Castro–Stephens coupling

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]

Castro–Stephens coupling
Named after	Charles E. Castro Robert D. Stephens
Reaction type	Coupling reaction
Identifiers
RSC ontology ID	RXNO:0000525

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]