Catalytic N-Alkylation of (Hetero)Aromatic Amines and Tandem Annulation Reactions

A general and practical approach for N-alkylation of heteroaromatic amines with heteroaromatic alcohols is always challenging and rarely reported. Here, we designed and synthesized phosphine-free, robust, and efficient N,N-bidentate-Co(II) complexes for a universal N-alkylation of amines strategy. This present catalytic methodology can be applied to a wide range of substrates by varying alcohols, including aryl, aliphatic, acyclic, and cyclic groups, with heteroaromatic amines such as aminopyridine, 2-aminopyrimidine, and aminoquinoline to provide diverse monoalkylated organonitrogen compounds in good to excellent yields (108 examples). In addition, the utility of the developed catalytic protocol was also extended successfully for the dehydrogenative synthesis of biologically important quinoline derivatives (11 examples). Particularly, 8-aminoquinoline reacted differently with tandem N-alkylated-transfer hydrogenative byproduct (N-benzyl-1,2,3,4-tetrahydroquinolin-8-amine) was obtained, revealing the catalytic activity of the complex I. The reaction proceeded under environmentally benign conditions, which liberates water as the sole byproduct. Notably, a concise synthesis of acetylcholinesterase inhibitors (AChEIs) scaffolds as potential cognition enhancers illustrated the utility of the present protocol. Interestingly, various control and deuterium-labeled experiments were performed, suggesting that the reaction proceeds via the borrowing hydrogen pathway.