N-Heterocyclic Carbene/Cobalt Cooperative Catalysis for the Chemo- and Regioselective C-N Bond Formation between Aldehyde and Amines/Amides

A novel methodology for the construction of various secondary (4 examples), tertiary amides (31 examples), and imides (16 examples) by a Cobalt(II) catalyzed oxidative amide coupling in aqueous media. The Co(III)-TMC was reacted with N-Heteroatom Carbene to form active catalyst Co(II)NHC-TMCin situwhich involves in the coordination with Breslow's intermediate and SET for the activation of aldehyde and amides. The mechanism for activation of amide and amine differs on the basis of SET based nucleophilic addition and ligand exchange respectively. The regeneration of the catalyst was achieved using Fe(III)(EDTA)-H(2)O(2)as oxidant. The use of Co(II)TMC-O(2)was also found equally efficient in the process. The method is found regioselective for N-H activation in the presence of equally susceptibleortho-C-H bond activation. And amines were found more susceptible then the corresponding amide for the reaction.