Acetylide formation, Castro-Stephens reaction

More often such bromo- and iodoalkynes are employed with another synthetic goal in mind, namely, in the Cadiot-Chodkiewicz reaction for the formation of symmetric or asymmetric 1,3-diynes by reaction of the haloalkyne with a terminal alkyne (Figure 13.25). Additional reagents essential for the success of this reaction are one equivalent or more of an amine and a substoichiometric amount of Cul. As with the Cacchi and Stephens-Castro coupling reactions of Section 13.3.4, a Cu-acetylide is the reactive species in the Cadiot-Chodkiewicz coupling. It is formed in step 1 of the mechanism illustrated in Figure 13.25. 

In 1963, Castro, Stephens, and co-workers reported a novel indole formation from 2-iodoaniline 201 and copper acetylides 202 in DMF (Scheme 19.52) [97]. When the reaction was conducted in pyridine, the product composition varied from exclusively uncyclized 2-alkynylindoles 199a to mixtures of 200a and 199a, depending on the nature of the acetylide. They confirmed that the cyclization of 199a to 200a... 

Processes similar to the Suzuki coupling reaction have been observed with alkynes. Thus, the Stephens-Castro reaction between unsaturated iodides (aryl, vinyl) and copper(l) acetylides in pyridine solvent results in the formation of new... 

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