Double C–H Functionalization to Construct Polycyclic Heteroarenes Catalyzed by an Ionic Salt of a Pd Complex with an N‐Heterocyclic Carbene Ligand

A new ionic salt, cis ‐[Pd(L)(PPh 3 )(H 2 O) 2 ](SO 3 CF 3 ) 2 ( A ), in which L is an amido‐functionalized N‐heterocyclic carbene (NHC) ligand, has been prepared by the salt metathesis reaction between [Pd(L)(PPh 3 )Cl 2 ] and AgOTf in wet acetonitrile. It was successfully characterized by NMR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction analysis. Complex A was found to be effective in catalyzing the double C–H functionalization of various nitrogen‐ and sulfur‐containing heteroarenes to form fused polycyclic heteroaromatic compounds with alkynes in the presence of Cu(OAc) 2 and tetra‐ n ‐butylammonium bromide. Indoles, thiophenes, imidazo[1,2‐ a ]pyridine, and imidazoles were used as substrates. In particular, intriguing imidazo[5,1,2‐ cd ]indolizine compounds could be obtained under the conditions employed.