“…According to the optimal reaction conditions reported by our group, 24) all experiments were performed with 2.0 eq of acetylene, 0.8 eq of an additive, 20 mol% of copper salt, and 200 eq of pyridine in N,NЈ-dimethylformamide (DMF) at 80°C. 32) However, bidentate ligands such as trans-N,NЈ-dimethylcyclohexane-1,2-diamine, 2,2Ј-bipyridine, L-proline, and 1,10-phenanthroline, which are typically used in copper-mediated coupling reactions, 25,26) were ineffective in promoting the reaction (Table 1, entries 3-6). In contrast, most inorganic bases proved applicable and furnished the cyclized product 4aa in 13-63% yields with K 2 CO 3 being suitable ( To determine the optimal copper salts, reactions with various copper(I) (CuI, CuBr, and CuOTf) and copper(II) salts (CuO, CuBr 2 , and CuCl 2 ) 33) were examined.…”