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'-b ipyridines in good yield. When the reaction is carried out in boiling dioxa ne only 5-(heteroaryl)1,2,4-triazines are formed. The latter, bearing methy lsulfanyl substituents, are oxidized with potassium permanganate to the cor responding methylsulfonyl derivatives, which easily undergo Diels-Alder rea ctions with different enamines to give unsymmetrical, annulated 2,2'-bipyri dines. (C) 2000 Elsevier Science Ltd. All rights reserved.