1,3-Dipolar character of six-membered aromatic rings. Part 52. 2π+ 8π Cycloaddition reactions of 1-substituted 3-oxidopyridinium betaines

Abstract

Dichloroketen and a series of aryl(bromo)ketens react with various 1-substituted 3-oxidopyridiniums to give novel bicyclic compounds by addition across the C(4)–O and the C(2)–O positions. Frontier-MO theory is used to rationalise the orientation of these cycloadditions. Acid-catalysed hydrolysis of the C(2)–O adducts (9) yielded 3-hydroxy-2-benzylpyridines.