Alkynylcopper Stephens-Castro reaction

The reaction of aryl halides 1 with alkynylcopper(I) 2 under reflux in pyridine to prepare internal arylacetylenes is known as the Stephens-Castro reaction [Eq. (1)] [2]. The reaction has proved to be particularly important in the synthesis of a wide range of tolan and heteroaromatic alkynes [3]. Vinyl and allenic halides can also be used and several reviews... 

As described above (Section 5.2), the Stephens-Castro reaction of alkynylcopper with aryl and vinyl halides in boiling pyridine is a useful route to aryl and vinyl acetylenes. Direct cross-coupling of organic halides, such as sp halides, with terminal alkynes is a more convenient procedure. Such a reaction is not so easy, but it can be done using a Pd-complex catalyst [41]. Especially facile Pd-catalyzed cross-coupling of aryl and alkenyl halides with terminal alkynes proceeds smoothly under mild conditions in the presence of a cocatalyst of cuprous iodide in amine solvents [Eq. (28)] [42]. This methodology is now used widely for the constiuction of conjugated arylalkyne or enyne systems [43], as described below. It is attractive from a synthetic point of view because mild reaction conditions and simplicity of the procedure are associated with recent developments in modem acetylene chemistry [44]. 

The reaction of aryl halides 29 with alkynylcoppers 30 is known as the Stephens-Castro reaction, which has proved to be particularly important in the synthesis of a wide... 

To avoid the isolation of the relatively unstable and often explosive Cu acetyhde, a modification of the original Stephens-Castro protocol involving generation of the alkynylcopper species in situ from the corresponding terminal acetylene and Cul in DMSO (dimethyl sulfoxide) or DMF (N,N-dimethylformamide) has been developed (9). The Stephens-Castro reaction can also be performed at sub-mol%... 

The Castro-Stephens reaction entails coupling of alkynylcopper(I) reagents with aryl or heteroaromatic halides in refluxing pyridine to furnish arylacetylenes. The cuprous alkynylides are prepared by adding the 1-alkynes to an aqueous ammonia solution of cuprous iodide. Since dry copper alkynylides have the tendency to explode, they must be handled with great care and should only be used in a slightly damp state. ... 

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