Plausible PEPPSI catalysts for direct C-H functionalization of furans and pyrroles

Abstract

The worth of bi(hetero)arenes in ongoing medicinal and industrial research fields promotes their efficient synthesis by Pd-PEPPSI-bearing NHC spectator ligands encapsulated as site-selective direct C-H functionalization agents. Eight new asymmetric N-heterocyclic carbenes ligands and their plausible pyridine-assisted Pd (II) complexes are reported in this work. The synthesized compounds were thoroughly characterized by respective spectroscopic techniques, such as 1H, 13C, FTIR and elemental analysis. The structures of synthesized pro-ligand salts and complexes were determined by Single Crystal XRD. The on/off mechanism of pyridine assisted Pd-NHC complexes made them the best C-H functionalized catalysts for regioselective C5 arylated products. Five membered heterocyclic compounds such as 2-acetyl furan, furfuryl acetate and 1-methyl-2-pyrrole-carboxylaldehyde were treated with numerous aryl bromides under optimal catalytic reaction conditions. Furfuryl acetate was used for the first time as a substrate in the present research work. Interestingly, all the prepared catalysts possessed essential structural features that facilitated the formation of desired coupled products in quantitative yield with excellent selectivity.