Castro-Stephens protocol

I 6 Arylation Reactions of Alh/nes The Sonogashira Reaction Castro-Stephens protocol... 

Although the authors call this reaction a Castro-Stephens reaction, they point out that it is really a Linstrumelle modification of the Sonogashira protocol. 

In 1975, three different protocols were available in the literature, each describing the synthesis of internal alkynes. Cassar described palladium- or nickel-mediated reactions between aryl or vinyl halides and alkynes complexes with phosphine as ligands in the presence of NaOMe [1]. As a second protocol, Heck pubhshed a variation of the Mizoroki-Heck couplings, in which the olefins were replaced by alkynes and coupled with (hetero)aryl, as weU as alkenyl bromides or iodides at 100 °C in the presence of a basic amine [2]. More than a decade earUer, Stephens and Castro had described the details of a palladium-free coupling of aryl iodides with cuprous acetylides in refluxing pyridine [3]. 

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%... 

On the basis of the Negishi protocol, C(sp)-C(sp) cross-couplings between alkynylzinc reagents and iodoalkynes have been developed as a mild and copper-free alternative to traditional protocols such as the Stephens-Castro or the Cadiot-Chodkiewicz [272]. 

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