... Tetrahedron Letters. Volume 48, Issue 24, 11 June 2007, Pages 4207–4210. ... As shown in Table 1, without the aid of a ligand, treatment of substrate 1a with 2a, CuI and Cs 2 CO 3 in DMF afforded only a trace amount of the corresponding product 3a after 24 h (entry 1), whereas ...