Mechanism

Proceeds via radical intermediate (Scheme 16).

Scheme 16

Examples:

3.5.6 Castro-Stephens Coupling

The coupling of alkynes with aryl halides employing copper salt in the presence of base affords aryl acetylenes (Scheme 17).

Scheme 17

Mechanism

The reaction takes place via oxidative addition followed by reductive elimination (Scheme 18).

Scheme 18