Application of intramolecular cycloaddition/retro cycloaddition reactions for the synthesis of unsymmetrical 2,2′-bipyridine and 2-benzofuropyrazin-2-ylpyridine analogues

Abstract

1,2,4-Triazines bearing cycloalkeno[ c]pyridine substituents at the 5-position, 2a– d , prepared by an intermolecular Diels–Alder reaction of bi-5,5-triazines with cyclic enamines, were provided with an alkynyloxy or a 2-cyanophenoxy group at the 3-position of the triazinyl unit. A subsequent intramolecular Diels–Alder reaction of the former, followed by loss of N 2 leads to two new classes of 2,2′-bipyridine analogues containing different heterocyclic units, namely cycloalkeno[ c]pyridine and 2,3-dihydrofuro- or 2,3-dihydropyrano[2,3- b]pyridine 8a– h ; the intramolecular reaction of the 2-cyanophenoxy compound gives benzo[4,5]furo[2,3- b]pyrazine 10a– c .