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43.2.1.1.1 Oxidative Homocoupling

DOI: 10.1055/sos-SD-043-00067

Diederich, F.; Tykwinski, R. R.; Nielsen, M. B.Science of Synthesis, (200843119.

The oxidative coupling of two terminal alkynes was first reported in 1869 by Glaser[‌2‌] (see Sections 43.1.1.1.1.1 and 43.1.2.1.1.1), who discovered that copper(I) phenylacetylide exposed to air undergoes smooth oxidative dimerization to diphenyldiacetylene (Scheme 1). The apparent need to isolate the potentially explosive copper acetylide before oxidation hindered the widespread application of this coupling reaction. In the late 1930s, Zalkind and Aizikovich determined that coupling could be accomplished in situ and isolation of the copper acetylide was not actually necessary,[‌3‌] a process later refined by Reppe in 1955.[‌4‌] In 1956, Eglinton and Galbraith[‌5‌] introduced the now-common protocol involving copper(II) salt oxidation in methanolic pyridine, which avoids isolation of the intermediate copper acetylide. By using a copper(II) salt, this procedure also eliminates the need for oxygen within the reaction mixture, and greatly expands the breadth of unsaturated molecules that can be formed. Nowhere is this more evident than in the subsequent work of Sondheimer on annulenes.[‌6‌] Shortly after Eglinton and Galbraith's report, Hay showed in 1962 that, in the presence of oxygen, the oxidative coupling is also quite successful in the presence of catalytic amounts of the bidendate ligand N,N,N,N-tetramethylethylenediamine and copper(I) chloride, a method ultimately providing great solubility to the reactive species.[‌7‌] An overview of historical developments and mechanistic investigations has been published.[‌8‌]

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