A systematic study into the Sonogashira cross-coupling of 1,1′-diiodoferrocene (fcI₂) confirms that the Pd(0)–P(^tBu)₃ system provides a remarkable rate increase over Pd(0)–(PPh₃)₂. Attempts to couple 4-ethynylphenylthioacetate (2) with fcI₂ instead produced a novel cyclic trimer of the former, from syn addition of S–Ac across CC.