The Castro–Stephens coupling is a cross coupling reaction between a copper(I) acetylide and an aryl halide in pyridine, forming a disubstituted alkyne and a copper(I) halide.
[1][2] The reaction was described in 1963 by chemists Castro and Stephens.
[1][2] The reaction is similar to the much older Rosenmund–von Braun synthesis (1914)[3][4] between aryl halides and copper(I) cyanide and was itself modified in 1975 as the Sonogashira coupling by adding a palladium catalyst and preparing the organocopper compound in situ, allowing copper to also be used catalytically.
[5][6] A typical reaction diphenylacetylene is obtained by the coupling of iodobenzene with CuC2C6H5 in hot pyridine:[1] Unlike the Sonogashira coupling, the Castro–Stephens coupling can produce heterocyclic compounds when a nucleophilic group is ortho to the aryl halide, although this typically requires use of dimethylformamide (DMF) as solvent.
[7][8]