The Iridium(III)-Catalyzed Direct C(sp2)– and C(sp3)–H Alkynylation of 2‑Acylimidazoles with Various Alkynyl Bromides: Understanding the Full Catalytic Cycle

An imidazole moiety was introduced as a removal directing group for carboxylic acid derivatives in the Ir­(III)-catalyzed alkynylation of C­(sp2)–H and C­(sp3)–H bonds with various alkynyl bromides, including TIPS- and Ar-substituted alkynyl bromides, and Br-propargyl-silyl ethers. The mechanism was explored in detail by investigating the intermediate produced in each individual step. The structures of six-membered iridacycles that were produced as intermediates were confirmed by X-ray crystallographic analysis and NMR and/or FAB-MS.