[1,4] and [5,5] thermal sigmatropic rearrangements of 2-pentadienyloxypyridine N-oxides

Abstract

2-Pentadienyloxypyridine N-oxides (3) are smoothly transformed on heating into N-pentadienyloxy-2-pyridones (4) and N-hydroxy-5-pentadienyl-2-pyridones(5). These reactions are shown to be regiospecific and are believed to proceed in a concerted fashion. The [5,5) sigmatropic rearrangement (3)→(5) takes place under moderate conditions and in good yield, although it presumably involves a ten-membered cyclic transition state.