Ligand Assisted Co(II)-Catalyzed Multicomponent Synthesis of Substituted Pyrroles and Pyridines.

Herein, we describe a sustainable Co(II)-catalyzed synthesis of pyrroles and pyridines. Using a Co(II)-catalyst [Co (L)Cl] (1 a) bearing redox-active 2-(phenyldiazenyl)-1,10-phenanthroline) (L) scaffold, various substituted pyrroles and pyridines were synthesized in good yields, taking alcohol as one of the primary feedstock. Pyrroles were synthesized by the equimolar reaction of 2-amino and secondary alcohols. A series of 2,4,6-substituted symmetrical pyridines were prepared via a three-component reaction of NHOAc with 1 : 2.2 molar primary and secondary alcohols, respectively. Unsymmetrically substituted 2,4,6-trisubstituted, 2,4,5,6-tetrasubstituted, and 2,3,4,5,6-pentasubstituted pyridines were achieved via a multi-component coupling reaction of alcohols and NHOAc. Catalyst 1 a showed encouraging results during the gram-scale synthesis of these N-heterocycles. Mechanistic investigation revealed synergistic involvement of cobalt metal and the ligand during the catalytic reactions.