Synthesis studies toward chloroazaphilone and vinylogous γ-pyridones:: Two common natural product core structures

[GRAPHICS] Chloroazaphilone is a common structure found in a number of natural products. Reported herein is a practical synthesis of a model chloroazaphilone that utilizes Pb(OAc)(4) oxidation of HClO4/HOAc pyrinium salt in a key one-pot operation. Reaction of this chloroazaphilone with various primary amines to afford the corresponding vinylogous gamma-pyridones was also fully investigated. The isolation of stable enamine intermediates provided direct evidence of reaction mechanisms.