1,2,4-triazines in organic synthesis.: Part 11 -: A novel one-pot synthesis of annulated 2,2′-bipyridine ligands by inverse electron demand Diels-Alder reaction of 5,5′-bi-1,2,4-triazines

The Diels-Alder reaction of 5,5'-bi-1,2,4-triazines with cyclic enamines in the absence of a solvent leads to a range of symmetrical, annulated 2,2'-bipyridines in good yield. When the reaction is carried out in boiling dioxane only 5-(heteroaryl)1,2,4-triazines are formed. The latter, bearing methylsulfanyl substituents, are oxidized with potassium permanganate to the corresponding methylsulfonyl derivatives, which easily undergo Diels-Alder reactions with different enamines to give unsymmetrical, annulated 2,2'-bipyridines. (C) 2000 Elsevier Science Ltd. All rights reserved.