A Facile Route to Symmetrical and Unsymmetrical Cycloalkeno[<i>c</i>]fused 2,2′-Bipyridine Ligands via Inverse Electron Demand Diels-Alder Reaction of 5,5′-bi-1,2,4-Triazines

Abstract

A series of 6,6′-bisfunctionalized symmetrical cycloal­keno[c]fused 2,2′-bipyridines 4a-h or unsymmetrical cycloal­keno[c]fused 2,2′-bipyridines 6a-g is described. They were prepared by the Diels-Alder reaction of 3,3′-disubstituted 5,5′-bi-1,2,4-triazines 2a,b with cyclic enamines 3a-d. The regioselective reaction of 1-vinylimidazole (3e) with 2a leads to 5-(2-pyridyl)-1,2,4-triazine 9 which undergoes Diels-Alder reaction with cyclic enamines 3a-d to give unsymmetrical 2,2′-bipyridines 10a-d with one cycloalkene ring attached.