1,3-Dipolar character of six-membered aromatic rings. Part 48. Novel conversions of pyridines to isoquinolines

Abstract

1-Heteroaryl-3-oxidopyridinium dimers with dienamines give cycloadducts which are dehydrogenated to ‘mixed dimers’ of the corresponding 2-heteroaryl-4-oxidoisoquinolinium with the starting 1-heteroaryl-3-oxidopyridinium. The ‘mixed dimer’(21) is also effectively prepared by a two-step sequence of a novel intramolecular oxidation–reduction, followed by oxidation of the resulting alcohol. The ‘mixed dimers’ undergo reversible thermal dissociation and in one case the corresponding monomers could be trapped as various cycloadducts.