The Glaser coupling reaction is carried out in aqueous ammonia or an alcohol/ammonia solution in the presence of catalytic amounts of a copper-I salt. The required copper-II species for reaction with the acetylide anion R-C=C are generated by reaction with an oxidant—usually molecular oxygen. For the Eglinton procedure, equimolar amounts of a copper-II salt are used in the presence of pyridine as base. 

The coupling of terminal alkynes with aryl or alkenyl halides catalysed by palladium and a copper co-catalyst in a basic medium is known as the Sonogashira reaction. A Cu(I)-acetylide complex is formed in situ and transmetallates to the Pd(II) complex obtained after oxidative addition of the halide. Through a reductive elimination pathway the reaction delivers substituted alkynes as products. 

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. 

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